A Simple Wireless Power Charging Antenna System: Evaluation of Ferrite Sheet

Abstract

We report a simple wireless power charging (WPC) antenna system (50 mm x 40 mm x 0.1 mm) for use in simulating power transfer efficiency (eta) with and without ferrite and a metallic object (battery case), thereby identifying suitable magnetic parameters and ferrite sheet thickness. The simulation results suggest that magnetic loss tangent (tan delta(mu)) and permeability (mu') need to be less than 0.05 and higher than 125 at 13.56 MHz, respectively, to achieve at least 75% of the transfer efficiency (eta(max)) of the WPC antenna without ferrite and the metallic object. Accordingly, we have fabricated NixZn(0.85-x)Cu(0.15)Fe(2)O(4) (x = 0.32 - 0.38) spinel ferrites using a one-step sintering process and obtained relatively high mu' of 169 and low tan delta(mu) of 0.1 with a nickel (Ni) concentration of 0.38. This magnetic loss is still too high to achieve 75% of the eta(max) value. In order to further reduce the magnetic loss, a two-step sintering process was used. The two-step sintered Ni0.38Zn0.47Cu0.15Fe2O4 shows mu' of 132 and a tan delta(mu) of 0.03 at 13.56 MHz, respectively. Therefore, this ferrite meets criteria identified by the transfer efficiency simulation and is a good candidate for 13.56-MHz wireless power transfer charging antenna system. In addition, our designed WPC system is capable of evaluating other magnetic materials that are suitable for WPC antenna applications.