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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.
Xue et al. (Thu,) studied this question.