High Efficiency Metamaterial-based Multi-scale Wireless Power Transfer for Smart Home Applications

This paper presents a high efficiency multi-scale wireless power transfer (MSWPT) system using a metamaterial slab consisting of 2×2 spiral unit cells, which operates at 6.78 MHz (AirFuel Alliance standard frequency) for near-field WPT and 433 MHz (ISM band for smart home devices) for far-field WPT. The MSWPT system is configured to have the power transfer efficiency (PTE) greatly enhanced with the MTM slab which has an electromagnetic wave focusing capability for both frequency bands. A prototype of the MSWPT system is designed, fabricated, and characterized. The PTE of the fabricated MSWPT at a distance of 50 cm is increased from 5.42 % to 50.12 % with the MTM slabs at 6.78 MHz, i.e. 9.25 times enhancement while the PTE at a distance of 2.5 m is increased from 0.72 % to 3 % with the MTM slabs at 433 MHz, i.e. 4.17 times enhancement. It is concluded that the transition from 6.78 MHz near-field WPT to 433 MHz far-field WPT is advantageous in the MSWPT when the distance is greater than 90 cm.