Unveiling Extreme Anisotropy in Elastic Structured Media

Abstract

Periodic structures can be engineered to exhibit unique properties observed at symmetry points, such as zero group velocity, Dirac cones and saddle points; identifying these, and the nature of the associated modes, from a direct reading of the dispersion surfaces is not straightforward, especially in three-dimensions or at high frequencies when several dispersion surfaces fold back in the Brillouin zone. A recently proposed asymptotic high frequency homogenisation theory is applied to a challenging time-domain experiment with elastic waves in a pinned metallic plate. The prediction of a narrow high-frequency spectral region where the effective medium tensor dramatically switches from positive definite to indefinite is confirmed experimentally; a small frequency shift of the pulse carrier results in two distinct types of highly anisotropic modes. The underlying effective equation mirrors this behaviour with a change in form from elliptic to hyperbolic exemplifying the high degree of wave control available and the importance of a simple and effective predictive model.

5 pages, 4 figures

References in corpus (6)

• The electronic properties of graphene
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• Purcell effect in Hyperbolic Metamaterial Resonators
• Controlling solid elastic waves with spherical cloaks
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• Pathway towards programmable wave anisotropy in cellular metamaterials
• Flat Lensing by Graded Line Meta-arrays
• Scattering theory and cancellation of gravity-flexural waves of floating plates
• Kirigami-based Elastic Metamaterials with Anisotropic Mass Density for Subwavelength Flexural Wave Control
• Tunneling of Elastic Waves in a Tapered Waveguide