Experiments on reflection and transmission of acoustic porous metasurface with composite structure

doi:10.1016/j.compstruct.2017.11.054

Composite Structures

Volume 185, 1 February 2018, Pages 508-514

https://doi.org/10.1016/j.compstruct.2017.11.054 Get rights and content

Abstract

A composite structure made by a metal-based porous material, namely porous metasurface here, is designed for good sound absorption performance considering both reflection and transmission. The proposed configuration is a periodic structure containing four slits filled with the porous samples with different thicknesses in one period. Through designing the thicknesses of porous samples, linear phase gradients are generated on reflected and transmitted surfaces respectively, which play key roles for the reflected and refracted behaviors. Using the diffraction theory, the associating behaviors are predicted analytically and also validated by simulations and laboratory tests. Good agreements add confidence on the studies of sound absorption performance. Through adjusting the period length, the good sound absorption can be obtained over a wide range of incident angles at the designed frequency. The proposed composite structure has potential to be applied for noise isolation and sound absorption, where sound transmission is unavoidable.

Introduction

Sound isolation and absorption are important aspects in noise control and they are applied widely in architecture, ground transportation and even air transportation, e.g. roadside noise barriers, panels of car body and aircraft fuselage, etc. There is always a conflict between less sound transmission and less reflection, so that good sound absorption cannot be obtained. The dense materials with large acoustic impedance, e.g. metal and concrete, usually allow very little sound transmission. However, this kind of materials are heavy and reflect sound waves severely, which may cause secondary noise pollution. On the contrary, the materials with the impedance which can match with the air are able to cause less sound reflection, e.g. porous foam with high porosity, whereas they allow a large mount of sound transmission. It is a challenge to balance the reflection and transmission simultaneously to realize efficient noise control. It is expected that a composite structure or material is designed to reduce both the sound reflection and transmission to get good sound absorption performance.

In the current studies, there are many studies on the sound absorption performance and acoustic impedance of materials and composite structures [1], [2], [3], [4]. Thus, there arise a kind of artificially designed structures, so-called acoustic metamaterials [5], [6], which are carefully designed to obtain some uncommon acoustic properties that cannot be found in nature. Most acoustic metamaterials are studied based on passive control actions without external control load, however, there also arise some works about active control actions on elastic wave metamaterials [7]. In the current works on acoustic metamaterials for sound absorption, the focus of most attention is the material backed by a rigid wall [8], [9], [10], which is a common case for the applications of sound absorbers, e.g. sound absorption panel on the wall and acoustic liner in engine. In many cases, such as panels of car body and aircraft fuselage, the material is sandwiched by two plates for practical applications [11], [12]. Due to small thickness and elasticity of the plates, the sound will propagate through the structure and transmission is a necessary factor.

In addition to the acoustic performance, there are also some factors which should be considered in engineering applications, such as space limitation, corrosion and fire resistance etc. Under this background, a porous metasurface is designed in this work, resulting in less reflection and less transmission at the same time to obtain good sound absorption performance. The refracted behaviors and transmitted regularities of a periodic structure have been studied [13], while the reflected and transmitted phenomena will be considered at the same time during designing the composite structure in this work.

Section snippets

Conceptual design

When a sound wave incidents on a periodic structure and propagates through it, there are not only specular reflection and direct transmission. There occur additional reflected and refracted waves, which can be explained completely by the diffraction theory [14]. The diffraction theories for the reflection and refraction can be expressed as: $\begin{matrix} n_{i} \sin (θ_{r}) - n_{i} \sin (θ_{i}) = m_{r} \frac{λ_{i}}{2 π} \frac{d Φ_{r}}{dx}, reflection, \\ n_{t} \sin (θ_{t}) - n_{i} \sin (θ_{i}) = m_{t} \frac{λ_{i}}{2 π} \frac{d Φ_{t}}{dx}, refraction, \end{matrix}$ where $θ_{r}$ , $θ_{t}$ and $θ_{i}$ are the reflected, refracted and incident angles,

Analytical predictions and simulations on reflected and refracted behaviors

In this section, the reflected and the refracted behaviors are predicted analytically by the diffraction theory and validated by the numerical simulations. The simulation parts are implemented through solving the Helmhotz equation by a finite element solver COMSOL Multiphysics. The size of the maximum element is set as $λ_{i} / 45$ to guarantee the accuracy and convergence of the results. The incident wave is set as a plane wave at 2,000 Hz. The reflection region, metasurface domain and the refracted

Conclusion

An acoustic metasurface with composite structure is proposed for sound isolation and absorption considering both the reflection and transmission. It is a periodic structure containing four slits filled with a porous material in one period. The thicknesses of porous materials are designed to generate linear phase gradients for both the reflected and transmitted waves, which play key roles for the reflected and refracted phenomena. The regularities including the number of the reflected and the

Acknowledgement

Part of the study was supported by Hong Kong Innovation and Technology Commission (ITC) Project No. ITS/038/15FP. Yi Fang also wishes to thank Hong Kong University of Science and Technology for supporting part of Ph.D. thesis research.

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Experiments on reflection and transmission of acoustic porous metasurface with composite structure

Abstract

Introduction

Section snippets

Conceptual design

Analytical predictions and simulations on reflected and refracted behaviors

Conclusion

Acknowledgement

J Sound Vib

Appl Acoust

J Sound Vib

Appl Acoust

Acoustic metamaterial panels for sound attenuation in the 50–1000 Hz regime

Appl Phys Lett

Dark acoustic metamaterials as super absorbers for low-frequency sound

Nat Commun

Enhancing the absorption properties of acoustic porous plates by periodically embedding Helmholtz resonators

J Acoust Soc Am

Controlling sound with acoustic metamaterials

Nat Rev Mater

Acoustic metamaterials

MRS Bull

Active feedback control of elastic wave metamaterials

J Intell Mater Syst Struct

Extraordinary absorption of sound in porous lamella-crystals

Sci Rep

Acoustic metamaterial panels for sound attenuation in the 50–1000 Hz regime