Asymmetrical Coils for High Efficiency Wireless Power Transfer System Under Various Angular Misalignments

Wireless power transfer (WPT) systems are being increasingly used and it important to obtain the maximum mutual inductance since the power transfer efficiency is strongly related to it. If the transmitting coil (Tx coil) and receiving coil (Rx coil) are not perfectly aligned or have a specific angular misalignment, a decrease in mutual inductance is inevitable. In this paper, a trapezoid coil, whose upper side wire and lower side wire have different length, is proposed to achieve high mutual inductance between results of the comparison Tx and Rx coils under angular misalignment. The mutual inductance between the two coils is derived using a geometrical approach based on the Biot-Savart law. To verify the proposed coils, theoretical analysis, simulation, and experimental verification were conducted. Three asymmetrical Tx coils, one symmetrical Tx coil, and one Rx coil were designed for experiments and the mutual inductance and power transfer efficiency were measured using the fabricated coils. The experimental results supported that the asymmetrical coils provided the maximum power transfer efficiency by achieving the maximum mutual inductance as the angle between two coils became more inclined.