Study type: Medical/biological study (experimental study)

Thermophysiological responses of human volunteers during controlled whole-body radio frequency exposure at 450 MHz med./bio.

By: Adair ER, Kelleher SA, Mack GW, Morocco TS
Published in: Bioelectromagnetics 1998; 19 (4): 232-245
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Aim of study (acc. to author)

To study thermoregulatory responses of heat production and heat loss in seven volunteers during exposure to 450 MHz continuous wave radiofrequency fields.

Background/further details

Two power densities were tested at each of three ambient temperatures (24, 28, and 31°C).

Endpoint

Exposure

Exposure Parameters
Exposure 1: 450 MHz
Modulation type: CW
Exposure duration: continuous for 45 min

Exposure 1

Main characteristics
Frequency 450 MHz
Type
Charakteristic
Exposure duration continuous for 45 min
Modulation
Modulation type CW
Exposure setup
Exposure source
Distance between exposed object and exposure source 102 cm
Chamber The anechoic chamber was 2.44 x 2.44 x 3.05 m. A small climate-conditioned cubicle was created by a 5-cm thick Styrofoam partition. The dipole antenna was mounted in a 90° aluminium corner reflector.
Setup Subjects wearing a bathing suit sat in a light plastic chair with their back towards the antenna. The electric field vector of the incident plane wave was aligned with the long axis of the subject's body (E-polarization).
Sham exposure A sham exposure was conducted.
Additional info After 30 min of equilibration to the prevailing temperature (24, 28, or 31 °C), the subjects were exposed or sham exposed for 45 min.
Parameters
Measurand Value Type Method Mass Remarks
power density 18 mW/cm² maximum measured - -
SAR 6 W/kg maximum measured - at the surface
power density 24 mW/cm² maximum measured - -
SAR 7.68 W/kg maximum measured - at the surface
Additional parameter details

Power densities (PD) specified above were determined with the E-field probe placed on the antenna boresight at the location of the subject's center back. Verification measurements of these PDs were made at 2- to 3-week intervals during the course of the study.

Measurement and calculation details

Forward and reflected powers were monitored by power meters. Field uniformity at the subject's location was determined over a 60 x 90 cm plane centered on the boresight and at 130 cm from the antenna using a broadband isotropic radiation detector fitted with an E-field probe. PD across the central 20 x 40 cm portion of this plane showed a 14% nonuniformity with the chair present. Dosimetric evaluations were conducted on a 70-kg soft plastic mannequin model, 174 cm tall, filled with simulated muscle tissue and placed on the chair with its back at a distance of 102 cm from the antenna. After equilibration, the model was irradiated for 10 min at three PD values. The maximum surface SAR of 0.32 W/kg per mW/cm² was calculated from the greatest temperature rise occurring at the lower back [Chou et al., 1996]. A second set of temperature readings was taken for comparison with the probes inserted 2 cm below the surface and exposure for 45 min. SAR could, however, not be calculated from these because the E-field was unknown for the points.

Reference articles

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

No changes in metabolic heat production occurred under any irradiation conditions. Vigorous increases in sweating rate on back and chest, directly related to both ambient temperature and power densities, cooled the skin and ensured efficient regulation of the deep body temperature to within 0.1°C of the normal level.

Study character:

Study funded by

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