Simplified Class E Inverter for 13.56MHz Low Power Wireless Power Transfer Applications

Wireless power transfer systems have been widely studied, especially at 13.56MHz. However, the power level is usually high, and applications up to 1W have not received too much attention, although there are relevant applications emerging in the market, such as Near Field Communication (NFC) charging. Therefore, in this paper, a low-power wireless power transfer system operating at 13.56MHz is designed and its efficiency for power levels below 1W is analyzed. The prototype system, based on a class E inverter, allows the receiver to move freely on a surface of 8cm x 4cm with an efficiency between 50% and 61% for a delivered power between 250mW and 1W. In addition, it is proposed to adopt a method to measure more accurately the impedance during the power transfer.