Design and Study of EMAT-MFL-Based Hybrid Sensor for Defect Detection in Ferromagnetic Materials

The single nondestructive testing (NDT) techniques face the problem of low resolution when simultaneously detecting different types and locations of defects. Composite inspection methods, which combine different NDT techniques, have been widely studied due to their high defect detection accuracy. However, most of the existing composite detection methods require complex sensor systems or rely on complex signal-processing algorithms. Therefore, this article proposes a novel hybrid sensor based on the electromagnetic acoustic transducer (EMAT) and the magnetic flux leakage (MFL) mechanism, which allows to accurately detect defects in ferromagnetic materials. This hybrid sensor employs a straightforward EMAT-MFL configuration, which only requires a single permanent magnet to generate the requisite magnetic field for the EMAT and MFL sensor components. In addition, it adopts a unique orthogonal butterfly coil design for the detection of cracks. The obtained results show a significant frequency difference between the EMAT and MFL signals, which demonstrates their independence and lack of interference. This eliminates the potential issue of signal aliasing decoupling. The hybrid sensor can fully use the advantages of the EMAT and MFL technologies to simultaneously detect defects and cracks on the top and bottom surfaces of ferromagnetic materials. Furthermore, the wall thinning defects can be detected with a maximum detection error of only 4.48%. This article proposes a feasible approach for miniaturizing hybrid sensors and increasing their detection performance.