In this paper, an efficient wireless power transfer (WPT) system integrating with highly sub-wavelength metamaterials is proposed. The negative refractive index (NRI) and negative permeability (MNG) metamaterials for operation at radio frequencies are designed and applied to WPT system for improvement of power transfer efficiency. A dual-layer design which consists of a planar spiral on one side and a meander line touching with narrow metallic strips on the other side produces the properties of effective negative permittivity and permeability simultaneously, i.e., negative refractive index. In addition, the structure of double spirals produces a negative permeability. The cell size of the NRI and MNG metamaterials is about 253 times smaller than the operation wavelength. By integrating one, two, three or four metamaterial slabs between the two coupling copper rings, the transfer efficiency is improved significantly. The measured results show that the contribution of high transfer efficiency is due to the property of negative permeability which can make the WPT system work in the mechanism of magnetic resonance.
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