Loosely Coupled Transformer Coil Design to Minimize EMF Radiation in Concerned Areas

Wireless power transfer (WPT) technology as a convenient and reliable charging method, its electromagnetic field (EMF) radiation, and its compliance with human electromagnetic exposure limits have recently been studied. Different from the current research, which validates the EMF radiation level of a predesigned WPT system, this paper presents the loosely coupled transformer design method to minimize the EMF in the concerned area. The energy storage in the primary and secondary coils is studied for all popular compensation topologies in recently reported research. The coil of the loosely coupled transformer is designed with the S-S compensation topology as an example. The EMF radiation level is optimized to below the International Commission on Non-Ionizing Radiation Protection guideline in the concerned area. A 3.3-kW WPT system for electric vehicle wireless charging with an LCC-LCC compensation topology is designed with detailed process and experiment results, verifying that the EMF radiation is controlled as designed. The numerical analysis of human exposure is performed with the finite-element method, and the results show compliance as expected.