Dissertations / Theses on the topic 'Acoustic surface waves'
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1
Kumon, Ronald Edward. "Nonlinear surface acoustic waves in cubic crystals /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Haskell, Reichl B. "A Surface Acoustic Wave Mercury Vapor Sensor." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/HaskellRB2003.pdf.
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Bright, Victor M. "Shear horizontal surface acoustic waves." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/14831.
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4
Rostad, Torbjørn. "Optical Detection of Surface Acoustic Waves." Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9487.
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This project was worked on during the autumn 2005 at the Norwegian University of Science and Technology, Department of Electronics and Telecommunications. The assignment was to write a new LabVIEW programme that is to run the measurement procedure of a laser probe setup. The setup is used in characterization of surface acoustic waves(SAW). A programme was written that contained the necessary functionality and proved to operate satisfactorily. Several measurements were made on a SAW transducer, accurately picturing the wave. Fourier analysis were performed on the collected data in order to separate the propagation directions. An absolute amplitude measurement was made on a heterodyne interferometer, and the result was compared to a similar scan made using the laser probe. The work shows that the setup is ready for calibration against the heterodyne interferometer, in order to enable the laser probe to measure absolute amplitude by itself.
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Mutti, Paolo. "Surface acoustic waves for semiconductor characterization." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357598.
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Harvey, Alan Paul. "Nonlinear surface acoustic waves and applications." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255827.
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Damani, Shishir. "Excitation of Acoustic Surface Waves by Turbulence." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/104742.
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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 trapped acoustic surface waves when excited by a turbulent flow source. The metamaterial and flow were interfaced using a Kevlar covered single cavity whose Kevlar side faced the flow to ensure no significant disturbance to the flow and the other side was open to a quiescent (stationary) environment housing the metamaterial. Acoustic measurements were performed very close to the surface of the metamaterial in the Anechoic Wall Jet Facility at Virginia Tech using two probe-tip microphones and correlation analysis yielded the structure of the surface waves. Two different metamaterials; slotted array and meander array were tested and characterized by their dispersion relations, temporal correlations, and spatial-temporal structure. The measurements proved the existence of surface waves with propagating speeds of a tenth of the speed of sound, when excited by a turbulent boundary layer flow. These waves were much weaker than the overlying flow exciting them but showcased excellent attenuation properties away from the source of excitation. Measurements along the length of the unit-cell geometry of the metamaterial demonstrated high coherence over a range of frequencies limited by the dimension of the cell. This was a surprising behavior provided the cavity was excited by a fully developed turbulent flow over a flat plate and indicated to an area averaging phenomenon.
A wall normal two-dimensional particle image velocimetry (2D-PIV) measurement was performed over the Kevlar covered cavity and a smooth surface to study the effects of the cavity on the flow. The field of view was the same for both cases which made direct flow comparison possible. Flow characteristics such as the boundary layer profiles, Reynolds stress profiles and fluctuating velocity spectrum were studied over the cavity and at downstream locations to quantify the differences in the flows. The boundary layer profiles collapsed in the inner region of the boundary layer but there were small differences in the outer region. The Reynolds stress profiles were also very similar with differences within the uncertainties of processing the images and it reflected similar average behavior of the flow over a smooth wall and a Kevlar covered cavity. The fluctuating velocity spectrum studied over the cavity location showed some differences at low frequencies for all wall normal locations while at higher frequencies the differences were within ±3 dB. These measurements showcased the underlying physics behind the interaction of acoustic metamaterials and turbulent boundary layer flows creating possibilities of using these devices for flow control although further analysis/optimization is needed to fully understand the capabilities of these systems. The demonstration of no significant effect on flow by the Kevlar covered cavity stimulated development of sensors which can average over a region of the wall pressure spectrum.M.S.
In the field of physics, acoustic metamaterials have gained popularity due to their ability to exhibit certain properties such as sound manipulation which cannot be seen in regular materials. These materials have a key feature which is the periodic arrangement of geometric elements in any dimension. These materials can support a phenomenon termed as acoustic surface waves which are essentially pressure disturbances in the medium which behave differently than some known phenomenon such as sound waves when excited by a broadband pressure signal in a stationary medium. Also, it has been shown that these materials can change the nature of the acoustic surface waves if their geometry is changed. Here a successful attempt has been made to link two different fields in physics: acoustic metamaterials (acoustics) and turbulent flows (fluid dynamics). The study here uses turbulent boundary layer flows to excite these metamaterials to show the existence of acoustic surface waves. This is done by creating an interface between the flow and the metamaterial using a Kevlar covered through cavity which is essentially a through hole connecting to different sides: flow side and the stationary air/quiescent side. This cavity acted as the source of excitation for the metamaterial. The Kevlar covering ensures that the flow does not get disturbed due to the cavity which was also proved in this study using a visualization technique: Particle Image Velocity (PIV). Two microphones were used to study the pressure field very close to two metamaterials; one was referred to as the slotted array comprised of slot cavities arranged in one dimension (along the direction of the flow), while the other was termed as the meander array and it comprised of a meandering channel. The pressure field was well characterized for both the acoustic metamaterials and it was proved that these metamaterials could support acoustic surface waves even when excited by a turbulent flow. The idea here was to fundamentally understand the interaction of acoustic metamaterials and turbulent flows, possibly finding use in applications such as trailing edge noise reduction. The use of these metamaterials in direct applications needs further investigation. A finding from the pressure field study showed that the pressure measured along the length of the Kevlar covered cavity was uniform. The flow visualization study looked at the turbulent flow on a smooth wall and over a Kevlar covered cavity. This was done by injecting tiny particles in air and shooting a laser sheet over these to illuminate the flow. Images were recorded using a high-speed camera to track the movement of these particles. It was found that the flow was unaffected with or without the presence of a Kevlar covered cavity. This result coupled with the pressure field uniformity could have some wide applications in the field of pressure sensing.
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Terrill, Eric J. "Acoustic measurements of air entrainment by breaking waves /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9907829.
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Ash, Benjamin James. "Locally resonant metamaterial for surface acoustic waves." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34380.
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The control of surface acoustic waves (SAWs) using arrays of annular holes was investigated both experimentally and through numerical modelling. Periodic elastic composites, phononic crystals (PnCs), were designed using these annular holes as constituent elements. Local resonances associated with the annular hole structure were found to induce phonon bandgaps of a highly frequency tailorable nature, at frequencies where radiation of acoustic energy into the bulk of the substrate medium is avoided. These bandgaps are numerically demonstrated to exhibit order-of-magnitude improved extinction ratios for finite numbers of PnC elements, relative to the commonly used cylindrical pillar architecture. Devices fabricated on commercially available lithium niobate SAW delay lines verify the predicted behaviour. Through laser knife-edge detector vibrometry, a bandgap attenuation of 24.5 dB at 97 MHz was measured, in excellent agreement with finite element method (FEM) simulations. The first reported experimental evidence of subwavelength confinement of propagating SAWs was realised using the same annular hole PnC concept. Defect holes of perturbed resonant frequencies are included within the PnC to define waveguides and cavities. Confinement within these defects was demonstrated to occur at subwavelength frequencies which was experimentally observed in fabricated cavities using standard SAW transducers, as measured by laser Doppler vibrometry. The success of this result was attributed to the impedance matching of hybridised modes to Rayleigh SAWs in un-patterned substrates at the defect resonance. The work here has the potential to transform the field by providing a method to enhance SAW interactions, which is a route towards the realisation of many lab-on-chip applications. Finally, the use of annular hole arrays as negative refraction metamaterials was investigated. The symmetry was broken of the unit cells by alternating either the locally resonant frequencies or the distance separating the constituent elements. Both methods, called the bi-dispersive and bi-periodic methods, were numerically demonstrated to exhibit negative group velocity bands within the first Brillouin zone. Preliminary experimental results show that the design has the potential to be used in superlensing, where a SAW spot was imaged over a subwavelength flat lens. Future research looks to demonstrate that this result can be attributed to negative refraction.
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Manenti, Riccardo. "Circuit quantum acoustodynamics with surface acoustic waves." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:3b29e5b7-cb1d-4588-81ec-d1aa659cbf6e.
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A highly successful architecture for the exchange of single quanta between coupled quantum systems is circuit quantum electrodynamics (QED), in which the electrical interaction between a qubit and a high-quality microwave resonator offers the possibility to reliably control, store, and read out quantum bits of information on a chip. This architecture has also been implemented with mechanical resonators, showing that a vibrational mode can in principle be manipulated via a coupled qubit. The work presented in this thesis consists of realising an acoustic version of circuit QED that we call circuit quantum acoustodynamics (QAD), in which a superconducting qubit is piezoelectrically coupled to an acoustic cavity based on surface acoustic waves (SAWs). Designing and building this novel platform involved the following main accomplishments: a systematic characterisation of SAW resonators at low temperatures; successfully developing a recipe for the fabrication of Josephson junction on quartz and diamond; measuring the coherence time of superconducting 3D transmon qubits on these substrates and demonstrating the dispersive coupling between a SAW cavity and a qubit on a planar geometry. This thesis presents evidence of the coherent interaction between a SAW cavity and a superconducting qubit in several ways. First of all, a frequency shift of the mechanical mode as a function of qubit frequency is observed. We also measure the acoustic Stark shift of the qubit due to the population of the SAW cavity. The extracted coupling is in agreement with theoretical expectations. A time delayed acoustic Stark shift serves to further demonstrate that the Stark shifts that we observe are indeed due to the acoustic field of the SAW mode. The dispersive coupling between these two quantum systems offers the possibility to perform qubit spectroscopy using the SAW resonator as readout component, indicating that these acoustic resonators can, in principle, be adopted as an alternative qubit readout scheme in quantum information processors. We finally present preliminary measurements of the direct coupling between a SAW resonator and a transmon on diamond, suggesting that strong coupling can in principle be obtained.
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Reese, Owein. "Homogenization of acoustic wave propagation in a magnetorheological fluid." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-101629.
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Naseer, Shahid Mohammad. "Shaping surface acoustic waves for cardiac tissue engineering." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7740/.
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The heart is a non-regenerating organ that gradually suffers a loss of cardiac cells and functionality. Given the scarcity of organ donors and complications in existing medical implantation solutions, it is desired to engineer a three-dimensional architecture to successfully control the cardiac cells in vitro and yield true myocardial structures similar to native heart. This thesis investigates the synthesis of a biocompatible gelatin methacrylate hydrogel to promote growth of cardiac cells using biotechnology methodology: surface acoustic waves, to create cell sheets. Firstly, the synthesis of a photo-crosslinkable gelatin methacrylate (GelMA) hydrogel was investigated with different degree of methacrylation concentration. The porous matrix of the hydrogel should be biocompatible, allow cell-cell interaction and promote cell adhesion for growth through the porous network of matrix. The rheological properties, such as polymer concentration, ultraviolet exposure time, viscosity, elasticity and swelling characteristics of the hydrogel were investigated. In tissue engineering hydrogels have been used for embedding cells to mimic native microenvironments while controlling the mechanical properties. Gelatin methacrylate hydrogels have the advantage of allowing such control of mechanical properties in addition to easy compatibility with Lab-on-a-chip methodologies. Secondly in this thesis, standing surface acoustic waves were used to control the degree of movement of cells in the hydrogel and produce three-dimensional engineered scaffolds to investigate in-vitro studies of cardiac muscle electrophysiology and cardiac tissue engineering therapies for myocardial infarction. The acoustic waves were characterized on a piezoelectric substrate, lithium niobate that was micro-fabricated with slanted-finger interdigitated transducers for to generate waves at multiple wavelengths. This characterization successfully created three-dimensional micro-patterning of cells in the constructs through means of one- and two-dimensional non-invasive forces. The micro-patterning was controlled by tuning different input frequencies that allowed manipulation of the cells spatially without any pre- treatment of cells, hydrogel or substrate. This resulted in a synchronous heartbeat being produced in the hydrogel construct. To complement these mechanical forces, work in dielectrophoresis was conducted centred on a method to pattern micro-particles. Although manipulation of particles were shown, difficulties were encountered concerning the close proximity of particles and hydrogel to the microfabricated electrode arrays, dependence on conductivity of hydrogel and difficult manoeuvrability of scaffold from the surface of electrodes precluded measurements on cardiac cells. In addition, COMSOL Multiphysics software was used to investigate the mechanical and electrical forces theoretically acting on the cells. Thirdly, in this thesis the cardiac electrophysiology was investigated using immunostaining techniques to visualize the growth of sarcomeres and gap junctions that promote cell-cell interaction and excitation-contraction of heart muscles. The physiological response of beating of co-cultured cardiomyocytes and cardiac fibroblasts was observed in a synchronous and simultaneous manner closely mimicking the native cardiac impulses. Further investigations were carried out by mechanically stimulating the cells in the three-dimensional hydrogel using standing surface acoustic waves and comparing with traditional two-dimensional flat surface coated with fibronectin. The electrophysiological responses of the cells under the effect of the mechanical stimulations yielded a higher magnitude of contractility, action potential and calcium transient.
13
Sen, Rahul. "Acoustic scattering by discontinuities in waveguides." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/81021.
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The scattering of acoustic waves by boundary discontinuities in waveguides is analyzed using the Method of Matched Asymptotic Expansions (MAE). Existing theories are accurate only for very low frequencies. In contrast, the theory developed in this thesis is valid over the entire range of frequencies up to the first cutoff frequency. The key to this improvement lies in recognizing the important physical role of the cutoff cross-modes of the waveguide, which are usually overlooked. Although these modes are evanescent, they contain information about the interaction between the local field near the discontinuity and the far-field. This interaction has a profound effect on the far-field amplitudes and becomes increasingly important with frequency. The cutoff modes also present novel mathematical problems in that current asymptotic techniques do not offer a rational means of incorporating them into a mathematical description. This difficulty arises from the non-Poincare form of the cross-modes, and its resolution constitutes the second new result of this thesis. We develop a matching scheme based on block matching intermediate expansions in a transform domain. The new technique permits the matching of expansions of a more general nature than previously possible, and may well have useful applications in other physical situations where evanescent terms are important. We show that the resulting theory leads to significant improvements with just a few cross-mode terms included, and also that there is an intimate connection with classical integral methods. Finally, the theory is extended to waveguides with slowly varying shape. We show that the usual regular perturbation analysis of the wave regions must be completely abandoned. This is due to the evanescent nature of the cross-modes, which must be described by a WKB approximation. The pressure field we so obtain includes older results. The new terms account for the cutoff cross-modes of the variable waveguide, which play a central role in extending the dynamic range of the theory.Ph. D.
14
Furnell, G. D. "A study of acoustic wave propagation within curved ducting systems /." Title page, table of contents and abstract only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09phf987.pdf.
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Leek, Peter James. "Charge transport in carbon nanotubes using surface acoustic waves." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614064.
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Parmar, Biren Jagadish. "Development Of Point-Contact Surface Acoustic Wave Based Sensor System." Thesis, Indian Institute of Science, 2006. https://etd.iisc.ac.in/handle/2005/279.
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Surface Acoustic Waves (SAW) fall under a special category of elastic waves that need a material medium to propagate. The energy of these waves is confined to a limited depth below the surface over which they propagate, and their amplitudes decay with increasing depth. As a consequence of their being a surface phenomenon, they are easily accessible for transduction. Due to this reason, a lot of research has been carried out in the area, which has resulted in two very popular applications of SAW - SAW devices and in Non-Destructive Testing and Evaluation.
A major restriction of SAW devices is that the SAW need a piezoelectric medium for generation, propagation and reception. This thesis reports the attempt made to overcome this restriction and utilize the SAW on non-piezoelectric substrates for sensing capabilities. The velocity of the SAW is known to be dependent purely on the material properties, specifically the elastic constants and material density. This dependence is the motivation for the sensor system developed in the present work.
Information on the survey of the methods suitable for the generation and reception of SAW on non-piezoelectric substrates has been included in the thesis. This is followed by the theoretical and practical details of the method chosen for the present work - the point source/point receiver method. Advantages of this method include a simple and inexpensive fabrication procedure, easy customizability and the absence of restrictions due to directivity of the SAW generated. The transducers consist of a conically shaped PZT element attached to a backing material. When the piezoelectric material on the transmitter side is electrically excited, they undergo mechanical oscillations. When coupled to the surface of a solid, the oscillations are transferred onto the solid, which then acts as a point source for SAW. At the receiver, placed at a distance from the source on the same side, the received mechanical oscillations are converted into an electrical signal as a consequence of the direct piezoelectric effect. The details of the fabrication and preliminary trials conducted on metallic as well as non-metallic samples are given.
Various applications have been envisaged for this relatively simple sensor system. One of them is in the field of pressure sensing. Experiments have been carried out to employ the acoustoelastic property of a flexible diaphragm made of silicone rubber sheet to measure pressure. The diaphragm, when exposed to a pressure on one side, experiences a varying strain field on the surface. The velocity of SAW generated on the stressed surface varies in accordance with the applied stress, and the consequent strain field generated. To verify the acoustoelastic phenomenon in silicone rubber, SAW velocities have been measured in longitudinal and transverse directions with respect to that of the applied tensile strain. Similar measurements are carried out with a pressure variant inducing the strain. The non-invasive nature of this setup lends it to be used for in situ measurement of pressure.
The second application is in the field of elastography. Traditional methods of diagnosis to detect the presence of sub-epidermal lesions, some tumors of the breast, liver and prostate, intensity of skin irritation etc have been mainly by palpation. The sensor system developed in this work enables to overcome the restrictive usage and occasional failure to detect minute abnormal symptoms. In vitro trials have been conducted on tissue phantoms made out of poly (vinyl alcohol) (PVA-C) samples of varying stiffnesses. The results obtained and a discussion on the same are presented.
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Parmar, Biren Jagadish. "Development Of Point-Contact Surface Acoustic Wave Based Sensor System." Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/279.
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Surface Acoustic Waves (SAW) fall under a special category of elastic waves that need a material medium to propagate. The energy of these waves is confined to a limited depth below the surface over which they propagate, and their amplitudes decay with increasing depth. As a consequence of their being a surface phenomenon, they are easily accessible for transduction. Due to this reason, a lot of research has been carried out in the area, which has resulted in two very popular applications of SAW - SAW devices and in Non-Destructive Testing and Evaluation.
A major restriction of SAW devices is that the SAW need a piezoelectric medium for generation, propagation and reception. This thesis reports the attempt made to overcome this restriction and utilize the SAW on non-piezoelectric substrates for sensing capabilities. The velocity of the SAW is known to be dependent purely on the material properties, specifically the elastic constants and material density. This dependence is the motivation for the sensor system developed in the present work.
Information on the survey of the methods suitable for the generation and reception of SAW on non-piezoelectric substrates has been included in the thesis. This is followed by the theoretical and practical details of the method chosen for the present work - the point source/point receiver method. Advantages of this method include a simple and inexpensive fabrication procedure, easy customizability and the absence of restrictions due to directivity of the SAW generated. The transducers consist of a conically shaped PZT element attached to a backing material. When the piezoelectric material on the transmitter side is electrically excited, they undergo mechanical oscillations. When coupled to the surface of a solid, the oscillations are transferred onto the solid, which then acts as a point source for SAW. At the receiver, placed at a distance from the source on the same side, the received mechanical oscillations are converted into an electrical signal as a consequence of the direct piezoelectric effect. The details of the fabrication and preliminary trials conducted on metallic as well as non-metallic samples are given.
Various applications have been envisaged for this relatively simple sensor system. One of them is in the field of pressure sensing. Experiments have been carried out to employ the acoustoelastic property of a flexible diaphragm made of silicone rubber sheet to measure pressure. The diaphragm, when exposed to a pressure on one side, experiences a varying strain field on the surface. The velocity of SAW generated on the stressed surface varies in accordance with the applied stress, and the consequent strain field generated. To verify the acoustoelastic phenomenon in silicone rubber, SAW velocities have been measured in longitudinal and transverse directions with respect to that of the applied tensile strain. Similar measurements are carried out with a pressure variant inducing the strain. The non-invasive nature of this setup lends it to be used for in situ measurement of pressure.
The second application is in the field of elastography. Traditional methods of diagnosis to detect the presence of sub-epidermal lesions, some tumors of the breast, liver and prostate, intensity of skin irritation etc have been mainly by palpation. The sensor system developed in this work enables to overcome the restrictive usage and occasional failure to detect minute abnormal symptoms. In vitro trials have been conducted on tissue phantoms made out of poly (vinyl alcohol) (PVA-C) samples of varying stiffnesses. The results obtained and a discussion on the same are presented.
18
Xu, Liwei. "Computational methods for a class of problems in acoustic, elastic and water waves." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 203 p, 2009. http://proquest.umi.com/pqdweb?did=1833647381&sid=12&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Chiu, Ching-Sang Denner Warren W. "Report on the Office of Naval Research USA-China Conference on Shallow Water Acoustics, December 18-21, 1995." Monterey, CA : Naval Postgraduate School, 1997. http://catalog.hathitrust.org/api/volumes/oclc/37486128.html.
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Ead, Richard M. "Predicting the effects of sea surface scatter on broad band pulse propagation with an ocean acoustic parabolic equation model." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FEad.pdf.
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Hwang, Sukyeon. "Acoustic seismic modeling in the slowness-time intercept domain /." Access abstract and link to full text, 1993. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9318174.
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Turton, Andrew Charles. "Microfabricated liquid density sensors using polyimide-guided surface acoustic waves." Thesis, Durham University, 2006. http://etheses.dur.ac.uk/2605/.
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The simultaneous measurements of liquid density and refractive index on the same liquid sample are desirable. This thesis investigates the development of a micro- fabricated liquid density sensor that can be integrated into existing refractometers. A discussion of density sensing techniques and review of suitable sensors is given, leading to the choice of a Love mode surface acoustic wave (SAW) device. Love modes are formed by focussing the acoustic energy in a thin waveguide layer on a surface acoustic wave device. The horizontal-shear wave motion reduces attenuation in liquid environments, and the high surface energy density theoretically gives the highest sensitivity of all SAW devices. This study follows the development of a Love mode liquid density sensor using a polyimide waveguide layer. The novel use of polyimide offers simple and cheap fabrication, and theoretically gives a very high sensitivity to surface loading due to its low acoustic velocity. Love mode devices were fabricated with different polyimide waveguide thicknesses. The optimum thickness for a compromise between low loss and high sensitivity was 0.90 - 1.0 μm. These devices exhibited a linear shift in frequency with the liquid density-viscosity product for low viscosities. The response was smaller for high viscosities due to non-Newtonian liquid behaviour. Dual delay-line structures with a smooth 'reference' and corrugated 'sense' delay- lines were used to trap the liquid and separate the density from the density-viscosity product. A sensitivity up to 0.13 μgcm(^-3)Hz(^-1) was obtained. This is the highest density sensitivity obtained from an acoustic mode sensor. Experimental results show a zero temperature coefficient of frequency is possible using polyimide waveguides. These are the first Love mode devices that demonstrate temperature independence, highlighting the importance of polyimide as a new waveguide material.
23
Son, Seok-Kyun. "Electron transport by surface acoustic waves in an undoped system." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708763.
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Gan, Tian S. M. Massachusetts Institute of Technology. "Design and fabrication of granular materials for surface acoustic waves." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100133.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 134-147).
Granular materials with structural discreteness and periodicity can lead to novel propagation behaviors of mechanical waves. Acoustic studies of granular media typically involve macroscopic particles whereas contact-based vibrations of microparticles remain largely unexplored. The adhesion which can be neglected on millimeter scale is significant on micron scales and therefore microparticles are expected to yield qualitatively different dynamics. We model the microparticle array as locally resonant metamaterials for surface acoustic waves by using the effective medium approach. In experiment, we employ the convective assembly method to fabricate the centimeter-sized, two-dimensional granular crystal consisting of 1[mu]m silica spheres adhered to the substrate. Laser-induced transient grating technique is used to generate and detect surface acoustic waves in microsphere array samples. We demonstrate, both experimentally and by theoretical analysis, that the Rayleigh wave in the substrate interacts with the contact resonance of microspheres leading to hybridization and "avoided-crossing" at a high frequency regions~10 2 MHz. Furthermore, we fabricate the microsphere waveguide structure by template-assisted-self-assembly. By using the same laser technique, we have observed the waveguide behavior in experimental measurement.
by Tian Gan.
S.M.
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Tan, Lin. "Development of micro-acoustic devices with applications of viscous effects." Diss., Online access via UMI:, 2006.
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Rinker, Brett A. "A single-sided access simultaneous solution of acoustic wave speed and sample thickness for isotropic materials of plate-type geometry." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4585.
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Thesis (M.S.)--University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 17, 2009) Vita. Includes bibliographical references.
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Schlottmann, Robert Brian. "A path integral formulation of elastic wave propagation /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004372.
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Vaughan, Derek E. L. "Surface acoustic waves in optical communication devices : the development of tunable acousto-optic filters." Thesis, Bangor University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333618.
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Gross, Johann. "Evaluation of near surface material degradation in concrete using nonlinear Rayleigh surface waves." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45810.
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Comparative studies of nondestructive evaluation methods have shown that nonlinear ultrasonic techniques are more sensitive than conventional linear methods to changes in material microstructure and the associated small-scale damage. Many of the material degradation processes such as carbonation in concrete, corrosion in metals, etc., begin at the surface. In such cases, ultrasonic Rayleigh surface waves are especially appropriate for detection and characterization of damage since their energy is concentrated in the top layer of the test object. For the civil engineering infrastructure, only a limited number of field applicable nonlinear ultrasonic techniques have been introduced. In this paper a nonlinear ultrasonic measurement technique based
on the use of Rayleigh waves is developed and used to characterize carbonation in concrete samples. Wedge transducer is used for the generation and an accelerometer for detection of the fundamental and modulated ultrasonic signal components. The measurements are made by varying the input voltage and along the propagation distance. The slope of the normalized modulated amplitudes is taken as the respective nonlinearity parameter. Concrete samples with two different levels of damage are
examined, and the difference of the two fundamental frequencies is used to quantify
damage state.
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Pendergraft, Karen Anne. "Frequency dependent acoustic transmission in nonuniform materials." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43265.
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A one dimensional normalized model for the frequency response of the acoustic power transmitted through nonuniform materials is developed. Using the ideal mixture model to relate acoustic velocity and impedance, this normalized model demonstrates that the power transmission characteristics are completely determined using only a composition profile and the parameters defining percent variation in acoustic velocity and impedance. For purposes of comparison, an analytically exact solution for exponential tapers is obtained.Master of Science
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Nagaraj, Nagaraj. "Effects of Dissipation on Propagation of Surface Electromagnetic and Acoustic Waves." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc115126/.
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With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. with this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. the first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an efort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. a dielectric-metal-¬dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metal-dielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectric-metal-dielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. an equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a Kronig-Penny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. in the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the metal plates, I derive a dispersion equation that gives resonant frequencies, which coincide with those observed in the experiment that was performed by Wave Phenomena Group at Polytechnic University of Valencia, Spain. Two eigenmodes with different polarizations and phase velocities are obtained from the dispersion equation. at certain critical aperture of the channel, an interesting cutoff effect, which is unusual for an acoustic wave, is observed for one of the eigenmodes with symmetric distribution of the pressure field. the theoretical prediction of the coupling and synchronization of Rayleigh waves strongly supports the experimentally measured shift of the resonant frequencies in the transmission spectra with channel aperture. the observed high level of absorption may find applications in designing metamaterial acoustic absorbers.
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RUIZ, ALBERTO. "SURFACE ACOUSTIC WAVE VELOCITY MEASUREMENTS ON SURFACE-TREATED METALS BY LASER-ULTRASONIC SPECTROSCOPY." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1077302192.
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Kalinski, Michael E. "Determination of in situ V[subscript s] and G[subscript max] using surface wave measurements in cased and uncased boreholes /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Hill, Steven. "Measurements of low frequency acoustic backscatter from the sea surface." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/31022.
Full textAbstract:
The overall objective of this thesis was to predict, model and measure low frequency acoustic backscatter from the sea surface zone (SSZ). In particular, the objectives were fourfold: to relate the acoustic backscatter Doppler spectrum to the directional waveheight spectrum (DWS) through a perturbation analysis; to develop instrumentation suitable for measuring the properties of acoustic backscatter from the SSZ; to design and implement signal processing hardware and software to process raw data from the instrument; and to deploy the instrument and make measurements to test the validity of the predictions of the theoretical development.
A theoretical framework was developed to enable a test of the acoustic analogue of the Coastal Ocean Dynamics Applications Radar (CODAR) technique, using beamforming techniques to simulate the CODAR antennas. Expressions relating the CODAR antenna outputs to the output of an array of omnidirectional acoustic point sensors were developed, and mathematical algorithms and techniques were derived to extract information about the DWS of surface gravity waves from acoustic Doppler backscatter measurements with the array. Models were developed and implemented, showing the expected form of the power spectral density of the acoustic Doppler backscatter seen by single omnidirectional receivers, and the expected form of data products of the beamformed array.
An acoustic instrument — the Upward-Looking Sonar Array System (ULSAS) — was developed for stand-alone, remotely controlled operation in both bottom-situated and deep-water, surface-tethered configurations. This device can collect and store large quantities of acoustic data from a multi-element array, under the control of a distant operator over a radio link. The bottom-situated version was deployed in the coastal waters of British Columbia, and the deep water version was deployed in the recent Surface Wave Processes (SWAPP) experiment.
A preliminary test of the acoustic CODAR technique was made, yielding information consistent with the known wind and wave field. The form of the non-directional part of the extracted DWS followed approximately the expected k⁻⁴ shape for k values above saturation. Beamforming results using frequency-domain data show that the Doppler-shifted acoustic backscatter is directional in nature. These are the first results of this kind to be reported.
The deep-water version of ULSAS was tested for the first time during the SWAPP cruise. In spite
of a problem limiting the power output of the projector, estimates of the surface scattering strength parameter over angles of incidence less than 45° were made, showing some surprising departures from the Chapman-Harris empirical formula for S₅ , and interesting angular structure. Measurements of the ambient noise field were also made under calm conditions and during 14 kt winds.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Statuto, Nahuel. "Magnetic Excitations Induced by Surface Acoustic Waves and Spin-Polarized Currents." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667710.
Full textAbstract:
The goal of this thesis is to explore and control the magnetization dynamics on magnetic multilayered thin films through two different techniques: the application of strain and spin- polarized currents, which represent lower-power consumption approaches to the control of magnetization dynamics compared with conventional techniques.
The ferromagnetic materials with nanometric thickness used in this thesis are magnetic materials widely used in research. Aside the purely scientific interest, these materials are potentially applicable in telecommunications or technologies for storing and transmitting information at high speeds.
1. Magnetization Dynamics Induced by the Application of Oscillating Strain
The first part of the thesis studies the magnetization dynamics induced by the application of dynamic strain on the magnetic material. The strain deforms the magnetic material and induces a change in the direction and intensity of the magnetic anisotropy. Therefore, the magnetic states are affected by this variation and align with the new direction of magnetic anisotropy inducing dynamics in the magnetization.
The main result of the first part of the thesis is the simultaneous time- and space-resolved observation of both the piezoelectric voltage wave associated to the SAW and the induced magnetization excitations on the ferromagnetic thin film of Nickel (Ni). We have found that manipulation of magnetization states in ferromagnetic thin films with SAWs is possible at the picosecond scale with efficiencies as high as for the static case. In Chapter 3 we have studied Ni nanostructures whose magnetization dynamics are governed by the intrinsic configuration of the magnetic domains and by their orientation with respect to the SAW- induced strain resulting in considerable delays between strain and magnetization. In Chapter 4 we have studied extended Ni thin film, on which SAWs induce spin waves that propagate millimeter distances and have a rotation amplitude of about 25 deg.
2. Magnetization Dynamics Induced by the Spin-Polarized Current
The second part of the thesis studies the magnetization dynamics induced by the application of spin-polarized current through the magnetic material that exchanges magnetic moment with the magnetic spins of the electrons in the current. The current density has to be high to induce dynamics on the magnetization (~106-107 A/cm2) and this results in a reduction of the diameter of the electrical contact 50-200 nm.
The main results of the second part of the thesis are related with the stability and the nucleation process of magnetic solitons. On the one hand, we have showed that magnetic solitons can exhibit multiple stable states, which are tunable with current or magnetic field. We also have correlated the existence of unstable states with an increment of low- frequency noise. Using simulations, we have identified the low-frequency spectra with the existence of drift resonances and we have observed that any asymmetry on the effective magnetic field suffered by the magnetic soliton can leads to drift resonances. On the other hand, we have experimentally observed that the processes of nucleation and annihilation of magnetic solitons have different intrinsic times, and using simulations we have identified a waiting time associated with the creation process, which make it a longer than annihilation. We also have studied, using micromagnetic simulations, the initial magnetization states that lead to the nucleation of topological and non-topological magnetic solitons.La tesis gira en torno al estudio de la dinámica de la magnetización en capas y multicapas delgadas ferromagnéticas. Sin embargo, los sistemas estudiados son diversos y pueden clasificarse por la técnica utilizada para la excitación de la dinámica de la magnetización. Este hecho queda plasmado en la estructura de la tesis que consta de una introducción general, Capítulo 1, y luego de dos partes independientes y separadas, a su vez, en varios capítulos. El orden en la exposición de los resultados pretende seguir una linea lógica para su compresión. Como contrapartida, los resultados son presentados sin seguir un orden cronológico. La primera parte de la tesis estudia la dinámica de la magnetización inducida por la aplicación de tensión dinámicamente sobre el material magnético, que al deformarlo induce en él un cambio en la dirección e intensidad de la anisotropía magnética. Por lo tanto, los estados magnéticos se ven afectados por esta variación y cambian para alinearse con la nueva dirección de anisotropía magnética induciendo dinámica en la magnetización. La segunda parte de la tesis estudia la dinámica de la magnetización inducida por la aplicación de corriente polarizada a través del material magnético que intercambia momento magnético con los espines magnéticos de los electrones de la corriente. Para que esta transferencia de momento magnético sea efectiva la densidad de corriente ha de ser elevada (~106-107 A/cm2) y para conseguirla se reduce hasta los 50-200 nm el diámetro del contacto eléctrico. Los materiales ferromagnéticos con grosor nanométrico usados en esta tesis son materiales magnéticos usados ampliamente en la investigación. Aparte del interés puramente científico, estos materiales son potencialmente aplicables en telecomunicaciones o tecnologías del almacenaje y transmisión de información a altas velocidades.
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Codron, Fabien. "Detection of surface waves in the ground using an acoustic method." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17396.
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Fenneman, Douglas. "An acoustic method for the detection of surface waves in sand." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/21802.
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Kelling, Sven. "Enhancing CO oxidation over Pt single crystals by surface acoustic waves." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624114.
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Schneble, Robert Jeffery. "Control of electrons for quantum information processing using surface acoustic waves." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613276.
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Sritharan, Kumudesh. "Applications of surface acoustic waves (SAW) for chemical and biological analysis." kostenfrei, 2008. http://d-nb.info/994505051/34.
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Swacek, Christian Bernhard. "Optical generation of tone-burst Rayleigh surface waves for nonlinear ultrasonic measurements." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45812.
Full textAbstract:
Conventional contact ultrasonic methods suffer from large variability, which
is known to originate from a number of sources such as coupling variability, and the
surface roughness at the transducer/specimen interface. The inherently small higherharmonic
signals can be significantly influenced by the changes in contact conditions,
especially in nonlinear ultrasonic measurements. For this reason, the noncontact
generation and detection techniques are very attractive. This research first focuses
on the optical generation of tone-burst surface acoustic waves in a metallic specimen.
Two methods that use laser light as an optical source are compared for generating
surface acoustics waves in the 5 MHz range. Both the shadow mask and diffraction
grating are used to convert a laser pulse to a tone-burst signal pattern on the specimen.
The generated signals are detected by a wedge transducer at a fixed location and then
the harmonic contents in the generated signals and the repeatability of the methods
are evaluated. Finally, the developed method is used to characterize the material
nonlinearity of aluminum (Al 6061) and steel (A36). The results showed repeatable
measurements for ablative signal excitation on aluminum.
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Cameron, Thomas P. "Low-voltage SAW amplifiers on multilayer GaAs/ZnO substrates." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/15463.
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O'Rorke, Richard. "The spatial control of particles in microfluidic systems using surface acoustic waves." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590299.
Full textAbstract:
Control over particle positioning is of particular importance in microfluidic systems. Acoustic techniques offer a low- power, minimally invasive method of achieving such control. This thesis discusses such control using surface acoustic waves. Mathematical models are first developed to describe the control over particles in liquids using acoustic radiation forces , which highlight the influence of acoustic power and particle size. The formation of both one and two dimensional particle arrays in fluidic channels are t hen demonstrated experimentally in a range of fluidic channels. Particle acceleration during array formation is shown by experiment to be directly proportional to the acoustic power level, indicating both fast and slow regimes of operation for this technique. Additionally, the time taken for particle arrays to form is shown to follow an inverse square relationship with particle size, allowing the possibility of sorting particles according to their size. A method of transporting particle arrays is reported, by sequential increments in the acoustic frequency. This is a cyclic process and the controlled transport of arrays of micron-sized particles by distances greater than 100 11m is demonstrated. A biocompatible microfluidic device is presented, which enables the use of the techniques presented here with biologically relevant samples. A significant biological application is demonstrated by the formation and transportation of arrays of microbubbles. This could allow the characterisation of individual micro bubbles in targeted drug delivery studies, for example.
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McEnaney, Kevin Bernard. "Magneto-absorption of surface acoustic waves by a 2-dimensional electron gas." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293651.
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Benesh, Matthew Joel. "Charge transport dynamics of surface acoustic waves in a GaAs/AlGaAs 2DEG." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608252.
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Mishra, Harshad. "Magnetic field sensor based on micro-structured magnetoelastic surface acoustic waves devices." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0147.
Full textAbstract:
Au cours des dernières décennies, on a assisté à une croissance considérable dans le domaine des technologies des capteurs magnétiques. Le domaine est passé de simples dispositifs micro-usinés à base de silicium à des microsystèmes intégrés plus complexes combinant des transducteurs de haute performance ainsi que des interfaces sans fil. Cependant, presque tous ces appareils fonctionnent avec un mécanisme complexe tout en étant alimentés simultanément de l'extérieur et coûteux. Il y a donc un besoin profond de développer un capteur magnétique qui surmonte ces défis. Ces travaux de recherche ont porté sur le développement de capteurs à ondes élastiques de surface (SAW) pour la détection des champs magnétiques. La configuration résonateur a été considérée dans cette étude afin de permettre une interrogation sans fil. La première partie de notre travail est consacrée à l’étude de la physique et à l'interaction entre les ondes élastiques et les couches magnétostrictives lorsqu'elles sont soumises à un champ magnétique. Nous avons donc étudié des résonateurs SAW en utilisant le niobate de lithium comme substrat et un empilement multicouches [TbCo2/FeCo] comme électrode et matériau sensible. Nous avons étudié et montré le rôle de l'effet de forme dans le magnétisme résultant de la géométrie de l'électrode. Un banc de mesure expérimental a été mis au point pour démontrer l’utilisation d’un capteur magnétique SAW pour la mesure du courant électrique le long d’une lignes hautes tension. Par la suite, nous avons développé un capteur auto-compensé en température rendant sa fréquence de résonance uniquement sensible à l’intensité du champ magnétique. Ce capteur à structure multicouche utilise la coupe ST du quartz comme substrat avec comme direction de propagation des ondes X+90°C. Cette direction de la coupe ST présente un coefficient de température positif (TCF) qui a été compensé par le les couches de ZnO et du CoFeB qui présentent un TCF négatif. Enfin, en combinant nos connaissances sur les effets de forme magnétiques et sur le comportement des structure SAW multicouche pour développer un dispositif qui non seulement annule les effets de la température sur la fréquence de résonance mais également sur l'anisotropie magnétique. De plus, cette structure présente également la possibilité de réaliser un dispositif multisensoriel puisque dans le même dispositif, plusieurs modes sont générés. En plus du mode compensé en température qui permet de mesurer l’intensité du champ magnétique, un autre peu sensible au champ magnétique, permettra de mesurer la température de l’environnement de fonctionnementThe last few decades have seen tremendous growth in the area of magnetic sensor technologies. The field has grown from simple micro-machined silicon based devices to more complex integrated microsystems combining high performance transducers as well as wireless interfaces. However, almost all of these devices operate with a complex mechanism while simultaneously being externally powered as well as expensive. Thus, there arises a deep need to develop a magnetic sensor that overcomes the challenges. This research work focused on the development of surface acoustic wave (SAW) sensors for the detection of magnetic field. Owing to the possibility of wireless interrogation, SAW devices of the resonator configuration have been considered in this study. The first part of our work aims to address the physics and interaction between the acoustic waves and magnetostrictive layers when subjected to a magnetic field. We investigated SAW resonators using LiNbO3 as the substrate and multi-layered [TbCo2/FeCo] as the electrode and sensitive material. We studied and showed the role of the shape effect in magnetism arising from the electrode geometry. A model experimental set-up was developed to demonstrate an application of the fabricated device as a sensor for detection of current along a cable. Subsequently, we developed a device that is self-compensated for the effects of temperature on the resonance frequency. The multi-layered sensor was based on ST-cut Quartz as the substrate whose positive temperature coefficient of frequency (TCF) was compensated for by the negative TCF of ZnO and CoFeB. Finally, we combine our understandings of the shape effects in magnetism and the multi-layered TCF compensated SAW structure to develop a device that is not only compensated for the effects of temperature on the resonance frequency but also on the magnetic anisotropy. In addition, this structure also presents the possibility of a proof-of-concept multi-sensory device because along with the temperature compensated resonance peak, there exist other resonances which are highly sensitive to any change in the temperature while at the same time immune to magnetic field
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Al, lethawe Mohammed abdulridha. "Band gaps and waveguiding of surface acoustic waves in pillars-based phononics crystals." Thesis, Besançon, 2015. http://www.theses.fr/2015BESA2057.
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[…] Dans ce travail de thèse, nous nous sommes intéressés à ces bandes interdites et à ces modes de propagations dans le cas d’un cristal photonique constitué d’une matrice de piliers déposés en surface d’un milieu semi-fini. L’étude des interactions entre les piliers résonants localement avec la surface du milieu semi fini nous a permis d’identifier de nouveaux modes de propagation […]Nous avons également montré comment obtenir une réfraction négative omnidirectionnelle[…] La dernière partie de ce travail a été consacré à l’étude des mécanismes permettant la propagation et le confinement d’ondes guidées[…] .Nous avons également explicité les mécanismes qui permettent de crée ce type d’ondes guidées sub-longeur d’onde et le confinement des photons de surface[...] We present the features of the interaction between surface acoustic wave and locally resonant pillar on the top of demi infinite medium. We shown that the photonic crystal we proposed possess an acoustic metamaterial feature for surface acoustic waves in the manner that pillars on the top of the surface introduce new guide modes in the non radiative region of the substrate outside sound cone. We also demonstrate the these guided modes are resonant modes that have frequencies greatly lower than those expected from the Bragg mechanism. […]
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Ohm, Won-suk. "Effects of dispersion on nonlinear surface acoustic waves in substrates laminated with films /." Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3038194.
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Magnusson, Einar B. "High-spin impurities and surface acoustic waves in piezoelectric crystals for spin-lattice coupling." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:09d23fb2-f501-4be2-a25f-b69ada0ce5b1.
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In this thesis we investigate various aspects of SAW devices and strain sensitive spin species in ZnO and LiNbO3 for coupling surface acoustic waves to spin ensembles. Firstly, we performed a series of ESR experiments exploring the potential of Fe3+ impurities in ZnO for spin-lattice coupling. This spin system has already been identified as a high potential quantum technology component due to its long coherence time. We show that the system also has good properties for spin-lattice coupling experiments, with a strain-coupling parameter G33 = 280 ± 5GHz/strain, which is about 16 times larger than the largest reported for NV centres in diamond. We found that the LEFE effect as well as the spin Hamiltonian parameter D have a linear temperature dependence. As the relative change in each coincide, this strongly supports the notion that the modification of D by an electric field is a multiplicative effect rather than an additive one, D = D0(1 + κΕ). The LEFE coefficient we measured is several times larger for Fe3+:ZnO than for Mn2+:ZnO. Secondly, we have fabricated and characterised SAW devices on bulk ZnO crystals and Fe doped lithium niobate. We found that the nominally pure ZnO was conductive at room temperature due to n-type intrinsic doping, and electrical losses inhibited any transmission through a SAW delay line above T = 200K. The one-port resonator measured down to milli-Kelvin temperatures showed excellent quality factors of up to Q ≃ 1.5 x 105 in its superconducting state. Finally, we performed a surface acoustic wave spin resonance (SAWSR) experiment using a one-port SAW resonator fabricated on Fe2+:LN. We observed a clear signal at T ≃ 25 K, at a field near the expected one for a Δms = 2 transition between the |â1⟩ and |+1⟩ states. We concluded it to be a transition induced by acoustic coupling since the signal intensity did not tend to zero when the magnetic field was parallel to the crystal anisotropy axis. Furthermore, this tells us that the coupling is due to a modulation of the E zero-field splitting parameter rather than D. We investigated the dependence on microwave power and found the saturation limit. We performed a measurement of Fe3+:LN as well to reassure ourselves that the resonance is not magnetically excited by the field around the IDT.
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Hou, Hangtian. "Low-dimensional electron transport and surface acoustic waves in GaAs and ZnO heterostructures." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288235.
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A surface acoustic wave (SAW) is a combination of a mechanical wave and a potential wave propagating on the surface of a piezoelectric substrate at the speed of sound. Such waves are widely applied in not only the communication industry, but also in quantum physics research, such as nanoelectronics, spintronics, quantum optics, and even quantum information processing. Here, I focus on low-dimensional electron transport and SAWs in GaAs and ZnO semiconductor heterostructures. The ability to pattern quantum nanostructures using gates has stimulated intense interest in research into mesoscopic physics. We have performed a series of simulations of gate structures, and having with the optimised boundary conditions and we find them to match experimental results, such as the pinch-off voltage of one-dimensional channels and SAW charge transport in induced n-i-n and n-i-p junctions. Using the improved boundary conditions, it is straightforward to model quantum devices quite accurately using standard software. With the calculated potential, we have modelled the process how a dynamic quantum dot is driven by a SAW and have analysed error mechanisms in SAW-driven quantisation (I=Nef, where N is the number of electrons in each SAW minimum, and f is the SAW resonant frequency). From energy spectroscopy measurements, we probe the electron energy inside a SAW-driven dynamic quantum dot and find that the small addition energy, which is around 3meV, is the main limitation for the SAW quantisation. To increase the confinement of SAW-driven quantum dots, we deposit a thin ZnO film, with a better piezoelectric coupling than GaAs, on a GaAs/AlGaAs heterostructure using high-target-utilisation sputtering (an Al2O3 buffer layer is deposited to protect the 2DEG during sputtering). With the ZnO, the SAW amplitude is greatly improved to 100 meV and the RF power required for pumping electrons using a SAW is greatly reduced. Finally, we have studied low-dimensional electron transport in a MgZnO/ZnO heterostructure. We have developed a technique for patterning gates using a parylene insulator, and used these to create one-dimensional quantum wires and observe electron ballistic transport with conductance quantised in units of 2e2/h The increasing electron effective mass as the 1D electron density decreases indicate that the electron-electron interaction in this MgZnO/ZnO heterostructure is strong. Because of these strong interactions, the 0.7 anomaly is observed just below each quantised plateau, and are much stronger than in GaAs quantum wires. Furthermore, we have also calculated the SAW-modulated spontaneous and piezoelectric polarisation in the ZnO heterostructure, and have observed a sign of this SAW-modulation in 2DEG density, which is different from the classical SAW-pumping mechanism. Our results show that a ZnO heterostructure should provide a good alternative to conventional III-V semiconductors for spintronics and quantum computing as they have less nuclear spins. This paves the way for the development of qubits benefiting from the low scattering of an undoped heterostructure together with potentially long spin lifetimes.