Design and Implementation of a Multi-Purpose TMR Sensor Matrix for Wireless Electric Vehicle Charging

A cost-effective technology to monitor the charging performance and detect coil misalignment and foreign metal objects is indispensable to the commercialization of wireless power transfer (WPT) on electric vehicle (EV) charging. This paper presents a multi-purpose tunneling magnetoresistive (TMR) sensor matrix, which can monitor the charging performance as well as detect both coil misalignment and metal objects for wireless EV charging. The magnetic field distribution between coils is measured by the TMR sensor matrix to provide the critical information about charging performance, coil misalignment position and existence of metal objects. The mutual inductance and charging power are derived from the measured z-components of magnetic flux densities. Lateral misalignment position is determined by the symmetry coefficients of the time-varying magnetic field distribution in the range of ±150 mm. Metal objects are detected by the measured magnetic field offsets. In this work, both 3D finite-element-method (FEM) modeling and experimental results were presented to demonstrate the effectiveness of the proposed approach. A 14 × 14 TMR sensor matrix with high sensitivity of 80 mV/V/mT was designed and implemented to measure the magnetic field distribution in order to demonstrate the technology.