Filtering and manipulation of quasi-Lamb waves in aluminum plates based on heterostructure proximity

Bandgap modulation of classical waves has been a hot topic in the past decades. Based on the recent artificial phonon crystals and acoustic metamaterials composed of periodic structures, bandgap structures of acoustical waves can take rich and interesting changes. Here, we propose a heterojunction waveguide based on periodic undulated boundaries for elastic waves to benefit applications of their propagation control. Based on the laser ultrasonic system we built, a type of quasi-Lamb waves (QLWs) propagating along the sidewall of a thin aluminum plate is investigated. The elastic wave heterojunction is formed by connecting two plates with different undulations but similar frequency bandgaps. In the bandgap, QLWs cannot propagate through the plate, but the plate becomes transparent at a specific frequency in the gap when the heterojunction is structured. An additional transmission peak can be found in the bandgap and its frequency is very sensitive to the proximity of the two different undulations, which can realize the filtering and manipulation of QLWs. Furthermore, the local enhancement of QLWs near the heterojunctions is observed in the experiments of laser vibrometer scanning. The simulation with the finite element methods, as well as the experimental measurements confirm the filtering and manipulation effect of the interface state on QLWs induced by heterojunctions, which not only enrich our knowledge on the elastic wave manipulation, but also pave the way for engineering applications of elastic wave signal processing.