Thin PCB-Type Metamaterials for Improved Efficiency and Reduced EMF Leakage in Wireless Power Transfer Systems

Current wireless power transfer (WPT) technology can only allow power transfer over a limited distance because, as the distance between the transmitter (Tx) and receiver (Rx) coils increases, the power transfer efficiency (PTE) decreases with a steep slope, while the electromagnetic field (EMF) leakage increases. In order to increase the PTE and decrease the EMF leakage simultaneously, we need to develop a method to concentrate the magnetic fields between the Tx and Rx coils. In this paper, we proposed a novel metamaterial structure to realize high efficiency and low EMF leakage. Metamaterials can confine the magnetic fields between the Tx and Rx coils by negative relative permeability. We designed and fabricated a thin metamaterial using a 1.6-mm dual layer printed circuit board (PCB) with a high dielectric constant substrate and a fine pattern to achieve a negative relative permeability with low loss at 6.78 MHz. The thin PCB-type metamaterial has a wide range of applications with low fabrication cost, light weight, and a simple fabrication process. We demonstrated a 44.2% improvement in the PTE and 3.49-dBm reduction in the EMF leakage around the WPT system at 20-cm distance. Furthermore, we first analyzed metamaterials from an EMF point of view using the 3-D magnetic field scanner. Finally, we discussed a combination of metamaterials and ferrites to further improve the PTE and reduce the EMF leakage for long-distance mobile WPT systems.