Design of Double-Layered Detection Coil for Metal Object Detection in Wireless Power Transfer Systems for Electric Vehicles

In this paper, double-layered detection coil set, which can detect metal objects by the change of the induced voltage, is proposed in wireless power transfer (WPT) systems for electric vehicles (EVs). The proposed detection coil is designed considering different magnetic flux densities according to each position of transmitting (Tx) pad. Therefore, it can detect a small metal object at all positions with an effective algorithm. In addition, the loss of the detection coil is negligible because of the magnetic flux cancellation. In order to introduce the design guide of the proposed detection coil set, finite element method (FEM) simulations are conducted and the induced voltage changes are analyzed in various conditions. Finally, a prototype of the WPT system with the proposed detection coil set is established and the performance of the proposed detection coil set is verified by experimental results.