An EMAT for improving the purity and amplitude of S0 Lamb waves

Different waves of the Lamb waves may be superimposed in practical tests due to their multimodal characteristics and dispersion characteristics, thus significantly increasing the difficulty of later signal analysis and creating a massive limitation to their application in non-destructive testing. Only a single magnet was used to generate a static magnetic field in the traditional S-0 mode Lamb wave (S-0 wave) electromagnetic acoustic transducer (EMAT), which resulted in a less pure S-0 wave. Additionally, the accompanying A(0) mode Lamb wave (A(0) wave) will decrease the accuracy of the results in defect detection and increase the difficulty of the signal processing. To obtain a single-mode S-0 wave, a periodic magnet structure EMAT structure was proposed in this study. Finite element models were established, and the effect of single and periodic magnet structure on the static magnetic field was analyzed. The periodic magnet structure EMAT can substantially enhance the S-0 mode Lamb wave amplitude by increasing the flux density of the local magnetic field using periodically arranged magnets. However, it also causes enhancement to the A(0) wave and decreases the detection accuracy. An improved EMAT was further proposed to increase the S-0 wave amplitude with no enhancement to the A(0) wave amplitude. Experiments were conducted, and two types of EMAT were comparatively investigated, which agreed with the simulated results. The S-0 wave amplitude can be increased by seven times with the improved EMAT compared to traditional EMAT, and the A(0) wave is completely submerged in the noise. The improved EMAT proposed in this study can provide guidance for single-mode S-0 wave defect detection.