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1. Cebrecos Ruiz, Alejandro. Transmission, reflection and absorption in Sonic and Phononic Crystals .

Degree: 2015, Universitat Politècnica de València

[EN] Phononic crystals are artificial materials formed by a periodic arrangement of inclusions embedded into a host medium, where each of them can be solid or fluid. By controlling the geometry and the impedance contrast of its constituent materials, one can control the dispersive properties of waves, giving rise to a huge variety of interesting and fundamental phenomena in the context of wave propagation. When a propagating wave encounters a medium with different physical properties it can be transmitted and reflected in lossless media, but also absorbed if dissipation is taken into account. These fundamental phenomena have been classically explained in the context of homogeneous media, but it has been a subject of increasing interest in the context of periodic structures in recent years as well. This thesis is devoted to the study of different effects found in sonic and phononic crystals associated with transmission, reflection and absorption of waves, as well as the development of a technique for the characterization of its dispersive properties, described by the band structure. We start discussing the control of wave propagation in transmission in conservative systems. Specifically, our interest is to show how sonic crystals can modify the spatial dispersion of propagating waves leading to control the diffractive broadening of sound beams. Making use of the spatial dispersion curves extracted from the analysis of the band structure, we first predict zero and negative diffraction of waves at frequencies close to the band-edge, resulting in collimation and focusing of sound beams in and behind a 3D sonic crystal, and later demonstrate it through experimental measurements. The focusing efficiency of a 3D sonic crystal is limited due to the strong scattering inside the crystal, characteristic of the diffraction regime. To overcome this limitation we consider axisymmetric structures working in the long wavelength regime, as a gradient index lens. In this regime, the scattering is strongly reduced and, in an axisymmetric configuration, the symmetry matching with acoustic sources radiating sound beams increase its efficiency dramatically. Moreover, the homogenization theory can be used to model the structure as an effective medium with effective physical properties, allowing the study of the wave front profile in terms of refraction. We will show the model, design and characterization of an efficient focusing device based on these concepts. Consider now a periodic structure in which one of the parameters of the lattice, such as the lattice constant or the filling fraction, gradually changes along the propagation direction. Chirped crystals represent this concept and are used here to demonstrate a novel mechanism of sound wave enhancement based on a phenomenon known as "soft" reflection. The enhancement is related to a progressive slowing down of the wave as it propagates along the material, which is associated with the group velocity of the local dispersion relation at the planes of the crystal. A model based on the… Advisors/Committee Members: Picó Vila, Rubén (advisor), Sánchez Morcillo, Víctor José (advisor).

Subjects/Keywords: Periodic Structures; Sonic Crystals, Phononic Crystals; Transmission; Reflection, Absorption; Band Structure; Dispersion Relation; Focusing; Focalization; Collimation; Spatial dispersion; Beam; Acoustic Beam; Ultrasonic Beam; Axisymmetric; Symmetry Matching; Gradient Index; Lens; Lenses; Homogenization; Refraction; Refractive devices; Long-wavelength; Effective medium; Effective properties; Paraxial approximation; Isofrequency lines; Isofrequency contours; Wave vector; Chirped; Tappered; Rainbow trapping; Mirage effect; Chirped crystals; Wave Enhancement; Soft reflection; Group velocity; Slowing down; Coupled Mode Theory; CMT; Linear Chirped; Exponential chirped; Dissipation; Losses; Porous absorber; Porous material; Porous layers; Dissipative couple mode theory; Modulation; Loss modulation; Band structure calculation; Elastic waves; Acoustic waves; Time-marching; Algorithm; Bloch vector; Bloch boundary conditions; Boundary conditions; Unit cell; Vibrational modes; Resonant peaks; Resonant modes; Accuracy; Convergence; Computation time; Solid-Solid; Solid-fluid; Lamella cyrstal; Extraordinary absorption; Interaction strength; Time delay; Fourier Transform

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APA (6th Edition):

Cebrecos Ruiz, A. (2015). Transmission, reflection and absorption in Sonic and Phononic Crystals . (Doctoral Dissertation). Universitat Politècnica de València. Retrieved from http://hdl.handle.net/10251/56463

Chicago Manual of Style (16th Edition):

Cebrecos Ruiz, Alejandro. “Transmission, reflection and absorption in Sonic and Phononic Crystals .” 2015. Doctoral Dissertation, Universitat Politècnica de València. Accessed August 14, 2020. http://hdl.handle.net/10251/56463.

MLA Handbook (7th Edition):

Cebrecos Ruiz, Alejandro. “Transmission, reflection and absorption in Sonic and Phononic Crystals .” 2015. Web. 14 Aug 2020.

Vancouver:

Cebrecos Ruiz A. Transmission, reflection and absorption in Sonic and Phononic Crystals . [Internet] [Doctoral dissertation]. Universitat Politècnica de València; 2015. [cited 2020 Aug 14]. Available from: http://hdl.handle.net/10251/56463.

Council of Science Editors:

Cebrecos Ruiz A. Transmission, reflection and absorption in Sonic and Phononic Crystals . [Doctoral Dissertation]. Universitat Politècnica de València; 2015. Available from: http://hdl.handle.net/10251/56463

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