Stable and Efficient Class E2 Wireless Power Transfer System Based on Parity-Time Symmetry

Class E2 topology is attractive for high frequency wireless power transfer (WPT) due to the soft-switching properties of both the power amplifier (PA) and the rectifier. Meanwhile, the efficiency and output power of a Class E2 WPT system depends highly on the coupling coefficient, which is variable in practical applications. The purpose of this paper is to achieve stable and efficient power transfer under varying coupling coefficient by introducing parity-time (PT) symmetry into the Class E2 WPT system. The theoretical analysis based on coupled-mode theory (CMT) shows that the proposed system automatically stabilizes the output power with constant transfer efficiency against the variation of the coupling coefficient. The experimental results indicate that the proposed system can transfer around 40 W of power with an approximately constant system efficiency of 91% over a range of coupling coefficients.