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Bragg Scattering Applications for Un...

Joffre, Dagny.

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Bragg Scattering Applications for Underwater Passive Localization Improvement.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Bragg Scattering Applications for Underwater Passive Localization Improvement./
作者:	Joffre, Dagny.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2019,
面頁冊數:	225 p.
附註:	Source: Dissertations Abstracts International, Volume: 80-12, Section: B.
Contained By:	Dissertations Abstracts International80-12B.
標題:	Naval engineering. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13862945
ISBN:	9781392264492

Bragg Scattering Applications for Underwater Passive Localization Improvement.
Joffre, Dagny.

Bragg Scattering Applications for Underwater Passive Localization Improvement. - Ann Arbor : ProQuest Dissertations & Theses, 2019 - 225 p.

Source: Dissertations Abstracts International, Volume: 80-12, Section: B.

Thesis (Ph.D.)--University of Massachusetts Lowell, 2019.

This item must not be sold to any third party vendors.

Sonar arrays use vibrations induced by acoustic signals to detect and locate the acoustic source. Noise significantly reduces an array's detection ability, and array size limits the array directivity. Bragg scattering is a phenomenon where a wave, propagating in a periodic medium, will scatter off the periodic inclusions and combine constructively to create new, smaller wavelength signals. This dissertation characterizes the Bragg replicate waves in an experimental ribbed panel, called the AGATE panel, and studies the benefits to array directivity and detection when the smaller Bragg replicate waves are used.Test data and a Comsol model were used to characterize Bragg scattering in the AGATE panel. The experimental point force measurements determined that excitations below 500 Hz did not noticeably scatter, and Bragg replicate amplitudes increased as the frequency increased. The Comsol model was used to predict the Bragg scattered response to plane wave excitation, which also showed scattering was frequency dependent.A Matlab model and test data were used to study the potential directivity improvements from beamforming Bragg replicate waves. Bragg replicate waves did not inherently improve the array directivity, so a non-traditional algorithm was developed. The non-traditional algorithm used the smaller Bragg waves to mathematically stretch the array, increasing the array aperture to improve directivity. However, the algorithm could not be effectively applied to the full Bragg replicate wavenumber region. Therefore, directivity could not be improved with traditional Bragg scattering. Additional directivity calculations were performed to show that an array with angle-dependent scattering could inherently improve array directivity.The Comsol model was used to study array detection improvements. A scattering characterization study found that low frequency excitations scattered less efficiently than high frequency excitations, so low frequency hull noise should not appear in the Bragg replicate region. Signal to Noise Ratio (SNR) calculations showed that the SNR was higher in the Bragg replicate region than in the traditional wavenumber region when the excitation signal frequency was appropriately high. Additional ROC curve calculations confirmed that signal detection could be improved if Bragg replicate waves were used in the array calculations.

ISBN: 9781392264492Subjects--Topical Terms:

3173824
Naval engineering.
Subjects--Index Terms:

Array design

Bragg Scattering Applications for Underwater Passive Localization Improvement.
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520 $a Sonar arrays use vibrations induced by acoustic signals to detect and locate the acoustic source. Noise significantly reduces an array's detection ability, and array size limits the array directivity. Bragg scattering is a phenomenon where a wave, propagating in a periodic medium, will scatter off the periodic inclusions and combine constructively to create new, smaller wavelength signals. This dissertation characterizes the Bragg replicate waves in an experimental ribbed panel, called the AGATE panel, and studies the benefits to array directivity and detection when the smaller Bragg replicate waves are used.Test data and a Comsol model were used to characterize Bragg scattering in the AGATE panel. The experimental point force measurements determined that excitations below 500 Hz did not noticeably scatter, and Bragg replicate amplitudes increased as the frequency increased. The Comsol model was used to predict the Bragg scattered response to plane wave excitation, which also showed scattering was frequency dependent.A Matlab model and test data were used to study the potential directivity improvements from beamforming Bragg replicate waves. Bragg replicate waves did not inherently improve the array directivity, so a non-traditional algorithm was developed. The non-traditional algorithm used the smaller Bragg waves to mathematically stretch the array, increasing the array aperture to improve directivity. However, the algorithm could not be effectively applied to the full Bragg replicate wavenumber region. Therefore, directivity could not be improved with traditional Bragg scattering. Additional directivity calculations were performed to show that an array with angle-dependent scattering could inherently improve array directivity.The Comsol model was used to study array detection improvements. A scattering characterization study found that low frequency excitations scattered less efficiently than high frequency excitations, so low frequency hull noise should not appear in the Bragg replicate region. Signal to Noise Ratio (SNR) calculations showed that the SNR was higher in the Bragg replicate region than in the traditional wavenumber region when the excitation signal frequency was appropriately high. Additional ROC curve calculations confirmed that signal detection could be improved if Bragg replicate waves were used in the array calculations.
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653 $a Detection
653 $a Directivity
653 $a Localization
653 $a Metamaterial
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