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arXiv · 1610.04884

Unveiling Extreme Anisotropy in Elastic Structured Media

Gautier Lefebvre·Tryfon Antonakakis·Younes Achaoui·Richard Craster·Sebastien Guenneau·Patrick Sebbah
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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.

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Gautier Lefebvre, Tryfon Antonakakis, Younes Achaoui, Richard Craster, Sebastien Guenneau, Patrick Sebbah. 2016-10-16. Unveiling Extreme Anisotropy in Elastic Structured Media. https://doi.org/10.1103/physrevlett.118.254302

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