Optimized Planar Spiral Coil Design for Efficient Wireless Power Transfer in Implantable Medical Devices ^†

This paper presents a five-coil array integrated wireless power transfer (WPT) system designed for implantable medical devices. The proposed structure features a collaborative design of driving and radiating coils, where each driving coil excites its corresponding radiating coil to emit power. All coil units are precisely tuned to operate at the 13.56 MHz ISM band. The unique array configuration generates a highly uniform magnetic field distribution within the target area, enabling excellent tolerance to lateral misalignment. System analysis based on scattering parameters (S-parameters) confirms the design’s outstanding power transfer efficiency at the operating frequency. By integrating the five-coil array onto a double-layer printed circuit board, the system achieves the miniaturization and high integration level required for implantable applications. The experimental results demonstrate that the system reaches a maximum transfer efficiency of 55% under ideal alignment conditions (with a transfer distance of 10–20 mm). Notably, even with a lateral displacement of 5–10 mm at a 10 mm transfer distance, the system maintains stable performance, with efficiency consistently exceeding 50%. These results validate the system’s capability for reliable and efficient wireless power delivery in clinical settings.