Practical realisation of an active acoustic metamaterial building block

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 optimal 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 optimal control source strengths required for both single monopole and single dipole control sources to minimise the effective bulk modulus and the effective density respectively have been calculated via an optimisation procedure. The ability of the proposed active AMM building blocks to achieve broadband negative effective material properties is tested experientially through offline simulations using measured frequency responses. Interestingly, the optimised single monopole and optimised single dipole control sources achieve broadband negative effective bulk modulus and density respectively. However, when combining the two optimised control sources, the active control system only achieves bands of double negativity and, thus, only exhibits bands of negative refractive index.

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ORCID for Jordan Cheer: orcid.org/0000-0002-0552-5506

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