Optimization of applied magnetic field methods for various shape defects by eddy current testing using magneto resistive sensor

In this study, we investigated the optimization of applied magnetic field methods for defect detection for various shapes of defects made of magnetic and non-magnetic materials using the eddy current testing with a highly sensitive magnetic sensor. From the experiment and simulation results, it was found that the change of the magnetic field distribution caused by the eddy current increased when the sensor was placed directly above the induction coil of the wire-type method. Moreover, in the solenoid coil system, it was found that the detection sensitivity increased when the magnetic sensor was placed close to one side of the coil compared to that placed at the center. In addition, it was found that the signal change was different in the electromagnetic characteristics of the measurement sample. For the non-magnetic material, as the frequency increased, the signal to noise ratio (SNR) of the detected defect signal increased because the signal was generated from only the eddy current. On the other hand, for the magnetic material, there was an optimum frequency for detecting the defect because the signal was generated due to both the magnetization and the eddy current. As a results, the optimum applying method of magnetic field for the eddy current testing using magnetic sensor was clarified.