GMR Based Eddy Current System for Defect Detection

The Giant Magneto Resistance (GMR) sensor is successfully used in eddy current testing because of its good low frequency detection characteristics and high sensitivity. In order to obtain more information about defects, this paper designed a GMR based eddy current system with Field Programmable Gate Array (FPGA) for defect detection. The system can get both the amplitude of the GMR sensor's output signal and the phase related to the exciting current at the same time. Through a series of detection experiments with defects of different widths of 6mm, 8mm and 10mm, it is found that both the amplitude and the phase can clearly reflect the magnetic field changes caused by various defects. By comparing the data curves, it is proved that the phase information matches better with the real size of the defects than the amplitude information. The conclusion is beneficial for further quantitative defect detection.