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Controlling wave propagation with acoustic and elastic metamaterials
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Kelsten, Matthew J. Controlling wave propagation with acoustic and elastic metamaterials. Retrieved from https://doi.org/doi:10.7282/t3-na3d-x069

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TitleControlling wave propagation with acoustic and elastic metamaterials
NameKelsten, Matthew J (author); Norris, Andrew (chair); Singer, Jonathan (member); Bottega, William (member); Haberman, Michael (member); Rutgers University; School of Graduate Studies
Date Created2021
Other Date2021-10 (degree)
SubjectAcoustics, Engineering, Physics, exceptional points, finite element method, impedance tube, metamaterials, pentamode, wave propagation
Extent1 online resource (xx, 156 pages)
DescriptionThe topics deliberated in this dissertation are ingrained in the idea of controlling wave transmission through artificial domains. This is accomplished through modeling, simulating, design, and testing of acoustic and elastic metamaterials for both air and water applications. Effective properties of metamaterials vastly increase the design-space used toachieve high, low, anisotropic, or one-wave transmission. Each idea presented is focused on realizing or optimizing one of those transmission types.
The first topic visited is optimal attenuation in air-filled ducts. Non-Hermitian systems can exhibit “exceptional points” (EPs) at which modes coalesce. The connection between EPs and acoustic damping goes back to the observation of Cremer (1953) that optimal attenuation in a duct occurs when the two lowest modes have equal complex-valued eigenvalues. An EP existence condition is derived, doing so allows for the determination of the complete set of all possible passive impedance conditions that give rise to EPs, and from these to select impedances appropriate to a particular frequency band. We consider a novel approach to feasibly achieve the aforementioned wall impedance with the use of simple resonators, which can be shown to exhibit mode coalescence at distinct frequencies when treated as a unit cell component of a larger metasurface. The second topic discussed delves into the interest for developing the three-dimensional (3D) anisotropic pentamode (PM), i.e. a structure designed to support a single longitudinal wave with sound speed that depends on the propagation direction, specifically for underwater applications. The presented work attempts to experimentally verify anisotropic sound speeds predicted by finite element simulations using additively manufactured anisotropic 3D PM samples made of titanium. Simulation techniques are given for the computational evaluation of PM sound speeds and the acoustic response of PM materials. Measurements involved suspending samples in front of a plane-wave source emitting a broadband chirp in a water tank to measure time of flight for wavefronts with and without the PM present.

The final topic covers periodic lattice metamaterials like that of the square honeycomb, hexagonal honeycomb, and Kagome lattices which have proven themselves useful in structural applications with their ability to exhibit broadband vibration suppression at subwavelength scales. In the context of periodic lattices, it can be difficult to model all cases extensively. In an attempt to help bridge the analytical gap, we consider classic 2D lattice designs. By doing so we can solve for dynamic stiffness matrices which drive the characterization of band diagrams and their modal structure. A semi-analytical modeling approach is introduced which highlights the explicit dependence of band diagram features on resonator parameters.
NotePh.D.
NoteIncludes bibliographical references
Genretheses
Persistent URLhttps://doi.org/doi:10.7282/t3-na3d-x069
LanguageEnglish
CollectionSchool of Graduate Studies Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.
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