Controlling the resonances of indefinite materials for maximizing efficiency in wireless power transfer

In this article, we investigate the possibility of improving efficiency in wireless power transfer (WPT) using metamaterials. Our analysis differs from previous works on the metamaterial design for WPT in that we focus on the design of thin metamaterial slabs. Specifically, three types of metamaterials are considered: the double negative material, the mu-negative material, and the indefinite material (IM). Although in general, all three types of materials are capable of amplifying evanescent waves, when the thickness is small, the slab formed by IM offers the best performance in enhancing WPT efficiency, as the locations of the resonances introduced by the slab can be controlled more readily. Thus, we propose a tuning method by varying its material parameters to maximize the WPT efficiency. Full-wave simulations of a WPT system equipped with a thin IM slab show that the system efficiency can be enhanced by an order of magnitude, comparing with the conventional design. As an example, implementation of the thin IM slab, the capacitively loaded split-ring resonators are considered, and the enhancement of WPT efficiency shows a similar performance to the ideal homogeneous IM slab. (c) 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:867-875, 2014