Tri-Loop Impedance and Frequency Matching With High- $Q$ Resonators in Wireless Power Transfer

Resonant wireless power transfer (WPT) using magneto quasi-static fields is an attractive means for delivering power in many applications. Central to the efficient delivery of power in these systems is the use of high-ratio impedance transformers to impedance-match the load to the source via the WPT network. Mini-loop transformers, which use a resonant tank for impedance matching, have become popular as they provide high-ratio impedance matching and low loss. Key to the low loss is the use of high- Q resonators. There are two challenges with this approach. The first is impedance matching the resonators to source/load impedances, and the second is adjusting the center frequency of resonance to exactly match the operating frequency, which can be very difficult with helical coils that use their parasitic capacitance for resonance. In this letter, we introduce a tri-coil impedance-matching network for WPT that provides accurate impedance matching and precise frequency tuning for high- Q coils to overcome these limitations.