I. Introduction
Inductive power link (IPL) is a popular approach to realize short-distance wireless power transfer. An IPL is typically composed of two conductive coils that are magnetically coupled. The IPL efficiency depends on the operating frequency , the inductance , and the quality factor of the transmitting and receiving coils, and coupling factor [1], [2]. For biomedical applications, typically, is poor since the size of the implanted receiving coil is limited due to safety concerns (i.e., 5 mm × 5 mm for a neural implant chip [3]), and separation distance is relatively large (i.e., 5 mm [4] for neural implants just beneath the scalp to 12 mm [4], [5] for deep brain implants). The key challenge to maximize the IPL efficiency is to implement an implanted receiving coil with large and high under the size constraint.