Variable-Gain Load-Independent Class-E Rectifier for High-Frequency Wireless Power Transfer <Abstract> This article proposes a variable-gain load-independent (LI) class-E rectifier for high-frequency wireless power transfer (WPT) systems. Featuring a reconfigurable resonant network, the proposed rectifier dynamically adjusts its voltage gain across multiple levels, enabling the system to maintain a nearly constant output voltage under varying load and coil misalignment conditions. Comprehensive circuit analysis is conducted to derive explicit expressions for both the voltage gain and input reactance of the LI class-E rectifier. Based on this analysis, a systematic design methodology is presented to realize dynamic gain adjustment while preserving zero-voltage switching (ZVS) and constant input reactance. A 6.78-MHz WPT prototype was constructed and evaluated. The rectifier effectively adapted its gain in response to coupling variations, eliminating the need for external regulators. Moreover, the rectifier not only achieved ZVS operation itself but also maintained ZVS in the transmitter by providing constant input reactance. As a result, switching losses were significantly reduced, and the system achieved a high overall efficiency of 88.0%. |