Practical realisation of an active acoustic metamaterial building block

Tan, Joe, Cheer, Jordan and Daley, Stephen (2019) Practical realisation of an active acoustic metamaterial building block. The Journal of The Acoustical Society of America, 146 (4). (doi:10.1121/1.5136803).

Abstract

Acoustic metamaterials (AMMs) have been demonstrated as an alternative approach to achieving high levels of noise control using an array of subwavelength unit cells, exhibiting behaviour not seen in conventional materials. Specifically, active AMMs offer the potential for greater levels of broadband wave manipulation, tunability and adaptability. However, determining the control source strengths that achieve broadband negative effective material properties is not straightforward. This study presents a practical method of designing an active system that directly minimises the effective material properties. The source strengths required for both single monopole and dipole control sources to minimise the effective bulk modulus and the effective density respectively have been calculated via an optimisation procedure in the frequency domain. A finite impulse response (FIR) filter has then been designed in each case to match the optimised frequency responses and enable real-time implementation. The performance of the designed FIR filters has been tested by implementation using the two different control sources in a one-dimensional duct and the ability of the proposed active AMM building blocks to achieve broadband negative effective material properties is tested. Interestingly, by combining the two optimised control sources, double negativity can be achieved, offering the potential for negative refraction.

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Contributors

Author: Jordan Cheer

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