Design method of multi-band coil using high order resonance in wireless power transfer

Wireless power transfer (WPT) has been a popular research topic in recent years. The allowed frequencies for WPT are limited by the industrial, scientific, and medical (ISM) radio bands and the laws of the respective countries. Different applications of wireless power transfer require different frequency bands. A single transmitter coil that can adapt to multiple frequency bands is needed to reduce the number of transmitter coils. In this paper, a transmitter coil design for two frequencies using a high order resonant frequency of an open end coil and a short end coil are proposed. Two types of multi-band coils, an open end coil and a short end coil are discussed. In the case of the open end type, for fundamental study, the second resonant frequency is set at 13.56MHz (ISM band) by adjusting the coil shape. It is confirmed that only the second resonant frequency can be set by adjusting the coil shape parameters and can be used for WPT by experiment. In the case of the short end type, the first resonant frequency is set at 85 kHz (for Electric Vehicles) by using capacitor. The second resonant frequency is set at 6.78MHz (ISM band) by adjusting the coil shape. It is confirmed that the second resonant frequency can be set by adjusting the coil shape parameters and can be used for WPT by experiment. Finally, it is confirmed that a short end coil with a capacitor is superior to an open end coil because two resonant frequencies can be set independently.