E PA/OR P 73-;
ENVIRONMENTAL EXPOSURE TO
NONIONIZING RADIATION
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
111
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ENVIRONMENTAL EXPOSURE
TO NOKIOMZIKG RADIATION
Proceedings of a Session on Environmental
Exposure to Non-ionizing Radiation, Annual
Meeting of the American Public Health
Association
Atlantic City, New Jersey, November 143 1972
May 1973
Cosponsored by
AMERICAN PUBLIC HEALTH ASSOCIATION
Radiological Health Section
and
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
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FOREWORD
The Office of Radiation Programs carries out a National program
designed to evaluate the exposure of man to ionizing and nonionizing
radiation, and to promote the development of controls necessary to
protect the public health and safety and assure environmental quality.
Within the Office of Radiation Programs, the Field Operations
Division conducts programs related to sources and levels of environ-
mental radiation and the resulting population exposure. Reports of
the findings are published in Radiation Data and Reports, appropriate
scientific journals, and special technical reports.
The technical reports allow comprehensive publication of the
results of intramural, contract, and sponsored projects. Readers of
these reports are invited to comment on their contents or to request
further information.
W. D. Rowe
Deputy Assistant Administrator
for Radiation Programs
ill
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PREFACE
The session on environmental exposure to nonionizing radiation
was held to promote an interchange of information, among investigators
and health personnel, on various problems related to protection against
possible hazards of such radiation.
Joint sponsorship by the American Public Health Association and
the Office of Radiation Programs of the Environmental Protection Agency
reflects growing concern about the impact of increasing uses and sources
of nonionizing radiation. It is hoped that the published proceedings
of this session will serve to stimulate interest and efforts to assure
that the growth of technology in this field will be consistent with the
protection of health.
We acknowledge with appreciation the contributions of the partici-
pants and of the editors whose efforts made early publication possible.
'Charles L. Weaver
Director
Field Operations Division
: I //. // /'/,//
/ (. ; -( '-" *- ' "
William A. Mills, Ph.D.
Session Chairman
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CONTENTS
Page
Foreword Hi
Preface v
Introductory Remarks
W. A. Mills, Session Chairman 1
i
The Management of the Radio Spectrum and Its Relationship
to the Environment
Donald M. Jansky 3
Electromagnetic Environments in Urban Areas
James C. Toler 19
Environmental Nonionizing Radiation Exposure: A Preliminary
Analysis of the Problem and Continuing Work Within EPA
Richard A. Tell 47
Electromagnetic Compatibility, Electromagnetic Interference,
and Susceptibility as Related to Medical Devices
Paul S. Ruggera
Mays L. Swicord 69
The Growth of Microwave Systems and Applications
Jeffrey Frey 79
Space Solar Power: An Option for Power Generation
Peter E. Glaser 97
Federal Program on Biological Effects of Electromagnetic
Energy
H. Janet Healer 123
vii
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INTRODUCTORY REMARKS
W. A. Mills, Session Chairman
Electromagnetic radiation has, for the sake of convenience in
assessing environmental and public health implications, been charac-
terized into two major categories, namely ionizing and nonionizing
radiation. The point of differentiation between the two categories has
been defined in terms of the amount of quantized energy (described in
terms of wavelength) required to attain the ionization potential of
atoms. The session on Environmental Exposure to Nonionizing Radiation
concerns itself with that portion of the electromagnetic radiation
spectra having energies sufficiently below the atomic ionization poten-
tials such that the energy transfer occurring is primarily through
atomic vibrations and rotations. Included in this spectrum are radi-
ation popularly designated as microwaves, television waves, and radio
waves.
These forms of nonionizing radiation, particularly microwave
radiation, have recently become of national concern because of rapid
increase in their industrial, communication, and consumer applications
and their potential harm to public health; the latter a major point of
controversy because of the lack of sufficient biologic data.
In planning this session, we have attempted, by the mechanism of
invited papers, to outline a program which will scope the extent of
nonionizing radiation in the environment, describe some of its appli-
cations and growth, including the potential for delivering solar energy
as an alternative energy source, examine some of the nonbiologic "side
effects," and conclude with an overview of the Federal activities in
this area. The program was designed to exclude presentations on the
biologic effects of microwaves and radio waves, since this has been the
topic discussed in many recent scientific meetings.
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THE MANAGEMENT OF THE RADIO SPECTRUM
AND ITS RELATIONSHIP TO THE ENVIRONMENT
Donald M. Jansky, M.S.E., Office of Telecommunications Policy,
Executive Office of the President, Washington, D.C.
In addressing this subject, one might first ask what constitutes
use of radio in the United States such that it requires being managed?
There has been some form of management of the use of radio in this
country for over fifty years. Such management has been necessitated
t
by the fact that man has learned how to build and design equipments
which provide controlled radio emissions of various types for the
transmission of information carrying energy from one point to another.
These emissions consist of oscillatory radio energy. The specific
frequency of these oscillations vary from very small, i.e., a few
cycles per second, to many hundreds of millions of cycles per second.
The required magnitude of the energy involved in these emissions to
effectively send a signal to a particular destination is a function
of the frequency involved, the amount of information to be sent and
the distance over which that information is to be sent. During these
fifty years communication system designers have found many needs for
i
the use of radio frequencies as a means of communications and in the
process have created many equipments to accomplish this. Management
has been required to establish and enforce the boundary conditions which
will permit the maximum number of such emissions to take place without
simultaneously causing harmful interference to other systems attempting
to do similar kinds of information transfer.
Presented at the Session on Environmental Exposure to Nonionizing
Radiation, November 14, 1972.
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The fact that limits must be placed on these emissions indicates
that there is an upper boundary on the number of a particular kind and
type of radio emission which may be utilized in a particular geographical
area without causing such undue interference with other radio equipments
in the same area. Because of these limitations on the availability
of radio frequencies, they are often referred to as natural resources
and are managed in a fashion which has many analogies to other natural
resources such as water and land.
Furthermore, as with these other resources, the radio spectrum
is increasingly being considered part of the environment to which man
may, or already has done damage, and therefore must be put under
increasing scrutiny to effectively conserve it. In this connection,
during the past two years, it has become increasingly necessary for
radio spectrum managers to be aware of the real and potential harm
that radio energy could do to the biological environment and, in
particular, man. It is this latter concern which serves as the nexus
of this paper.
Dimensions of Radio,. Use
The next several charts and diagrams provide a basis for apprecia-
ting the terrific dependence that our society presently has on availa-
bility of radio frequencies. In fact, as these charts will illustrate,
the United States has as much dependence on availability of radio
frequencies as we do on availability of energy resources. The tele-
communication systems that are supported by availability of radio fre-
quencies provide a virtual nervous system of our society. Figure 1
indicates the vast range of the kinds of services performed by systems
4
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RADIO SERVICE BY SOCIAL FUNCTION
SOCIAL FUNCTIONS
RADIO SERVICE
DEFENSE
PUBLIC INFORMATION AND ENTERTAINMENT
PRIVATE COMMUNICATION
PUBLIC SAFETY
RECREATION AND EXPLORATION
HEALTH
RESOURCE MANAGEMENT
INDUSTRIAL CONTROL
COMMAND AND CONTROL. DETECTION.
SURVEILLANCE, IDENTIFICATION.
MISSILE GUIDANCE
TV, AM. FM BROADCASTING
RADIO RELAY OF TELEPHONE. TELE-
GRAPH. FACSIMILE, TWO-WAY
TELETYPE
POLICE. FIRE, AVIATION, RAILROAD
MARINE. HIGHWAY. FOREST PROTECTION
AMATEUR RADIO. CITIZENS BAND,
RADIO ASTRONOMY, SPACE
TV. AM. FM BROADCASTING, RADIO
RELAY OF TELEPHONE, POLICE, FIRE
FORESTRY CONSERVATION, WEATHER
REPORTING. FUEL AND ELECTRIC POWER
SUPPORT, AIR AND WATER POLLUTION,
WILD LIFE CONTROL
TAXI. TRUCK. BUS, OFFSHORE OILRIGS,
INTRAPLANT COMMUNICATIONS
Figure 1
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using the radio spectrum. Figure 2 shows the quantity of assigned
frequencies to Federal Government systems as of July of this past year.
These assignments give authorization to various Federal agencies to
operate radio equipments. The subsequent charts (Figs. 3, 4 and 5) give
an indication of the way the kinds of systems use these assignments.
An assignment may represent anywhere from one to several hundreds
of equipments operating on the same frequency. These numbers are an
indication of how only the Federal Government uses the radio spectrum.
Authority to get these frequencies is obtained from the Office of
Telecommunications Policy with advice from the Interdepartment Radio
Advisory Committee. The non-governmental use of radio is managed by
the Federal Communications Commission. Users of radio frequencies
managed by this organization are much more widely known. They include
your various business radio services, such as taxicabs, all your
broadcasting stations (AM, FM, television both UHF and VHF) and the
American Telephone and Telegraph Company (AT&T), which has
extensive frequencies for microwave systems which crisscross the
United States providing great volumes of communication service. Of
course, to obtain an authority to operate under the jurisdiction of
the Federal Communications Commission, one must have a license. A
license and an assignment are roughly equivalent.
An indication of the economic impact of telecommunication systems
which depend upon radio is indicated in Figure 6. Here, it is evident
how there has been a tenfold growth in communication-electronic equip-
ments and today the net worth of its presently owned communication-
electronic equipment is $50 billion.
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SUMMARY OF USERS
(As of July 1, 1972)
Department/Agency
(Air Force
46.95% (Navy
(Army
20.69% (FAA
(Coast Guard
(Interior
(Justice
26.08% (Agriculture
(Commerce
(AEG
7.17% * Other. -
TOTAL
Assignment*
21, 047
19,523
13,760
15,816
8,595
7.449
9,010
7,718
4,289
2,297
8,464
117, 968 on
17.84
16.54
11.66
13.40
7.28
6.31
7.63
6.54
3.63
1.94
7.17
100.00
12, 571 Frequencies
*EPA, FCC, Federal Reserve System, GPO, GSA, HEW, HUD, IBWC,
DOT, Library of Congress, NSF, NASA, OMB, Department of Labor,
OEP, Postal Service, Smithsonian Institution, Supreme Court, DOS,
TVA, Treasury, Capitol Police, USIA, VA, Architect of the Capitol.
Figure 2
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DEPARTMENT OF THE INTERIOR
{ 13 Operating Bureaus & Agencies
EXTENT( > 7400 Assignments
( > 950 Frequencies
( - $68 Million Equipment Investment
Management & Law Enforcement
1/2 CONUS West of Denver
90% ALASKA
CIVIL COMMUNICATIONS —
Trust Territory of the Pacific Islands - American Samoa
- Mobile - 75 ships; 75 aircraft
> 50,000 VHF portable/mobile stations
EXAMPLES -
NATIONAL PARK SERVICE -
Fire Suppression & Safety — 200 Million Visitors/Vear
BUREAU OF INDIAN AFFAIRS
Fire Suppression, Law enforcement. Management & Utility Operations.
1/2 Million Indians & Alaskan Natives.
50 Million Acres.
BUREAU OF LAND MANAGEMENT -
Management & Protection
~1/5 of Nation's Gross Area -
Nearly 1/2 Billion Acres
Figure 3
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FEDERAL AVIATION ADMINISTRATION
(3rd largest spectrum user)
FUNCTION -
To provide for the safe and expeditious movement of aircraft.
The Federal Aviation Administration uses radio frequencies for communications
and radionavigation to carry out its responsibility to provide for the safe
and efficient use of the airspace by both civil and military aircraft.
SUPPORT -
>15,800 Frequency Assignments.
>$440 Million Electronic Equipment.
INVESTMENT BY RADIO FREQUENCY BANDS -
200-415 kHz $ 2,900,000
1.6-27.5 MHz 4,300,000
72-100 MHz (Alaska Links) 380,000
75 MHz (Markers) 1,608,000
108-118 MHZ 77,140,000
118-136 MHz 32,000,000
162-174 MHz 3,360,000
225-400 MHZ 18,400,000
328.6-335.4 MHz 10,780,000
406-420 MHz 100,000
960-1215 MHz 98,682,000
1300-1350 MHz 111,600,000
2700-2900 MHz 55,350,000
7125-8400 MHz 26,165,000
9000-9200 MHz 4,120,000
23,600-24,470 MHz 2,700,000
$449,585,000
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CSM
Figure 5
APOLLO FREQUENCY SUPPORT
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JO SI II 9) 54 SS J* »7 S» Sf 40 41 42
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As is evident, there are many resources that are inexorably
entwined with availability of radio frequencies. As a consequence,
any new boundary conditions or limitations imposed upon users of radio
may have considerable ramifications in terms of the ability of a
particular system to continue performing its intended information
transfer function, and in doing so severely inhibit the effective
accomplishment of numerous national goals. Therefore, it is incumbent
upon the managers of the radio spectrum to be particularly alert to
appreciating how radio energy may adversely affect the health of the
people it is intending to serve.
Nature of Environment Impact
As alluded to earlier, the users of the radio spectrum have an
environmental impact of two major varieties. The first concerns the
impact that a new communication-electronic system has on the operation
of existing communication-electronic syster>s. The second concerns how
a communication-electronic system effects may impact on man.
The first type of environmental impact is termed electromagnetic com-
patibility. In this case the impacted environment consists of all
other communication-electronic equipments which may be susceptible to
functional modification by the radio energy of other communication-
electronic equipments. In other words, the emissions from various
radio transmitters may be received unintentionally by communication-
electronic systens which were not intended to be receptors of such
radio emissions. These unintended received emissions may be of
sufficient magnitude or character that they prove deleterious to the
ability of the receptor to actually receive its intended information
12
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carrying signal. Therefore, it is becoming increasingly necessary
that there be a comprehensive analytical study of the impact of any
new radio system before its introduction into the radio environment
where it intends to operate. Such an analysis n>ay also include a
determination as to whether the existing communication-electronic
systems in the environment will do harm to the functioning of the
new system. In the near future it will become a matter of policy
that a new user of the radio system will not be permitted to operate
until he has given conclusive proof that such compatibility does
exist.
Needless to say, the ensuring that there are capabilities within
the Federal Government to perform such analyses and that such analyses
are being performed in the most congested parts of the radio spectrum
are becoming an increasingly large part of the spectrum management
process.
Another name for these analytical studies preliminary to
implementation of a new radio system is spectrum engineering. Inevitably,
if it appears that a radio system cannot satisfactorily operate and
yet there is a sufficient demand for its information transfer function,
remedial actions must be taken to permit the new system to operate.
These remedial actions may take the form of additional filters, improved
antennas and/or a decrease in the amount of emitted power. These
modifications are predicated on conforming to a set of boundary condi-
tions between the new system and the existing systems which will permit
there mutual coexistence.
13
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The second form of environmental impact is biological. This, of
course, concerns the potential of radio energy to have biologically dele-
terious effects. This concern is increasingly being considered as one
requiring environmental protection. As you may know, the Environmental
Protection Act of 1970, Section 102, requires that Federal agencies file
environmental impact statements. Already several such statements have
been filed in connection with major Government communication-electronic
systems and considerable research has been undertaken to ascertain the
nature of these potential impacts. Additionally, the Federal Communications
Commission has recently issued a Notice of Inquiry to ascertain what form
of requirement it should place upon its licensees in connection with
environmental impact. Furthermore, there are increasing instances of public
concern being raised over the potentially deleterious effects of radio energy,
and our uncertainty with regard to the nature of these effects is giving
rise to heighted fears associated with the increasing population of radio
transmitting equipment.
Therefore, it has become a matter of some urgency to come to grips
with the nature of this biological impact in order to establish the
necessary boundary conditions which on the one hand will be protective
of health and on the other hand permit the functioning of telecommunica-
tion systems. In response to the need to adequately define this problem,
the Office of Telecommunications Policy (DTP) has advising it the Electro-
magnetic Radiation Management Advisory Council. Almost a year ago, this
Council recommended a program for coordinating efforts within the Federal
Government with respect to research dealing with the biological effects
of nonionizing electromagnetic radiation. The OTP approved this program
and subsequently forwarded it to the various participating Government
14
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agencies and organizations for implementation. You will hear more about
where we stand on this effort later in this program.
What boundary condition or conditions will establish the basis for a
meaningful protection guide in the area of potential and real biological
effects of nonionizing electromagnetic radiation, particularly those
emanating from Federal Government radio communication facilities? The
answer is at present unknown. Today when confronted with the need for
stating some form of number for protective purposes we fall back on the
2
number of 10 yw/cm . The fact of the matter is that we are uncertain as
f
to the biological effects of electromagnetic energy because we have not
been systematically looking for the effects, particularly those which may
occur over long periods of time at low levels. We have not performed the
adequate experiments; we do not have the necessary dosimetry to know what
we are measuring, and we have not investigated the low level effects of
nonionizing radiations in anywhere near a fashion which is commensorate
with the variety of modulation forms presently employed by communication-
electronic equipment. Meanwhile we are continually confronted, particularly
in highly exposed governmental positions, to an increasing number of
public incidents and fragmentary evidence that in fact, nonionizing electro-
magnetic energy does cause some effects at levels below 10. It is
incumbent upon the community who is knowledgeable about the various aspects
of this problem, including both electronic and medical disciplines, to
initiate the necessary research projects leading towards its resolution.
Formulation of Protection Guides in Relation to Radio Spectrum Use and Policy
There is no question that the juxtaposition of public health concerns,
with the concerns of achieving national goals through the utilization of
15
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various kinds of radio telecommunication emissions, poses national policy
problems. There may in fact be a problem of real concern to public
health. Support for such a view may be found in a recent law of the
Peoples Republic of Poland where a safe level of exposure to nonionizing
f\
electromagnetic radiation is considered to be in the order of 10 yw/cnr
fully one thousand times less than the presently accepted U.S. standard.
On the other hand, were the United States to follow such a protection
guide literally, we would probably create an even more hazardous situation
for passengers on airplanes as the radars used in air traffic control would
have to be turned off because they would not be able to conform to such
a standard. Furthermore, our space program would be put into jeopardy and
we would probably not be able to have broadcasting radio and television
network systems similar to those we have today.
Should this disparity in protection guides present you with any great
concern, let me also point out that in this same public law of the
Peoples Republic of Poland there is an Article 10 which essentially states
that the communication-electronic systems under the purview of the Ministry
of the Interior and Defense need not pay any attention to it.
Finally, in addressing the relationship between environmental impact
and management of the radio spectrum, I would like to make a special
appeal to the medical people among you to exert particular effort in pro-
viding the necessary medical description of the deleterious effects that
low-level nonionizing electromagnetic radiation may cause. The radio
spectrum is to a large degree managed by people who have electrical
engineering or telecommunication engineering backgrounds. And, while
they and their colleagues are competent in developing techniques for
16
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measuring levels of radio energy, they are dependent upon you for
providing an adequate description of the effects that such energy
may cause to the human body. At present we are deficient in this
understanding and therefore I appeal to you to help us solve it.
Thank you.
17
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ELECTROMAGNETIC ENVIRONMENTS IN URBAN AREAS
J. C. Toler
Engineering Experiment Station
Georgia Institute of Technology
Atlanta, Georgia
1. Introduction
From conception until death, man is literally submerged in and
buffeted by the environment within which he exists. This environment
t
tends to be highly variable and the individual components of which it
is composed are generally complex and innumerable. Many of these com-
ponents are quite visible and are therefore readily recognizable; others
are equally non-visible, and are recognized only by the technically
trained and/or scientifically inquisitive.
Electromagnetic fields provide a good example of a component
within the environment that is generally unrecognized. Yet these
fields undoubtedly influence in significant ways the functioning of
biological systems. At least in part, these influences can be attri-
buted to the fact that numerous biological functions are in response to
electrical stimuli. Many of the electromagnetic field influences on
biological systems have been extensively investigated and are rather
well understood. Others have been investigated in only a peripheral
fashion such that the results are somewhat confused and subject to con-
siderable controversy. It is also possible that still other electro-
magnetic field influences on biological systems have not as yet even
been scientifically recognized. These influences may then provide chal-
lenging research areas in future decades.
19
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The matter of electromagnetic radiation protection guides for
biological systems is representative of areas in which only peripheral
or limited investigations have been conducted to date. These investi-
gations have resulted in the promulgation of radiation protection
guides in the form of safe exposure levels as a function of time. How-
ever, these levels vary drastically depending upon the country within
which they were developed and upon the primary effect radiation was
assumed to have on biological systems. The most obvious of these expo-
2
sure level variations is the United States limit of 10 mW/cm relative
2
to the Russian limit of 0.01 mW/cm . The United States limit is based
primarily on thermal stress induced into the biological system while
the Russian limit supposedly accounts for thermal as well as more subtle
nonthermal effects of a behavioral nature. Both limits are specified
for exposure to average power densities for given time periods, under
normal environmental conditions, and over particular frequency ranges.
In view of the large magnitude difference in the exposure limits
and the possibility that nonthermal biological effects have not been
accounted for, it is not difficult to understand that the United States
protection guide is under severe scrutiny. This scrutiny is directed
to, among other things, (1) the adequacy of the exposure level magni-
tude, (2) the applicability of the 10 MHz to 100 GHz frequency range,
(3) whether power density is a suitable electrical parameter for speci-
fying damage to biological systems, and (4) near-field versus far-field
effects of radiation exposure, etc. A further problem exists in the
fact that the United States limits are applicable only over the 10 MHz
to 100 GHz frequency range. Since there are high power electronic
20
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systems operational at frequencies below 10 MHz, there is a tendency to
2
assume that the 10 mW/cm limit is equally applicable to these systems.
This assumption ignores technical extrapolations which indicate the
relationship between wavelength of the radiated field and power depo-
sition in the biological system.
The uncertainties regarding radiation protection guides are attri-
butable in part to the fact that there is a scarcity of data defining
the ambient electromagnetic environments to which the public is con-
i
tinually exposed. Because of this situation, a limited research
project was undertaken to (1) investigate technically feasible and cost
effective techniques for the measurement of electromagnetic environ-
ments and (2) obtain electromagnetic environment data over at least a
portion of the frequency spectrum. Since most of the United States
public is concentrated in urban areas, the measurements were conducted
in the Atlanta metropolitan area. This area wac considered representa-
tive of urban areas with populations of approximately one million or
more. The following paragraphs report the results of the research
project.
2. Literature Review
The initial efforts consisted of compiling technical information
regarding both past and current efforts to determine spectrum conges-
tion1. Reports on major work sponsored by the Federal Communications
Commission (FCC), the Office of Telecommunications Management (OTM),
and the National Academy of Engineering (NAE) were obtained for review.
Additionally,- numerous articles and editorials on spectrum management,
engineering,~and utilization were obtained from the commonly available
21
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technical periodicals. All of these documents and publications were
reviewed and analyzed in terms of their pertinence to the objective of
this project. Of particular interest were the test equipments and
equipment configurations that have been used to obtain band occupancy
and ambient noise level data. These equipments and configurations
directly influence the accuracy of resulting data, dynamic range over
which data can be obtained, parameters that can be monitored, receiver
spurious responses that must be accounted for, etc.
3. Band Occupancy Measurements
After the review and analysis of relevant literature, efforts were
directed toward an experimental investigation of methods for determin-
ing the occupancy of selected frequency bands. The first method inves-
tigated consisted of various antennas used with a spectrum analyzer and
strip chart recorder. The test configuration was as shown in Figure 1.
Band occupancy data was initially taken over the 0 to 1.2 GHz frequency
range of the spectrum analyzer, and is shown in Figure 2. An analysis
of this data resulted in the following conclusions: (1) a large per-
centage of the transmissions in some frequency bands were not detected
because they were intermittent and not intercepted by the spectrum
analyzer sweep, (2) the frequency range covered was so broad and re-
quired so many different test equipments, test configurations, etc.,
that an indepth investigation of measurement methods was difficult, and
(3) the spectrum analyzer/recorder configuration yields data difficult
to reduce in terms of band occupancy.
In view of the above conclusions, it was decided to narrow the
range of measurement effort to only the 25 to 50 MHz frequency band
22
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Antenna
HP
Spectrum
Analyzer
8553/8552A
Brush
Mark 220
Recorder
Figure i.
Test Configuration for Measuring Frequency
Band Occupancy.
23
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Frequency In MHz
Figure 2(a). Band Occupancy Data Over the 0 to 5 MHz Frequency Range
1 :
•
\
1
III
ll
.:
It
;
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il
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k.
II
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10
Frequency in MHz
Figure 2(b). Band Occupancy Data Over Che 5 MHz to 10 MHz Frequency Range.
Frequency in MHz
Figure 2(c). Band Occupancy Data Over the 10 MHz to 30 MHz Frequency Range.
i
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. '
li
I
I
1
,
| j
..
|
I*
8
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1
30
50
Frequency in MHz
Figure 2(d). Band Occupancy Data Over the 30 MHz to 50 MHz Frequency Range.
24
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Frequency in MHz
Figure 2(e). Band Occupancy Data Over the 50 MHz to 100 MHz Frequency Range.
1
1
1
1
1
1
, ,
1
1
1
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ll I
trt
1
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100
Frequency Range
Figure 2(f). Band Occupancy Data Over the 100 MHz to 200 MHz Frequency Range.
:oo
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1 1
III]
—
i
1
1
200
Frequency In MHz
Figure 2(g). Band Occupancy Data Over the 200 MHz to 700 MHz Frequency Range.
JOO
700
Frequency in MHz
Figure 2(h). Band Occupancy Data Over the 700 MHz to 1200 MHz Frequency Range.
1200
25
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assigned for land mobile usage. This not only significantly limited
the frequency range of concern, but assured that attention would be
devoted to a severely congested range of frequencies within which inter-
mittent transmissions are common. It was further decided that an im-
proved means of monitoring the land mobile frequency bands was necessary
in order to obtain reliable band occupancy data. Requirements that the
improved band monitoring scheme must possess included the ability to
(1) rapidly scan a frequency range which could be varied from test-to-
test, (2) provide an indication each time a transmission was present
within the established frequency range, (3) accumulate the data indi-
cating transmissions at discrete frequencies within a given band, and
(4) dump the data after scanning of the frequency range was complete.
A block diagram of the system developed to fulfill these requirements
is shown in Figure 3.
Major components of the improved measurement system were a
Hewlett-Packard Model 8553/8552A Spectrum Analyzer, a Fabri-TEK. Model
1070 Signal Averager, a differential comparator, & 2.5 second trigger
oscillator, and an X-Y recorder. In the operational mode of the system,
the spectrum analyzer provided the required frequency scan capability
and the signal averager provided data processing and storage. The sig-
nal averager included a memory capable of storing 1024 18-bit words.
During these measurements, this memory capability was utilized as 1024
bins within which incoming data was stored. The spectrum analyzer and
signal averager were both operated in the external sweep mode and syn-
chronized by the trigger oscillator. The vertical output of the spec-
trum analyzer, which was a DC voltage directly proportional to the RF
26
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Antenna
50:
;
rHyb
,
-Id
HP-606
Signal
Generator
Spectrum
Analyzer
(Trigger
Differential
Comparator
Tr igger
i
2.5 Second
Trigger
Oscillator
Fabrt-Tek
Series 1070
SIGN
AVERAG
SVST
]
ING
EM
Mo s 1 e y
X-Y
Recorder
Figure 3. Test Configuration for Measuring Band Occupancy
of Land Mobile Bands.
I
100
30
32
34 36 38
Frequency In MHz
42
Figure It. Percent Band Occupancy Over the Frequency Range of 27
to 47 MHz, 6:30AM to 8:30AM.
'
27
-------
input signal, was coupled to the differential comparator. The compa-
rator generated a constant amplitude £quare wave, with a time duration
equal to that of the input signal, whenever the input signal exceeded
the preset bias voltage of the comparator. This output was then '
coupled to the signal averager, digitized, and stored in the data bin
corresponding to the measured frequency increment. This procedure was
repeated at the rate of the trigger oscillator and percent usage of the
frequency increment was obtained from the accumulation of stored -sig-1- '
nals. The accumulated signals in the 1024 data bins could be displayed
(1) individually in a numerical form or all together in a composite -
form on a CRT scope, (2) in a composite form on an X-Y recorder, or i:
(3) in a punched paper tape format. The probe antenna was a half-waVe
dipole tuned to 37 MHz. Preliminary scans were made to determine'
whether the antenna polarization should be horizontal or vertical. The
resulting data indicated a vertical polarization was desirable; conse-
quently, this polarization was used during subsequent testing. '• e <•
For the measurements described herein, the spectrum analyzer- was
operated to scan the 27 to 47 MHz frequency band with a scan time of
2.0 seconds and an IF bandwidth of 3 kHz. The signal averager was oper-
ated with a scan time of 2.05 seconds, which gave a dwell time of 2.0
milliseconds for each of the 1024 data bins. Thus, each of the bins1
represented a frequency interval of 20 kHz. The total scanning peribd,^
controlled by the trigger oscillator, was 2.5 seconds' resulting Jin a
lapsed time of 0.5 seconds between scans. The comparator, in-conjunc-
tion with the spectrum analyzer, was adjusted to gefterjate aiE output for:
a received signal with an amplitude of -85 dBm or-greater at" the •'
28
-------
spectrum analyzer input. The -85 dBm threshold signal level was used
because it was 6 dB above the background noise level. The 6 dB margin
was considered necessary since the band occupancy measurements were
concerned with intentional and discrete manmade transmissions as op-
posed to the ambient noise level.
For calibration purposes, it was desired to add a discrete fre-
quency signal to the input signal. This added signal would represent
100 percent usage of one of the frequencies within phe 27 to 47 MHz
range, and would provide an indication that the system was properly
operating. Preliminary scanning of the 27 to 47 MHz band indicated no
transmissions at 46 MHz; consequently, this frequency was chosen for
continuously injected calibration signal.
The resultant test data is shown in Figures 4, 5, and 6. Scans
with two-hour durations were conducted over the following time intervals:
6:30 to 8:30 a.m., 11:30 a.m. to 1:30 p.m. and 4:00 to 6:00 p.m. The
data indicates that essentially continuous transmissions exist at 28,
30, 31.9, 35.45, 35.5, and 43.5 MHz. Also, the congestion in the 27 to
28 MHz region is obviously serious. In all other portions of the 27 to
47 MHz frequency range, the band occupancy is quite low. During the
noon iand late afternoon time intervals, the 43.5 to 44.4 MHz frequency
band appears to be noticeably more occupied than it was during the
early morning hours. Also, the 28 to 29 MHz band is considerably more
occupied at noon than it is at either the early morning or late after-
noon hpurs.
4^ ^ad^rpund Electromagnetic Environment Measurements
At this point, the emphasis of the experimental investigations
29
-------
100 —
80
70 '
60 '
50
m
M
40 _i;
30-
m
m
iii!
i^-iii
20 '
10
i
j
i
iplBJlafei
.4 46
28
30
32
34 36 38
Frequency In MHz
Figure 5. Percent Band Occupancy Over the Frequency Range of 27
to 47 MHz, 11:30AM to 1:30PM.
I
30
32
34 36 38
Frequency in MHz
40
42
Figure 6. Percent Band Occupancy Over the Frequency Range of 27
to 47 MHz, 4PM to 6PM.
30
-------
shifted from band occupancy measurement techniques to determination of
the ambient electromagnetic background or noise level. Such a shift in
emphasis was necessary at this point because only a limited amount of
time remained before the project had to be completed. The noise level
measurements were made over a 0 to 1.2 GHz frequency range and at three
locations in the metropolitan Atlanta area. These locations were as
follows: (1) a northwest location at 3540 Dunn Street in Smyrna,
Georgia, (2) a northeast location at the Georgia Tech Field Site near
*
Stone Mountain, Georgia, and (3) a downtown Atlanta location on the
roof of the Systems and Techniques Department Building on the Georgia
Tech campus. The test equipment consisted of a suitable antenna, spec-
trum analyzer, and strip chart recorder configured as shown in Figure 1.
The video output of the spectrum analyzer was coupled to the recorder
to provide a plot of spectral components as a function of frequency.
It was necessary to divide the 0 to 12 GHz frequency range into 13 sepa-
rate bands in order to provide measurement antennas. These bands and
the antenna used for each are shown in the following:
Frequency Band Antenna Antenna Tuned
(MHz) Type Frequency
0 to 0.5 41" monopole 0.15 to 0.36 MHz band
0.35 to 0.85 41" monopole 0.36 to 0.75 MHz band
0.5 to 2.5 41" monopole 0.87 to 2.1 MHz band
1 to 6 41" monopole 2.1 to 5.2 MHz band
4 tc 14 41" monopole 5.2 to 12.7 MHz band
11 to 31 41" monopole 12.7 to 30 MHz band
3C to 80 Half-wave dipole 55 MHz
65 to 115 Half-wave dipole 90 MHz
100 to 200 Half-wave dipole 150 MHz
200 to 300 Half-wave dipole 250 MHz
250 to 350 Half-wave dipole 300 MHz
350 to 850 Cavity-backed spiral Broadband
800 to 1300 Cavity-backed spiral Broadband
31
-------
The measurement procedure for each frequency band consisted of
first terminating the 50 ohm spectrum analyzer input with its charac-
teristic impedance. The internal noise level of the measurement equip-
ment was then recorded. Ambient noise levels were recorded next by
substituting the appropriate antenna for the 50 ohm impedance at the
receiver input.
The resulting data, for each of the 13 frequency bands, taken on
the Georgia Tech campus is shown in Figure 7. Recorder data for the
other two locations is not presented because of its volume and the fact
that it is nearly identical in appearance to that obtained from the
campus location. Transmissions from AM radio stations are clearly evi-
dent in the data recorded over the 0.35 to 0.85 MHz and 0.5 to 215 MHz
frequency bands. Further, FM radio station transmissions arc obvious
on the data recorded over the 65 to 115 MHz frequency band. Television
audio and video transmissions for channels 2, 5, 11, 17, and 30 appear
on the data at the following frequencies:
Video Audio
Channel Tr ansmis s ion Transmission^
2 55.25 MHz 59.75 MHz
5 77.25 MHz 81.75 MHz
11 199.25 MHz 203.75 MHz
17 489.25 MHz 493.75 MHz
30 567.25 MHz 571.75 MHz
* , !
Considerable discrete frequency activity not directly related to radio
or television transmissions appeared in the general frequency range of
5 to 20 MHz. The specific ambient noise level data extracted from the
recordings made on the Georgia Tech campus is presented in Table I.
This table also shows the various factors which must be reflected in
32
-------
-30
1
L
n
1
i
I
m
tfta
_-.
—
• —
•
•
' '
\
'
**
-130-
• •*•
Instrumentation Noise Calibration over the 0 to 0.5 MHz Frequency Band
-30
-130
Frequency in MHz
Figure 7(a) . Spectral Components Measured from Roof of Electronics Research
Building Over the 0 to 0.5 MHz Frequency Band.
' :
-30
-130
-30
Instrumentation Noise Calibration Over the 0.35 MHz to 0.85 MHz Frequency
Band
Frequency In MHz
Figure 7(b). Spectral Components Measured from the Roof of the Electronics Research
Building over the 0.35 MHz to 0.85 MHz Frequency Band.
0.85
33
-------
-30
-130'
Instrumentation Noise Calibration Over the 0.5 MHz to 2.5 MHz Frequency
Band
-30
2.5
Frequency in MHz
Figure 7(c). Spectral Components Measured from the Roof of the Electronics Research
Building Over the 0.5 MHz to 2.5 MHz Frequency Band.
-30
Instrumentation Noise Calibration over the 1 MHz to 6 MHz Frequency Band
-30
-130
Frequency in MHz
Figure 7(d).
Spectral Components Measured from the Roof of the Electronics Research
Building over the 1 MHz to 6 MHz Frequency Band.
34
-------
-30
-130
Instrumentation Noise Calibration over the 4 MHz to 14 MHz Frequency Band
-30
-130
Frequency in MHz
Figure 7(e). Spectral Components Measured from Roof of Electronics Research
Building over the 4 MHz to 14 MHz frequency Band.
-30
-130
Instrumentation Noise Calibration over the 11 MHz to 31 MHz Frequency
Band
-30
-130
Frequency in MHz
Figure 7(f). Spectral Components Measured from Roof of Electronics Research
Building over the 11 MHz to 31 MHz Frequency Band.
35
-------
-30
I I
-130
Instrumentation Noise Calibration over the 30 MHz to 80 MHz Frequency
Band
-130
30
Frequency in MHz
Figure 7(g).
Spectral Components Measured From Roof of Electronics Research
Building over the 30 MHz to 80 MHz Frequency Band.
•30
I
-130
Instrumentation Noise Calibration over the 65 MHz to 115 MHz Frequency
Band
-30
-130
Frequency in MHz
Figure 7(h). Spectral Components Measured from Roof of Electronics Research
Building over the 65 MHz to 115 MHz Frequency Band.
115
36
-------
-30
-130
Instrumentation Noise Calibration Over the 100 MHz to 200 MHz Frequency
Band
-JU
' •:••
10
III
3
| !
Ill
i
1
•
|
i
• •
1
:
i
I
!
1
•
!
I
'
j i
4
i . .1
i !
I
•
.
.
.
il| i
l ! j ; i I ;:,::,:::;
tj j
•^ JnUm^U^ ^f^
• r '• ^"^ •
20
Frequency In MHz
Figure ;(i). Spectral Components Measured from Roof of Electronics Research
Building over the 100 MHz to 200 MHz Frequency Band.
-30
-130
i
1
i
—
-
•
L
=t
t
.
-
i
Instrumentation Noise Calibration over the 200 MHz :o 300 MHz Frequency
Band
-30
:
:-
-130 —
200
_
.
|
'
•
' "
|
;
. . .
. . .
....
.
....
. .
;
. . . . .
30
Frequency in MHz
Figure ~(j). Spectral Components Measured from Roof of Electronics Research
Building over the 200 MHz to 300 MHz Frequency Band
37
-------
-30
-no
- H
Instrumentation Noise Calibration Over the 250 MHz to 350 MHz Frequency
Band
-JO
-130
250
350
Figure 7 (k).
Frequency in MHz
Spectral Components Measured from Roof of Electronics Research
Building over the 250 MHz to 350 MHz Frequency Band.
-30
-130-
Instrumencation Noise Calibration over the 350 MHz to 850 MHz Frequency
Band
-30
-130
0
1
1
ft
j
850
Frequency In MHz
Figure 7 (1). Spectral Components Measured from the Electronics Research
Building over the 350 MHz to 850 MHz Frequency Band.
38
-------
-30
-130
Instrumentation Noise Calibration over the 800 MHz to 1300 MHz Frequency
Band
-30
130
80(
)
-
-
-
•
-
-
•
—
-
-
-
•
1
-j-J
i
1
:
•
:
btfUrj
. ) .....
130
Frequency in Mllz
Figure 7(m). Spectral Components Measured from Roof of Electronics Research
Building over the 800 MHz to 1300 MHz Frequency Band.
39
-------
TABLE I. Ambient Electromagnetic Noise Level Measured
on the Georgia Tech Campus
Frequency
Band
MHz
0-.5
.35-. 85
.5-2.5
1-6
4-14
11-31
30-80
65-115
100-200
200-300
250-350
350-850
800-1300
Rcvr .
Noise
Level
dBm
-116
-122
-123
-120
-120
-118
-114
-113
-110
-110
-110
-106
-106
Rcvr. +
Ambient
Noise
Level
dBm
-111
-112
-118
-117
-117
-116
-112
-108
-110
-110
-110
-106
-106
BW
Factor
dB
-4.8
-4.8
-4.8
0
0
0
4.8
4.8
4.8
4.8
4.8
10
10
Adjusted
Rcvr.
Noise
Level
dBm/kHz
-111.2
-117.2
-118.2
-120
-120
-118
-118.4
-117.8
-114.8
-114.8
-114.8
-116
-116
Adjusted
Rcvr. +
Ambient
Noise
Level
dBm/kHz
-106.2
-107.2
-113.2
-117
-117
-116
-116.4
-112.8
-114.8
-114.8
-114.8
-116
-116
Ambient
Noise
Level
dBm/kHz
-108
-107.7
-114.8
-120
-120
-120.3
-120.7
-114.5
<-120
<-120
<-120
<-122
<-!22
Antenna
Factor
dB
-35.6
-30.4
-26.4
-22.4
-17.4
-14.4
+ 6.72
+ 1.64
- 3.0
- 7.3
- 8.8
-10
-12
Ambient
Noise
Field
Intensity
dBm/m2/kHz
- 72.4
- 77.3
- 87.4
- 97.6
-102.6
-105.9
-127.4
-115.1
<-117
<-113
<-lll
<-112
<-110
-------
the raw data before arriving at a final value for the ambient noise
level. Corresponding ambient noise level data for the other two test
locations is presented in Table II. As was expected, the highest ambi-
ent noise levels were recorded at the lowest frequencies. Another
expected result was revealed in the fact that the ambient noise level
was higher at the downtown location than either of the suburban loca-
tions. At frequencies above approximately 100 MHz, the measurement
equipment was not sensitive enough to determine ambient noise levels.
t
Only discrete frequency transmissions were measured above this 100 MHz
frequency. A comparison of ambient noise levels in the Atlanta area
relative to typical metropolitan areas can be made by referring to
Table III. Data in this table is a compilation of typical noise levels
in both suburban and urban areas as a function of frequency. For ex-
2
ample, the typical urban noise level at 20 MHz is -95 dBm/m /kHz. In
the Atlanta area, the corresponding level measured was approximately
2
-127.4 dBm/m /kHz. The considerably lower level in the Atlanta area
could be attributed to such possibilities as (1) the Atlanta area does
not have many of the heavy industries which contribute significantly to
the ambient noise level in many typical cities or (2) the single measure-
ment location in Atlanta was not representative of the total urban area.
5. Conclusions
The research efforts undertaken were limited and consequently, the
resulting data is correspondingly limited. Therefore, caution must be
exercised in drawing firm conclusions from the measured results.
In terms of the review of literature available on spectrum monitor-
ing, surveys, congestion, etc., it is concluded that an appreciable
41
-------
TABLE II. Ambient Electromagnetic Noise Level Measured
At Two Metropolitan Locations.
Frequency
Band
MHz
0-.5
.35-. 85
.5-2.5
1-6
4-14
11-31
30-80
65-115
100-200
200-300
250-350
350-850
800-1300
Ambient Noise Field
Field Site
- 78.7
- 77.0
- 89.1
<-100
-101.6
<-107
-113.4
- 87.6
<-110
<-105
<-105
<-105
<-103
2
Intensity dBm/m /kHz
Smyrna Site
- 80.7
- 69.8
- 93.1
96.1
-100.9
-107.6
<-120
<-120
<-117
<-112
<-112
<-110
<-107
-------
TABLE III. Typical Urban and Suburban Field Intensities/
URBAN
Frequency
MHz
1
2
4
8
10
20
40
80
100
200
300
400
500
Field
Intensity
In
p.V/m/10 kHz
(Graph)
170
103
80
53
50
35
26
20
18
14
12.5
11.4
10.6
Field
Intensity
In
2
dBm/ra /kHz
81.2
85.5
- 87.8
- 91.3
- 91.8
- 95.0
- 97.5
-100
-100.7
-103
-103.8
-104.7
-105.3
SUBURBAN
Field
Intensity
In
p.V/ra/10 kHz
(Graph)
50
23
17'
13
12
11
10.1
9.8
9.6
9.4
9.2
9.1
9.1
Field
Intensity
In
dBm/m2 /kHz
- 91.8
- 98.5
-101.2
-103.5
-104.2
-105.2
-105.7
-106
-106.1
-106.3
-106.5
-106.6
-106.6
NOTE: Taken from Graphs in "Reference Data for Radio Engineer," 4th
Edition, 1962.
43
-------
amount of literature is available on the broad subject of ambient elec-
tromagnetic environments. Very little of this data is concerned with
the possible influence of these environments on public health.
As for the investigation of feasible measurement techniques, it is
concluded that the configuration involving signal averaging equipment
is a significant improvement over that reported in the available liter-
ature. The extent to which a selected frequency band is utilized by
either continuous or intermittent transmissions can be precisely deter-
mined with the signal averager. In fact, the occupancy of the 27 to
47 MHz frequency band was shown by the measured data to be considerably
less severe than anticipated. The signal averaging measurement tech-
nique is considered to be worthy of further investigation.
The major conclusion drawn from the ambient noise level data was
that the measure techniques, resulting data, and data usefulness are
comparable to similar data obtained during other investigations. The
ambient noise level in the Atlanta urban location appeared to be below
published typical levels; however, firm conclusions to this effect would
be difficult to draw without more data.
6. Future Efforts
Future efforts will be directed along three lines as follows:
a) The measurements will be repeated periodically to determine if
increases in the magnitude of the electromagnetic environment
are apparent.
b) The frequency bands over which the measurements are made will
be expanded to include a significantly increased frequency
coverage.
44
-------
c) Antennas which are applicable over broader frequency ranges
will be used in future measurements to reduce the number of
equipment changes necessary between 0-12 GHz.
45
-------
ENVIRONMENTAL NONIONIZING RADIATION EXPOSURE:
A PRELIMINARY ANALYSIS OF THE PROBLEM AND CONTINUING WORK WITHIN EPA
RICHARD A. TELL
U.S. Environmental Protection Agency
Office of Radiation Programs
5600 Fishers Lane
Rockville, Maryland 20852
47
-------
ENVIRONMENTAL NONIONIZING RADIATION EXPOSURE:
A PRELIMINARY ANALYSIS OF THE PROBLEM AND CONTINUING WORK WITHIN EPA
The fact that electromagnetic energy in the radiofrequency
and microwave portions of the spectrum can induce dangerous effects
on human tissues when applied with sufficiently high intensity has
been known for many years. With the invention of radar in 1935 and
its rapid development and deployment during World War II, it became
common knowledge among radar workers that microwave frequencies
could interact with tissue leading to significant heating, depending
upon the relative heat dissipation capabilities of the particular
part of the anatomy exposed. Warnings about the possible induction,
from over exposure, of cataracts of the eye and temporary sterility
became commonplace.
Since those early days of microwave hazard concern, the
expanded use of radiofrequency, or RF, and microwave energy for
various applications such as widespread communications systems and
industrial operations has elicited a new and more critical concern
over the possible health implications of this form of nonionizing
radiation (1, 2, 3). This new concern is with low level exposure
and it has arisen because (a) the environmental levels are unknown,
(b) the number of sources is increasing, and (c) the controversy
over nonthermal effects which is illustrated by the discrepancy
between human exposure standards used in the United States and in
the Soviet Union. The purpose of this presentation is to share
some of our thoughts and planned activities within the Office of
Radiation Programs and to discuss quantification of the population
exposure to RF and microwave fields in our environment.
Table 1 illustrates some of the different maximum permissible
exposure standards around the world. The most striking aspect of
this listing is the apparent difference in recommended levels
between the U.S.A. and the U.S.S.R., Czechoslovakia, and Poland.
In general, this discrepancy can be summarized by simply stating
that the United States's standard is 1,000 times higher than those
in these other countries. For example, a difference between
10 mW/cm2 power density in the U.S. and 10 ja,W/cm2 power density in
the U.S.S.R.
In order to better appreciate some of these quantities in
the different exposure standards, several RF and microwave
definitions are necessary. When I refer to the electromagnetic
48
-------
Country and
Source
Radiation
Frequency
Maximum
Recoirmcnded
Level
Condition or Remarks
USA (USASI)
US Army and
Air Force
Great Britain
(Post Office
Regulation)
NATO (1956)
Canada
Poland
German Soc.
Republic
U.S.S.R.
Czech. Soc. Rep.
10 MHz to 100 GHz 10 mVi/cm
1 mW hr/cm2
10 mW/cm2
10 to 100 mW/cmz
30 MHz to 30 GHz
10 MHz to 100 GHz
300 KHz
0.1 to 1.5 MHz
1.5 to 30 MHz
30 to 300 MHz
300 MHz
0.01 to 300 MHz
300 MHz
100 i*l/cm2
10 nW/cm2
0.5 mW/cm2
1 mW hr/cm*
10 mW/cmz
10 nW/cm2
100 wW/cm2
1 mW/cm2
10 mW/en>2
20 V/m
5 amp/m
20 V/m
5 V/m
10 nW/cm2
100 nK/cm2
1 mW/cm2
10 V/m
25 nW/cm2
10 nW/cm2
Periods of 0.1 hr.
Averaged over any
0.1 hr. period
Continuous exposure
Maximum exposure
time in minutes at
W(mW/cm2)
No occupancy
6000W
-2
Continuous 8-hr.
exposure, average
power density
Averaged over any
0.1 hr. period
Periods of 0.1 hr.
6 hr. exposure/day
2 to 3 hr/day
15 to 20 min/day
Alternating magnetic
fields
6 hr/day
2 hr/day
IS min/day
8 hr/day
6 hr/day, CW operation
8 hr/day, pulsed (for
shorter exposures
see Figures 11 and
12)
Table 1. Maximum Recommended RF Levels for Human Exposure
spectrum, I am encompassing all frequencies from zero Hertz, or
the point at which an alternating current becomes a direct current,
to the highest frequency emanations known. In this enormous frequency
region, of course, lie the ultraviolet, visible, and infrared spectra,
as well as the ionizing radiation spectrum. Generally, the radio-
frequency spectrum is taken to cover the 30 kHz to 30 MHz region,
the microwave spectrum from 30 MHz to 300 GHz, and an area not
before mentioned, the ELF, or extremely low frequency area, between
dc and 30 kHz. Table 2 gives the designations for the various
nonionizing frequency bands.
49
-------
FREQUENCY BAND NOMENCLATURE
FREQUENCY RANGE
3
30
300
3,000
30
300
3,000
30
300
30 KHz
300 KHz
- 3,000 KHz
- 30,000 xHz
- 300 MHz
- 3,000 MHz
- 30,000 MHz
300 GHz
- 3,000 GHz
VLF
If
MF
HF
VHP
UHF
SHF
EHF
—
BAND DESIGNATION
VERY-LOW FREQUENCY
LOW FREQUENCY
MEDIUM FREQUENCY
HIGH FREQUENCY
VERY-HIGH FREQUENCY
ULTRA-HIGH FREQUENCY
SUPER-HIGH FREQUENCY
EXTREMELY-H16H FREQUENCY
Table 2. Nonionizing Radiation Frequency Band Nomenclature
When an electromagnetic wave is propagated through some
medium, such as space, there are two methods of describing the
amplitude of this wave intensity. One approach usually employed
in the microwave region is to specify the power density of the
exposure field in terms of power flow per unit area in the wave.
At lower frequencies in the RF spectrum, it is common practice to
specify the field strength of the incident waves in units of
volts per meter. Though this partition in the units of field
specification is attributed to a basic difference in the
instrumentation normally employed for these two different
frequency ranges, fields specified in terms of one unit may
readily be specified in terms of the other by a simple conversion.
For plane waves in free space, this conversion is illustrated in
Figure 1. From this graph, it is apparent that a field density
of 10 mW/cm2 is equivalent to a field strength of 194 V/m, while
a field density of 1 mW/cm2 corresponds to about 67 V/m.
Generally, we will be interested in two different forms of
signals, those which are continuous wave, or CW, and those which
are pulsed. Examples of CW signals, for our purpose include
broadcast stations, both radio and television, two-way radio
services, and satellite communications stations. An example of
a pulsed source is radar where signals are sent in a series of
50
-------
pulses. In a radar, the peak transmitted power may be many times
the average power because the average power depends upon the pulse
duration and how often the pulse is repeated.
Finally, it is important to understand the meaning of
effective radiated power, or as it is abbreviated—ERP. The ERP
of a source refers to an effective power which takes into account
the focusing effect of the source's transmitting antenna. This
concentrating effect of the antenna upon the emitted radiation
pattern is measured by the gain of the antenna, the higher the
Figure 1. Relationship Between Field Strength and Power Density
in Free Space
gain of the antenna, the greater its focusing effect. In short,
rather than letting the transmitter's power be radiated uniformly
in all directions, it limits the angular divergence of the power
in order to concentrate it in some preferred direction. Thus,
when viewing the source antenna from that particular orientation,
it appears that the source has an effective radiated power of
something greater than the actual transmitter power. The concept
of ERP is important in estimating the distant exposure field from
a particular source.
51
-------
With these ideas in mind, let us take a quick look at the
extent of some of the RF sources in our electromagnetic environment
and then examine some of these sources in more detail.
Table 3 offers an introduction to the number of sources within
the United States which are involved in creating the radiobackground
in which we live. This chart indicates total numbers of some of
the various sources by class. Keep in mind that this table does not
take into account many sources, including mobile radio authorizations,
amateur radio stations, microwave oven installations, and others,
nor any type of classified source. Figures 2-6 give as examples,
the geographical display for AM standard broadcast, FM, television,
radar, and microwave sources revealing their quite widespread and
homogeneous nature (4).
AM STANDARD BROADCAST* ...........
FM BROADCAST* ...............
TV BROADCAST* ...............
UNCLASSIFIED RADAR** ..... . ......
MICROWAVE POINT-TO-POINT"
2.859
918
-2.900
~ 72 ,000
* AS OF JULY 17, 1972
** AS OF JUNE 1970
Table 3. Some Types and Numbers of Radiofrequency and
Microwave Sources
AM BROADCAST
J./V, ':i:$&$f
Figure 2. Geographical Distribution of AM Broadcast Stations
in United States
52
-------
FM BROADCAST
Figure 3. Geographical Distribution of FM Broadcast Stations
in United States
Figure 4. Geographical Distribution of TV Broadcast Stations
in United States
f
!> = •• •'•..' ..>.,
Figure 5. Geographical Distribution of Radar Facilities
in United States (unclassified)
53
-------
!' '",'',' 'l:>i'\Y . .'
SitA
Figure 6. Geographical Distribution of Microwave Point-to-Point
Installations in United States
A recent computer search by the Electromagnetic Compatibility
Analysis Center, Annapolis, Maryland, has identified the most
powerful sources in the United States. Figure 7 illustrates the
distribution of the 20 most powerful nonpulsed, unclassified
emitters found. The highest effective radiated power of this
collection is 32 x 109 W or 32 GW produced by source number 1.
LOI.ATION *M> ROk IV ORDER OK [IKRHMM. t.t KK.ITIVF.
RADUTKII I'«I«KK Of I (>!• 20 MINN |>t.l> I M.I.ASM Flr.ll f.MITTF.Rs
Figure 7. Location and Rank in Order of Decreasing Effective
Radiated Power of Top 20 Nonpulsed Unclassified Emitters
54
-------
Table 4 indicates that these sources descend in power to
5 GW for the 20th ranked source. The interesting aspect to this
collection is that all are utilized for various satellite purposes.
Since this original search was accomplished in August of this
year, a new much higher powered source located in California has
very recently initiated experimental operation. This new source
has an effective radiated power of approximately 3.2 x 1012 or
3.2 TW average effective radiated power, placing it well above
even the highest source on this display. Figure 8 illustrates a
similar distribution for the 20 most powerful unclassified pulsed,
or radar sources. Here we find that the number one source, again
located in the Boston vicinity, has a peak effective radiated
power, during its pulse, of 2.8 TW while the lowest one in this
set has a peak power of 35 GW. Table 5 gives more details on
these emitters. These presentations are illustrative of a
practical type of indicator for us as to where to make field
measurements. Assuming that an individual could get into the
main beam of one of these satellite communications stations, a
power density of 10 mW/cms could be found at a distance from the
source of three miles assuming it had an average effective power of
32 GW, or at a distance of about 32 miles for the new source in
California. Distances with possible exposures this high imply the
need for a careful look at the particular characteristics of the
source to ascertain the possibility of a hazard.
Rank
1
2
3
it
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
City /State
West ford, Mass.
Lakehurst, N.J.
Roberts, Calif.
Rosman, N.C.
Pauraalu, Hawaii
Jamesburg, Calif.
Etam, W. Va.
Brewster, Wash.
And over, Maine
Bartlett, Alaska
Archer City, Texas
Mojave Desert, Calif.
Pt. Loraa, Calif.
lielemano, Hawaii
Ft. Moranouth, N.J.
Brandywine, Md.
Camp Parks, Calif.
Wild wood, Alaska
Floyd Test Annex, N.Y.
Elgin, 111.
Frequency
(MHz)
7748
8004
7985
5925
5925
5925
5925
5925
5925
5925
217
5985
7997
7990
7990
79S6
7990
7986
7986
8004
Use
Satellite
Communication
"
11
it
"
'*
it
"
"
It
II
"
It
11
It
tt
II
"
"
Average
ERP (GW)
31.6
20.0
20.0
11.3
7.9
7.9
7.9
7.9
7.9
7.9
6.4
6.4
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
144 nonpulsed, unclassified sources have average ERP's of 1 MW or greater.
Of 79 nonpulsed, classified emitters, none had an ERP greater than the
20th ranked emitter in the unclassified group.
Table 4. Source Parameters for Top 20 Nonpulsed Emitters
55
-------
LOCATION AND RANK IN ORDER OF DECREASING EFFErTMF
RADIATED POWER OF TOP 20 PILSED I Nf I ASSI Fl El> EMITTERS
Figure 8. Location and Rank in Order of Decreasing Effective
Radiated Power of Top 20 Pulsed Unclassified Emitters
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
City/State
Tyngsboro, Mass.
Newstead, N-Y.
Wallops, Va.
Wallops, Va.
Wallops, Va.
Wallops, Va.
Pillar Ft., Calif.
Vandenburs AFB, Calif.
Lakeside, Utah
Westford, Mass.
Boron AFS , Calif.
Savannah AFS, Ga .
Elgin AFB, Fla.
White Sands, N. Mex .
White Sands, K. Mex.
North Dakota
Grover, Colo.
Ft. Morgan, Colo.
Greeley, Colo.
Glbbsboro AFS, N.J.
Frequency
(MHz)
7840
2850
9378
2820
2840
5400
5555
5840
2900
1295
5400
5400
5480
5490
5600
3100
2700
2700
2730
2700
Average
ERP
840 MW
605 MW
640 MW
608 MW
608 MW
25.2 MW
94.3 MW
20.8 MW
115 MW
9.6 GW
149 MW
147 MW
12.7 MW
8.7 MW
8.7 MW
...
...
23.6 Mis-
Peak ERP
2.8 TW
2.2 TV
1.0 TV
0.95 TO
0.95 TW
0.63 TO
0.59 TO
0.52 TO
0.35 TO
0.32 TO
99.8 CW
99.8 CW
79.2 CW
47.5 CW
47.5 CW
39.8 CW
39.8 GW
39.8 GW
39.7 fiW
35.4 GW
229 pulsed, unclassified sources have peak ERP's of 10 GW or greater.
Of 146 pulsed, classified emitters, none had an ERP greater than the
6th ranked emitter in the unclassified group.
Table 5. Source Parameters for Top 20 Pulsed Emitters
56
-------
The number and variety of RF sources which produce emanations
in the publicly accessible environment is large. Considering the
divergent types and uses of RF and microwave energy which carry
the potential of environmental electromagnetic pollution, I have
selected two different categories of sources to focus our attention
on this afternoon for examining possible exposure levels. One
category includes the high power radar and satellite stations which
employ very intense, focused beams. Though the chances of a person
getting into a very directive antenna beam are small, because of
the high powers involved, the greatest hazard may lie within this
category of sources. The other category consists of the large
number of lower power broadcast sources which purposely illuminate
the population with their energy. Though small segments of the
population may be exposed to the intense sources, all of the
population is exposed to these lower powered sources.
f
A theoretical analysis of the radiation fields from broadcast
stations can be divided among the different types of transmitting
antennas utilized by the stations (3) . AM broadcast stations
occupying the 535 to 1605 kHz frequency band normally always use
vertically polarized transmitting towers in order to propagate a
ground wave signal to their primary audience in the surrounding
area. In the United States, AM standard broadcast stations may use
authorized maximum transmitter powers of 50 kW and when coupled
with the low gain antenna towers that they use (low gain because
a single tower will not concentrate the emitted wave into a
particular direction) do not normally produce adversely high field
intensities in their vicinity except, perhaps, at distances
extremely close to the transmitting tower itself. Figure 9
graphically illustrates the field strength of a maximum powered
AM station of 50 kW using a single vertical monopole antenna as
a function of distance from the tower. Though the field strength
varies according to the conductivity of the ground over which the
wave passes, normally as an upper limit, a field strength on the
order of 4 V/m may be expected at a distance of about 1/2 mile
from the tower. This would correspond to an equivalent power
density of about 4
In some cases, AM stations will employ a series of towers in
order to radiate their signal in some preferred direction, either to
serve a selected audience or to minimize interference with some
other station operating on the same frequency but in a distant
town. In this case, the antenna system as a whole exhibits a
higher gain, in some direction, than just a single tower. Consequently,
the field intensity from a station of this sort will be higher than
before according to the number and configuration of the towers. In
practical instances, such tower combinations will account for a
field density increase of only two to four times in the maximum
direction. This would change our previous estimate to something
on the order of 8 V/m, or 16 u-W/cnr at 1/2 mile. And still, in
terms of a thermal hazard level of 10 mW/cm2 this seems to be well
on the safe side. 57
-------
Figure 9. Groundwave Field Strength of 50 kW AM Standard
Broadcast Station
Commercial EM and television broadcast stations may be analyzed
as another type due to the similarity in the antennas used for
transmitting. Due to the nature of propagation of waves in the
VHF and UHF frequency bands used in FM and TV, most, stations employ
high gain antennas atop very tall supporting towers. Before one
can accurately estimate the exposure from such a source, however,
the radiation pattern of the particular station must be incorporated
into the calculation to account for distance from the antenna
supporting tower. With the antennas used in the VHF and UHF region,
the tower is acting merely as a supporting member rather than
radiating itself as is the case with AM stations. From the vertical
gain pattern for a specific antenna as shown in Figure 10 and
knowledge of the tower height, the field density at any given
distance from the tower at ground level may be computed. Obviously,
as one goes up in elevation along side one of these towers, the
field density will increase since you are approaching the primary
radiation beam which is normally aimed at the horizon. For the
various authorized effective radiated powers for commercial FM and
TV stations, Figure 11 illustrates field strength vs. exposure
58
-------
MAJOR LOBE
POWER GAIN-24.0
HOR. GAIN-20.3
CEGBCES FROM HORIZONTAL PLANE
Figure 10. Vertical Gain Pattern of Typical Medium Gain
UHF Transmitting Antennas (Courtesy RCA, Camden, N.J.)
100 r 1 1 1 | Mill \ 1 1 I I I I
01
1 10
DISTANCE FROU ANTENNA IHILES)
Figure 11. Field Strength vs. Distance for 3 ERP's
Used in Broadcasting
59
-------
distance from the source, assuming that one is in the main beam
of the transmitting antenna. Obviously, for this to be applicable,
a person would have to be in a tall building adjacent to one of
these transmitting towers; however, such situations are very possible
in certain metropolitan instances. Under many practical circumstances,
the ground level intensities from most FM and TV emitters are found
not to exceed about 1 V/m; see Table 6. In the case of UHF TV
allocations with maximum effective radiated powers of 5 MW, a
distance of 212 feet corresponds to an exposure of 10 mW/cm2 in the
main beam while if we relax the exposure level to the Russian standard
of 10 (iW/cm3 we find that the distance has increased to 1.2 miles.
In crowded metropolitan areas such an increase in the effective
exposure area from something less than a square city block to
4 1/2 square miles could indicate that in some cases certain portions
of the general population are routinely exposed to levels exceeding
the Russian exposure standards.
In the other category, radar stations represent sources that
operate in the microwave frequency range, use pulsed powers which
are often extremely high, and usually utilize very high gain or
directive antennas. In general, this means that radar stations may
yield high exposure fields at relatively great distances if one is
ever struck by the radar beam. In other words, because the antennas
used are so directive, the probability of being in the main beam of
a radar at any given time is generally quite low. Also, there is
the rotational factor of many radars which further reduces the
chances of prolonged exposure. Nevertheless, careful analysis of
the radar exposure situation is warranted since there are cases in
which the radar beam is intentionally swept near ground level for
specific navigational purposes.
SERVICE
MAXIMUM
ALLOWABLE
ERP, KW
TOWER
HEIGHT,
METERS
FIELD
INTENSITY,
MV/M
FMRADio 100 152.4 1023
VHP TELEVISION
CHANNELS 2-6 100 301,8 807
CHANNELS 7-13 316 304.8 191
UHF TELEVISION
CHANNELS W-83 5000 301.8 380
Table 6. Maximum Powers, Typical Tower Heights, and Ground
Level Field Intensities for Various Broadcast Services
Estimated at One-Mile Upper Limits
60
-------
The most powerful sources in the U.S., however, turn out to be
the satellite communications stations with average effective
radiated powers as high as 3.2 TW. An important comment is in
order about average vs. peak power. Though a radar may have a much
higher peak power, it is the time-averaged, or effective heating
power to which the present U.S. standard of 10 mW/cm2 applies.
Considerable comment on the relative hazards of pulsed vs. continuous
wave exposure has been made by foreign scientists. Yet, at this time,
there have not been any demonstrations by American scientists that a
pulsed field can be any more dangerous than a continuously applied
field of the same average power density (5). Thus, for present
hazard analysis purposes, we will consider only the level of a field
from its average power density standpoint. It is possible, however,
that pulsed emissions can cause detrimental interference with cardiac
pacemakers and other health related electronic devices (6).
•t
The crux of the problem in defining the RF exposure to humans in
our environment lies in the relationship between potential exposure
as calculated from technical data on a particular source, and the
actual human exposure which takes place when individuals are living or
working in the true exposure area of a source. It is a relatively easy
task to determine the potential exposure level to which a person might
become exposed but another much more difficult task to map a truly
reliable, calculated exposure pattern into a population distribution
in the source's area. A primary reason for this difficulty lies in
the nonavailability or difficulty in obtaining accurate source antenna
information and analytical solutions to complex environments filled
with buildings, power lines, and other obstacles, and the highly
dynamic nature of man-made RF levels, i.e., on-off times. In many cases,
this information may be totally absent for the source or sources in
question or be exceedingly laborious to obtain and utilize. Conse-
quently, there does not exist any known source of information from
which a very detailed and accurate computation of exposure can be
quickly made on a multiple source basis. Antenna information will
usually be dug out and calculations made en a specific individual
source basis using simplifying assumptions about the exposure environ-
ment. As a result, any attempt to map the total exposure levels in
a given geographical area from the totality of sources which exist
in that general region will necessarily be only an approximation to
what may really be the case. Any more sophisticated attempt, trying
to take into account transmitter on-off times, actual radiation
patterns, and building and terrain effects which can easily account for
differences of several orders of magnitude in the actual levels as
compared to calculated levels (7, 8), appears to be excessively
prohibitive in cost in terms'of the usefulness of the output data.
Because of this rapidly fluctuating exposure environment (i.e., daily
activity of the general population and mobility of many RF sources) the
only possible, meaningful approach to mathematically describing non-
ionizing exposure would appear to be statistical in nature.
61
-------
Nevertheless, if properly interpreted, exposure maps using the
utmost in simplistic assumptions can be useful as indicators of points
where actual field measurements should be made to determine the true
hazard potential. Representative maps, showing simply the location
of fixed sources are being prepared by us as guides to finding loca-
tions where the largest numbers of people are exposed. I must repeat
my caution on interpretation of this type of display for purposes of
estimating population exposure. If we ask from what class, type, or
frequency range of sources do most people receive the greatest amount
of nonionizing radiation exposure, we can see that it is not necessar-
ily the housewife who stays at home all day in her house which is a few
blocks away from the local radio or TV station that receives the
greatest total RF exposure (i.e., a measure of radiation intensity and
the duration of exposure). It may well be her husband who drives
himself to work being radiated with the relatively intense ignition
system for a short period of time, or the passengers in cabs who get
periodic pulses of relatively intense exposure from the two-way radio
system in the taxi. Thus, the questions of who receives the most
radiation from what, where are the highest exposure environments in
a city, and what is the daily average human RF dose, averaged over
the whole population are very complex and difficult questions to
accurately answer.
As interesting as these exposure maps which I have mentioned
may be, because of the potentially wide variation between the actual
environmental levels of RF and what one may theoretically predict
from the best information available in large computer data files,
actual field measurements are necessary in many cases to verify model
predictions and indicate the real exposure level.
To this end, I will describe one of our forthcoming field studies
and the instrumentation which goes into making RF field measurements.
You have seen that, from a gross, high power level analysis,
the most potential for selected site hazardous exposure may occur
at the superpower satellite communications stations about our
country. We, in the Electromagnetic Radiation Analysis Branch, are
in the process of selecting a few of these sources for detailed
investigation including field density surveys to begin in the near
future. Measurements will be made of field levels at locations,
about each of the selected sources, at which unrestricted individuals
might occupy from time-to-time. The exact subset of these sources
which we will be surveying is being selected primarily on the basis
of antenna orientation procedures for tracking of the various
satellites which they service. Some satellite orbits require that
tracking antennas use elevation angles approaching the horizon. In
such cases, high fields may be observed at ground levels in the
source vicinity. Results of these initial measurements will aid
in determining the potential hazard from this class of sources.
62
-------
At this time our branch is in the process of establishing an
instrumentation laboratory which will be used as the basis for
developing measurement systems to be applied to the environmental
nonionizing radiation problem area and to support various field
studies. The present measurement capability of the branch consists
of wideband, relatively high level, frequency integrative devices
such as will be used for our satellite station survey and uncali-
brated spectrum signature instruments which allow us to determine
the relative field intensities of signals in the electromagnetic
background. Figure 12 illustrates what just the FM broadcast band
spectrum signature looks like in the Washington, D.C., area.
Relative field intensity is presented as a function of frequency.
We are presently developing a system whereby such spectra as this
one can be accurately collected, instrumentally, in terms of the
true signal amplitude and then subsequently integrated over any
desired frequency band to ascertain the true total integrated
spectral power density; i.e., the summation of the field intensity
of each of the individual signals comprising this composite spectrum.
88 90 92 94 96 98 100 102 104 106 108 MHZ
UJ
U-
LU
:>
Figure 12. FM Broadcast Spectrum in Washington, D.C., Area
One of the most important aspects to making meaningful field
measurements in the environment is to have a sensing antenna which
is responsive to all spatial polarization components of the impinging
waves at each frequency of measurement interest. This implies the
use of isotropic receiving antennas such that, regardless of the
nature of the mixed polarization of the incoming waves, for example,
depolarization caused by propagation effects, the output of the
antenna system will be proportional to the total isotropically
63
-------
induced antenna power. We are currently working with orthogonal
dipole systems to approximate such an antenna. This concept is
diagrammatically illustrated in Figure 13. It is envisioned that
several such orthogonal antenna systems will be employed to cover
the wide frequency spectrum of interest. Our system depicted in
Figure 14 is being configured around a spectrum analyzer, an
instrument which produced the spectral display of the FM broadcast
band, calibrated, equivalently isotropic reception antennas, and a
data acquisition and processing system which will allow rapid
acquisition and analysis of the incoming spectral data.
As a closing note, I would like to leave in your mind a feel for
the potential magnitude of this nonionizing radiation pollution problem
in our environment. Figure 15 shows the total number of sources within
the U.S. which are capable of producing an exposure power density of
10 mW/ctn3 as a function of distance from the source. As you can
readily see, as we increase the exposure distance, the number of
emitters decreases, simply indicating that, as you might have suspected,
there are fewer high powered sources than lower powered sources.
However, look at the actual numbers of sources involved. Remember
that this is for the currently accepted U.S. guide level of 10 mW/cm3.
where
Figure 13. Total Power Density Measurement with Orthogonal Dipoles
64
-------
ORTHOGONAL LOOPS OK I HIM.ON XI. IMI'OLKS
HKK SPEC'I Kl M 4N VI.\ /Ml
SCAN CON I HOI
DVIV U 01 ISM ION s\ STKM
INKOKMVIION KIK I N I K K I'K K I \ I I ON
Figure 14. Conceptual System Approach to Environmental
RF Measurements
NUMBER OF EMITTERS
_ 5
_bo
- o o o
— o o o o
21.379
5.097
2,366
1,654
565
84
15
1
3.17 10 31.7 100 317 1,000 3,170 10.000 31.700
DISTANCE (meters)
Figure 15. Cumulative Distribution of Emitters in the United
States Capable of Producing a Power Density Equal t6 or
Greater than 10 mW/cm8, as a Function of Distance
65
-------
Now let's reduce this allowable level to 1 mW/cm3, see Figure 16.
Obviously, more emitters are capable now of producing 1 mW/cm3 in
each given distance interval. Now let's reduce our allowable level
to 0.1 mW/cm2, see Figure 17. The numbers continue to grow. Finally
let's look at what happens if we accept the Russian standard of
0.01 mW/cm3 or 10 |j,W/an3, see Figure 18. Quite clearly, the dimensions
of our problem have increased hundreds of times from what was the case
utilizing the present U.S. guide. Thus, the controversy over thermal
vs. nonthermal effects has serious implications in terms of U.S.
environmental RF fields, should nonthermal effects be proven to exist
and to be hazardous.
Through some of these ideas I have discussed today and the field
measurements EPA will soon be implementing, we hope and expect to
better define the actual RF levels to which we are exposed each day
and, subsequently, to better understand any possible health impli-
cations of our electromagnetic environment.
Jj 10.000
^-
UJ
u.
o
cc
UJ
m
5
:D
1.000 .
100 ..
10
45.513
16,153
5,099
2,366
1,654
565
84
15
3.17 10 31.7 100 317 1,000 3,170 IQOOO 31.700
DISTANCE (meters)
Figure 16. Cumulative Distribution of Emitters in the United
States Capable of Producing a Power Density Equal to or
Greater than 1 mW/cm2, as a Function of Distance
66
-------
NUMBER OF EMITTERS
6
- b b
5 8 8 §
54.545
V
4
30.096
16,174
5.099
2,366
1.654
565
84
3.17 10 31.7 100 317 1,000 3.170 IO.COO 31.700
.DISTANCE (meters)
Figure 17. Cumulative Distribution of Emitters in the United
States Capable of Producing a Power Density Equal to or
Greater than 0.1 mW/ctn2, as a Function of Distance
55.444
48,106
Q:
UJ
h- 10,000
h-
UJ
U. 1,000 .
o:
UJ
5 loo
i
to
30,102
16,174
t
5.099
2,366
1 CKA
*
565
3.17 10 31-7 100 317 (.000 3.170 IO.OOO 31.700
DISTANCE (meters)
Figure 18. Cumulative Distribution of Emitters in the United
States Capable of Producing a Power Density Equal to or
Greater than 0.01 mW/cm3, as a Function of Distance
67
-------
REFERENCES
1. Mills, W.A., Tell, R.A., Janes, D.E., and Hodge, D.M. "Nonionizing
radiation in the environment," Proc. Third Annual Nat'l Conf.
on Radiation Control, Scottsdale, Ariz., May 2-6, 1971, DREW
Publication (FDA) 72-8021, BRH/ORO 72-2.
2. Baird, R. (chairman of session on radiation safety). Conference
on Precision Electromagnetic Measurements, June 26-29, 1972,
National Bureau of Standards, Boulder, Colorado, Proc. published
as IEEE Cat. No. 72 CHO 630-4 PREC.
3. Tell, R.A. "Broadcast radiation: how safe is safe?", IEEE
Spectrum, Vol. 9, No. 8, August 1972, pp. 43-51.
4. Electromagnetic Compatibility Analysis Center, Dept. of Defense,
VICA Environmental Displays, Annapolis, Md., May 17, 1971.
5. Schwan, H.P. "Microwave radiation: biophysical considerations
and standards criteria," IEEE Transactions on Biomedical
Engineering, Vol. BME-19, No. 4, July 1972, pp. 304-312.
6. Ruggera, P.S., and Elder, R.L. "Electromagnetic radiation
interference with cardiac pacemakers," U.S. Dept. of Health,
Education, and Welfare, Report BRH/DEP 71-5.
7. Gierhart, G.D., Hause, L.G., Farrow, J.E., and Decker, M.T.
"Insertion loss of a frame wall at SHF," NBS Report 7273,
June 26, 1962.
8. Rice, P.L., Longley, A.G., Norton, K.A., and Barsis, A.P.
"Transmission loss predictions for tropospheric cummunications
circuits," NBS Technical Note 101, Vol. 1, issued May 7, 1965,
revised January 1, 1967.
68
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ELECTROMAGNETIC COMPATIBILITY, ELECTROMAGNETIC
INTERFERENCE AND SUSCEPTIBILITY AS RELATED TO
MEDICAL DEVICES
Paul S. Ruggera and Mays L. Swicord
Product Testing and Evaluation Branch
Division of Electronic Products
November 1972
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Food and Drug Administration
Bureau of Radiological Health
Rockville, Maryland 20852
69
-------
ABSTRACT
This paper presents a review of cooperative work of the
Bureau of Radiological Health with the U.S.A.F. School of
Aerospace Medicine and the Society of Automotive Engineers
in determining cardiac pacemaker susceptibility to electro-
magnetic interference. The preliminary results of surveys
conducted in the hospital environment, directed at determining
EMI levels present and their possible effect on medical
electronic equipment, are also discussed.
70
-------
ELECTROMAGNETIC COMPATIBILITY, ELECTROMAGNETIC
INTERFERENCE AND SUSCEPTIBILITY AS RELATED TO
MEDICAL DEVICES
The purpose of the Radiation Control for Health and Safety Act
of 1968, Public Law 90-602, is to protect the public from hazardous
exposure to radiation from electronic products. To accomplish this
purpose, an electronic product radiation control program including
the development and administration of performance standards has
been established by the Secretary of the Department of Health,
Education, and Welfare. The Food and Drug Administration's Bureau
of Radiological Health has been made responsible for conduct of the
program. As a part of the program, the Bureau is instructed by the
Act to "study and evaluate emissions of, and conditions of exposure
to, electronic product radiation and intense magnetic fields."
The concept of protecting the public health from excessive
electromagnetic radiation has long been based on evidence of
adverse biological effects. In the hospital environment, where
sensitive electronic instrumentation is utilized to monitor
physiological function, and maintain life function, the conditions
°f exposure to a patient may well be different from those assumed
by the groups who have recommended human exposure control standards.
In such an environment, the interaction of electromagnetic
radiation with sensitive electronic instrumentation, rather than
directly with the biological systems, may be the primary factor in
71
-------
determining if a specific level of radiation is hazardous. The
Division of Electronic Products of the Bureau of Radiological Health
has undertaken a program to examine the basis of present exposure-
limit criteria, and determine if new standards or legislation are
necessary.
For the past two years, interference to a specific product,
the cardiac pacemaker, was of primary concern. More recently, this
effort has been directed to critical hospital areas which utilize
instrumentation for monitoring or aiding patients. This discussion
summarizes the past activity of the Bureau concerning an affected
device, the cardiac pacemaker, and the present program aimed at
determining what levels of potential interference exist in
hospitals and elsewhere, and to pinpoint the sources of these
interferences.
Implanted cardiac pacemaker dysfunction due to external
electromagnetic interference (EMI) has been reported in the
literature for several years. Most of the literature about sources
of EMI concerns those products and frequency ranges that a person
would most likely encounter in a normal existence. Pacemaker
dysfunction has been reported to occur near electrocautery (!_, 2)
and diathermy apparatus (!_, 3^, 4), electric shavers (5), and
internal combustion engine ignition systems (2^, 4). In recent
years, incidents of interference caused by radar (6), communication
systems (3^, 2), and microwave ovens (8) have been reported in the
72
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literature. Because a pacemaker wearer could unknowingly expose
himself to these high frequency sources, it was considered necessary
to evaluate the interference potential of these sources.
After a series of meetings with representatives of the
scientific, medical and manufacturing communities, it was surmised
that the possibility of interference to some models did exist.
With the cooperation of the Association for the Advancement of
Medical Instrumentation, warning letters were distributed through
professional channels in the fall of 1970. These letters were
mailed to hospital administrators for general distribution to their
staffs, and to physical therapists who daily utilize equipment
known to be potential sources of interference. These letters
mentioned several potential sources of interference, one of which
was the microwave oven.
In April 1971, the Bureau published a report (9) which dis-
cussed the electromagnetic interference to cardiac pacemakers.
This report, written in layman's language, was widely distributed
and is available from the Bureau's Information Office.
Through the voluntary cooperation of pacemaker manufacturers
and the Society of Automotive Engineers, AE-4 Committee, pacemaker
models available in June 1971 were subjected to one set of prototype
open-air test procedures. The results of this testing were given
to the manufacturers for their individual evaluation of their
product, as well as the suitability of the test procedure. A
73
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representative of the Bureau of Radiological Health formally presented
the results of this test procedure development to the Working Group on
Environmental Interference of the Association for the Advancement of
Medical Instrumentation in November 1971.
Concurrent with these activities, the Division of Electronic
Products had been cooperating with the U.S. Air Force School of
Aerospace Medicine in its studies utilizing pacemaker-implanted
canines. In the spring of 1972, these canines were exposed to con-
trolled sources of electromagnetic energy which simulated radar and
microwave oven emissions. The complete results of these studies
were published in the IEEE International Electromagnetic Compati-
bility Symposium Record (10) in July 1972. In general, both studies
showed that the most easily determined effect of EMI, that of no
pacemaker output, occurred under varied conditions of frequency,
amplitude, and modulation. All pacemakers resumed normal operation
after exposure.
The signal utilized to simulate microwave ovens was a half-
wave modulated carrier with additional modulation to simulate the
mode stirrer. Under these conditions the most sensitive implanted
pacemaker produced no output at calculated average power densities
*\
of about 15 microwatts/cm . Assuming an inverse square relationship
f\
with distance, for a microwave oven leaking 5 milliwatts/cm at
5 cm, an average power density of about 15 microwatts/cm2 will exist
at three feet. Under higher exposure, six other pacemakers
74
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displayed some rate alterations, while two of the units appeared to
be unaffected under these conditions of testing.
These findings indicate that a person wearing one of the more
sensitive models tested might experience arrhythmia within a three
foot radius of a microwave oven leaking at 5 milliwatts/cm2. This
could include ovens of all types manufactured both prior to and
after the effective date of the recent DHEW microwave oven radiation
emission standard, because the standard was not designed to restrict
radiation leakage to the low levels found to affect pacemakers.
The signal utilized to simulate radar was a square wave modu-
lated carrier with varied time interval between pulses. Under these
conditions the most sensitive unit produced no output pulse at
o
calculated average power densities of about 0.3 microwatts/cm . In
general some effects were noted in all but two of the models tested
under increased exposure and appropriate pulse repetition rates.
On May 17, 1972, as a result of these data, letters summarizing
these findings were mailed to all known U.S. and foreign pacemaker
manufacturers. In addition, questions regarding the specific steps
taken to improve interference susceptibility of their products were
asked. Shortly after the letters were sent, the Commissioner, Food
and Drug Administration decided that the activities concerning the
susceptibility of implanted cardiac pacemakers to interference could
be more effectively administered by separating the responsibility
into two disciplinary areas. The Bureau of Radiological Health is
75
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currently responsible for investigating the technical aspects of the
pacemaker problem in relation to the identification and control of
the sources emitting radiation which would affect such devices. It
also provides technical support to the Office of Medical Devices.
The Office of Medical Devices has assumed responsibilities concern-
ing the pacemaker itself since the pacemaker is a medical device
which does not emit electromagnetic radiation. This includes
attempting to determine the sensitivity of pacemakers to outside
interference, developing standardized test procedures, and dealing
with manufacturers in order to encourage the development of less
susceptible pacemakers.
Since January 1972, the Division of Electronic Products has
been developing the laboratory capability for generating and
measuring electromagnetic fields, principally for calibrating and
evaluating radiation detecting instruments for field use. Because
of the administrative transfer of the cardiac pacemaker responsi-
bility, more time can be devoted to these aspects of EMI. Having
developed an adequate capability to measure electromagnetic
radiation levels, the Bureau has recently responded to one request
to investigate the level of EMI in critical areas inside hospitals.
Other requests have been received including a municipal airport,
and a Public Health Service Hospital which happens to be the tallest
Federal building in the area with its roof being used for government
communication antennas.
76
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Electromagnetic field surveys were conducted on September 11-15,
1972, at the University of California Medical Center and at the
USPHS Hospital in San Francisco, California. The primary purpose
was to establish base line measurements of electromagnetic radiation
levels in critical hospital locations which will be compared with
similar measurements taken at a later date. Levels at some
frequencies are expected to increase as a result of the construction
of a large, multiple-frequency broadcast tower in the vicinity.
The data collected at the two hospitals have been stored on two
analog magnetic tapes. Approximately 400 orthogonal spectrum sweeps
were recorded for frequencies between 30 hertz and one gigahertz.
At the present time the Bureau personnel are reducing the data
for analysis and recalibrating checkpoints for the receiving antenna.
A report will not be available until the return visit to the hospitals
can be made, after the tower is energized, and these data can then be
compared. Preliminary results indicate at present that the highest
discrete signal levels in one polarization are approximately
2
10 microwatts/cm .
77
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REFERENCES
(_1) MANSFIELD, P. B. On interference signal and pacemakers.
Amer. J. Med. Electronics 5:61-63 (1966).
(2) PARKER, B., S. FURMAN, and D. J. W. ESCHER. Input signals to
pacemakers in a hospital environment. Ann. N.Y. Acad. Sci.
111:823-834 (1964).
(3) LIGHTER, I., J. BORRIE, and W. M. MILLER. Radiofrequency
hazards with cardiac pacemakers. Brit. Med. J. 1:1513-1518
(1965).
(4) CARLETON, R. A., R. W. SESSIONS, and J. S. GRAETTINGER.
Environmental influence of implantable cardiac pacemakers.
JAMA 190:160-162 (1964).
(5) FURMAN, S., B. PARKER, J. KRAUTHAMER, and D. J. W. ESCHER.
The influence of electromagnetic environment on the
performance of artificial cardiac pacemakers. Ann. Thorac.
Surg. 6:90-95 (1968).
(6) YATTEAU, RONALD F. Radar-induced failure of demand pacemaker.
New Eng. J. Med. 283:26, 1447 (December 24, 1970).
(7) PICKERS, B. A. and M. J. GOLDBERG. Inhibition of a demand
pacemaker and interference with monitoring equipment by
radiofrequency transmissions. Brit. Med. J. 2:504-506 (1969).
(8) KING, GERALD R., ALBERT C. HAMBURGER, FOROUGH PARSA,
STANLEY J. KELLER, and RICHARD A. CARLETON. Effect of
microwave oven on implanted cardiac pacemaker. JAMA 212:7.
1213 (May 18, 1970).
(9) RUGGERA, PAUL S. and R. L. ELDER. Electromagnetic radiation
interference with cardiac pacemakers. USDHEW PHS FDA BRH,
Rockville, Md. 20852, Report DEP 71-5 (April 1971)
(10) 1972 IEEE INTERNATIONAL ELECTROMAGNETIC COMPATIBILITY
SYMPOSIUM RECORD. IEEE 72CH0638-7EMC, pp. 5-9, 17-18.
78
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THE GROWTH OF MICROWAVE SYSTEMS AND APPLICATIONS
Jeffrey Frey, Ph.D.
School of Electrical Engineering
Cornell University
Ithaca, N. Y. 14850
The term "microwave" describes electromagnetic radiation occupying
a particular portion of the spectrum of all such radiation; the micro-
Q
wave band is generally taken to mean the frequency range 10 to some-
thing over 10 Hz, comprising radiation in free space with wavelengths
from 30 cm. (at 10 Hz) to under 0.3 cm. The relationship of the
microwave portion of the spectrum to other labeled bands is illustrated
in Figure 1.
Microwave radiation possesses two particular advantages over
radiation at lower frequencies, advantages which assure the application
of microwaves to certain problems, regardless of the cost involved.
First, microwave radiation covers a very wide portion of the frequency
spectrum (note that the abscissa of Figure 1 is logarithmic). The
large bandwidth available for microwave beams allows these beams to
carry more information than beams at lower frequencies. Second, the
small wavelength of microwave radiation allows microwave beams to be
focused and pointed relatively easily. While the frequency range
above 10 Hz is even more advantageous from these points of view,
as yet no devices to generate and control energy in this frequency
Radiological Health Section, 14 November 1972.
79
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-------
range are available that match the output power, cost, and reliability
of analogous devices in the microwave band. In addition, at very high
frequencies signals are much more subject to attenuation due to mois-
ture in the atmosphere than at microwave frequencies.
The bandwidth and directionality properties of microwave radiation
have dictated the general types of uses to which these systems have
historically been put. The first microwave system 'to be developed,
Just before and during the 1939-45 war, was radar, which utilizes the
directional properties of microwave radiation. The second major
application of microwave systems was in relaying network TV programs
across the country; in this case the wide-band capability of microwaves
was as important as beam directionality, which enabled precise aiming
of the beam from transmitter to receiver. Microwaves, then, are useful
for guidance and control (e.g., radar) and communications. The trend
of development of microwave systems since their first application has
been from very expensive systems, purchased by armies and communications
monopolies, to somewhat less expensive ones, purchased by smaller func-
tional units, such as airlines. Recent technological developments,
however, indicate that a large proliferation in the numbers of microwave
systems in use can be expected, with microwave system ownership reaching
the individual level.
Current Microwave Systems and Applications
The least expensive widespread microwave system now available is
the microwave oven, ubiquitous in snack bars and increasingly appearing
81
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in homes as the price reaches the $200 level. With prices around $400,
345,000 of these ovens were sold for home use in 1970.
Most systems currently in use, however, cost several thousands of
dollars, rather than several hundreds. Radar, of course, is universal
on military aircraft and on civilian passenger aircraft costing more
than $100,000. A very large percentage of the 73,602 (as of 1970)
US registered yachts and other vessels exceeding 4.5 tons displacement
are also equipped with radar. Microwave communication systems in the
civilian sector have been operated primarily by A.T.& T. and Western
Union; cumulative data for FCC authorizations for such stations, to
2
1969, is shown in Figure 2. Since the 1969 FCC decision to allow
carriers other than A.T.& T. and Western Union to compete with the
common carriers in providing wide-band microwave links for data and
other private communications, roughly two thousand applications for
new microwave stations, from firms not previously involved in the field,
have been filed with the FCC.
New Technology and Microwave Proliferation
Microwave technology has changed considerably over the last 10 years,
and new developments are now beginning to mature into production units.
A relative measure of the impact of these developments is shown in
Figure 3. In the last 10 years the invention of new solid-state micro-
t
wave generating devices has increased the radio frequency (r.f.) power
available from low-cost solid state units four orders of magnitude;
simultaneously, the application of integrated circuit techniques to
82
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6000
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2000
1000
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1955 56 57 58 59 60 61 62 63 64 65 66 67 68 69
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microwave systems has reduced their size and cost two orders of magni-
tude. Further, through the use of automated analysis and design proce-
dures, the engineering costs of microwave systems have also been greatly
reduced. On an absolute scale, reliable microwave sources, adequate
for use in such systems as small radars or for communications over a
distance of several miles, can be purchased now for $20 to $50;
klystron sources, typical of the devices that would have had to be used
in such systems until recently, sell for upwards of $500. Consequently,
microwave systems for use in individual homes, automobiles, boats, and
private aircraft, can be expected to proliferate, and the use of micro-
waves by commercial organizations can also be expected to increase.
Developments in computer technology, and increases in computer
usage, will also stimulate the growth of microwave systems. Transmis-
sion of information between remote computer terminals and a central
computer—say, between a branch bank and its central office—can be
performed using telephone lines; however, a private microwave system,
with the capability for transmitting a thousand times as much informa-
tion in the same time as the telephone system, may be more efficient.
Further, wideband data links are required in order to hook computers
up. These computer-oriented uses of microwave systems can be expected
to increase regardless of any new developments in microwave technology,
but the microwave developments described above will facilitate the use
i* .'
of computers as, for example, by enabling the personal data link to
accompany the personal computer, when it becomes available.
85
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At least one factor may mitigate against great proliferation of
microwave systems: crowding of the electromagnetic spectrum. Unless
great attention is paid to monitoring and controlling spectrum use,
and to requiring most-efficient system design, there soon may not be
enough spectrum to go around.
Microwave Applications
New cost parameters and the development of complementary technology
will lead, as shown above, to new applications for microwave systems,
and more widespread use of these systems to perform historically
important tasks.
In the field of guidance and control, microwave systems should
soon appear on commercial vehicles, trucks and buses, for collision
avoidance and automatic braking. There are roughly 20 million such
commercial vehicles on American roads today. Eventually, microwave
systems should appear on private automobiles, for collision avoidance,
triggering of passive restraint systems, and backup warning; with a
manufacturing cost of $10 per unit foreseen, the Department of Transpor-
tation foresees the entire new car market—10 million units per year—
equipped with such systems.
It will soon be possible for light aircraft to carry both
altimeter and collision-avoidance radars at costs comparable to those
for other general aviation electronic equipment. For example a small
radar, which indicates by audible signal the presence of another air-
craft within a sphere of surveillance surrounding the observing aircraft,
86
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has recently been announced at a price of about $2000. Within the decade,
collision avoidance radar might be required on all aircraft equipped for
instrument flight—a significant fraction of the 200,000 private air-
craft registered.
Radars for small boats will become practical, particularly for
operation at night or in areas where fog is frequent. A hand-held
unit selling for $695 has already been announced. ,
Small radars can be used for any purpose where a process is
i
triggered by motion. Systems are on the market which automatically
open hospital doors or detect when beer bottles have been filled to the
proper level. The same principles apply to intrusion alarms also;
microwave units for this purpose can alrady be bought at prices below
$300. Similar principles are used in shoplifting alarms, in which a
radar set is made sensitive not to motion in general, but only to the
presence of a coded reflecting tag hidden on items in a shop. The
alarm is triggered if the tag passes a detector at the exit of the
3
shop. About 600 of these units are already installed.
Microwaves can be used for the control of industrial processes.
Microwave systems have already been applied to monitoring the thickness
of latex applied to the back of carpeting, and experiments with other
processes involving parameters to which microwave systems are sensitive
are being performed.
A large expansion in microwave systems can be expected due to
increased needs for wideband communications, and the growth of entirely
87
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new communications systems, particularly satellites. As frequencies
at the lower end of the microwave band become filled with stations,
communicators will have to move upward in frequency. However, the
higher the frequency, the greater the attenuation of microwave radia-
tion by the atmosphere, and the greater the increase in attenuation
in the presence of atmospheric moisture. Thus, higher-frequency systems
require either high-power microwave sources, or relay stations between
sources. For example almost 15 times as many microwave transmitters are
required to cover a long distance in a 18 GHz system as in an 8 GHz
4
system.
Satellite communications systems can utilize direct transmission
from satellite to home. A system is under investigation in Germany
that would utilize such direct transmission to add three to five
channels to the crowded terrestrial German television bands. The ATS-F
satellite, shortly to be launched, will be used to conduct an experiment
with the relay of instructional TV programs from New Delhi to thousands
of village receivers in India. In this country the use of satellites
for the relay of network programs to CATV installations, two-way voice
communication, and general TV networking, has been proposed. Possibly
over a hundred satellites, and thousands of earth stations—millions,
if direct satellite broadcasts to homes are utilized—may be in use by
the end of this century.
In addition to being used for the trunk systems that connect city
to city, it is now feasible to use microwaves in local distribution—say,
-------
from a suburban telephone switching plant to its downtown central
office or between the trunk terminal of a data carrier to a local sub-
scriber. The Bell system has had an experimental pole-mounted micro-
wave relay station, intended for such use, in operation for 4 years.6
Automobile telephones may become very common if microwaves are
used. The band currently assigned to auto telephone systems is too
narrow to accommodate even a small fraction of the
-------
heating processes are any more efficient than more well-known processes,
and the extent of their application is questionable.
Finally, the development of technologies only now foreseen, not
yet reduced to hardware, may also result in a proliferation of microwave
systems. At a recent long-range planning symposium sponsored by the
Electronics Industries Association a number of technological events,
with years considered likely for their realization, were forecast;
those events relevant to the growth of microwave applications include:
individual portable two-way communications devices carried by most
Americans (1990) ; computer-controlled network stock transfer system
(1978); integrated financial services, with automated transfer of funds
(1978) ; TV systems used for instruction in 10% of all schools (1977) ;
TV networks linking campuses (1980); use of radar prosthetic devices,
e.g., radar for the blind (1985).
An idea of the magnitude of growth of microwave systems use can
i
be obtained by correlating the current size of the market for the systems
concerned with an approximate estimate of penetration 'of that market
as a function of price. For example, $2000 is currently the Isvel of
r
acceptability for electronics equipment in aircraft; $10-100 is the
level appropriate to private automobiles. A chart summarizing the data
is given in Figure 4. It is seen that by the time that microwave systems
reach the $10-100 level — which may be within the next decade — hundreds
of millions of small microwave Systems will be brought into use.
90
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Consequences of the Proliferation of Microwave Systems
Large increases in the number of microwave systems in use can be
expected to result in considerable crowding in the microwave portion
of the spectrum, with consequent increases in mutual interference among
neighboring systems, and problems in the satisfaction of competing
interests. In addition, individual exposure to microwave beams will be
much more likely than it is now, and the health hazards of such exposure
have not yet been satisfactorily quantified.
Spectral congestion will be an international problem once communi-
cations satellite proliferate, but even now this congestion is severe
in some localities. Table 1 shows some of the results of a recent
2
study done for the FCC ; the table lists the ratio of FCC-authorized
stations to the total number of frequency assignments available in
each band, for Los Angeles, New York City, and Venice, Louisiana. In
bands where the ratio exceeds unity, advantage must be taken of the
directional properties of microwave radiation, or space between trans-
mitters. In New York and Los Angeles, which are commercial arid enter-
tainment centers, the 4, 6, and even the newer 11 GHz common carrier
bands are virtually saturated; in Venice, La., the safety and'special
services bands are nearly full, with microwave communications" links
among offshore oil-drilling platforms almost saturating the safety and
special service bands. Spectral congestion can only be expected to
increase and techniques for regulating spectral allocation and mutual
interference must be kept abreast of needs.
92
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TABLE 1.
Ratio R of authorized stations to individual frequency assignments
available
R for R for R for
Los Angeles New York Venice
1.850-1.990 GHz 3.8 0.5 1.8
Operational fixed
(industrial and public
safety)
1.990-2.110 0.9
TV pickup, TV intercity
2.500-2.690 ' 0.5 0.5
Operational fixed
(industrial, instructional
TV)
3.700-4.200 , 1.9 4.0
Fixed public
(common .carrier & Connn.
satellite)
5.925-6.425 1.3 3.2 0.1
Fixed public
(common carrier & comm.
satellite)
6.575-6.875 4.1 0.5 0.9
Operational fixed
(industrial, public safety)
6.875-7.125 0.7 0.2
TV pickup, TV relay
10.700-11./OO ^ 2.4 3.2
Fixed public
(common carrier)
93
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Since very large numbers of microwave systems can soon be expected
to be in the relatively unsupervised control of private individuals,
it is necessary that the biological effects of microwave radiation be
fully quantified. Microwave radiation can certainly cause profound
effects on living animals; the oven that can roast a turkey in 5
minutes can roast a child's hand in even less time. Legislated standards
and safety interlocks can render such heating apparatus reasonably safe,
but no standards exist for the regulation of low-power microwave
systems. For, no one really knows the effect of long-term exposure
to very low levels of microwave radiation such as would, for example,
be impinging on a traffic policeman monitoring an intersection through
which radar-equipped cars were passing.
Conclusions
In a large part because of advances in microwave technology
resulting in much cheaper microwave systems than were heretofore
possible, the use of microwave radiation for guidance and control,
communications, and industrial processing, can be expected to increase
in the next several decades to a point where millions of small micro-
wave systems will be in active use. This proliferation will result in
great pressure on the microwave frequency spectrum, and in a great
increase in environmental exposure to microwave radiation. The former
problem carries with it the implication that regulatory processes
must be modernized to properly balance the forces competing for the
spectrum; the latter fact should cause concern that not enough is yet
known about the biological effects of such exposure.
94
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REFERENCES
1. Scott, A. W. Opening up the commercial market. Microwave
Journal 15:49 (June 1972).
2. Communications and Systems, Inc. Frequency assignment techniques
for microwave systems. Study prepared for the Federal Communica-
tions Commission (August 1970).
3. Microwave system flights shoplifters. Electronics 44:31
(November 22, 1971).
r
4. Tillotson, L. C. Use of frequencies above 10 GHz for common
carrier applications. Bell Sys. Tech. J. 48:1563 (1969).
5. Special issue on satellite communications. Astronautics and
Aeronautics 9 (September 1971).
6. Ruthroff, C. L., et. al. Short hop radio system experiment.
Bell Sys. Tech. J. 48:1577 (1969).
7. Christansen, D. Electronics 1985. IEEE Spectrum 9:50 (July 1972)
95
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SPACE SOLAR POWER:
AN OPTION FOR POWER GENERATION
Peter E. Glaser, Ph.D.
Vice President
Arthur D. Little, Inc.
Cambridge, Massachusetts
97
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ABSTRACT
Recently solar energy has been reexamined as a
viable alternative to produce power on a very large
scale. The potential of this source of energy is
I
discussed against the background of presently per-
ceived energy demand and supply. The major concepts
for the large-scale use of solar energy are briefly
reviewed to provide a basis for examination of a
satellite solar power station which would have the
capability to convert solar energy to microwaves
which are beamed to a receiving antenna on Earth.
The principles of this satellite solar power station
are reviewed with particular attention to technical
feasibility. The economic, social, and environ-
mental impacts of this alternative to power produc-
tion are presented.
98
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SPACE SOLAR POWER:
AN OPTION FOR POWER GENERATION
Peter E. Glaser, Ph.D.
Vice President
Arthur D. Little, Inc.
Cambridge, Massachusetts
I. INTRODUCTION
The energy crisis generated by the massive production and use of
r
i
energy is today a major public concern. ' As various solutions are
f
offered to overcome the crisis, inadequate consideration is often given
to technical developments, economic constraints, resource conservation,
public health, international trade and politics, environmental protec-
t
tion, and social equity which are typical of the issues involved in the
massive production and use of energy. Attempts are being made to
grapple with the interacting, conflicting, and cumulative effects of
actions already taken or planned for the future. A consensus is
emerging that new research initiatives, institutional mechanisms, and
criteria have to be developed and coordinated to evolve a rationale
for national energy policies of benefit to society.
The use of energy has been the key to the social development of
man and an essential component to improving the quality of life beyond
the basic activities necessary for survival. The striking feature of
the history of exploitation of energy sources and their comsumption is
its exponential growth over the last century. This growth cannot
continue forever. In a world with limited natural resources and a
99
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finite ceiling upon undesirable interactions of energy production systems
with tho environment, an assured nvnilahiHty of energy resources poses
a multitude of problems. Projected increases in energy demand indicate
that the pressures on energy resources will be experienced world-wide
because each nation will aspire to attain a larger share of finite re-
sources to maintain and improve the quality of life for its people.
The common objective must be to meet energy demands as far as
reasonable, while preserving the natural environment in the face of
increasing pollution. The public is demanding substantially more
electrical power and is expecting the power to be available—without
shortages or rationing. At the same time the public is expressing an
unprecedented concern about environmental quality and has not yet faced
up to the price it may have to pay to achieve this quality. One major
fact emerging as a result of the pressures generated by the ever-
increasing energy demands is that alternative energy production methods
will have to be developed. Among the different sources of energy,
whether they be non-renewable—such as fossil or nuclear fuels—or con-
tinuous—such as tidal or geothermal—none has a greater potential than
solar energy.
Man worshipped the sun aeons ago, but today feels less beholden
to it and has forgotten how intricately all life is linked to it. The
sun is the controlling influence over the planet Earth. A high level
of sophistication is required to apply solar energy for society's
long-term benefit consistent with the balance of nature. Indications
are that this point is now being reached. Several concepts have re-
(2345)
cently been advanced to achieve the large-scale use of solar energy. ' ' *
100
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One concept is based on the evolving ability to utilize space for prac-
tical purposes. The technology developed to reach out beyond the
confines of the Earth opens up the possibility of tapping the most basic
energy source available to man—the sun.
II. SOLAR ENERGY CONVERSION IN SPACE FOR USE ON EARTH
Maximum utilization of solar energy can be made in an orbit around
the sun. The first step towards the fullest use of solar energy is
represented by a satellite in orbit around the Earth. There, solar
i
energy is available nearly 24 hours a day. This approach permits solar
energy conversion to be carried out where it can be most effective with only
the final step arranged to take place on Earth, Similar to the impact
on worldwide communications of already existing satellites, power from
1
space has the potential of providing an economically viable and environ-
3
mentally and socially acceptable means of meeting future energy require-
ments.
Figures 1 and 2 show the design concept for a satellite solar power
station (SSPS). Photovoltaic solar energy conversion with two large,
symmetrically arranged solar cell arrays represents the basic principle
of the SSPS which will be designed to produce electricity in synchronous
orbit. This electricity is fed to microwave generators, arranged to
form an antenna located between the two arrays. The antenna directs a
microwave beam to a receiving antenna on Earth where the microwave energy
I*
is efficiently and safely converted back to electricity. In synchronous
orbit around the equator, the satellite will be stationary with respect
to a desired location on Earth. The use of the microwave beam allows
101
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FIGURE 1 DESIGN CONCEPT FOR A SATELLITE SOLAR POWER STATION
-------
X
D
JD
O
C/D
Receiving Antenna
Solar Collector
5000 Mw
Transmitting Antenna
Synchronous Orbit
Solar Collector
M'illHI ? DESIGN CONCtl'T FOR A SATtl I I fl SULAH I'OWl H STATION
-------
all-weather transmission so that full use can be made of the nearly 24
hours of solar radiation available. This availability, except for short
periods near the equinoxes, when the satellite enters the Earth's shadow
for a maximum of 72 minutes a day, provides a 6- to 15-fold advantage of
solar energy conversion in space compared to a terrestrial installation
where useful operations are limited by weather conditions and the day-
and-night cycle and require energy storage techniques. This advantage
is translatable in terms of reduced land use and capital costs. The
very high efficiency of direct microwave energy rectification into
electricity by the receiving antenna on Earth reduces the waste heat
generated on Earth to a fraction compared with any thermodynamic conver-
sion method.
The SSPS can be designed so that it can generate electrical ppwer
on Earth at a specific power output ranging from 3,000 to 15,000 MW.
Over this range, the orbiting portion of the SSPS exhibits the best
power-to-weight characteristics. Power can be provided to a receiving
antenna in a desired geographic location. These antennas could either
supply major load centers individually, or when a number of SSPS's are
operating, be tied into a transmission grid to meet a significant portion
of the energy demands on a national and eventually a world scale.
The status of a significant technology required to achieve an oper-
ational SSPS is reviewed in the following sections.
A. Solar Energy Conversion
Solar energy conversion into electricity by the photovoltaic process
is well suited for the purposes of an SSPS. In contrast to any process
based on thermodynamic energy conversion, there would be no moving parts
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no material would be consumed, and 1n principle the operation of a
photovoltaic solar cell could continue for long periods of time without
maintenance. There has been a substantial development in photovoltaic
energy conversion since the first laboratory demonstration of efficient
silicon solar cells in 1953. Today, they are a necessary part of the
power supply system of nearly every unmanned spacecraft, and considerable
experience has been accumulated to achieve long-term and reliable opera-
tions under the conditions existing in space. As a result of many years
of operational experience, a substantial technological base exists on
which further developments can be based. These developments are directed
toward increasing the efficiency of solar cells to about 18%, reducing
their weight to about 2 Ib/kW, and their cost to about $1/W and achieving
efficient operation over a 30-year lifetime. Although solar cells pro-
duced from single-crystal silicon have been most widely used, recent
advances in gallium arsenide solar cells indicate that further increases
in efficiency and weight reduction may be possible.
III. MICROWAVE POWER GENERATION, TRANSMISSION, AND RECTIFICATION
An electromagnetic beam link can transmit power from the SSPS in
synchronous orbit to a receiving antenna on the Earth. The choice of
wavelengths for this beam are dictated by the desire to (1) obtain
efficient transmission of large amounts of power across long distances
with minimal losses in the ionosphere or atmosphere, (2) maintain power
flux densities at levels low enough so that undesirable environmental
and biological effects can be avoided, and (3) use devices based on known
technology to generate, transmit, and rectify the beamed power with very
105
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high efficiency. These conditions can best be met when the microwave
portion of the spectrum is selected for tho beam link.
Considerable background and experience exist in high-power micro-
wave generation, transmission, and rectification. Already in 1963, it
was demonstrated that large amounts of power can be transmitted by
(8)
microwave. The efficiency of microwave power power transmission will
be high when the transmitting antenna in the satellite and the receiving
antenna on Earth are large, thus excluding the efficient transmission of
small amounts of power. The size of the transmitting antenna is in-
fluenced by the efficiency of the microwave generator; the area required
for radiators to reject waste heat to space, and structural considerations.
The antenna size and weight will be reduced as the average flux density
on the ground is reduced and as higher frequency microwave transmission
is used. The size of the receiving antenna is influenced by the choice
of the microwave power flux density, the illumination pattern of the
antenna, and the minimum flux density required for efficient microwave
rectification.
Microwave generators can convert DC to microwaves with demonstrated
efficiencies of about 76%. The use of a newly developed, permanent
magnet material—samarium cobalt—will lead to substantial weight reduc-
tions. Thus, the output of an individual microwave generator, weighing
a fraction of a pound, can range from 2 to 5 kW. The use of pure metal,
cold cathodes will greatly increase the reliability and operational life-
time of this device. An efficient microwave generator can radiate waste
heat directly into space by means of heat radiators. A series of micro-
wave generators can be combined into subunlts with individual phase
106
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controls. The subunits are assembled into a slotted array-type
transmitting antenna to obtain a microwave beam of a desired distribution.
For efficient microwave transmission, the transmitting antenna
should have a diameter of about 1 km. With this size antenna, about
99% of the microwave beam will be received on Earth. A receiving
antenna diameter of about 7 km will intercept about 90% of the beam.
Ionospheric attenuation of microwaves having wavelengths between
3 and 30 cm will be less than 1% if microwave power flux densities are
r
2
less than about 50 mW/cm . Atmospheric attenuation is low for microwave
wavelengths of about 10 cm. Moderate rainfall attenuates microwave
transmission by approximately 10% at a wavelength of 3 cm and 3% at a
wavelength of 10 cm. Thus, a 10-cm microwave wavelength corresponding
to a frequency of 3000 MHz appears to be a reasonable choice. The re-
ceiving antenna intercepts and rectifies microwaves into DC which can
then be fed into high-voltage DC transmission lines or converted into
60-Hz AC. Rectification is accomplished by diodes combined into circuit
elements which act as half-wave dipoles. The dipoles are uniformly dis-
tributed throughout the receiving antenna. Rectification efficiencies
of about 75% have already been demonstrated, and 90% efficiencies should
be achievable with improved circuits and diodes. The overall efficiency
of microwave transmission from DC in the SSPS to DC on the ground is
projected to be about 70% with further device development.
IV. SYSTEM CONSIDERATIONS
Figure 3 indicates the major dimensions of the SSPS to generate
5000 MW on Earth. Each half of the solar collector is about 5 by 5 km.
As these dimensions indicate, the SSPS orbital system is orders of
107
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4.95 km
Solar
Collector
Transmittin
Antenna
5.2km
Solar Cell Array
Continuous Support
Structure
Mirrors and Support
Structure
FIGURES SSPS DIMENSIONS
108
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magnitude larger than any spacecraft launched today. From an overall
spacecraft design s: .'Midpoint, the basic technology problems involved
are related to its large size and the goal of a 30-year operating life-
time. However, the principles governing the design are founded on ad-
vances from an existing technology base.
The SSPS structure is composed of high current-carrying structural
elements which will induce loads or control forces into the structure
by electromagnetic effects. New design approaches will have to be
developed to satisfy orientation requirements of such a large spacecraft.
Flexible spacecraft structures, such as the large solar cell array for
space stations, have been studied in che past, including the maintenance
of inertial pointing capabilities of structures such as a large 1000-foot
diameter antenna. Low-thrust, ion propulsion systems appear promising
for flight control purposes, particularly because of their continuous
short-term impulse capabilities and lifetimes which are compatible with
the overall objective to achieving 30 years of operation.
An SSPS, capable of providing 5000 MW of power on Earth, will weigh
about 25 million pounds. Such a massive satellite will require a trans-
portation system from Earth to synchronous orbit which will be an out-
growth of the present space-shuttle development. This transportation
system will have to be designed for high-volume transport of payloads
to low-Earth orbit, followed by delivery of partially assembled elements
to synchronous orbit for final assembly and deployment. A second-
generation space shuttle, utilizing returnable boosters rather than
present space-shuttle solid propellants, would have inherent cost ad-
vantages. An ion engine propelled tug which, over a period of 6 to 12
109
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months followed a spiralling trajectory to synchronous orbit, could
provide an effective complement to the spacu shuttle. For a combined
chemical/ion propulsion system, about 500 Earth to orbit flights would
be required to deliver the elements of a 25-million-pound spacecraft to
synchronous orbit. Cost projections for this type of transportation
system are about $100 per pound to synchronous orbit.
An interesting possibility exists to launch payloads into orbit with
(9)
high-power lasers. A laser propulsion system has the advantage that
almost all of the equipment needed is on the ground, rather than requir-
ing massive rocket engines. Laser propulsion, which would operate only
a few minutes for each launch, would have an immense capacity for putting
payloads into orbit. It would be possible to orbit masses that are huge
compared to those presently orbited with rocket propulsion devices. Air
is used as a propellant medium; thus polluting substances would not be
contaminating the atmosphere. Although the possiblity of high-power
laser propulsion is still largely unexplored, new possibilities are
opened up, particularly for a concept such as the SSPS.
A prototype SSPS can be demonstrated by 1990, based on the necessary
steps required for the development of such a system. Figure 4 shows the
program schedule by which the development could proceed in a logical and
well laid out fashion.
A series of well-formulated development goals with identified ob-
c
jectives would assure that R&D expenditures during the development phase
could be limited and controlled. Major funding commitments would not
have to be made until system verification tests had demonstrated the
capability of meeting stated objectives.
110
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Technology Development
Verification/Exploitation
Prototype System
Development/O perati on
Operational System
Development/Operation
1973
Flight and
Ground Tests
Flight
Operations
Federal Support
Commercial
Venture
FIGURE 4 PROGRAM PHASING
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V. ENVIRONMENTAL CONSIDERATIONS
The Impact of any new technology must be assessed. Such a technology
assessment must include, in addition to the purely physical impact of SSPS,
the economic and social Impacts. The key environmental effects of an
SSPS are discussed below.
1, Microwave Biological Effects
An extensive and coordinated effort to establish biological effects
of microwaves is presently planned by the Office of Telecommunications Policy
as part of a program to control electromagnetic pollution. At present, var-
ious standards for microwave exposures have been established, ranging from
2 (10^ 2
10 mW/cm for the United States v ' to 0.01 mW/cm for the Soviet Union.
The major difference in these standards can be traced to the uncertainty
in the interpretation of laboratory observations of microwave exposure.
The U.S. standard is based on microwave heating of body tissues. On
the basis of experience with microwave equipment over several decades and
the resulting exposure of a significant population to microwaves, there are
remarkably few reported incidences of biological damage. Soviet investigators
have indicated that the central nervous system is affected by microwaves,
even at very low exposure levels. These considerations have lead the Soviet
2
Union to set a continuous exposure standard at 0.01 mW/cm .
In view of this very basic difference in interpretation of the effects
of microwave exposure, there is a need to develop experimental procedures
so that certain byproducts of microwave-generating equipment operation, such
as X-rays, ozone, and oxides of nitrogen, in addition to extraneous environ-
mental conditions imposed on laboratory test objects, would not lead to a
misinterpretation of the laboratory observations.
112
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The doaign npprnuch for an SS^S must recogr.i/.e that a range of frequen-
cies and microwave power flux densities may have to be accommodated and
design features will have to be adjusted accordingly. An understanding
of the specific SSPS-tnduced environment, predictions, analyses, and mea-
surements will be an essential component of the development program.
Precise control of the microwave bear through transmitting antenna
stabilization and automatic phase control vill assure that the microwave
power will be efficiently transmitted to the receiving antenna. The an-
tenna size, the shape of the microwave power distribution across the
antenna, and the total power transmitted will determine the level of micro-
wave power flux densities in the beam reaching the Earth.
The SSPS design will incorporate several fail-safe features, including
a self-phasing signal transmitted from the ground to the transmitting an-
tenna, to assure precise beam-pointing. Loss of acquisition of the signal
will lead to demodulation of the microwave beam. In addition, remotely
operated switches in the SSPS solar collector will instantaneously open-
circuit the solar cell arrays and shut off power to the microwave generators.
A wide latitude in microwave power flux densities can be obtained by
selecting the transmitting and receiving antenna diameters. The receiving
antenna has to cover only an area consistent with achieving overall high
efficiency of operation. A guardring of a few kilometers can be provided so
that the level of microwave exposure outside this ring will be less than
1 uW/cm2 which is one order of magnitude below the Soviet microwave exposure
standard. (See Figure 5.)
In addition to direct biological effeccs, interference with electronic
equipment, medical instrumentation, or electro-explosive devices must be
113
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10'
CM
O
0>
Q
o
a.
10
10
r2
10
r3
10"
10'
p0= 100 mw/cm2
= 1.89 Km
p = 25 mw/cm2
pr = 3.78 Km
P0 = 10 mw/cm2
= 5.95 Km
P0 = rf Power Density at Beam Center
pr = Radius of Circle through Which 63%
of Energy Falls
i I. .
\
1
\
04 8 12 16 20
Distance from Beam Center (Km)
24
Note: Total power held constant at 1.17 x 107 kilowatts.
FIGURE 5 DISTRIBUTION OF MICROWAVE POWER
DENSITY FROM THE BEAM CENTER
114
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avoided. The lack of sensitivity of this equipment to a low level of
microwave exposure will have to be confirmed, .ind if required, Industrv-
wide standards will have to be established.
The effects on birds flying through the beam is not known. Research
on the effects of microwave on birds at the level to be encountered in the
microwave beam will have to be carried out as well. Preliminary evidence
indicates that birds can be affected at levels of microwave exposure of
2
25 to 40 mW/cm of radiation in the X-band. The evidence suggests an
avoidance reaction by birds to the exposure.
The effects of microwave exposure on aircraft flying through the beam
must also be considered. The shielding effects of the metal fuselage and
the very short time of flight through the beam would not result in signifi-
cant human exposure. The means for protecting aircraft fuel tanks from
electrical discharges are now standard design features, but the absence of
microwave-induced hazards will have to be confirmed. In addition, the ex-
tent of possible interference with aircraft communications and radar equip-
ment will have to be established.
2. Interference with Radio Communications
World-wide communications are based upon internationally agreed-upon
and assigned frequencies. Because a frequency band spanning the most de-
sirable operating frequency of the SSPS (S-band) is already in heavy use,
the potential for radio frequency interference (RFI) of the SSPS with exist-
ing communication systems is high. The design of the microwave generators
used in the SSPS can eliminate most spurious output characteristics, but
RFI could occur during the shutdown of the generators as the SSPS enters
the Earth shadow, or result from noise side-bands about the operating
115
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frequency or from inadequate suppression of frequency harmonics. RF filter-
ing can greatIv reduce these undesirable effects. However, the very large
power output of the SSPS may pre-empt certain frequencies which are now in
general use. The understanding of RFI effects and international agreement
on frequency assignments represent issues which will have to be faced at
various stages during the SSPS development.
3. Environmental Effects
The SSPS represents an approach to power generation which does not use
naturally occurring energy sources, but relies on a constant and inexhaust-
ible energy source. Thus, environmental effects associated with mining,
transportation, or refining of natural energy sources are absent. Natural
resources will have to be used to produce the components for the SSPS and the
propellents for transportation to orbit. Nearly all the materials to be
used for the components are abundant. Rare materials, such as platinum or
gallium, would require less than 2% of the yearly supply available to the
United States for each SSPS. Electrical power required to manufacture the
various components and to launch the SSPS into orbit will be equivalent to
about 9 months of power generated during SSPS operation.
Environmental effects include a slight heat addition to the atmosphere
due to absorption of the microwaves as the beam passes through the atmo-
sphere. The possible effects of this heat addition on atmospheric circula-
tion patterns will have to be established.
Heat will also be added to the atmosphere during launch operations.
Because a substantial launch frequency is required to place each SSPS in
orbit, e.g., 500 launches for a 25-million pound SSPS, local heating ef-
fects will have to be investigated as well as the addition of products of
116
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combustion of chemical propulsion systems (primarily water vapor). Tf
laser propulsion'should prove to he feasible, the air could serve ns the
propellant medium; reducing the environmental impact of repeated launches.
Noise pollution from the high-frequency launch operation would be of con-
cern in the immediate vicinity of the launch facility and would have to be
reduced by suitable design techniques and the choice of a suitable location
for the launch facilities.
The very high efficiency of microwave to DC conversion at the receiving
antenna, e.g., 90%, will greatly reduce the waste heat addition to the
environment compared to any other power generation method based on thermo-
dynamic principles. The heat exchange to the surrounding atmosphere from
the receiving antenna element can take place by natural convection. This may
lead to the formation of a "heat island" of about the same magnitude as en-
countered over an urban area.
The visual impact of the large receiving antenna, e.g., 7 km diameter,
can be decreased either by suitable landscaping or by incorporating the antenna
in an industrial park.
4. Land Use
Substantial flexibility exists in choosing a suitable location for the
receiving antenna. The area has to be contiguous, but need not be completely
flat terrain. The location can be in a region where land is available vfeich
is not suitable for other uses, e.g., a desert, previously strip-mined land,
or in an area where majdfr electrical power users, e.g., aluminum smelters,
are located. The antenna could be located in an industrial park to serve
several major users. Roofs and covered roadways could be designed to exclude
microwaves from working areas completely.
117
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The antenna structure can he designed to be mostly open so that sun-
light and rain can reach the land beneath it. Vegetation growing beneath
the antenna would be effectively shielded from microwaves and could be
harvested, precluding the land from becoming a biological desert.
IV. ECONOMIC CONSIDERATIONS
Business feasibility and cost to consumers have been overriding con-
siderations concerning energy production in the past, and it cannot be
assumed that it will be otherwise in the future. However, as the popula-
tion grows, pressure on resources, environmental constraints, and almost
certain requirements for vast increases in the availability of electricity
will make it equally unsafe to assume that established economic criteria
will be enough to decide the choice of a particular power generating
system. Based on present estimates, a prototype SSPS will cost about
3 to 5 times more than comparable available energy-production technology,
based on fossil or nuclear fuel. Inspection of the components making up
the cost projection indicates major costs are contributed by the solar cell
arrays and by the Earth-to-orbit transportation system. There are reason-
able expectations that these costs can be substantially reduced through
well-directed research and development programs using approaches which,
although definable, are now beyond the present state-of-the-art.
Standards to establish the true cost for energy production will have
to be developed and hidden costs, which at present are not charged to other
i
methods, will have to be identified so that, relative costs of other- systems
can be established on a comparable basis. There Is as yet no consensus on
the procedures which will have to be used; agreement on appropriate stan-
dards will be essential to meaningful analysis of economic impact.
118
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Major capital expenditures will be required independently of the
specific energy-production technology to provide electrical power to
meet demands. These capital requirements are projected to be at least
*
$600 billion over the next 30 years, with an additional $30 billion re-
quired during that time to carry out the necessary research and develop-
ment on energy conversion, transmission distribution, and environmental
controls. Therefore, energy production will continue to require a
significant fraction of available capital, indicatiag that one important
limit to the exponential growth of energy consumption will be the rate
of capital formation.
The economic and technical feasibility and the environmental and
social desirability of the SSPS will have to be established prior to any
major commitment to the development of this alternative energy-production
method based on solar energy. What is required is that sufficient in-
formation be made available so that the option represented by the SSPS can
be pursued, if other approaches should appear to be less attractive, whether
as the result of energy resource, environmental, or social considerations.
VII. SOCIAL CONSIDERATIONS
To deal with the social Impact of the SSPS, an assessment is required
which will serve to identify all of the effects of the specific technologies
employed (physical, environmental, economic; direct and derivative, immediate,
intermediate, and long term), so that the social desirability or undesirability
of these effects can be evaluated.
Panels, commissions and committees have addressed the questions of
social desirability over the last few years. Agreement, however, has not
yet been reached on how to express "social costs" either on the most detailed
119
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level or on an accounting basis for American society as a whole. Social
indicators of society's health and growth will have to be identified to
determine costs of the SSPS to society as a whole in the same way that
today the gross national product is used to express our status in the
(12)
field of economics. Appropriate standards and criteria which are
developed during a process of social impact analysis will have to be
tested with various groups having an interest in energy production methods,
and appropriate comparisons between solar and other energy production
systems will have to be made as well.
Many groups, individuals, and sectors of American society as well as
institutions will interface in relation to SSPS. To some degree, each of
these interfaces must be analyzed and understood. Various communication
methods will have to be employed to inform the public of the projected im-
pact of the technologies being developed at appropriate stages of the
development program in support of the SSPS objectives.
VIII. CONCLUSION
There are several other energy sources in addition to solar energy
which have the potential of meeting future energy requirements, but only
very few have a limited impact on the environment and are conserving the
finite resources of the Earth. Solar energy applications, such as rep-
resented by the SSPS, are still in an early stage of development. Thus,
it is too early to tell which of the approaches now being studied will be
judged to have the greatest potential to be of overall benefit to society.
As more is learned about the operating characteristics of potentially
competitive electrical energy generating systems, the views on what "best"
performance represents will continue to evolve. Thus, the criteria for
120
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decision-making - whether based on cost, resource conservation, or environ-
mental protection - may be quite different over the next decades, and will
continue to change as long as technical developments continue actively on
the various energy-production systems.
Development of energy-production systems, such as the SSPS, over the
next few decades will permit society to look beyond the year 2000 with the
assurance that future energy requirements will be met without endangering
the planet Earth. But even successful development of large-scale applica-
tions of solar energy still will require that efforts be made to reduce
energy consumption and to slow growth for growth's sake.
Technology change is creating a climate leading to institutional and
social changes which, in their overall impact, can be expected to rival
the 19th century industrial revolution. Those individuals and groups which
are charged by society with responsibility for leadership must face these
new challenges and opportunities. Instead of creating "dark satanic mills,"
there must be the realization that to survive, man must learn to "replenish
the Earth" and not just "subdue it."
IX. ACKNOWLEDGEMENT
The author greatfully acknowledges the encouragement and support of his
associates at Arthur D. Little, Inc., and the cooperation of the staff of
Grumman Aerospace Corporation, Raytheon Company and the Spectrolab Division of
Textron Inc., whose interest and commitment to the potential of power from
space were essential to the development of the concept of a satellite solar
power station.
121
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REFERENCES
1. Briefings before the Task Force on Energy of the Subcommittee on
Science, Research and Development of the Committee on Science and
Astronautics, U.S. House of Representatives, 92nd Congress, Second
Session, Series Q, March 1972, U.S. Government Printing Office,
Washington, 1972.
2. Meinel, A.B., and Meinel, M.P., "Physics Looks at Solar Energy,"
Physics Today. Vol. 25, No. 2, (February 1972), pp. 44-50.
3. Eckert, E.R.G., et al, "Solar-Thermal Power Conversion System,"
unpublished report, University of Minnesota, 1972.
4. Hildehrandt, A.F., et al, "Large-Scale Concentration and Conversion
of Solar Energy," Ecology. Vol. 53, No. 7, (July 1972), pp. 684-692.
5. Anderson, J.H., and Anderson, J.H., Jr., "Thermal Power from Sea-
Water," Me£h^mjc^_EjigJjieering_, Vol. 88, No. 4, (April 1966). pp.
41-46.
6. Glaser, P.E., "Power from the Sun: It's Future," Science, Vol. 162,
22 November 1968, pp. 857-861.
7. The Journal of Microwave Power. Special Issue on Satellite Solar Power
Station and Microwave Transmission to Earth, Vol. 5, No. 4, (December
1970).
8. Brown, W.C., "Experiments in the Transportation of Energy by Microwave
Beams," 1964 IEEE Int. Conv. Record, Vol. 12, pt. 2, pp. 8-17.
i
9. Kantrowitz, A., "Propulsion to Orbit by Ground-Based Lasers," As_tron-
autics j^ Aeronautics^ May 1972, p. 76.
10. Temporary Consensus Standard on "Nonionizing Radiation," issued under
the Occupational Safety and Health Act of 1970, published in the
Federal Register. Vol. 36, No. 105, Sec. 1910.97, May 29, 1971, pp.
10,522 - 10,523.
11. Committee on Public Engineering Policy, National Academy of Engineering,
"A Study of Technology Assessment," Committee on Science and Astro-
nautics, Washington, D.C., July 1969. '
12. Bauer, R.A., ed., Social Indicators. MIT Press, Cambridge, Mass., 1970.
122
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FEDERAL PROGRAM ON BIOLOGICAL EFFECTS OF ELECTROMAGNETIC ENERGY*
H. Janet Healer
Office of Telecommunications Policy
Executive Office of the President
Washington, B.C. 20504
I. INTRODUCTION
When speaking of the interaction of electromagnetic radiation with the
environment, it is no longer adequate to treat less than the total
environment, physical and biological. Most commonly we have focused
on the interaction with physical environment—particularly, on the
compatibility of sources and receivers of radiation with each other and,
more recently, on the degradation of electronic components and circuit
performance. Of equal importance, however, is the interaction with the
biological environment as a whole, and man in particular. Unintended
effects (often referred to as "side effects") from the purposeful use
of electromagnetic energy can affect our use of the spectrum. There-
fore, such effects can be significant factors requiring consideration
by both Government and the technical community in the design, installa-
tion, and operation of radiating systems.
The impact of this energy on man and the biosphere must be adequately
assessed in order to ensure their protection without unnecessarily
restricting our use of the spectrum resource and the benefits it
provides.
Recent legislation in the consumer, environmental, and health fields
already calls for the establishment of safety standards and regulations.
Rapid technological and economic developments in recent times have
resulted in an ever-increasing proliferation of sources and uses of
nonionizing electromagnetic radiation (EMR), providing valuable service
to mankind: communications systems, radio and television broadcasting,
radars, plus a host of other uses—power production, medical practice,
industrial processing and many consumer products. At the same time,
these benefits may introduce new forms of pollution—electromagnetic
pollution—which can result in annoying and hazardous interference,
physical degradation of electronic systems, and, at sufficient energy
levels, biological hazards.
Biological effects and potential hazards of electromagnetic radiations
(0 Hz - 3000 GHz) even at relatively low power densities are a matter
of concern to a number of Federal agencies and non-Government
organizations.
*Presented at the American Public Health Association Centennial Annual
Meeting, Session on Environmental Exposure to Nonionizing Radiation,
Atlantic City, N.J., November 14, 1972. 123
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II. THE ENVIRONMENT
Man-made radiation is relatively new as an environmental factor.
Knowledge of its possible biological consequences is limited and
incomplete.
Since approximately 1948, the growth in radiation sources has been
phenomenal and is continuing at an accelerated rate. World War II
stimulated the demand for widespread communication networks and the
application of science and technology resulted in new and expanded
technology which spawned today's electronics industry. In 1940, a
construction permit was issued for the first FM radio station and in
1945 the first commercial communications using microwaves were estab-
lished between New York and Philadelphia. Microwave communication
stations now number over 71,000. By 1968 the FCC had authorized over
6 million transmitting devices. This number is exclusive of Federal
Government systems. The estimated depreciated capital investment of
the U.S. Government alone in communications and electronics equipment
currently exceeds $50 billion.
To illustrate, Figure 1, based on FCC data, shows the increase in
radio and television stations in the United States from 1945-1969.
It is interesting that these curves are very similar to the
population growth curve over this same period.
Figures 2-6 illustrate the distribution of some EM sources in the United
States: microwave relay towers, radar stations (unclassified), and
television, FM and AM broadcast stations. As would be expected, the
density distribution of Figs. 4-6 together corresponds to that of the
population distribution.*
In terms of consumer products, it is predicted that by 1975 the annual
sales of microwave ovens for the home will reach 375,000 with a total
in use of approximately 800,000. Power levels in and around American
cities, airports, military installations, and tracking centers, ships
and pleasure craft, industry and the home may already be biologically
significant. \
Power outputs of many radio frequency (RF) sources are increasing also.
III. THE EFFECTS
Microwave and other KF radiations at sufficiently high
intensity are known to cause adverse biological effects due to the
generation of heat in the organism. Effects observed at high levels
include pathologically observable lesions, secondary injury from
hyperthermia and cataract formation. The extent and importance of
more subtle changes (e.g., biochemical, functional or behavioral)
which may occur at lower intensities particularly with continued or
long-term exposure are not known adequately.
* Figures and data above courtesy of EPA based on FCC and ECAC data.
124
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5000
'/
TOTAL BROADCAST
STATIONS. U.S.
YEAR
1945
1950
1955
1960
1965
1S69
TV
6
97
421
562
674
847
RADIO
930
2,832
3,310
4,255
5,537
6,442
1 1
"""
2
4000 I
C-7
O
5
m
•so
3000
2000
55
60
65
70
YEAR
FIGURE 1
Increase in Radio and TV
Broadcast Stations in the U.S.
125
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&'• {Y£& . • ;:!': :"•. -.•„.•• V ,
!• ••.:\-:-lCy..v- •. :':-.- :'-'.^'/.:;- * , .
( ^fx-^
\ • .,"';•'•! '';- ' : • ' ••;.••' Vi"''-^
V :.: •.:'::;;..^.v:i:.j,;Vlly^iv ^.^
Figure 2. Geographical Distribution
of Microwave Point-to-Point
Installations in the United States
0
Figure 3. Geographical Distribution
of Radar Facilities in the
United States (unclassified)
126
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Figure 4. Geographical Distribution
of TV Broadcast Stations in the United States
Figure 5. Geographical Distribution
of FM Broadcast Stations in the United States
AM BROADCAST
v\
< u .
•'
Figure 6. Geographical Distribution
of AM Broadcast Stations in the United States
127
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Within the Federal Government a coordinated multiagency program* was
promulgated by the Office of Telecommunications Policy (OTP) of the
Executive Office of the President in January 1972 to develop the
necessary understanding for assessing this situation and a rational
scientific basis for establishing safety and reiredial measures where
and as warranted.
The OTP's concern stems from its responsibilities for Government use
of the spectrum and the fact that the U.S. Government is the largest
single user of the spectrum. Inherent in these responsibilities is
OTP's concern for establishing rational risk/benefit criteria to
assure protection of the public while permitting effective use of
radiative equipments.
The Federal Communications Commission (FCC) is responsible for authorizing
the use of radio by non-Government entities; all Government use on the
other hand is the responsibility of the President. The Director,
Telecommunications Policy carries out this responsibility. He
• serves as the principle advisor to the President on
telecommunications matters;
• coordinates Government use of communications-electronics;
and
• presents Administration views on national matters
concerning telecommunications policy.
The Electromagnetic Radiation Management Advisory Council (EKMAC) was
formed in 1968 to assist the Director advising on side effects and
the adequacy of control of electromagnetic radiations arising from
communications activities. The Council reviews, evaluates and recommends
measures to investigate and mitigate potential undesirable effects on
the environment.
As an early undertaking the Council conducted a comprehensive assessment
of current knowledge, ongoing programs and potential problems pertaining
to biological effects. Representatives of cognizant Government agencies
participated and contributed.
Concluding that we do not know the potential impact of nonionizing
electromagnetic radiations on man with sufficient confidence and that
ongoing efforts were inadequate to resolve current issues and those
that could be anticipated in the future, the Council recommended a
Government-wide program.
"Program for Control of Electromagnetic Pollution of the Environment:
The Assessment of Biological Hazards of Nonionizing Electromagnetic
Radiation" — December 1971.
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Studies of effects around and above 100 raw/cm2 led to the general
acceptance in the United States and most western countries of a power
density of 10 raw/cm * as a safe level below which injury from heating
would not be expected except under conditions of moderate to severe
heat stress.
Despite some limited evidence of less definite effects including
psychological and functional changes, there is a lack of definitive
scientific data on the genetic/developmental, clinical, physiological,
and behavioral effects of .EMR at low power densities, e.g., around and
below the 10 mw/cm level. Without these data, the picture is incomplete
and the deduction of sound conclusions regarding hazards cannot be made.
Moreover, with the exception of thermal effects induced by the agitation
of polar molecules by the rapidly alternating electric field, little
or nothing is known about basic mechanisms of interaction between the
electromagnetic field and the molecular and cellular constituents of the
body, limiting our ability even to hypothesize or predict either effects
or hazards. This is in contrast to ionizing radiation where the basic
mechanisms of energy transfer to atoms and molecules are reasonably well
understood.
It is important to keep in mind that all effects are not necessarily
hazards. In fact, some effects may have beneficial applications under
appropriately controlled circumstances. However, RF induced changes
must be understood sufficiently so that their clinical significance
can be determined, their hazard potential assessed and the appropriate
benefit/risk analyses applied to establish tradeoffs. Such tradeoffs
are an integral and accepted part of our existence. For example,
many common factors in our daily lives can produce biological change
or effects—coffee which appears to affect chromosomes in somatic or
body cells and has an accelerating action on the cardiovascular
system. Even common drugs such as aspirin have contraindications.
It is important to determine whether an observed effect is irreparable
or merely transient or reversible, disappearing when the electromagnetic
field is removed or after some interval of time. Of course, even some
reversible effects may be unacceptable under some circumstances. For
example, subtle functional central nervous systems effects, even if
reversible, might affect the judgment or reactions of individuals
performing critical tasks—airline pilots, automobile drivers, factory
workers, etc. Thus some transient physiological and psychological
change or discomfort, even if not associated with permanent biological
damage, could pose indirect potential hazards.
* For example, see USASI, C95.1, 1966.
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Controversy exists among different groups as to the significance or
even presence of low level effects. Over a considerable period of
time Soviet and other Eastern European scientists have extensively
published research results dealing with low level, chronic exposure
effects on the nervous system of humans and experimental animals. Little
complementary or supplementary research has been performed by Western
scientists. There has even been a tendency to dismiss the Soviet
literature because of difficulties in interpretation due to its
frequently summary nature. Permissible exposure levels in the USSR
are, roughly speaking, lower than those of those in the USA by an
apparent factor of 1000 for long term exposures and a factor of 10
for exposures less than 6 minutes. To some extent, differences in
interpreting effects and what one considers a hazard may account for
some of the difference in permissible levels.
Growing concern and awareness in the Government, scientific community, and
public are evidenced by recent and proposed legislation relevant to the
question of biological effects. This legislation has, in turn, stimulated
the examination of biological effects, hazards, and safety standards.
The "Radiation Control for Health and Safety Act of 1968" (PL 90-602) ,
administered by HEW, is intended to protect the public health and safety
from the dangers of electronic product radiation including ionizing,
nonionizing, or particulate radiation.
Another recent enactment is "National Environmental Policy Act of 1969"
(PL 91-190), intended to promote efforts which will prevent or eliminate
damage to the environment and biosphere and stimulate the health and
welfare of man. It establishes the Council of Environmental Quality to
advise the President and requires all agencies of the Federal Government
to file environmental impact statements.
Associated with this is Reorganization Plan No. 3 of 1970, which
established the Environmental Protection Agency (EPA) . This agency
has standard-setting authority for environmental problems, including
radiation.
"The Occupational Safety and Health Act of 1970" (PL 91-596) is intended
to ensure safe and healthful working conditions. It authorizes the
Secretary of Labor to establish mandatory occupational safety and
health standards. He is also to conduct and publish studies of the
effect of chronic or low-level exposure to industrial materials,
processes, and stresses on the potential for illness', •'disease or loss
of functional capacity. Under this authority a standard for nonionizing
electromagnetic radiation from 10 MHz to 100 GHz has been promulgated.
(This is the ANSI, C95, 10 mw/cm2 standard.)
130
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The existence of a scientifically undefined possible hazard to large
numbers of people can and has already presented problems. Among these
is the establishment of defensible regulatory legislation and safety
standards required by these existing laws. There are medico-legal
controversies—some already in the courts—which may be improperly
resolved with long-term consequences by court or diplomatic actions
without benefit of adequate scientific basis for decision.
Radar and communication equipment operated by the U.S. Government at
overseas sites are vulnerable because of international differences in
safety criteria. Should host countries apply their own exposure limits,
the United States must have sufficient research data to argue their
reasonableness and practicality, in order to avoid unnecessary restraints
to operations.
IV. THE PROGRAM
In December 1971, the ERMAC recommended a coordinated program of survey,
testing and research among the cognizant Federal agencies. The estimated
5 year expenditure for this program was approximately $63 million over
the period FY 74-78, with annual expenditures of between $10 and $15 million/
year. For comparison, FY 72 appropriations were estimated to be approx-
imately $4 million—principally in DOD which provided roughly half and
in HEW and EPA which, together, accounted for somewhat less. FY 73
levels are approximately $6 million.
This program outlines fundamental research needs and program elements.
It provides guidelines and a framework for a coordinated national effort
to generate pertinent and dependable data for the evaluation of biological
hazards. It emphasizes low-level RF exposures and their significance.
Included are controlled laboratory experimentation, epidemiological
studies, and ecological studies where appropriate. Investigations of
basic mechanisms of interaction and tae development of measurement
techniques, instrumentation, and dosimetry are particularly critical.
Surveys will be conducted as of power density levels in selected urban
areas, airports, military installations, occupational and special
situations with estimates of the population(s) at risk. Initial
biological research priorities include:
1. Long-term genetic effects (and developmental)
2. Nervous system effects.
3. Gross physical condition.
4. Basic mechanisms of interaction between the EM field and
the living systems.
131
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A primary requisite is that findings be extrapolatable to man. (This
may be difficult to assure.)
Studies will cover a wide range of frequencies from quasistatic to
3000 GHz, a variety of wave forros and different exposure regimes.
The biological effect may be determined by various properties of the
EMR environment. Consideration must be given to near and far field
effects, polarization, cross modulations, harmonics, etc. There is
little knowledge of effects of different frequency regions and whether
or not there are biologically significant, narrow frequency regions,
such as molecular absorption resonances or natural body frequencies.
(This is important in determining permissible exposure levels—e.g.,
U.S. safety criteria currently apply one intensity level to the entire
range of frequencies from 10 MHz - 100 GHz.)
Early priorities should reflect frequencies affecting the largest
numbers of people.
In approximate order of priority these are:
Particular Regions
1. Microwave 915, 1850-2450, 2700-3700,
3700-4200, 6000-8000, and
8000-12000 MHz
(Includes: radars, microwave
radio, medical diathermy,
microwave ovens, etc.)
2. MF-UHF 2-50 MHz, 50-900 MHz
(Includes: radio and TV
transmitters, fixed and
mobile radar, land mobile, etcO
3. ULF-LF 0-5 Hz, 5-100 Hz, 10-50 kHz
(Includes: military communi-
cation systems, radio
navigation, etc.)
Effects of multiple frequencies and of RF in combination with other
factors will be examined. Emphasis is placed on chronic, long-term
exposures at the lowest intensity levels compatible with a biological
effect.
Another priority area is dosimetry. Early emphasis is needed in
instrumentation and measurement, particularly to enable the determina-
tion of the field at the biological point of interest and to relate
external to internal fields.
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V. STRUCTURE
Structurally, this is a multiagency program in which research and funding
responsibilities are shared. This is necessary since the problem is
not exclusively within the domain of any one agency. Many agencies
whose operations involve the use of RF energy or who may be affected
by its use have been and are currently conducting research appropriate
to their own responsibilities and missions. In aggregate, however,
the effort has been fragmented and current economy measures together
with competition for priorities and dollars within agencies could
perpetuate and exacerbate this situation. In the new program, partici-
pating agencies roles are based on their particular responsibilities
and special- capabilities which are coordinated to 'eliminate fragmenta-
tion and maximize the application of resources in eliminating question
marks which today exist in this field.
The DTP is responsible for coordinating the overall program and for
the elimination of unintended duplication and voids in the effort.
The ERMAC advises and assists DTP. For coordination within the
Government an interagency working group (Side Effects Working Group)
was formed. Comprised of agency representatives, this group has been
meeting monthly since April this year and is part of the Interdepartment
Radio Advisory Committee (IRAC) which advises OTP on the use of radio
within the Federal Government.
The agencies' roles are broadly outlined. Each develops the elements
and specifics of its own program and controls the administration
of funds recommended. The major participants are HEW, EPA and
DOD which together will account for approximately 80% of the effort.
As an example, in:'the plan HEW is responsible for a major biological
research program including controlled animal experimentation, basic
mechanism studies and effects on people. Emphasis is on long-term
exposures involved-in situations pertaining to public health and safety,
assessing hazards relating to the general public and to industry,
occupational uses and exposures, and, of course, nonionizing radiation
from electronic products.
EPA is concerned with assessing and determining control mechanisms
necessary for nonionizing radiations in the environment. Involved
are biological effects research, environmental surveillance including
supporting data banks'i and the capability to provide review and
analysis as to nonionizing electromagnetic aspects of environmental
impact statements.
The Defense Department ensures that the research programs of the
three military departments are coordinated in detail and complementary
with the programs of other agencies. Electronics systems under DOD
management (e.g., SANGUINE, SAFEGUARD, Shipboard, Air Traffic Control,
Field Radars, Air Defense Command Systems, etc.) will be assessed.
133
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The Army effort emphasizes research particularly related to specific
frequency ranges, device characteristics and operational environments
of their personnel. The Navy and Air Force activities are oriented
similarly.
The Department of Commerce is responsible for developing new methods
of instrumentation, dosimetric methodologies, and standardization of
measurement devices.
The National Science Foundation's role is to encourage and support
activities to fill the void of knowledge of basic mechanisms involved
in EMR interactions with biological systems.
Similarly, other agencies—involved in the use and management of the
radio spectrum—have responsibilities coincident with their basic
missions:
The Federal Communications Commission, which licenses all
non-Government use of the spectrum, is concerned with associated
exposures and safety.
The Federal Aviation Administration is concerned with exposures
of passengers, employees and the public in flight and airport environs.
The U. S. Information Agency operates very high powered HF
band communication systems.
The Department of Agriculture operates a forest service communi-
cations network and is concerned with effects on crops and livestock.
The National Aeronautics and Space Administration operates
extremely high powered tracking stations and is responsible for EMR
effects in space environments.
To summarize our present status, the programs of the various agencies
have been coordinated and the overall research effort is growing.
Since full implementation is expected in FY 74, current emphasis is
on ensuring the availability of adequate funds. We look forward to
having substantive results to report to you at future meetings.
VI. CLOSING REMARKS
In closing we—the public health community and the Government—are
unable, on the basis of current knowledge, to provide definitive
answers to the growing number of questions concerning the health
hazards of electronic systems involving exposures to energy levels
below those known to produce biologically significant heating.
The public and Congress are increasingly aware of health and environ-
mental issues including the question of EMR hazards. This is manifest
134
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in the press, recent legislation, claims of RF injury, and inquiries
as to the safety of various sources resulting in the reexamination
of some defense and other systems—e.g., SANGUINE, MW ovens, diathermy
devices, industrial processors, etc.
These factors further underscore the timeliness and need for this
program.
The program described today represents an exciting opportunity in
which the technical community and the Government, together, can delineate
and mitigate if necessary, a potential environmental problem of con-
siderable complexity before it has assumed the magnitude and dimensions
of others which have beleaguered you.
The public health community is a vital resource for this effort. We
need your experience and help. Thank you.
135
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THE ABSTRACT CARDS accompanying this report
are designed to facilitate information retrieval.
They provide suggested key words, bibliographic
information, and an abstract. The key word con-
cept of reference material filing is readily
adaptable to a variety of filing systems ranging
from manual-visual to electronic data processing.
The cards are furnished in triplicate to allow
for flexibility in their use.
136 »U.S. GOVERNMENT PRINTING OFFICE: 1973 5M-155/Z98 J-3
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ENVIRONMENTAL EXPOSURE TO NONIONIZING RADIATION,
EPA/ORP 73-2. Proceedings of a session: Annual Meet-
ing of the American Public Health Association, Atlantic
City, N.J., November 14, 1972. Cosponsors: American
Public Health Association and Office of Radiation Pro-
grams, U.S. Environmental Protection Agency (May 1973)
ABSTRACT: A series of papers discussing problems and
activities related to commercial, medical, and domestic
implications of nonionizing radiation.
KEY WORDS: Biological effects program; electromagnetic
spectrum; environment; monitoring; nonionizing radi-
ation; power generation; research.
ENVIRONMENTAL EXPOSURE TO NONIONIZING RADIATION,
EPA/ORP 73-2. Proceedings of a session: Annual Meet-
ing of the American Public Health Association, Atlantic
City, N.J., November 14, 1972. Cosponsors: American
Public Health Association and Office of Radiation Pro-
grams, U.S. Environmental Protection Agency (May 1973)
ABSTRACT: A series of papers discussing problems and
activities related to commercial, medical, and domestic
implications of nonionizing radiation.
KEY WORDS: Biological effects program; electromagnetic
spectrum; environment; monitoring; nonionizing radi-
ation; power generation; research.
ENVIRONMENTAL EXPOSURE TO NONIONIZING RADIATION,
EPA/ORP 73-2. Proceedings of a session: Annual Meet-
ing of the American Public Health Association, Atlantic
City, N.J., November 14, 1972. Cosponsors: American
Public Health Association and Office of Radiation Pro-
grams, U.S. Environmental Protection Agency (May 1973)
ABSTRACT: A series of papers discussing problems and
activities related to commercial, medical, and domestic
implications of nonionizing radiation.
KEY WORDS: Biological effects program; electromagnetic
spectrum; environment; monitoring; nonionizing radi-
ation; power generation; research.
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