Active strategies for the control of acoustic scattering

Abstract

The ability to acoustically cloak an object, such that the soundfield with the presence of the object is identical to that without the presence of the object, has potential applications across a variety of industries and, for this reason, is an active area of research. An object can potentially be acoustically cloaked using either passive or active methods, and this thesis addresses the challenges related to practically implementing active strategies. Active acoustic cloaking has the potential to significantly reduce the acoustic scattering from an object over a broad frequency range, however, examples of practical active acoustic cloaking systems in the literature currently rely on a-priori information that is not practical to obtain in most scenarios, and mostly consider tonal disturbances. The robustness of active acoustic cloaking systems to practical uncertainties has also not yet been considered, which is a key requirement for many practical implementations. The work presented in this thesis will address some of these challenges, using experimental and numerical studies, and provides a number of key insights into the active cloaking problem. The work presented in this thesis initially considers the acoustic scattering from a rigid sphere, upon which an active acoustic cloaking system is implemented using both tonal and broadband control strategies. The robustness of these systems to realistic perturbations is assessed, and various methods of increasing the robustness are presented. A method of estimating the scattered acoustic pressure in real-time is proposed, which aims to address the requirement for acoustic sensors in the far-field of the scattering object, as well as the challenges associated with directly measuring scattered acoustic pressure, and the performance of this system is quantified. The acoustic cloaking of flexible bodies is more challenging than that of rigid bodies, due to the presence of resonant scattering components and, therefore, the latter part of this thesis considers the acoustic scattering from a flexible cylinder. The relationship between the structural response of the scattering body and the scattered acoustic field is analysed, and the acoustic effect of implementing Active Vibration Control on the scattering body is investigated. An active structural acoustic cloaking system is also implemented experimentally, and a significant reduction in the scattered acoustic pressure is realised.

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Identifiers

ORCID for Charlie House: orcid.org/0000-0002-9653-3594

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

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