Study type: Medical/biological study (experimental study)

Human exposure to 2450 MHz CW energy at levels outside the IEEE C95.1 standard does not increase core temperature. med./bio.

Published in: Bioelectromagnetics 2001; 22 (6): 429-439

Aim of study (acc. to author)

To study human thermoregulatory effciency in radiofrequency environments.
Permission was received to exceed the peak power density (35 mW/cm²) the authors had previously studied during partial body exposure of human volunteers at 2450 MHz (publication 2287).

Background/further details

Two additional peak power densities were tested (50 and 70 mW/cm²) at each of three ambient temperatures (24, 28, and 31°C). The thermophysiological data were combined with comparable data at power densities of 0, 27, and 35 mW/cm² from the previous study to generate response functions across power densities.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2,450 MHz
Modulation type: CW
Exposure duration: continuous for 45 min
  • power density: 50 mW/cm² maximum
  • SAR: 11 W/kg maximum (at the surface)
  • power density: 70 mW/cm² maximum
  • SAR: 15.4 W/kg maximum (at the surface)
  • SAR: 1 W/kg average over mass (whole body)

General information

Details of the exposure system, field measurements, and dosimetry appear in two earlier publications [Adair et al., 1999].

Exposure 1

Main characteristics
Frequency 2,450 MHz
Type
Charakteristic
Exposure duration continuous for 45 min
Modulation
Modulation type CW
Exposure setup
Exposure source
Chamber The subject's immediate environment was climate controlled for temperature, relative humidity, and air movement.
Setup Subjects wearing a bathing suit sat on a light plastic chair, facing the rear chamber wall.
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 50 mW/cm² maximum measured - -
SAR 11 W/kg maximum measured - at the surface
power density 70 mW/cm² maximum measured - -
SAR 15.4 W/kg maximum measured - at the surface
SAR 1 W/kg average over mass estimated whole body -

Reference articles

  • Adair ER et al. (1999): Human exposure at two radio frequencies (450 and 2450 MHz): similarities and differences in physiological response.

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 change in deep body core temperature or metabolic heat production was recorded at any power density in any ambient temperature.
At a power density of 70 mW/cm², skin temperature on the upper back (irradiated directly) increased 4.0°C in ambient temperature of 24°C, 2.6°C in ambient temperature of 28°C, and 1.8°C in ambient temperature of 31°C. These differences were primarily due to the increase in local sweat rate, which was greatest in ambient temperature of 31°C.
Also at a power density of 70 mW/cm², local skin blood flow on the back increased 65% over baseline levels in ambient temperature of 31°C, but only 40% in ambient temperature of 24°C.
Although ambient temperature becomes an important variable when radiofrequency exposure exceeds the IEEE C95.1 guideline partial body exposure limits, vigorous heat loss responses of blood flow and sweating maintain thermal homeostasis efficiently.

Study character:

Study funded by

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