New Theory for Resonant-Type Wireless Power Transfer

The design theory for a band pass filter (BPF) is applied for the analysis of the resonant-type wireless power transfer system. Since the system transmits the electromagnetic energy through evanescent wave coupling between two resonators, it is just a two-stage band pass filter, as long as the circuit matching is taken into account. The present design theory allows different terminal resistances, that is, the generator and load impedances can be different. Since the load for the power transfer varies according to the practical applications, matching ability for arbitrary load is quite important. In addition, the transfer loss is analytically derived by the BPF theory, which has not been given so far. The analytical expression shows what parameters are crucial for the wireless power transfer. Some comments are given about the term “magnetic resonance” that is frequently used among the researchers of wireless power transfer. It is only adequate to describe the resonance of the precession of spins (magnetic moments) that is magnetized. “Magnetic resonance” should be read “magnetic coupling” for the present system.