Relationship between power density and surface temperature elevation for human skin exposure to electromagnetic waves with oblique incidence angle from 6 GHz to 1 THz.

This study presents an investigation of human skin exposure to obliquely incident electromagnetic waves at frequencies from 6 GHz to 1 THz. We aim to clarify the relationship between the power density and the skin surface temperature elevation under various exposure conditions. A Monte Carlo simulation was conducted to assess the transmittance and surface temperature elevation considering the variation of skin tissue thickness. For the case of TM wave injection, transmittance increases with increasing incidence angle from the normal incidence because of the Brewster effect. The normal incidence is confirmed as the worst-case exposure condition when the incident power density is defined in an area normal to the propagation direction. In addition, we investigated the power density required to obtain the equivalent temperature elevation over the skin surface. The analysis shows that the incident power density defined in the direction normal to the skin surface may underestimate the temperature elevation when TM waves are incident over the normal incidence up to the maximum transmittance angle. Our results also show that the power density inside the skin surface strongly correlates with the surface temperature elevation but less dependent on the frequency and independent of the oblique incidence angle and polarization. The findings of this study are expected to be valuable for discussing how to use the different definitions of power density based on dosimetric characteristics as measures in safety guidelines to protect humans from excessive temperature elevation by millimeter and submillimeter-wave exposure.