Defect modes and localisation of quasi-Lamb waves along a sidewall of corrugated aluminium plates

This study presents an observation of quasi-Lamb wave (QLW) localisation in a periodically corrugated plate with defects. The QLWs are excited and detected on one side of aluminium plates that are periodically grooved on the upper and lower planes with a strip defect. The periodic grooves result in the frequency forbidden band, whereas the defect is responsible for the additional transmission in this band. The QLW-amplitude measurements along the aluminium plates exhibit the transmission spectra of the defect modes as well as the QLW localisation near the middle strip. The numerical and experimental results confirm the additional transmission of the QLW defect mode and its frequency shifting. As the defect length increases, the transmission peak moves from the upper to the lower edges of the forbidden band. Furthermore, the calculated dispersion curves of the QLWs break at the frequency of the forbidden bands, and a localised mode appears in the middle when the defect length is nonzero. The experimentally observed QLW defect modes in elastic plates not only enrich our knowledge on the interaction between elastic waves and structures but also significantly benefit related engineering applications, such as ultrasonic non-destructive evaluation, elastic-wave filtering, and undersea acoustic-signal enhancement.