Power transfer efficiency is an important issue in wireless power transfer (WPT). In actual applications, the WPT system may be exposed to a complex electromagnetic environment. The metal which is inevitably or accidentally close to the system will impact the power transfer efficiency. Most previous research has aimed at the effect of the metallic sheet paralleled to the resonant coil. This paper focuses on the effect of the metallic plate perpendicular to the resonant coils. Firstly, based on the theoretical analysis, a simulation model is setup using COMSOL Multiphysics. The efficiencies of the double-coils magnetic resonant WPT system with the presence of the parallel and vertical aluminum plate are studied comparatively. Efficiency improvement is observed with the vertical plate while the reduction appeared with the presence of the parallel plate. The vertical metallic plate has shown a magnetic field shielding effect according to the magnetic field distribution. It can reduce the radial magnetic field and enhance the axial magnetic field. Then, the effects of the position and size of the vertical plate are studied. It is found that the transfer efficiency has a preferable improvement when the vertical aluminum plate with a larger size is placed between the resonant coils and near outer edge of the windings. Finally, the experiment is carried out to verify the effect of the vertical aluminum plate on the WPT system.
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