A 13.56 MHz wireless power transfer system without impedance matching networks

A 13.56 MHz wireless power transfer (WPT) system is analyzed and implemented in this paper. This system consists of five subsystems: a class-D power amplifier, a pair of resonant coils, a rectifier, a DC/DC converter and various loads. By analyzing the transfer characteristics of the resonant coils, an optimum impedance is derived in order to minimize the power reflection. This impedance requirement is fulfilled by designing the rectifier and the DC/DC converter properly. The power reflection due to impedance mismatch can be controlled at 5%. When the load is a resistor, the system efficiency can reach 73% . When the loads are batteries or supercapacitors, the system efficiency can reach 66%.