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Experimental investigations of quasi-flat acoustic absorbers enhanced by metamaterial layers

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journal contribution
posted on 20.01.2017, 13:22 authored by Abdelhalim Azbaid El Ouahabi, Victor V. Krylov
The efficiency of acoustic absorbers used for noise control can be improved by providing a smooth transition from the impedance of air to the impedance of the absorbing material in question. In the present work, such a smooth transition is materialised via application of gradient index metamaterial layers formed by quasi-periodic arrays of solid cylinders (tubes) with their external diameters gradually increasing from the external row of tubes facing the open air towards the internal row facing an absorbing porous layer. If acoustic wavelengths are much larger than the periodicity of the array, such a structure provides a gradual increase in the acoustic impedance towards the internal row of cylinders. This allows the developer to achieve an almost perfect impedance matching between the air and porous absorbing materials, such as sponges, fibreglass, etc. In the present work, a wide range of measurements of sound reflection coefficients from different absorbing materials combined with matching metamaterial layers formed by the arrays of brass tubes have been carried out at the frequency range of 500-3000 Hz. Both normal and oblique incidence of sound have been considered. The results show that the presence of matching metamaterial layers brings substantial reduction in sound reflection coefficients, thus increasing the efficiency of acoustic absorbers.

Funding

The research reported here has been supported by the EPSRC grant EP/K038214/1.

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Aeronautical and Automotive Engineering

Published in

Noise Theory and Practice

Volume

2

Issue

4

Pages

2 - 16

Citation

AZBAID EL OUAHABI, A. and KRYLOV, V.V., 2016. Experimental investigations of quasi-flat acoustic absorbers enhanced by metamaterial layers. Noise Theory and Practice, 2 (4), pp. 2-16.

Publisher

Acoustic Design Institute

Version

VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Acceptance date

05/12/2016

Publication date

2016

Notes

This paper was published in the open access journal Noise Theory and Practice available at http://www.noisetp.com/en/home/.

ISSN

2412-8627

Language

en