Magnetic field exposure to wireless charging stations for mobile phones

Abstract

Overview

This study examines the magnetic field levels produced by wireless charging stations for mobile phones, particularly focusing on the human exposure during usage. A combination of measurement and simulation methodologies was employed.

Findings

• Most transmitters for inductive charging operate within a frequency window of 110 to 205 kHz.
• The highest instantaneous magnetic field levels are observed in standby mode, reaching a few 100 µT which surpasses the recommended reference levels.
• Simulation results indicate compliance with safety standards from a regulatory perspective, though induced electrical fields may approach basic restrictions under worst-case scenarios.
• Technically, today’s dominant market standard for inductive charging is Qi, with emerging technologies such as resonant power transfer expected to be commercialized soon.

Conclusion

The study concludes that while inductive charging stations generally comply with basic restrictions ICNIRP and IEEE recommend, there are occurrences where the incident magnetic flux densities notably exceed these recommendations. There are significant margins concerning internal electric fields and specific absorption rate (SAR), suggesting the necessity to re-evaluate the maximum power allowed for these systems to ensure safety regarding rapid changes in induced electric fields.