United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S2-83-018 Aug. 1983
ŁEPA Project Summary
Radiofrequency Radiation
Exposure Facilities for
Bio-Effects Research
Joseph S. AM and Claude Weil
This report describes the multi-user
radiofrequency radiation exposure
facilities for bio-effects research in use
at the Health Effects Research
Laboratory, Research Triangle Park,
NC. Four facilities are described: (1) a
100 MHz CW exposure system, (2) a
2450 MHz CW exposure system, (3) a
2450 MHz AM exposure system, and
(4) an X-band pulsed RF exposure
system. In the final report, the
individual facility descriptions include
construction details, specifications,
photographs, circuit drawings and
block diagrams. All of the facilities
incorporate environmental control
systems, and three have RF power-level
regulation.
This Project Summary was developed
by EPA's Health Effects Research
Laboratory. Research Triangle Park,
NC, to announce key findings of the
research project that is fully document-
ed in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
One of the missions of the
Environmental Protection Agency (EPA)
is to investigate the effects of
radiofrequency radiation (RFR) exposure
on biological organisms. The EPA has
been involved in this effort since its
creation in 1970. This report focuses on
the major RFR exposure facilities in use
by the Health Effects Research
Laboratory at the Research Triangle Park,
N.C.
The operating frequency of an
exposure system determines to a large
degree the types of exposure systems
that can be employed. For example,
transverse electromagnetic mode
transmission lines (TEM cells) are
generally not useful above approximately
1 GHz because of the small size required
to prevent the propagation of unwanted
higher order modes. Likewise, anechoic
chambers become impractical and
expensive below about 400 MHz because
of the large size of the anechoic material
and the chamber itself. Selection of the
operating frequency generally results
from one of two motives: (1) a facility is
designed to simulate some environ-
mentally occurring exposure situation
over some narrow portion of the RF
spectrum, or (2) an exposure system is
designed which maximizes the chance of
observing an effect based on a theoretical
model and therefore the research leads to
a better understanding of the mecha-
nisms of interaction.
Four exposure facilities are described
in this report. Each is a large, multi-
animal exposure system available to all
the research staff who quite
frequently design multidisciplinary
studies with these facilities. All of these
systems are located in the same "high-
bay" room which has been equipped
with an auxiliary air conditioning system
to precondition the air. The first facility
constructed was the 2450 MHz CW
exposure system. 2450 MHz has become
the defacto reference frequency in
biologic effects research. Probably more
work has been done at this frequency
than at any other, and most laboratories
involved in the research have had a
facility at this frequency. This happened
largely for three reasons: (1) the
availability of relatively low cost, high
power RF sources since 2450 MHz is an
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ISM band frequency (an ISM band
frequency is one of a number of
frequencies reserved for use by the
industrial, scientific, and medical
communities by the F.C.C.); (2) the
excellent coupling of this frequency to
laboratory animals and (3) the projected
explosive growth in sales of microwave
ovens, possibly leading to the exposure of
a significant portion of the population to
low-level radiation.
The X-band exposure facility, which
became operational in 1974, was
designed to simulate the RFR generated
by radar systems. Acquisition, naval ship,
aircraft and small marine radars all
operate in the 8.5 to 9.6 GHz range
covered by our system. The first from the
list above was the primary consideration
motivating the design of this facility. At
this high frequency, depth of penetration
of the RF energy into a biological target is
poor; however, these frequencies are in
extensive use in the environment and the
system provides a tool to investigate the
effects of high peak to average power
ratio fields on biological organisms.
The 100 MHz exposure facility was
designed to provide an irradiation facility
in the environmentally significant FM
band of radio frequencies. Radiation from
these sources is deliberately beamed
toward population centers for use in FM
radiobroadcasting and is one of the more
significant sources of manmade RFR in
human exposures1. This, coupled with
research studies showing the resonance
of the human body lies in the FM band2,
were strong arguments for EPA to
examine frequencies in this band for
potential biologic effects.
The 2450 MHz AM facility was
constructed for several purposes: (1) EPA
agreed to investigate for the Department
of Energy the biological impact of the use
of solar power satellites which would
collect solar energy using satellites in
geosymchronous orbit, convert this
energy to microwave energy at a
frequency of 2450 MHz and beam it down
to earth to be collected by large arrays of
antennas, (2) studies were published
reporting effects with low-level ampli-
tude modulated RFR. Because virtually all
of the U.S. population is exposed to low-
level amplitude modulated RFR, the EPA
has been interested in these reports.
The systems used for RFR biologic
effects studies are largely custom
designed to tailor the system character-
istics for the special needs of biological
effects research. A prime example of this
is the power level stability of RF sources.
In most commercial medium and high
power RF generators and amplifiers, the
RF power output is seldom regulated. The
usefulness of an airport radar or an in-
dustrial microwave oven is not se riously
compromised if the RF power output
drifts by 10% to 20%. However, such a
drift is of obvious concern in biologic
effects studies since the absorbed energy
is directly related to the stability of the RF
source. Other features that are important
in the design of RFR exposure facilities
are: (1) provisions for environmental
control, (2) spectral purity of the RF
source, (3) personnel safety, (4) provision
for automatically timed exposures and (5)
RF field uniformity. The latter has become
less important in recent years as the state
of the art has advanced both in the
determination of whole-body specific
absorption rate (SAR) and localized SAR.
As more becomes known about the
effects of low-level amplitude modulated
RFR, control of the spectral purity of test
generators may grow in importance. For
this reason, we have tried to characterize
the spectral content of the sources used
here where possible.
The EPA authors Joseph S. AH fatso the EPA contact, see below) and Claude M.
Weil are with the Health Effects Research Laboratory, Research Triangle Park,
NC 27711.
The complete report, entitled "Radiofrequency Radiation Exposure Facilities for
Bio-Effects Research," (Order No. PB 83-229 591; Cost: $10.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
Joseph S. AH can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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