Enhanced efficiency for wireless power transmission using an auxiliary loop on ferrite in metallic environment

An enhanced magnetic shield consisting of an auxiliary loop on a ferrite in a metallic environment at 6.78 MHz is described. Utilising an in-phase current of the auxiliary loop on the ferrite, the performances such as power transfer efficiency and the coupling coefficient are improved. The conventional shielding method that uses high-permeability ferrites has a limitation on the utilisation because of their high magnetic loss tangent. However, the proposed method using the auxiliary loop coated on the ferrite can provide better efficiency than the conventional method. In particular, at distance of 20 cm, the measured efficiency is improved by 30% after applying the auxiliary loop to the ferrite. The proposed method is considered to be useful to wireless power transmission systems having a ground plane.