Thermal Response of Human Skin to Microwave Energy: A Critical Review

Abstract

Overview

This is a critical review and modeling study that focuses on the heating of human tissue by microwave energy, specifically in frequencies ranging from 3 GHz to millimeter wave frequencies (30-300 GHz).

Findings

• A comprehensive review of the literature identified relevant studies that reported increases in skin temperature due to radiofrequency (RF) exposure.
• A simplified thermal model based on Pennes' bioheat equation (BHTE) was proposed, utilizing parameters from existing literature without additional adjustments.
• Model predictions aligned excellently with the empirical data.
• A parametric analysis highlighted two distinct heating regimes controlled by different heat transfer mechanisms depending on the size of the irradiated area.
• For areas less than approximately 0.5-1 cm in radius, heat transfer is mostly limited by conduction into deeper tissue layers.
• For larger areas, the temperature increase is primarily limited by convective cooling due to blood perfusion.

Conclusion

The study supports the employment of this thermal model for aiding in the development and refinement of RF safety standards, especially at frequencies over 3 GHz and for millimeter wave exposures. It also notes significant gaps in data, especially for longer exposure durations or larger skin areas, underlining the importance of further research to ascertain safe exposure limits.