Thermal Modeling for the Next Generation of Radiofrequency Exposure Limits: Commentary

Abstract

Overview

This commentary critically evaluates existing guidelines concerning human exposure to radiofrequency (RF) energy. It particularly focuses on frequencies above 3-10 GHz—termed the "transition" frequency—up to 300 GHz.

Findings

• The guidelines shift from using specific absorption rate to incident power density at these frequencies.
• A simple thermal model based on Pennes' bioheat equation (Pennes, 1948), assuming surface-only heating, is utilized for analysis.
• Current limits on temperature increases in tissue are analyzed as highly conservative compared to other safety standards for personal electronics.
• Issues in the guidelines, such as "averaging time" and "averaging area," are highlighted as inconsistent with the bioheat equation's scaling characteristics.
• Recommendations include the need for additional limits to protect against short, high-intensity RF pulses at millimeter wave frequencies.

Conclusion

The discussion is confined to thermal hazards. The paper explicitly avoids commenting on "non-thermal" effects, which are still contentious and would require further expert evaluation during guideline updates. Despite significant research, no conclusive low-level biological effects of RF have been established outside of phenomena like microwave hearing.