Dirac cones and chiral selection of elastic waves in a soft strip

Abstract

We study the propagation of in-plane elastic waves in a soft thin strip, a specific geometrical and mechanical hybrid framework which we expect to exhibit a Dirac-like cone. We separate the low frequencies guided modes (typically 100 Hz for a 1-cm-wide strip) and obtain experimentally the full dispersion diagram. Dirac cones are evidenced together with other remarkable wave phenomena such as negative wave velocity or pseudo-zero group velocity (ZGV). Our measurements are convincingly supported by a model (and numerical simulation) for both Neumann and Dirichlet boundary conditions. Finally, we perform one-way chiral selection by carefully setting the source position and polarization. Therefore, we show that soft materials support atypical wave-based phenomena, which is all of the more interesting as they make most of the biological tissues.

Viscoelastic dynamics of a soft strip subject to a large deformation

“…The index n refers to the mode order, which is equivalent to the number of nodes in the transverse direction e 3 . These modes have been documented in prior studies, 51,52 but their response to an external static stress remains unexplored. Note that the two fundamental modes (n = 0) correspond at low frequencies to the compression (S 0 0 ) and flexion (A 0 0 ) described previously.…”

Observation of elastic spin with chiral meta-sources

“…To construct such an effectively chiral elastic source in solids applicable for broad ultrasonic frequency regime, we elaborately design an array of sub-wavelength meta-sources with clockwise or anticlockwise phase shift, as shown in Fig. 1b , instead of adopting the macroscopic mechanical stirring in soft matters 34 . The chiral meta source constitutes four breathing rods labeled with Rod 1 to Rod 4.…”

Topological Metamaterials

“…664 Finally, Dirac cones and their inherent chiral properties have also been demonstrated in soft elastic strips made of a homogeneous silicone elastomer, opening the door to possible analogies with biological tissues. 665…”