Hybrid metamaterial slab with negative and zero permeability for high efficiency and low electro-magnetic field in wireless power transfer systems

Abstract

Current wireless power transfer (WPT) systems have limited charging distance and high induced electro-magnetic field (EMF) leakage. Thus, we first proposed a thin PCB-type hybrid metamaterial slab (HMS) combining two kinds of metamaterial cell structures. The metamaterial cells in the center area of the HMS have zero relative permeability and straighten the magnetic field direction. The metamaterial cells located at the edges of the HMS have negative relative permeability and change the outgoing magnetic fields to opposite direction by magnetic boundary condition. Therefore, the magnetic field can be more confined between transmitter (Tx) and receiver (Rx) coils, enhancing the power transfer efficiency, while decreasing the EMF leakage in a WPT system. In this paper, we demonstrated that increased power transfer efficiency from 39.1% to 65.5% and reduced EMF leakage from -19.21 dBm to -26.03 dBm in 6.78 MHz WPT system. Furthermore, we proposed new analysis method for relative permeability measurement of the metamaterial using a novel cubic structure with perfect electrical conductor and perfect magnetic conductor boundary.