Coils Parallelization: A Strategy for Improving Power Transfer Efficiency and Specific Absorption Rate in Wireless Power Transfer System for Implantable Medical Devices

This paper proposes a new single-turn coil design to improve Wireless Power Transfer (WPT) for brain implantable medical devices (IMDs). Our approach considers both near-field propagation and tissue interaction, primarily maximizing power transfer efficiency (PTE) while minimizing specific absorption rate (SAR). We present methods to adjust the feed line using Grounded Coplanar Waveguide (GCPW) and reduce coil impedance through the parallelization of coils, resulting in a reduction in electric field (E-field) and enhancement of magnetic field (H-field), thereby yielding superior PTE performance and SAR reduction. Furthermore, we investigate the optimized distance of the transmitter coil to the tissue, clarifying the crucial role of coil positioning in maximizing quality factor (Q factor) while minimizing SAR. Our proposed techniques are validated through simulations, showcasing a remarkable improvement in the maximum allowable transmitted power up to 23% and an increase in H-field up to 8% compared to conventional coil designs. The combination of coil parallelization and the capacitor segmentation method offers 35% of enhancements to the SAR. Additionally, this coil parallelization approach alleviates the undesirable H-field attenuation encountered with the capacitor segmentation technique, which is attributed to the ESR of additional capacitors.