Composite Sensor of EMAT and ECT Using a Shareable Receiver Coil for Detecting Surface and Bottom Defects on the Steel Plate

Compared with the current single inspection method, composite inspection methods have better capabilities in terms of accuracy and completeness for defect detection. The combination of eddy current testing (ECT) sensor and electromagnetic acoustic transducer (EMAT) is widely used to detect compound location defects. However, the method usually requires independently distributed sensor systems or complex signal processing algorithms, which increases the complexity of sensing systems. To tackle the problems, in this article, a composite sensor is designed using a shareable receiver coil. First, the work reports the commonality of detection principles and explores the mutual effects between the two detection methods. Second, a conical coil and a multilayer magnet configuration are designed to improve the sensing performance. Finally, the superiority of sensor performance is verified through experiments. The independent features of EMAT signals and ECT signals are easily extracted to detect bottom and surface defects using the filtering tool. Results showed that our composite sensor can increase the signal magnitude of EMATs by 49.7% and improve the capability of ECT in detecting surface defects up to 8 mm deep. Our work could provide a feasible idea for miniaturized sensor design and physical field reuse.