Enhanced Magnetic Imaging for Industrial Metal Workpiece Detection Through the Combination of Electromagnetic Induction and Magnetic Anomalies

The effective imaging of metal workpieces is of great significance in the field of nondestructive testing. However, most commonly used detection methods, including radiographic, magnetic flux leakage, and electromagnetic techniques, are easily affected by environmental influences and have small detection ranges. Therefore, a new active imaging approach for metal workpieces using a combination of electromagnetic induction and magnetic anomalies is proposed herein. A magnetization model of a metal workpiece is established based on the magnetic dipoles and molecular current. An active detection method is designed, where an H-bridge is used to drive the transmission coil and generate a bipolar excitation magnetic field that can magnetize the metal workpiece. A differential detection approach is adopted to further suppress the background noise. An active detection system is constructed using a $5\times $ 5 magnetic sensor array, which can achieve 3-D imaging using a cubic convolution interpolation algorithm. Intensive comparative experiments have been carried out, with the following conditions: different targets at the same height, the same target at different heights, and different targets’ tracking. The experimental results show that the proposed method can not only extend the detection range of metal workpieces but also effectively detect M15 studs, M4 studs, and other small metal workpieces under 20 cm in size.