Computation of Absorbed Power Densities in High-Resolution Head Models by Considering Skin Thickness in Quasi-Millimeter and Millimeter Wave Bands

The fifth-generation wireless communications system has been increasingly deployed by telecommunication companies worldwide. This system uses a high-frequency band ranging from 24 GHz to 28 GHz. However, the number of studies assessing the human protection from the electromagnetic fields is limited in this frequency band. In addition, two main international bodies—the International Commission on Non-Ionizing Radiation Protection and IEEE—have revised their guidelines and standard in 2020 and 2019, respectively. One primary change is the exposure metric and corresponding exposure limit at frequencies >6 GHz because the penetration depth of the electromagnetic waves in biological tissues is 1 cm or less for these frequencies. Therefore, modeling of the skin and subcutaneous tissues is important. This study evaluated the total absorbed power (TAP), the absorbed power density (APD), and variations in APD owing to skin thickness in seven types of realistic human head models with different skin thicknesses. Our results showed that the model without surface smoothing resulted in higher TAP than the model with smoothing. The amount of the TAP change in frequency domain in the model with realistically varied skin thickness was less than that in the model with uniform skin thickness because of the suppression of strong standing waves. The maximum variations in the APD, averaging over 4 cm2 or 1 cm2 with respect to skin thickness, were approximately 20% and 10%, respectively. For the limit of incident power density, APDs were below the guideline. These results will be useful for future revisions of international guidelines.