Simple design method of wireless power transfer system using 13.56MHz loop antennas

In this paper, we propose a simple design method of a wireless power transfer system using 13.56MHz loop antennas. This method can simple design a wireless power transfer system by only using the measurements of coupling coefficients and the equations for equivalent circuit model about loop antennas without the complicated electromagnetic analysis. Using the proposed design method, a wireless power transfer system with a pair of loop antennas operating at the frequency of 13.56MHz, which have a dimension of 50×50 cm², is designed and implemented. The input return loss, coupling coefficient, efficiency, and input impedance variation with respect to the distance between loop antennas were measured. The proposed design method provides good agreements between measured and predicted results. Also, the wireless power transfer system with impedance matching circuits designed by the proposed design method shows two times higher efficiency characteristics than the case with the general 50 Ω impedance matching circuits. Therefore, we verified that our design method could be an effective tool to design a wireless power transfer system.