Magnetic resonance wireless power transfer for laptop computer with a ground plane

This paper proposes a new method to increase the transfer efficiency of a wireless power transfer (WPT) system, having a source coil, a sprial transmitter (Tx) coil, a load coil and a ground plane, by utilizing the ground plane itself. The creation of cross slits at the ground center and employment of a lumped capacitor on the ground plane transform the ground plane into an additional resonator, which makes the original WPT system work as a 4-coil WPT system, producing a higher efficiency. By experiment, with an optimized capacitor on the ground plane of C = 2180 pF, the measurement of transfer efficiency shows a maximum improvement of 10% at a transfer distance of 40 cm, compared to the case without the ground plane. The transfer efficiency of the proposed system at transfer distance of 15 cm is 46%. Circuit theory and electromagnetic simulations are employed to analyze the proposed WPT system, giving results consistent with the measured ones. The operating frequency of the proposed system is 6.78 MHz.