Comparison of wireless power transmission characteristics using circular-coil array and elliptical coil as a transmission coil

Recently, wireless power transfer technology has drawn a lot of attention as a promising wireless power feeding and charging technology to mobile and wearable devices. Wireless power transmission using an excitation coil and several arrayed parasitic relay coils has been proposed in order to expand the power receiving area with highly efficient transmission. However, the efficiency of energy transmission using the arrayed parasitic relay coils may depend on the relative positions of the receiving coil and the transmitting coil array. In this study, we compared the transmission efficiency and magnetic field distribution using the circular-coil array with those using the same-sized single elliptical coil. As a result, it is found that the wireless power transmission characteristics using the circular-coil array behaved with different three modes at the frequencies of 64 MHz, 67 MHz, and 71.5 MHz, respectively. Furthermore, the wireless power transmission characteristics using the single elliptical coil behaved with only a single mode at a single resonance frequency of 67 MHz, and more stable transmission was achievable compared with the case using the circular-coil array.