Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 21 for “"Acoustic metamaterials"”.
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Acoustic Metamaterials at the Microscale
… ratio, or strength. However, dynamic and acoustic properties of micro-architected materials remain largely unexplored, partially because it is challenging to measure their response at these scales. Dispersion resulting from Bragg scattering occurs at wavelengths which are dictated by the …
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Acoustic metamaterials : microperforated shell and Helmholtz resonator
[EMBARGOED UNTIL 12/01/2026] Metamaterials have been extensively developed in many areas over the past two decades, a great deal of research has been conducted on acoustic metamaterials exhibiting unusual dynamic effective material properties produced by artificially engineered microstructures. …
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Design and Experimental Applications of Acoustic Metamaterials
<p>Acoustic metamaterials are engineered materials that were extensively investigated over the last years mainly because they promise properties otherwise hard or impossible to find in nature. Consequently, they open the door for improved or completely new applications (e.g. acoustic superlens that …
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Directionally Sensitive Sensor Based on Acoustic Metamaterials
… microphone arrays are valuable tools for aeroacoustic measurements that can measure the directivity of multiple acoustic sources. However, when deployed in closed test-section wind tunnels, the acoustics suffer due to intense pressure fluctuations contained in the wall-bound turbulent boundary …
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Low-Frequency Emission Enhancement by Resonant Acoustic Metamaterials
Omnidirectional and directional acoustic emission enhancements, at low frequencies as well as broad frequency bands, are highly demanded in audio, medical ultrasonics, and underwater acoustics. Emission enhancement and controlling the directivity of an acoustic source is however restricted to the …
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Wavefront Engineering and Computational Sensing with Acoustic Metamaterials
<p>Acoustic metamaterials are a family of engineered materials that can be designed to possess flexible acoustic properties. They are composed of subwavelength periodic structures that can be homogenized as effective materials within the designed frequency bands. Acoustic wave controlling devices …
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Low Frequency Noise Reduction Using Novel Poro-Elastic Acoustic Metamaterials
… sound absorption and transmission loss using acoustic metamaterials. The acoustic metamaterials investigated consist of poro-elastic acoustic heterogeneous (HG) metamaterials and microperforated (MPP) acoustic metamaterials. HG metamaterials consist of poro-elastic material with a periodic …
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Design optimization of acoustic metamaterials and phononic crystals with a time domain method
… derivatives for shape optimizations of acoustic metamaterials and phononic crystals is presented. The gradient-based design procedure is suitable for large numbers of design variables, and results are shown on achieving effective material properties with a unit cell and the broadband …
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Turbulent Boundary Layers over Rough Surfaces: Large Structure Velocity Scaling and Driver Implications for Acoustic Metamaterials
… to initiate the viability of controlling acoustic waves driven by pressure fluctuations from flow. A turbulent boundary layer scaling analysis was performed on zero-pressure-gradient turbulent boundary layers over rough surfaces, for 30,000≤〖Re〗_θ≤100,000. Relationships between fluctuating …
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Acoustic metamaterials comprised of dead-end pores and black hole effect for low frequency sound absorption in linear and nonlinear regimes
The aim of this work is to design and test acoustic metamaterial absorbers particularly for mitigation of low frequency sound of high intensity. The absorbers designed are formed of a series of plates with a central perforation, separated by air cavities. Two types of structures are investigated: …
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An Investigation on Acoustic Metamaterial Physics to Inspire the Design of Novel Aircraft Engine Liners
… of quiet aircraft. This thesis investigates acoustic metamaterials and their ability to achieve superior transmission loss characteristics not found in traditional honeycomb liners. The acoustic metamaterials investigated are an array of Helmholtz resonators with and without coupled cavities …
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Modelling of low frequency muffler based on acoustic black hole effect
This thesis investigates the influence of acoustic metamaterials, or linings with graded properties, on the performance of open termination ducts and mufflers working within low frequency range. The functioning of such linings has been associated to the Acoustic Black Hole effect. These structures …
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Broadband Acoustic Liner Optimization Study Using Novel Poro-elastic Materials
… aircraft engine noise, there is need for acoustic liner configurations that target broadband performance. This thesis experimentally and analytically investigates passive noise control methods to improve broadband frequency attenuation through various acoustic liner designs. The inclusion …
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Excitation of Acoustic Surface Waves by Turbulence
Acoustic metamaterials have been shown to support acoustic surface waves when excited by a broadband signal in a quiescent environment and these waves could be manipulated by varying the geometry of the structure making up the metamaterial. The study presented here demonstrates the generation of …
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Measurement and Analysis of Sub-Convective Pressure Fluctuations in Turbulent Boundary Layers: A Novel Methodology
… models. A novel measurement approach inspired by acoustic metamaterials was developed, employing sub-resonant cavity sensors that integrate seamlessly into existing geometries. These sensors, leveraging off-the-shelf pressure transducers, operate effectively in grazing flow environments without …
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Strongly nonlinear dynamics and acoustics of coupled granular sonic vacua: theoretical and experimental studies
… of highly discontinuous and adaptive granular acoustic metamaterials for shock wave redirection and control are discussed. Then we focus on another class of granular acoustic metamaterials, namely, one-dimensional single or coupled granular chains embedded in elastic matrix, and present …
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Geopolymer composites and their applications in stress wave mitigation
… behavior for stress wave mitigation and as acoustic metamaterials. The fabrication of geopolymer beads was achieved by simple injection into a Polydimethylsiloxane (PDMS) polymer mold. Based on the mechanical properties of geopolymers, the dynamic responses of homogeneous and dimer chains …
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An Exploration of Nonlinear Locally Resonant Metamaterials with Electromechanical and Topological elements
In recent years, the study of metamaterials has been a subject of much interest, with acoustic metamaterials being applied to a wide range of applications. This utility is in part due to the incorporation of various elements in their design. The addition of local resonators provides greater …
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Elastic wave tailoring at the macro/micro/nano- scales using intentional strongly nonlinear coupling
In acoustics, wave tailoring refers to the manipulation of the propagation of waves or energy that are generated due to some form of dynamic loading. It includes real world examples ranging from impact mitigation to sensors and communication applications and is typically accomplished through the …
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