Experimental Validation of Thermoregulatory Modeling for Human Back Exposure at 28 GHz

This study investigates skin temperature rise during dorsal exposure to 28 GHz quasi-millimeter waves using an electromagnetic–thermal computational modeling framework considering thermoregulation. Human exposure experiments were numerically reproduced using anatomically detailed models of Japanese adults augmented with age- and sex-related thermoregulatory functions. An exposure system with dielectric lens antennas provided controlled irradiation to the back, and the measured skin temperatures were compared with the computational predictions. The computational framework reproduced the experimental temperature rises well for both the 64-region of interest (ROI) and 1-ROI. Furthermore, the model reproduced the tendency that female participants exhibited higher temperature rises than males, which was mainly attributed to anatomical variations in muscle and fat composition. Age-related effects were modest, likely because the older adult group was approximately 65 years old. The predicted temperature rise was 2.48 °C, which is within the permissible limit of 2.5 °C (derived from the operational threshold of 5 °C with a reduction factor of 2) when evaluated at an absorbed power density of 100 W/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for occupational exposure, as specified in international exposure guidelines. These findings demonstrate the applicability of the thermoregulatory model to superficial absorption for exposure to quasi- and millimeter waves and support its use for assessment across different populations, such as those differing in age, sex, and thermoregulatory capacity.