Optimization of Low-Frequency Magnetic Metamaterials for Efficiency Improvement in Magnetically Coupled Resonant Wireless Power Transfer Systems

With the extensive applications of magnetically coupled resonant wireless power transfer (WPT), improving the power transfer efficiency (PTE) of WPT systems is critical. Magnetic metamaterials (MTMs) can effectively improve the PTE. However, currently the design of MTMs is mainly based on microwave or optical theory, and their applicability in low-frequency WPT systems needs to be further explored. In this paper, a fast and effective method for the design and optimization of low-frequency MTM is provided. Firstly, based on circuit theory and mutual inductance calculation, the PTE of WPT systems is concluded in an equation that concerns the position of a 2-D MTM slab and compensation capacitance of MTM unit coils. Two WPT systems with large differences in coil size of the transmitter (Tx) and receiver (Rx) and the same size are considered. In addition, a directly separating variables method is proposed to optimize the MTM slab position and the compensation capacitance of unit coils to maximize PTE when the MTM slab position changes axially between Tx and Rx. It is found that the optimal MTM slab positions for the two systems are remarkably different, and the PTE impressively presents a capacitance splitting phenomenon with the change of compensation capacitance. Finally, two MTM-enhanced WPT systems are established to verify the theoretical calculation. The experiments show that the maximum PTE is significantly increased by 144% and 31% respectively by adopting optimized compensation capacitance compared with that without MTM for the two systems with different or same transceiver coil size.