A Four-Coil-Configured Triple-Resonant-Tank Wireless Power Transfer System for Charging Devices Obstructed by a Metal Piston

Wireless power transfer (WPT) in enclosed metallic piston systems involves severe degradation due to magnetic shielding and eddy-current losses. To address this issue, a WPT architecture is proposed that utilizes the metallic piston as an energy relay, enabling efficient transfer across the barrier. A dual-coil resonant unit embedded within the piston forms a four-coil system, dividing the transfer path into two short-range coupling stages to mitigate coupling loss. Furthermore, a co-designed magnetic shielding structure enhances magnetic flux confinement and reduces parasitic losses. A 360-W prototype operating at 85 kHz achieves 361-W transfer across a 300-mm metallic piston with 86.5% DC-DC efficiency, demonstrating the effectiveness and practicality of the proposed approach for high-power WPT in extended metallic structures.