Design of a Resonant Reactive Shielding Coil for Wireless Power Transfer System

An investigation of a resonant reactive shielding coil for wireless power transfer (WPT) systems is presented in this work. The shielding coil attenuates the magnetic field above and to the side of air-core WPT coils. A parameterized coil model is used to allow arbitrary circular winding geometry and current direction. Detailed modeling and mathematical calculations are provided, and an optimized design algorithm is proposed. The design method is validated using an experimental prototype shielding coil applied to a 3.03 MHz electric vehicle (EV) WPT system operating at 500 W output power. Experimental results show that the peak flux density on the top-center area of the coil is suppressed from 105 μT to 50 μT, and the magnetic field to the side of the vehicle is maintained well below the safety standard. In addition, effect of the shielding coil in WPT systems with metal and ferrite plates is investigated.