Scheme for providing parity-time symmetry for low-frequency wireless power transfer below 20 kHz

We provided parity-time symmetry (PT symmetry) for a magnetic resonance wireless power transfer (WPT) system designed to operate below 20 kHz. A lightweight coil having a mass of 39.1 g and consisting of a Mn–Zn ferrite core and 0.6-mm-diameter copper wire is considered herein. The coil had a Q factor of 111.5 at 16.5 kHz. The proposed system oscillated at 16.5 kHz for a transmission distance of 15 mm. A transmission power of 7.6 W was achieved when the DC power supply voltage was 100 V. Under these conditions, the power efficiency between the two coils was 92.1%. The oscillation frequency was automatically tuned to the optimal frequency for obtaining the maximum efficiency for a changing transmission distance. The relationship between the transmission power and the transmission distance was very different from that of a conventional WPT system, and an effect of PT symmetry clearly appeared.