ABSTRACT: BACKGROUND: Because the possibility of
millimeter wave (MMW) exposure has increased, public concern about the health issues due to
electromagnetic radiation has also increased. While many studies have been conducted for MMW exposure, the effect of dielectric permittivities on
skin heating in multilayer/
heterogeneous human-body models have not been adequately investigated. This is partly due to the fact that a detailed investigation of
skin heating in a multilayer model by computational methods is difficult since many parameters are involved. In the present study, therefore, theoretical analyses were conducted to investigate the relationship between dielectric permittivities and MMW-induced
skin heating in a one-dimensional three-layer model (
skin, fat, and
muscle). METHODS: Approximate expressions were
derived for the temperature elevation and temperature difference in the
skin due to MMW exposure from analytical
solutions for the temperature distribution. First, the power absorption distribution was approximated from the analytical
solution for a one-layer model (
skin only). Then, the analytical expression of the temperature in the three-layer model was simplified on the basis of the proposal in our previous study. By examining the approximate expressions, the dominant term influencing
skin heating was clarified to identify the effects of the dielectric permittivities. Finally, the effects of dielectric permittivities were clarified by applying partial differentiation to the
derived dominant term. RESULTS:
Skin heating can be characterized by the parameters associated with the dielectric permittivities, independently of morphological and
thermal parameters. With the
derived expressions, it was first clarified that
skin heating
correlates with the total power absorbed in the
skin rather than the
specific absorption rate (SAR) at the
skin surface or the incident power
density. Using Debye-type expression we next investigated the effect of
frequency dispersion on the complex
relative permittivity of tissue. The parametric study on the total power absorbed in the
skin showed that
skin heating increases as the static permittivity and static conductivity decrease. In addition, the maximum temperature elevation on the body surface was approximately 1.6 times that of the minimum case. This difference is smaller than the difference caused by the
thermal and morphological parameters reported in our previous study. CONCLUSION: This paper analytically clarified the effects of dielectric permittivities on the thermally steady state temperature elevation and the temperature difference in the
skin of a one-dimensional three-layer model due to MMW exposure.
