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).
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.
|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.|
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.