Since 1994, the authors' research has demonstrated how thermophysiological responses are mobilized in human volunteers exposed to three radiofrequencies, 100, 450, and 2450 MHz. A significant gap in this frequency range is now filled by the present study, conducted at 220 MHz.
Three power densities were tested at each of three ambient temperatures (24, 28, and 31°C).
|Chamber||The electrically shielded anechoic chamber was 6.7 x 6.7 x 9.8 m³ and contained a horizontal Fiberglas™ grid deck allowing placement of an antenna (tuneable dipole in a vertical 90° corner reflector) and a chair.|
|Setup||Subjects wearing a bathing suit sat on a light plastic chair, elevated 53.8 cm above the grid floor, 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 changes in metabolic rate occurred under any test condition, while esophageal temperature showed small changes but never exceeded 37.3°C. As with similar exposures at 100 MHz (see publication 10249), local skin temperature changed little and modest increases in local skin blood flow were recorded. At 220 MHz, vigorous sweating occurred at power densities of 12 and 15 mW/cm², with sweating levels higher than those revealed for equivalent power densities at 100 MHz.
Human exposure at both 220 and 100 MHz results in far less skin heating than occurs during irradiation at 450 MHz (see publication 2256). However, the exposed subjects thermoregulate efficiently because of increased heat loss responses, particularly sweating.