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The control of propagation direction or path of edge states is difficult when the chirality of the excitation source and the boundary structures are determined. Here, we studied a frequency-selective routing for elastic wave based on two types of topological phononic crystals (PnCs) with different symmetries. By constructing multiple types of interfaces between different PnCs structures with distinct valley topological phases, the valley edge states of elastic wave could be realized at different frequencies in the band gap. Meanwhile, based on the simulation of topological transport, it is found that the routing path of elastic waves valley edge states highly depends on the operating frequency and the inputting port of the excitation source. By varying the excitation frequency, the transport path can be switched. The results provide a paradigm for the control of elastic wave propagation paths that could be employed for designing the frequency-dependent ultrasonic division devices.

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.

Valley topological refraction material (TRM) of elastic wave and its direction signal transmittance with robustness against structural disturbance is crucial for various applications such as communication, navigation and detection devices for medical and industrial purpose. However, the existing TRM is limited by the single topological band, which obviously hinders the exploration of the multi-band topological ultrasonic devices to guarantee its efficiency and stability. Here, we demonstrate the dual-band valley TRM for elastic waves, in which the valley edge states and their robustness are investigated. Furthermore, the topological refractions of the valley edge states from the interface into the free space at zigzag termination in two frequency bands are explored, where the mode conversion of the bulk elastic wave occurs at interface termination. Interestingly, the full mode conversion from longitudinal to transverse waves is revealed in the low frequency band while the non-full mode conversion between the longitudinal and transverse takes place in the high frequency band. The researched dual-band elastic TRM could facilitate the potential applications in multi-band and multi-directional devices.

We report the simultaneous existence of acoustic and optical asymmetric transmission by combining a periodic array of silicon rods in air with a periodic grating (grating-phoxonic crystals). Theoretically and numerically, we demonstrate that the grating-phoxonic crystals with a square lattice of silicon rods can exhibit simultaneous asymmetric propagation in the same reduced frequency range both for sound and light. The sound and light can transmit through the composite structure when incident from the grating interface but are completely reflected for the reverse direction incidence. Furthermore, when the silicon rods are tuned into a triangular lattice, reversed asymmetric transmissions are also achieved. Sound and light are blocked when incident from the grating interface while being fully able to pass through the composite structure for the reverse direction incidence. These two tunable dual acoustic and optical asymmetric transmissions show great potential for acoustic-optic devices by simultaneously manipulating sound and light.