Unveiling Extreme Anisotropy in Elastic Structured Media
Unveiling Extreme Anisotropy in Elastic Structured Media
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DOI：
10.1103/physrevlett.118.254302
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发表时间：
2017-06-20
影响因子：
8.6
通讯作者：
Sebbah, P.
中科院分区：
文献类型：
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作者：
Lefebvre, G.;Antonakakis, T.;Sebbah, P.
周期性结构可以被设计成在对称点处观察到的独特性质，例如零群速度、狄拉克锥和鞍点;从色散表面的直接阅读来识别这些和相关模式的性质并不简单，特别是在三维或当几个色散表面在布里渊区中折回时的高频下。最近提出的渐近高频均匀化理论应用于一个具有挑战性的时域实验与弹性波在一个钉扎金属板。一个狭窄的高频光谱区域的有效介质张量显着切换从正定到不定的预测实验证实，一个小的脉冲载波的频率偏移的结果在两种不同类型的高度各向异性模式。基本的有效方程反映了这种行为，其形式从椭圆形变为双曲线形，说明了可用的高度波浪控制以及简单有效的预测模型的重要性。
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 homogenization 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 behavior 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.