Unidirectional focusing of horizontally polarized shear elastic waves electromagnetic acoustic transducers for plate inspection

Abstract

The ultrasonic guided wave testing method is very effective in monitoring the safety of complex structures. The fundamental shear horizontal (SH) wave mode has the advantage that the propagation velocity does not change with the frequency. However, accurately recognizing the ultrasonic signal is difficult due to the SH guided wave’s bidirectional propagation characteristics generated by the Lorentz force mechanism. Therefore, it is necessary to achieve unidirectional focusing of Lorentz force-generated SH guided waves. A newly designed SH guided wave electromagnetic acoustic transducer (EMAT) is proposed with an interlaced periodic permanent magnet (PPM) and AC coils of different phases. A 3D model based on the electromagnetic mode and the solid mechanics mode using COMSOL software is calculated and compared with the bidirectional focusing EMATs. The results show that there are many influencing factors in the structural design of the transducers, and the focal radius and the angle of the individual PPMs are discussed in this work. The results indicate that the new unidirectional EMAT shows superiority in many cases, and the decrease of the focal radius with a suitable aperture angle will increase the focusing intensity of the signal.The ultrasonic guided wave testing method is very effective in monitoring the safety of complex structures. The fundamental shear horizontal (SH) wave mode has the advantage that the propagation velocity does not change with the frequency. However, accurately recognizing the ultrasonic signal is difficult due to the SH guided wave’s bidirectional propagation characteristics generated by the Lorentz force mechanism. Therefore, it is necessary to achieve unidirectional focusing of Lorentz force-generated SH guided waves. A newly designed SH guided wave electromagnetic acoustic transducer (EMAT) is proposed with an interlaced periodic permanent magnet (PPM) and AC coils of different phases. A 3D model based on the electromagnetic mode and the solid mechanics mode using COMSOL software is calculated and compared with the bidirectional focusing EMATs. The results show that there are many influencing factors in the structural design of the transducers, and the focal radius and the angle of the individual PPMs a...