使用透明五模透镜实现水下声音的宽带聚焦。

Broadband focusing of underwater sound using a transparent pentamode lens.

作者信息

Su Xiaoshi, Norris Andrew N, Cushing Colby W, Haberman Michael R, Wilson Preston S

机构信息

Mechanical and Aerospace Engineering, Rutgers University, Piscataway, New Jersey 08854, USA.

Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA.

出版信息

J Acoust Soc Am. 2017 Jun;141(6):4408. doi: 10.1121/1.4985195.

DOI:10.1121/1.4985195

PMID:28618832

Abstract

An inhomogeneous acoustic metamaterial lens based on spatial variation of refractive index for broadband focusing of underwater sound is reported. The index gradient follows a modified hyperbolic secant profile designed to reduce aberration and suppress side lobes. The gradient index (GRIN) lens is comprised of transversely isotropic hexagonal microstructures with tunable quasi-static bulk modulus and mass density. In addition, the unit cells are impedance-matched to water and have in-plane shear modulus negligible compared to the effective bulk modulus. The flat GRIN lens is fabricated by cutting hexagonal centimeter scale hollow microstructures in aluminum plates, which are then stacked and sealed from the exterior water. Broadband focusing effects are observed within the homogenization regime of the lattice in both finite element simulations and underwater measurements (20-40 kHz). This design approach has potential applications in medical ultrasound imaging and underwater acoustic communications.

摘要

报道了一种基于折射率空间变化的非均匀声学超材料透镜，用于水下声音的宽带聚焦。折射率梯度遵循修正的双曲正割分布，旨在减少像差并抑制旁瓣。梯度折射率（GRIN）透镜由具有可调准静态体积模量和质量密度的横向各向同性六边形微结构组成。此外，单元胞与水实现了阻抗匹配，并且其面内剪切模量与有效体积模量相比可忽略不计。扁平GRIN透镜是通过在铝板上切割六边形厘米级中空微结构制成的，然后将这些微结构堆叠起来并与外部水密封。在有限元模拟和水下测量（20 - 40 kHz）中，在晶格的均匀化范围内均观察到了宽带聚焦效应。这种设计方法在医学超声成像和水下声学通信中具有潜在应用。