Design of tunable optimal load circuit for maximum wireless power transfer efficiency

A tunable optimal load circuit (OLC) for maximum wireless power transfer efficiency is presented for a magnetically coupled resonant system at 13.56 MHz. The OLC is required to transform the standardized 50 Ω receiver impedance to an optimal load to achieve maximum efficiency without using cumbersome feeding loops. The OLC based on a lumped-element impedance converter is fabricated on a FR-4 substrate. The size of the OLC is 25 × 50 mm. The series branch of the OLC is composed of a tunable series capacitor block and an inductor. The shunt branch of the OLC consists of a varactor and a capacitor block with switches. The theoretical and experimental results both showed that even though the loss in the inductor somewhat limits the achievable maximum efficiency, the efficiency with OLC is significantly enhanced compared with that without OLC. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2619–2622, 2014