Limitations of Incident Power Density as a Proxy for Induced Electromagnetic Fields

Abstract

Overview

The current safety guidelines implement restrictions for EMF exposure at frequencies over 6 GHz based primarily on spatially and temporally averaged power density metrics inside the body. These standard assessments rely on incident power density as a measurable proxy.

Findings

The evaluation focused on the consistency of compliance with basic restrictions when using reference levels for incident power density. Various antennas such as dipole, loop, and more were examined at different distances:

• Comparisons of three power density definitions were made.
• The study identified potential underestimations of transmitted power density in the reactive near-field, which could exceed 6 dB, showing a fourfold difference under specific conditions.
• Modifying averaging areas and using the modulus of the Poynting vector provided more accurate assessments in near-field scenarios.

Conclusion

This research underscores the need to consider several complex interactions and measurement strategies in the evaluation of EMF safety compliance, particularly for wireless devices operating above 6 GHz. Specific attention should be given to increased near-field coupling effects and the modification of power density measurements to ensure a more faithful representation of actual exposure levels. Improved methods in near-field conditions at frequencies below 24 GHz involve direct assessment using skin simulating phantoms.