Titovich Alexey S, Norris Andrew N
Mechanical and Aerospace Engineering, Rutgers University, 98 Brett Road, Piscataway, New Jersey 08854.
J Acoust Soc Am. 2014 Oct;136(4):1601-9. doi: 10.1121/1.4894723.
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. The 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.
弹性圆柱壳配备有内部机构，该机构经过优化，以便在准静态状态下，组合系统呈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强件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的有效声学特性（体积模量和密度）。通过包含足够数量的此类加强件，可以抑制由加强件附着在壳中激发的亚音速弯曲波。通过使具有聚合物插入物的薄铝壳的特性与水的特性相匹配，证明了所提出的超材料的有效性。在频谱较低端的很宽频率范围内，水中的散射截面几乎为零。通过将调谐后的壳排列成阵列，所得的声学超材料能够操纵波。例如，通过根据单位圆到正方形的共形映射改变阵列中的体积模量，设计了一种圆柱面波透镜。
