Conformally Mapped Multifunctional Acoustic Metamaterial Lens for Spectral Sound Guiding and Talbot Effect.

He Gao,Xinsheng Fang,Zhongming Gu,Tuo Liu,Jie Zhu,Shanjun Liang,Yong Li

doi:10.34133/2019/1748537

Abstract

We demonstrate a conformally mapped multifunctional acoustic metamaterial Mikaelian lens. Mikaelian lens is a gradient medium with a hyperbolic secant refractive index profile that can realize functions like beam self-focusing. Unlike the conventional design approaches, with a conformal transformation method, only isotropic material parameters with gradient refractive index profiles are required for the construction of such lens. To realize desired gradient index distribution, we carefully design a new type of cross-channel-shaped acoustic metamaterial, whose refractive index can be effectively modulated by simply changing the slit opening size. The distinct capabilities of the metamaterial Mikaelian lens in manipulating acoustic waves are experimentally verified with the fabricated sample. Simultaneous sound guiding and Talbot effects, which normally require respective geometrical and wave acoustic approximations, are observed in simulations and experiments. Furthermore, those effects of shaping acoustic wave propagations were validated within a relatively wide frequency range. Our study reveals how the conformal transformation method can help to bridge the ray acoustics with wave acoustics. It offers opportunities to the development of novel multifunctional acoustic devices for various applications, such as sound and particle manipulations.

Highlights

Acoustic metamaterials exhibit novel constitutive properties that extensively broaden the acoustic research horizon
We present a multifunctional acoustic Mikaelian lens designed with conformal transformation acoustics
2D Maxwell’s fish-eye lens with a gradient index profile is considered, in which the refractive index varies according to n = α/ð1 + r2Þ, where r is the distance from the center of the lens and α is the refractive index at the center [42]

Summary

Introduction

Acoustic metamaterials exhibit novel constitutive properties that extensively broaden the acoustic research horizon. A generalized way to appreciate the implied capabilities of acoustic metamaterials is through the concept of transformation acoustics, which enables freewheeling steering of acoustic rays along arbitrary curves [7,8,9,10,11,12,13,14,15] This coordinate transformation method was first proposed to manipulate electromagnetic waves, which is based on the invariance of Maxwell’s equations under coordinate transformations [20,21,22,23]. The conformal transformation method was applied to design the isotropic media only spherical cloak [16]

Methods

Results

Conclusion