A Comprehensive Electromagnetic and Thermal Modeling Framework for Highly Focused Millimeter-Wave Beam Exposure on Rat Dorsal Skin

Abstract

This study presents a comprehensive dosimetry and thermal modeling framework for highly focused millimeter-wave (mmWave) exposure on rat dorsal skin. A 60-GHz dual-lens exposure system was developed to generate a localized beam with a spot size of approximately ${\mathbf{1}}\; {\text{cm}}^{2}$, facilitating precise heating. To address the multiscale computational challenge posed by the exposure distance and fine anatomical structures, a hybrid numerical method combining plane-wave spectrum expansion with the finite-difference time-domain method was employed. This approach yielded accurate dosimetry computation of the absorbed power density and resultant skin temperature rise within high-resolution anatomical models. While thermal simulation initially matched the transient experimental heating, discrepancies emerged in the steady-state phase due to dynamic thermoregulatory responses. To resolve this, a Weibull distribution-based approximation was introduced to characterize the time-dependent temperature rise behavior. Through an inverse fitting procedure, the blood perfusion rates of the skin and muscle layers, identified as the dominant cooling factors, were estimated and integrated into the Pennes’ bioheat transfer equation. The optimized thermal model demonstrated good agreement with experimental measurement. These findings establish a calibrated, experimentally validated framework for accurate mmWave dosimetry assessment, providing methodological support for future refinement of thermally based exposure assessment approaches in human protection guidelines.