High-efficiency wireless power transfer by optimal load and metamaterial slab

Abstract

In this letter, a two-coil wireless power transfer system is analyzed mathematically to obtain optimal source and load impedances, which are the most important factors that affect system efficiency. In addition, a near-zero refractive index metamaterial slab with a negative permeability was inserted between two resonant coils close to the transmitter to improve the efficiency in a large range. Finally, the wireless energy transfer system with the metamaterial slab was designed, fabricated and measured to evaluate the analysis method. The power transfer efficiency of 73.1% with the optimal impedances was enhanced to 81.3% using a 5 x 5 array metamaterial slab at the frequency of 13.56MHz and the distance of 20 cm between the transmitter and the receiver.