Enhanced Efficiency of Asymmetric Wireless Power Transmission Using Defects in 2D Magnetic Metamaterials

In this work, we investigate an asymmetric wireless power transfer (WPT) system constructed by a big transmitter (Tx) and a small receiver (Rx) operated at 13.56 MHz. Because of the high radius ratio between Tx and Rx coils, the efficiency of asymmetric WPT is lower than the symmetric one. Therefore, a compact metasurface placed between the Tx and Rx is used to enhance the efficiency of WPT. To further improve efficiency, we create a nonuniform metasurface by controlling the resonant frequency of the unit cells. This defect with higher resonant frequency than others is easily formed by tuning the external capacitor. This modified metasurface can strongly localize the magnetic field into the defect region at a deep subwavelength scale of 2.3 λ × 10 −3 and is, therefore, suitable for coupling to the small Rx of asymmetric WPT. There is an optimum position of metasurface for achieving the highest efficiency when the couplings between the defect, Tx, and Rx coils are appropriate. By using the optimization approach, the efficiency of the WPT increases significantly from 9.8% to 60.2% with a nonuniform metasurface. The performances of WPT at various locations of defect and receiver are also considered.