Tunable topological interface states and resonance states of surface waves based on the shape memory alloy

Topological interface state (TIS) of elastic wave has attracted significant research interest due to its potential prospects in strengthening acoustic energy and enhancing the signal accuracy of damage identification and quantification. However, previous implementations on the interface modes of surface waves are limited to the non-adjustable frequency band and unalterable mode width. Here, we demonstrate the tunable TIS and topological resonance state (TRS) of Rayleigh wave by using a shape memory alloy (SMA) stubbed semi-infinite one-dimensional (1D) solid phononic crystals (PnCs), which simultaneously possesses the adjustable mode width. The mechanism of tunability stems from the phase transformation of the SMA between the martensite at low temperature and the austenite at high temperature. The tunable TIS of Rayleigh wave is realized by combining two bandgap-opened PnCs with different Zak phases. The TRS with adjustable mode width is achieved in the heterostructures by adding PnCs with Dirac point to the middle of two bandgap-opened PnCs with different Zak phases, which exhibits the extraordinary robustness in contrast to the ordinary Fabry–Pérot resonance state. This research provides new possibilities for the highly adjustable Rayleigh wave manipulation and find promising applications such as tunable energy harvesters, wide-mode filters, and high-sensitivity Rayleigh wave detectors.