Effect of air-gap between metal strips and a ferrite plate on magnetic shielding

Abstract

Wireless power transfer (WPT) systems have been increasingly employed in modern electric vehicles and electronic devices [1]. Leakage magnetic fields from the WPT systems are an important design issue for mitigating electromagnetic field (EMF) hazard to human body [2]. In many cases of electric vehicles and electronic devices, inductive coils of the WPT systems are typically placed near metallic plates such as vehicles bodies or batteries of mobile devices. The metal plate is helpful for shielding efficiency, but it deteriorates the magnetic coupling between the coils due to eddy current cancellation. To enhance the magnetic coupling, a ferrite plate or sheet is typically employed and located between the coil and the metal plate. A metal strip structure instead of the solid plate is also considered to reduce the eddy current on the metal surface.