Impedance matching considering cross coupling for wireless power transfer to multiple receivers

In this paper, a method of impedance matching for wireless power transfer (WPT) to multiple receivers is presented considering cross coupling effects between non-adjacent coils. For maximizing power transfer efficiency, design of a source coil and optimal load impedance are achieved based on circuit analysis and mutual inductance calculation. For verification, a WPT system of a transmitter and three receivers is fabricated. The fabricated WPT system can obtain reflection coefficient of under -11 dB for the maximum three receivers at once by using a circular single loop coil without capacitance compensation or additional impedance matching circuit. The simulated results show that the WPT system using the proposed method has more than 85% efficiency regardless of the number of receivers while efficiency for the conventional method is severely changed according to the number of the receivers. Measured results of the proposed method are consistent with calculation results.