Subwavelength and broadband tunable topological interface state for flexural wave in one-dimensional locally resonant phononic crystal

2020 
The topological interface state for an elastic wave in a one-dimensional system, as reported in the literature, mainly occurs through Bragg scattering, making it difficult to achieve subwavelength wave control and flexible tunability. Here, inspired by the band-folding mechanism, this paper confirms that an interface state can likewise be excited by local resonance. The topological phase transition is accomplished by purposely arranging the locations of local resonators. The system is composed of a uniform thin beam with periodically attached local resonators made from an electrorheological elastomer subjected to adjustable electric fields. By simply doubling the primitive unit cell, the passing bands in the dispersion relation are folded and a folding point falls below the locally resonant bandgap, which can be lifted up by simply tuning the distance between two local resonators to realize a topological phase transition. Furthermore, we demonstrate the dynamic tunability of the working frequency of the topological interface state by using an external electric field to adjust the starting frequency of the local resonance. Since the excited frequency of the interface mode is lower than the resonance frequency, this work overcomes the ineffectiveness of the Bragg topological phononic crystal at low frequencies. Moreover, the use of an electroactive resonator whose parameters are readily tuned also enables the flexible design of a frequency-variable topological system without requiring a geometrical modification of the base structure. This technique may have potential applications, such as vibration isolation or in fabricating a robust waveguide.
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