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Spherical harmonic formulations for passive and active control of acoustic scattering around the sphere

Spherical harmonic formulations for passive and active control of acoustic scattering around the sphere
Spherical harmonic formulations for passive and active control of acoustic scattering around the sphere
Acoustic cloaking can be implemented using different strategies: passive, active, or a combination of both. The literature on this topic is rich when it comes to the passive methods, specifically on metamaterial designs. However, active and hybrid methods are less well explored. In this work, spherical harmonic decomposition is used to calculate the scattering from a spherical obstacle subjected to an incident, monochromatic plane-wave. Its surface is defined through boundary conditions equivalent to a uniform, locally reacting impedance (Robin condition). Secondary sources represented by point-monopoles on the sphere are used to form an active control system. In the absence of active control, at low-frequencies, the least scattering is achieved if the surface impedance is negative, purely imaginary and has a large absolute value. At high-frequencies, the best performance is realised with a real, positive impedance that is close to that of the exterior propagation medium. When adding active control, only the low-frequency regime shows improvement, given any impedance, and it is most beneficial to enhance for the previous case that exhibited the best passive performance. Thus, a promising hybrid cloaking approach is a combination of: a stiffened-controlled boundary with multi-channel active control at low-frequencies, and a passive, absorptive boundary at high-frequencies.
active control of sound, 3D sound scattering, spherical harmonics, locally-reacting sphere, impedance sphere, plane-wave scattering
0001-4966
144
Orita, Mihai
Elliott, Stephen
721dc55c-8c3e-4895-b9c4-82f62abd3567
Cheer, Jordan
8e452f50-4c7d-4d4e-913a-34015e99b9dc
Orita, Mihai
Elliott, Stephen
721dc55c-8c3e-4895-b9c4-82f62abd3567
Cheer, Jordan
8e452f50-4c7d-4d4e-913a-34015e99b9dc

Orita, Mihai, Elliott, Stephen and Cheer, Jordan (2018) Spherical harmonic formulations for passive and active control of acoustic scattering around the sphere. Journal of the Acoustical Society of America, 144 (3), 144, [1757]. (doi:10.1121/1.5067780).

Record type: Meeting abstract

Abstract

Acoustic cloaking can be implemented using different strategies: passive, active, or a combination of both. The literature on this topic is rich when it comes to the passive methods, specifically on metamaterial designs. However, active and hybrid methods are less well explored. In this work, spherical harmonic decomposition is used to calculate the scattering from a spherical obstacle subjected to an incident, monochromatic plane-wave. Its surface is defined through boundary conditions equivalent to a uniform, locally reacting impedance (Robin condition). Secondary sources represented by point-monopoles on the sphere are used to form an active control system. In the absence of active control, at low-frequencies, the least scattering is achieved if the surface impedance is negative, purely imaginary and has a large absolute value. At high-frequencies, the best performance is realised with a real, positive impedance that is close to that of the exterior propagation medium. When adding active control, only the low-frequency regime shows improvement, given any impedance, and it is most beneficial to enhance for the previous case that exhibited the best passive performance. Thus, a promising hybrid cloaking approach is a combination of: a stiffened-controlled boundary with multi-channel active control at low-frequencies, and a passive, absorptive boundary at high-frequencies.

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More information

e-pub ahead of print date: 19 October 2018
Published date: 19 October 2018
Additional Information: Abstract submitted for the 176th Meeting of the Acoustical Society of America, published as conference proceedings in the The Journal of the Acoustical Society of America 144, 1757 (2018)
Venue - Dates: 176th Meeting of the Acoustical Society of America joint with 2018 Acoustics Week in Canada, Victoria Conference Centre, Canada, 2018-11-05 - 2018-11-09
Keywords: active control of sound, 3D sound scattering, spherical harmonics, locally-reacting sphere, impedance sphere, plane-wave scattering

Identifiers

Local EPrints ID: 434379
URI: http://eprints.soton.ac.uk/id/eprint/434379
ISSN: 0001-4966
PURE UUID: f5860ff0-0e6e-4a61-bc0a-196da87b3ac3
ORCID for Jordan Cheer: ORCID iD orcid.org/0000-0002-0552-5506

Catalogue record

Date deposited: 23 Sep 2019 16:30
Last modified: 27 Jan 2020 13:44

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