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Rutgers University

1. Titovich, Alexey S. Acoustic and elastic waves in metamaterials for underwater applications.

Degree: PhD, Mechanical and Aerospace Engineering, 2015, Rutgers University

Elastic effects in acoustic metamaterials are investigated. Water-based periodic arrays of elastic scatterers, sonic crystals, suffer from low transmission due to the impedance and index mismatch of typical engineering materials with water. A new type of acoustic metamaterial element is proposed that can be tuned to match the acoustic properties of water in the quasi-static regime. The element comprises a hollow elastic cylindrical shell fitted with an optimized internal substructure consisting of a central mass supported by an axisymmetric distribution of elastic stiffeners, which dictate the shell’s effective bulk modulus and density. The derived closed form scattering solution for this system shows that the subsonic flexural waves excited in the shell by the attachment of stiffeners are suppressed by including a sufficiently large number of such stiffeners. As an example of refraction-based wave steering, a cylindrical-to-plane wave lens is designed by varying the bulk modulus in the array according to the conformal mapping of a unit circle to a square. Elastic shells provide rich scattering properties, mainly due to their ability to support highly dispersive flexural waves. Analysis of flexural-borne waves on a pair of shells yields an analytical expression for the width of a flexural resonance, which is then used with the theory of multiple scattering to accurately predict the splitting of the resonance frequency. This analysis leads to the discovery of the acoustic Poisson-like effect in a periodic wave medium. This effect redirects an incident acoustic wave by 90◦ in an otherwise acoustically transparent sonic crystal. An unresponsive “deaf” antisymmetric mode locked to band gap boundaries is unlocked by matching Bragg scattering with a quadrupole flexural resonance of the shell. The dynamic effect causes normal unidirectional wave motion to strongly couple to perpendicular motion, analogous to the quasi-static Poisson effect in solids. The Poisson-like effect is demonstrated using the first flexural resonance of an acrylic shell. This represent a new type of material which cannot be accurately described as an effective acoustic medium. The study concludes with an analysis of a non-zero shear modulus in a pentamode cloak via the two-scale method with the shear modulus as the perturbation parameter.

Advisors/Committee Members: Norris, Andrew N (chair), Bottega, William J (internal member), Liu, Liping (internal member), O'Regan, Stephen D (outside member).

Subjects/Keywords: Metamaterials – Acoustic properties; Underwater acoustics; Elastic analysis (Engineering)

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Titovich, A. S. (2015). Acoustic and elastic waves in metamaterials for underwater applications. (Doctoral Dissertation). Rutgers University. Retrieved from https://rucore.libraries.rutgers.edu/rutgers-lib/47596/

Chicago Manual of Style (16th Edition):

Titovich, Alexey S. “Acoustic and elastic waves in metamaterials for underwater applications.” 2015. Doctoral Dissertation, Rutgers University. Accessed September 27, 2020. https://rucore.libraries.rutgers.edu/rutgers-lib/47596/.

MLA Handbook (7th Edition):

Titovich, Alexey S. “Acoustic and elastic waves in metamaterials for underwater applications.” 2015. Web. 27 Sep 2020.

Vancouver:

Titovich AS. Acoustic and elastic waves in metamaterials for underwater applications. [Internet] [Doctoral dissertation]. Rutgers University; 2015. [cited 2020 Sep 27]. Available from: https://rucore.libraries.rutgers.edu/rutgers-lib/47596/.

Council of Science Editors:

Titovich AS. Acoustic and elastic waves in metamaterials for underwater applications. [Doctoral Dissertation]. Rutgers University; 2015. Available from: https://rucore.libraries.rutgers.edu/rutgers-lib/47596/

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