Safe and Efficient Hundred-Watt-Level Wireless Power Transfer in Room-Scale Spaces Through Electromagnetic Field Optimization

This article delves into magnetic resonance wireless power transfer (MR-WPT) for room-scale charging of electronic devices, such as laptops and smartphones. A system utilizing multiple large single-turn circular coils is specifically designed, with a focus on optimizing resonant frequency and coil current to maximize electromagnetic (EM) power flow within exposure constraints defined by the International Commission on Nonionizing Radiation Protection guidelines (2020), ensuring compliance with EM safety standards. To mitigate electric field effects, a novel approach employing capacitor-distributed compensation and parallel excitation for each coil is introduced. A compensation parameter design method is proposed to achieve uniform current distribution across coils, especially in high cross-coupling conditions. The system's EM safety is evaluated through finite element analysis of specific absorption rates (SAR) and spatial EM field in various scenarios. Additionally, the EM field was experimentally tested, and both simulations and experiments analyzed the thermal effects on metallic objects. A cylindrical room model (3 m diameter, 2.4 m height, 17 m³ space) is constructed for system testing. Results demonstrate the system's capability to transfer over 100 W of power at 46% efficiency using an iPad-sized receiver, and transfer 375 W at 70% efficiency with three receivers operating concurrently. In the typical space for electronic device usage, a single receiver maintains a power transmission of 40 W.