A new configuration of coil antennas for efficient wireless power transmission systems compatible with different loads

A new configuration of compact planar coil antennas is proposed for design of wireless power transmission (WPT) system. Within each antenna, the structures of one or more loop coil(s) placed outside and one spiral coil put inside are composed together and spaced closely. Based on this configuration, two cases of resonant mid-range WPT systems suitable with small and large load resistors can be both realized efficiently. It is shown that the maximum transfer efficiencies of the proposed WPT systems with loads of 320 mOhms and 50 Ohms arrive at around 49.1% and 56.9% respectively with resonant frequency of 19.22 MHz.