The Experimental Realization of an Acoustic Cloak in Air with a Meta-Composite Shell

Abstract

Anisotropic cloak shells can be used for the spatial transformation of a space to alter the propagation of acoustic waves by redirecting them along a pre-determined path. This paper outlines the design, fabrication, and experimental analysis of a circular acoustic cloak shell made of meta-composite material for in-air applications. Based on the three-dimensional coordinate transformation, we first designed an anisotropic circle meta-composite cloak shell according to its impedance values. The cloak shell comprises various layered structures with cavities and tubes, respectively, providing acoustic mass and compliance for the provision of anisotropic material properties. Secondly, we conducted numerical and experimental analyses under practice working conditions to demonstrate the efficacy of the acoustic cloak. The structure of the cloak shell, fabricated by three-dimensional printing (3D printing), is experimentally evaluated in a semi-anechoic room with a free-field environment. The simulation and experimental results demonstrate the acoustic cloaking effects in the scattering far field. Besides the scattering field, the sound field measurement results obtained with the region enclosed by the shell also shows the abilities of the cloak shell in altering the direction of wave propagation along a pre-determined path in air.

Acoustic Metamaterials in Aeronautics

“…Recent studies have tried to extend the existing theory of acoustic cloaking to the aeroacoustic domain, i.e., in the presence of flow [88][89][90][91][92] with interesting results (an example is given in Figure 10), even addressing complex turbulent flows via numerical optimization of the cloak design [93] and also exploiting a reinterpretation of the acoustics governing equations in four-dimensional space-time that exposes the relativistic structure of the phenomenon [94][95][96][97][98]. So far, however, practical realizations have been limited to static acoustics and, for the most part, intended for carpet cloaking of small objects [83,87] or based on large and/or massive devices [99,100]. Possibly the most interesting work has come from Mendez [78], who designed a feasible pentamode material for acoustic cloaking by topology optimization, starting from the desired metafluid acoustic characteristics, and numerically tested it.…”

Acoustic Metamaterials in Aeronautics

“…in presence of flow [88][89][90][91] with interesting results, even addressing complex turbulent flows via numerical optimization of the cloak design [92], and also exploiting a reinterpretation of the acoustics governing equation in a four dimensional space-time that expose the relativistic structure of the phenomenon [93][94][95][96][97][98]. However, practical realization are so far limited to the static acoustics and, for the most, intended for carpet cloaking of small objects [83,87] or based on large and/or massive devices [99,100], and maybe the most interesting work is from Mendez [78], who designs a feasible pentamode material for acoustic cloaking by topology optimization, starting from the desired metafluid acoustic characteristics, and numerically tests it.…”