Metal-loop effects in wireless power transfer systems analyzed by simulation and theory

This study presents wireless power transfer (WPT) from a transmitter coil to a receiver coil (WPT coils) with a metal loop in the vicinity of the coils by simulation and theoretical analysis. Power transfer efficiency S21 of the WPT system is set to have flat top level, pass-band, lower cut-off frequency, and upper cut-off frequency. The lower cut-off frequency of S21 shifts higher when a metal loop is in the vicinity. On the other hand, the upper cut-off frequency of S21 does not shift. The frequency shift of the lower cut-off frequency is proportional to square of the inductive coupling factor between the metal loop and the WPT coils. At frequencies near the upper cut off frequency, the currents on the WPT coils cancel each other to reduce induced current on the metal loop in the vicinity. The electromagnetic interference (EMI) of the WPT system reduces at the frequencies.