Classification and characterization of wireless power transfer systems of resonance method based on equivalent circuit derived from even- and odd mode reactance functions

Wireless connections by resonance method are promising for mobile and contactless power transfer, but the essential properties remain to be completely elucidated. This paper treats basic systems consisting of two equal lossless antennas of closed path type or open path type. Resonance and anti-resonance frequencies for even- and odd mode excitations are used to formulate the reactance functions and the image impedance of the system, from which a simple but accurate equivalent circuit with five different LC elements is derived. High image impedance frequency band is found to exist, which would broaden the possible applications.