Living object detection system based on comb pattern capacitive sensor for wireless EV chargers

A living object detection (LOD) system based on a comb pattern capacitive sensor with simple and cost-effective characteristics is applied to wireless EV chargers for the first time in this paper. The proposed LOD system mounted on a transmitter (Tx) pad adopts an optimal comb shape as a sensing pattern to obtain uniform capacitance capability. Unlike general applications using a capacitive sensor, the proposed capacitive sensor, which is applied to wireless EV chargers, inherently contains significant capacitive coupling between the living object and the ground. This capacitive coupling should be carefully considered in order to accurately sense any minimal capacitance change caused by the presence of a living object. In this paper, a static circuit model of the proposed capacitive sensor with a living object considering the ground effect and an RC integrator to detect even a tiny voltage difference are established and verified by experiments. The results show that when a living object is present, the measured capacitance by the proposed sensing pattern was increased by up to 27.5% compared to when there is no living object.