An A0 mode extraction method in Lamb waves based on dual-frequency group velocity matching

The multimodal nature of Lamb waves leads to mode mixing in detection signals, making it difficult to identify the corresponding modes of the defect echoes. To address this issue, this study proposes an A0 mode extraction method based on dual-frequency group velocity matching. The method excites dual-frequency Lamb waves whose A0 mode group velocities are closely matched, thereby inducing a distinctive ‘dual-frequency synchronization’ feature in the A0 mode. The identification of this feature subsequently enables the selective extraction of the A0 mode from multimodal signals. Based on this principle, a dual-frequency electromagnetic acoustic transducer (EMAT) was designed, and both simulation analysis and experimental validation were conducted. The results demonstrate that the proposed method can effectively extract the A0 mode under multimodal interference and achieve accurate defect localisation. Additional experiments conducted on plates of different thicknesses and using different frequency pairs further confirm the method’s generalisability. By actively enhancing the discriminability of the A0 mode to counteract multimodal interference, this method offers a concise and effective approach for addressing the multimodal interference challenges in Lamb wave-based non-destructive testing.