Department of Mechanical Engineering, The University of Texas at Austin, 204 East Dean Keeton Street, Stop C2200, Austin, Texas 78705, USA.
Applied Research Laboratories, The University of Texas at Austin, Austin, Texas 78713, USA.
Nat Commun. 2017 Jun 13;8:15625. doi: 10.1038/ncomms15625.
The primary objective of acoustic metamaterial research is to design subwavelength systems that behave as effective materials with novel acoustical properties. One such property couples the stress-strain and the momentum-velocity relations. This response is analogous to bianisotropy in electromagnetism, is absent from common materials, and is often referred to as Willis coupling after J.R., Willis, who first described it in the context of the dynamic response of heterogeneous elastic media. This work presents two principal results: first, experimental and theoretical demonstrations, illustrating that Willis properties are required to obtain physically meaningful effective material properties resulting solely from local behaviour of an asymmetric one-dimensional isolated element and, second, an experimental procedure to extract the effective material properties from a one-dimensional isolated element. The measured material properties are in very good agreement with theoretical predictions and thus provide improved understanding of the physical mechanisms leading to Willis coupling in acoustic metamaterials.
声超材料研究的主要目标是设计亚波长系统，使其表现出具有新颖声学特性的等效材料。其中一种特性是将应力-应变和动量-速度关系耦合起来。这种响应类似于电磁学中的双各向异性，在常见材料中不存在，通常被称为 Willis 耦合，是以首先在非均匀弹性介质动态响应的背景下描述它的 J.R. Willis 的名字命名的。这项工作提出了两个主要结果：首先，通过实验和理论证明，说明了 Willis 特性是获得仅源于不对称一维孤立单元局部行为的物理上有意义的等效材料特性所必需的，其次，提供了一种从一维孤立单元提取等效材料特性的实验方法。测量得到的材料特性与理论预测非常吻合，从而提供了对导致声超材料 Willis 耦合的物理机制的深入理解。
