Effect of Metamaterial on Characteristics of Inductive Power Transfer Systems

Abstract

Inductive power transfer (IPT) is a wireless power transfer technology based on magnetic field coupling. The power transfer capability of an IPT system decreases with the increase of the power transfer range due to the drop in the coupling coefficient. To extend the power transfer range, metamaterial (MM) is investigated as an artificial structure with passive distributed coils. MM has the ability of concentrating electromagnetic waves due to its negative effective refractive index within a frequency range from several hundred MHz to a few GHz. However, it is not clear whether it is effective for an IPT system which has a typical operating frequency range from kHz to hundreds of kHz. This thesis is to study the effect of MMs on the power transfer performance of IPT systems. Three coil configurations for MMs are proposed, namely Snake (SN), Doublespiral (DSP), and Spiral (SP). Simulation studies have shown that the DSP and SP configurations are more effective than SN configurations for IPT systems, although they have different requirements on the tuning inductances and capacitances at the resonant frequency. By extracting the S-parameters from the software package CST Microwave Studio, the operating frequency range of MMs with negative effective relative permeability are determined, and the operating frequency corresponding to the maximum power transfer is found. Both simulation and experimental results have shown that the power transfer capability can be enhanced by using MMs. The experimental results show that the power transfer capability can be increased 165 times by using DSP MMs and 123 times by using SP MMs compared to the counterparts without MMs. A practical IPT system using a push-pull current fed primary converter, a full-bridge pick-up rectifier, and a 5W LED load is developed for studying the effect of MMs on the power transfer range. Two types of MMs with DSP and SP coils are tested at the system resonant frequencies at 354 kHz and 279 kHz. The experimental results show that both types of MMs can increase the power transfer range by more than 20% of the size of the coil diameter at the same output power.