Physical Coupling Fusion of Electromagnetic Acoustic Guided Wave with ‘Near-Zero’ Magnetic Sensing System for Multi-type Defect Detection

Conventional shear horizontal (SH0) guided wave electromagnetic acoustic transducer (EMAT) has been widely used for pipeline detection due to its advantages of non-dispersion and simple vibration mode. While echo amplitude can be utilized to detect defects, it presents limitations in discerning between those residing on the surface and those located subsurface. This paper proposes a hybrid sensing methodology that integrates SH0 guided wave EMAT with permanent magnetic perturbation (PMFP) to enhance the accuracy of both defect identification and classification. From a physical coupling perspective, the system shares the same magnetic circuit structure and the sensing information is received by different receivers. In particular, the significant frequency difference between the PMFP and the EMAT signal can directly suppress mutual electromagnetic interference (EMI). In addition, the homopolar permanent magnet arrays in EMAT provide an inherent ’near-zero’ magnetic field region that improves the signal-to-noise ratio (SNR) of the PMFP signal. Both simulations and experiments have been undertaken to demonstrate the feasibility of the fusion sensing system. The system has also been validated with high sensitivity in detecting pits, slits and large corrosion defects in plates and pipes.