Designing Efficient Inductive Power Links for Implantable Devices

Due to limited battery life and size limitations, many implantable biomedical devices must be powered inductively. Because of weak coupling between implanted and external coils, obtaining high power efficiency is a challenge. Previous authors have addressed the issue of optimizing power efficiency in these systems. In this paper, we further this analysis for the case of planar spiral "pancake" coils at low RF frequencies (100 kHz -10 MHz). We consider practical design constraints such as component variation, power amplifier limitations, and coil voltage limits. We introduce a new, complete expression for total power link efficiency.