Abstract: Meander-line coil electromagnetic acoustic transducer (EMAT), linear coil in-plane EMAT, and linear coil out-of-plane EMAT are often used to receive ultrasonic waves in the Laser-EMAT Rayleigh wave (RW) detection of aluminum alloy plate. However, the reception performance and applications of these three types of EMAT are unclear. Therefore, a finite element model of the Laser-EMAT RW detection process for aluminum alloy was first established, and the effects of three types of EMAT configurations on the energy of RW, shear wave, and longitudinal wave modes of ultrasonic were analyzed. Secondly, the effects of the surface constraint mechanism on the RW amplitude and its purity were studied, and the surface defect detection capability of the three types of EMAT was explored. Finally, three types of EMAT probes were made, and the RW detection experiments were carried out with Laser-EMAT on aluminum alloy plates. The influence of the surface constraint mechanism on the amplitude of each mode of ultrasonic waves received by the three types of EMAT and the ability of surface defect detection was analyzed. The results show that compared to the linear coil in-plane EMAT, the meander-line coil EMAT and linear coil out-of-plane EMAT receive a higher purity RW and are more suitable for surface defect detection. The multi-mode ultrasonic wave received by the linear coil in-plane EMAT is obvious, which is more suitable for simultaneously detecting surface/internal defects. Compared to the non-surface constraint mechanism, the RW amplitude of three kinds of EMAT can be enhanced more than two times by using the surface constraint mechanism, with the most significant enhancement to the RW amplitude of the meander-line coil EMAT. Compared to the laser-linear coil in-plane EMAT without a surface constraint mechanism, laser-linear coil out-of-plane EMAT with a surface constraint mechanism can increase the received DW amplitude by more than 6 times.

Key words: Aluminum alloy, Laser-EMAT, Surface defect, Surface constraint mechanism, Resolution