Design and Analysis of Four-Layer MOD Coil Array with Printed Spiral Detection Coils for Wireless Power Transfer

Wireless charging for small devices such as mobile electronic devices and electrical appliances has increased for a convenience. The safety as well as the charging efficiency is important in wireless charging because strong magnetic field is induced between a power transmitter and a receiver. In particular, if a metal object(MO) is between the transmitter and the receiver, it would be raised temperature by the induced magnetic field, causing a risk of burns and fires. Therefore, MO detection method is required. This paper proposes an active detection coil array for detecting MOs. Two-layer coils are configured in two stages to improve the detection performance, and each the coil is matched impedance by a series resonance at 1 MHz. Using a Korean 100 won coin as a MO, MO detection performance is confirmed according to the coil structure and coin position.