Experimental investigation of 6.78MHz metamaterials for efficiency enhancement of wireless power transfer system

In this paper, we propose a concise unit-cell design of magnetic metamaterial. The effective permeability of the unit cell is derived by S parameter method and can be flexibly adjusted to meet specific requirements. 6×6 planar metamaterial slabs are constructed by the proposed unit cells to verify their effects in a 6.78MHz wireless power transfer system. The effects of 1-slab and 2-slab metamaterials on efficiency enhancement are analyzed by both S parameter measurement and power experiment. The optimal position of the 1-slab metamaterial and the optimal gap between two slabs are acquired by analyzing the transmission and reflection coefficients of the system. Finally, we set up a medium-power wireless power transfer system to explicitly demonstrate the efficiency enhancement by lighting up a 15W light bulb.