Tunable elastic waveguide based on a soft phononic crystal

Phononic crystals, a kind of acoustic metamaterial having translational symmetry or periodicity in space, can exhibit many anomalous properties, such as band gaps, negative refraction, collimation, and one-way transmission. A line defect in a phononic crystal, which is generated by removing or replacing a row of scatterers, can localize the wave propagating along it.

Wang et al. explored the possibility of designing a tunable elastic waveguide based on a soft, porous phononic crystal with hard inclusions. The designed waveguide can be tuned by applying an external force to adapt to various working frequencies and, therefore, different working environments.

“The external loading, which induces the buckling and post-buckling deformation, may act as a switch of the waveguide. Therefore, this work provides us a feasible way to design a tunable filter,” said author Yue-Sheng Wang. “Extended application of this work includes design of more complex tunable devices, such as tunable splitters, couplers, retarders, and diodes.”

The phononic crystal consists of a soft, porous matrix made of rubber with steel cylinders inside to act as hard inclusions. The finite element method was used to simulate buckling and post-buckling deformation of the structure, as well as elastic wave propagation in the undeformed and deformed structures. Experiments measured compressional buckling, post-buckling deformation, and wave propagation.

Localized buckling deformation appeared at the line defect when the structure was subjected to an external compression force, which enabled the waveguide’s tunability. For instance, a wave at a particular frequency may propagate along the line defect in the undeformed structure but cannot when the structure is compressed.

“We are now interested in the design, verification, and validation of other, more complex tunable acoustic devices,” said Wang.

This paper is part of the Phononic Crystals at Various Frequencies collection; learn more here .

Source: “Tunable guided waves in a soft phononic crystal with a line defect,” by Yueting Wang, Jian Li, Yuxin Fu, Ronghao Bao, Weiqiu Chen, and Yue-Sheng Wang, APL Materials (2021). The article can be accessed at http://doi.org/10.1063/5.0049574 .