Boosting Efficiency of Wireless Power Transfer in a Near-to-Receiver Manner: Metamaterials versus Relay Coils

Incorporating relay coils and metamaterials are two effective methods to improve the transfer efficiency or extend the range of high transfer efficiency without altering the original wireless power transfer (WPT) system. This paper performs a comparative study on the efficiency improvement ability of a relay coil and a metamaterial slab in a two-coil WPT system featuring asymmetric dimensions of transmitter and receiver. We intend to place either the relay coil or the metamaterial slab, with dimensions identical to the receiver, near the receiver to examine their ability to manipulate the already divergent magnetic field. Theoretical analysis reveals that the efficiency improvement of the metamaterial slab or the relay coil over the original WPT system varies depending on their relative position to the receiver. The metamaterial slab exhibits greater efficiency improvement when placed closer to the receiver, while the relay coil is more effective when positioned farther away. However, the metamaterial slab robustly retains its efficiency improvement capability within a range of relative position compared to the relay coil. Verification of the conclusion is achieved through results of combined numerical and finite element simulations.