Human Skin Model From 15 GHz to 110 GHz.

Compliance testing of wireless devices with absorbed power density (APD) limits requires body models that conservatively reproduce the absorption characteristics of human skin. Previous studies indicate that impedance-matching effects are caused by the stratum corneum (SC) layer. The objective of this study is to develop a single macroscopic dielectric model reproducing absorption of electromagnetic fields by the skin up to 110 GHz. The reflection coefficient of the skin of human volunteers was measured at frequencies of 15 to 43 GHz with open waveguide probes, complementing previous data from 45 to 110 GHz. The measurements were made at various regions of the body. The statistical analysis of the results shows that the reflection coefficient in dB follows normal distribution in regions with thin SC, which permits the development of a conservative skin model. In regions with thick SC, for example, the palms, the reflection coefficient is not normally distributed because the thickness of the SC depends on the mechanical stress the hands are exposed to. The measured data allow the derivation of dispersive two-layer models representing absorption and reflection at the skin surface with known uncertainty. The models can be used to conservatively demonstrate compliance with the APD limits of wireless devices in any of the 5G and 6G bands.