Skin heating effects of millimeter-wave irradiation - Thermal modeling results

Millimeter microwaves (MMWs) are a subset of RF in the 30-300-GHz range. Th e proliferation of devices that operate in the MMW range has been accompani ed by increased concern about their safety. As MMW irradiation has a very s hallow penetration in tissue, the specific absorption rate is not a relevan t parameter for dosimetry purposes. A thermal modeling program was used to investigate the tissue heating effects of MMW irradiation (100 GHz nominal) on the primate head. The objectives were to determine the extent to which the surface and subsurface tissue temperatures depend on applied energy den sity and the effects of blood flow and surface cooling on tissue temperatur es, Two power ranges were considered: short-duration exposure to high-power microwaves (HPMs), with power densities of 1.0, 1.5, 2.0, 2.5, or 3.0 W . cm(-2) for 3 s, and longer duration exposure to low-power microwaves (LPMs) , with power densities of 0.1, 0.15, 0.2, 0.25, 0.3 W . cm(-2) for 30 s. Th e applied energies were comparable for both HPM and LPM exposures. We found both surface and subsurface temperatures increase as the energy level incr eases, with HPMs having a higher peak temperature than the LPMs for similar exposure energy densities. The surface temperature increase is linear with energy density for the HPMs, except under combined conditions of high bloo d flow (blood-flow rate of 8 x 10(-3) g . s(-1) . cm(-3)) and high-energy d ensity (greater than 7.5 J . cm(-2)). The LPM surface temperatures are not linear with incident energy, The peak surface temperature is affected by en vironmental conditions (convection coefficient, sweat rate.) The magnitude of the temperature increase due to MMW exposure did not change with environ mental conditions. The subsurface temperature increases are considerably da mped, compared to the surface temperatures.