Design of reactive shield for reduction of low-frequency magnetic fields for wireless power transfer system

Abstract

Interest in wireless power transfer system has also been increased. Transfer power increase, and leak-age of electromagnetic field is generated more. Therefore, the safety issue appears as a critical issue for the point of view from electromagnetic field. Some methods have been applied to solve electromagnetic field problems such as conductive shield and magnetic shield etc. In this paper, we introduce conventional meth-ods for the magnetic field shielding and propose the concept and design methodology for a resonant reactive shield for the reduction of magnetic field leakage from a wireless power transfer systems. By using LC reso-nance, the reactive shield can generate a cancelling magnetic field to reduce the incident magnetic field from wireless power transfer coils and effectively reduce the total magnetic field without consuming additional power. The shielding effectiveness of the resonant reactive shield and its effect on wireless power transfer efficiency are analyzed with a simulation and measurements. For practical application to wirelessly charged electric vehicles, an automatic tuning system for the resonant reactive shield is also proposed and implement-ed. The effectiveness of the resonant reactive shielding is verified by experiments in an actual wirelessly charged electric bus.