High-Efficiency Wireless Power Transfer for Biomedical Implants by Optimal Resonant Load Transformation

TLDR

Wireless power transfer offers a safe, robust means of powering biomedical implants, where high efficiency is critical. The authors propose a new wireless power transfer technique that employs optimal resonant load transformation to markedly improve efficiency while adding only one extra chip inductor. They derive the optimal resonant load condition for maximum power transfer efficiency and implement it with printed spiral coils and discrete surface‑mount components operating at 13.56 MHz. The design achieves 58 % efficiency at a 10‑mm distance in tissue using a 25 mm × 10 mm, 0.5‑mm‑thick implantable coil, outperforming prior work and offering a compact, planar, tunable, batch‑produced, ferromagnet‑free, biocompatible solution.

Abstract

Wireless power transfer provides a safe and robust way for powering biomedical implants, where high efficiency is of great importance. A new wireless power transfer technique using optimal resonant load transformation is presented with significantly improved efficiency at the cost of only one additional chip inductor component. The optimal resonant load condition for the maximized power transfer efficiency is explained. The proposed technique is implemented using printed spiral coils with discrete surface mount components at 13.56 MHz power carrier frequency. With an implantable coil having an area of 25 mm × 10 mm and a thickness of 0.5 mm, the power transfer efficiency of 58% is achieved in the tissue environment at 10-mm distance from the external coil. Compared to previous works, the power efficiency is much higher and the structure is compact with planar integration, easy to tune, and suitable for batch production, as well as biocompatible owing to no incorporation of ferromagnetic core.