可调谐筒体作为声学超材料单元的研究
Tunable cylindrical shell as an element in acoustic metamaterial
摘要：
弹性筒体装配有内部机构，该内部机构被优化，使得在准静态状态下，组合系统表现出规定的有效声学特性。该机构由一个由轴对称分布的弹性加劲肋支撑的中心质量组成。通过适当选择内部机构的质量和刚度，可以根据需要调整壳体的有效声学特性（体积模量和密度）。通过增加足够多的加强筋，可以抑制壳体中由加强筋引起的亚音速弯曲波。所提出的超材料的有效性是通过将具有聚合物插入物的薄铝壳的性质与水的性质相匹配来证明的。水中的散射截面在光谱低端的宽频率范围内几乎为零。通过在阵列中布置调谐壳体，所得到的声学超材料能够操纵波。作为一个例子，通过改变阵列中的体积模量，根据单位圆到正方形的保角映射，设计了圆柱到平面波透镜。
英文摘要：
Elastic cylindrical shells are fitted with an internal mechanism which is optimized so that, in the quasi-static regime, the combined system exhibits prescribed effective acoustic properties. The mechanism consists of a central mass supported by an axisymmetric distribution of elastic stiffeners. By appropriate selection of the mass and stiffness of the internal mechanism, the shell's effective acoustic properties (bulk modulus and density) can be tuned as desired. Subsonic flexural waves excited in the shell by the attachment of stiffeners are suppressed by including a sufficiently large number of such stiffeners. Effectiveness of the proposed metamaterial is demonstrated by matching the properties of a thin aluminum shell with a polymer insert to those of water. The scattering cross section in water is nearly zero over a broad range of frequencies at the lower end of the spectrum. By arranging the tuned shells in an array the resulting acoustic metamaterial is capable of steering waves. As an example, a cylindrical-to-plane wave lens is designed by varying the bulk modulus in the array according to the conformal mapping of a unit circle to a square.
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