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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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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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3
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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4
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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5
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.
Testo completoAbstract (sommario):
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.
6
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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7
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/.
Testo completoAbstract (sommario):
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.
8
Buchine, Brent Alan. "Acoustics in nanotechnology: manipulation, device application and modeling". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26542.
Testo completoAbstract (sommario):
Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Wang, Zhong Lin; Committee Member: Degertekin, F. Levent; Committee Member: Liu, Meilin; Committee Member: Snyder, Robert L.; Committee Member: Tannenbaum, Rina. Part of the SMARTech Electronic Thesis and Dissertation Collection.
9
Yang, Jie. "Spatial Coherence in a Shallow Water Waveguide". Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14624.
Testo completoAbstract (sommario):
In shallow water environments, sound propagation experiences multiple interactions with the surface/bottom interfaces, with hydrodynamic disturbances such as internal waves, and with tides and fronts. It is thus very difficult to make satisfactory predictions of sound propagation in shallow water. Given that many of the ocean characteristics can be modeled as stochastic processes, the statistical measure, spatial coherence, is consequently an important quantity. Spatial coherence provides valuable information for array performance predictions. However, for the case of long-range, low frequency propagation, studies of spatial coherence influenced by various environmental parameters are limited insofar as having the appropriate environmental data with which to model and interpret the results.
The comprehensive Asian Seas International Experiment 2001 (ASIAEX01) examined acoustic propagation and scattering in shallow water. Environmental oceanographic data were taken simultaneously with the acoustic data. ASIAEX01 provided a unique data set which enabled separate study of the characteristics of the oceanographic features and their influence on long range sound propagation. In this thesis, the environmental descriptors considered include sediment sound speed and attenuation, background internal waves, episodic non-linear internal waves, and air-sea interface conditions. Using this environmental data, the acoustic data are analyzed to show the characteristics of spatial coherence in a shallow water waveguide. It is shown that spatial coherence can be used as an inversion parameter to extract geoacoustic information for the seabed. Environmental phenomena including internal waves and wind-generated surface waves are also studied. The spatial and temporal variations in the sound field induced by them are presented. In addition, a tank experiment is presented which simulates propagation in a shallow water waveguide over a short range. Based on the data model comparison results, the model proposed here is effective in addressing the major environmental effects on sound propagation in shallow water.
10
Poznic, Milan. "Nonlinear Interaction Between Ultrasonic Waves and Cracks and Interfaces". Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4604.
Testo completoAbstract (sommario):
The subject of this thesis is the development of new ultrasound inspection techniques for detection of cracks that are smaller than the wavelength of the inspecting wave and the characterization of cracks in fluid-filled pipes as either surface-breaking or subsurface. The spectrum of the scattered field of a partially closed crack comprises harmonic components not expected to be found in the case of linear scatterers such as pores or inclusions. Paper A presents an experimental investigation into the linear reflection and generation of the 2nd harmonic component following the incidence of an ultrasonic wave onto a dry or water-confining interface formed by elasto-plastic steel-steel surfaces in contact. The results indicate that water has an unexpected effect on the reflection, at low interfacial pressures, suggesting that fluid mediated forces play a role not accounted for in current models. The level of the generation of the 2nd harmonic measured provides support for further development of the technique for detection of dry, partially closed cracks or fluid-filled, nearly open cracks. A theoretical model describing the nonlinear scattering of acoustic waves by surface-breaking cracks with faces in partial contact is presented in Paper B. Both linear and nonlinear response of the crack are shown to be the largest for a SV wave incident on the surface containing the crack at an angle just above the critical angle for longitudinal waves. A method which provides information on whether a fracture is surface-breaking or subsurface has been modelled and its optimal experimental set-up examined in Paper C. The main assumption of the model is that water carried by pressurized pipes infiltrates and fills a surface-breaking crack, while a subsurface crack is dry. The model simulates an inspection in which the modulation technique is employed and the surface hosting the crack is not accessible. A parameter, constructed with signals recorded in backscattering configuration during a modulation cycle, is examined and shown to provide a clear criterion to distinguish subsurface from surface-breaking cracks when a SV wave at 45 degree incidence is employed as a probe. Finally, in Paper D the modulation technique is experimentally tested on steel beams that host surface-breaking fatigue cracks. The method is shown to be a successful tool to distinguish a dry from a fluid-filled crack. Furthermore, it is revealed that the dynamics of the fluid needs to be accounted for in a more accurate simulation tool.QC 20100906
11
Blimbaum, Jordan Matthew. "Finite element analysis of acoustic wave transverse to longitudinal coupling during transverse combustion instability". Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44757.
Testo completoAbstract (sommario):
Velocity-coupled combustion instability is a major issue facing lean combustor design in modern gas turbine applications. In this study, we analyze the complex acoustic field excited by a transverse acoustic mode in an annular combustor. This work is motivated by the need to understand the various velocity disturbance mechanisms present in the flame region during a transverse instability event. Recent simulation and experimental studies have shown that much of the flame response during these transverse instabilities may be due to the longitudinal motion induced by the fluctuating pressure field above the nozzles. This transverse to longitudinal coupling has been discussed in previous work, but in this work it is given a robust acoustic treatment via computational methods in order to verify the mechanisms by which these two motions couple.
We will provide an in-depth discussion of this coupling mechanism and propose a parameter, Rz, also referred to as the Impedance Ratio, in order to compare the pressure/velocity relationship at the nozzle outlet to quasi one-dimensional theoretical acoustic approximations. A three-dimensional inviscid simulation was developed to simulate transversely propagating acoustic pressure waves, based on an earlier experiment designed to measure these effects. Modifications to this geometry have been made to account for lack of viscosity in the pure acoustic simulation and are discussed.
Results from this study show that transverse acoustic pressure excites significant axial motion in and around the nozzle over a large range of frequencies. Furthermore, the development of Rz offers a defined physical parameter through which to reference this important velocity-coupled instability mechanism. Therefore, this study offers an in-depth and quantifiable understanding of the instability mechanism caused by transversely propagating acoustic waves across a combustor inlet, which can be applied to greatly improve annular combustor design in future low-emissions gas turbine engines.
12
Padilla, Scott T. "Novel Transducer Calibration and Simulation Verification of Polydimethylsiloxane (PDMS) Channels on Acoustic Microfluidic Devices". Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6922.
Testo completoAbstract (sommario):
The work and results presented in this dissertation concern two complimentary studies that are rooted in surface acoustic waves and transducer study.
Surface acoustic wave devices are utilized in a variety of fields that span biomedical applications to radio wave transmitters and receivers. Of interest in this dissertation is the study of surface acoustic wave interaction with polydimethylsiloxane. This material, commonly known as PDMS, is widely used in the microfluidic field applications in order to create channels for fluid flow on the surface of a piezoelectric substrate. The size, and type of PDMS that is created and ultimately etched on the surface of the substrate, plays a significant role in its operation, chiefly in the insertion loss levels experienced. Here, through finite element analysis, via ANSYS® 15 Finite Element Modeling software, the insertion loss levels of varying PDMS sidewall channel dimensions, from two to eight millimeters is investigated. The simulation is modeled after previously published experimental data, and the results demonstrate a clear increase in insertion loss levels with an increase in channel sidewall dimensions. Analysis of the results further show that due to the viscoelastic nature of PDMS, there is a non -linear increase of insertion loss as the sidewall dimensions thicken. There is a calculated variation of 8.31 decibels between the insertion loss created in a microfluidic device with a PDMS channel sidewall thickness of eight millimeters verse a thickness of two millimeters. Finally, examination of the results show that insertion loss levels in a device are optimized when the PDMS sidewall channels are between two and four millimeters.
The second portion of this dissertation concerns the calibration of an ultrasonic transducer. This work is inspired by the need to properly quantify the signal generated by an ultrasonic transducer, placed under a static loading condition, that will be used in measuring ultrasonic bone conducted frequency perception of human subjects. Ultrasonic perception, classified as perception beyond the typical hearing limit of approximately 20 kHz, is a subject of great interest in audiology. Among other reasons, ultrasonic signal perception in humans is of interest because the mechanism by which either the brain or the ear interprets these signals is not entirely understood. Previous studies have utilized ultrasonic transducers in order to study this ultrasonic perception; however, the calibration methods taken, were either incomplete or did not properly account for the operation conditions of the transducers. A novel transducer calibration method is detailed in this dissertation that resolves this issue and provides a reliable means by which the signal that is being created can be compared to the perception of human subjects.
13
Bozhko, Andrii. "Physical Boundary as a Source of Anomalies in Transport Processes in Acoustics and Electrodynamics". Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1404590/.
Testo completoAbstract (sommario):
Various anomalous effects that emerge when the interfaces between media are involved in sound-matter or light-matter interactions are studied. The three specific systems examined are a fluid channel between elastic metal plates, a linear chain of metallic perforated cylindrical shells in air, and a metal-dielectric slab with the interfaces treated as finite regions of smoothly changing material properties. The scattering of acoustic signals on the first two is predicted to be accompanied by the effects of redirection and splitting of sound. In the third system, which supports the propagation of surface plasmons, it is discovered that the transition region introduces a nonradiative decay mechanism which adds to the plasmon dissipation. The analytical results are supported with numerical simulations. The outlined phenomena provide the ideas and implications for applications involving manipulation of sound or excitation of surface plasmons.
14
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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Parpiiev, Tymur. "Ultrafast magneto-acoustics in magnetostrictive materials". Thesis, Le Mans, 2017. http://www.theses.fr/2017LEMA1044/document.
Testo completoAbstract (sommario):
Avec l’avènement du laser femtoseconde il est devenu possible de mesurer comment la démagnétisation femtoseconde peut permettre de sonder l’interaction d’échange dans les métaux ferromagnétiques. La démagnétisation induite par laser d’un matériau avec un fort couplage magnéto-élastique amène à la relaxation des contraintes mécaniques, générant ainsi des ondes acoustiques longitudinales (L) et transversales (T). Dans ce travail de thèse, la génération d’impulsions acoustiques picosecondes T par le mécanisme de démagnétostriction dans des matériaux fortement magnétostrictifs est traitée analytiquement et montrée expérimentalement dans le cas d’un alliage de Terfenol. En premier lieu, nous avons développé un modèle phénoménologique de magnétostriction directe dans un film monocristallin de Terfenol. Les expériences pompe-sonde linéaire MOKE résolues en temps montrent que la relaxation transitoire des contraintes magnéto-élastiques du film amène à l’excitation d’ondes GHz acoustiques L at T. Ces résultats sont la première observation expérimentale de l’excitation d’ondes acoustiques transversales picoseconde par mécanisme de démagnétostriction induit par laser. En second lieu, nous avons analysé le processus d’interaction d’ondes acoustiques L avec l’aimantation d’un film mince de Terfenol. L’onde acoustique picoseconde produit un changement de magnétisation du film et induit la conversion de modes acoustiques. C’est une autre voie de génération d’ondes acoustiques T que nous avons mis en évidence. La gamme de fréquence des impulsions générées est liée à l’échelle de temps de démagnétisation, qui corresponds à quelques centaines de GHz - 1 THzWith the advent of femtosecond lasers it became possible to measure how femtosecond optical demagnetization can probe the exchange interaction in ferromagnetic metals. Laser-induced demagnetization of materials with strong magneto-elastic coupling should lead to the release of its build-in strains, thus to the generation of both longitudinal (L) and shear (S) acoustic waves. In this thesis, generation of shear picosecond acoustic pulses in strongly magnetostrictive materials such as Terfenol is processed analytically and shown experimentally. In case of Terfenol with strong magneto-crystalline anisotropy, laser induced demagnetostriction is responsible for S excitation. First, the phenomenological model of direct magnetostriction in a Terfenol monocrystalline film is developed. The shear strain generation efficiency strongly depends on the orientation of the film magnetization. Time-resolved linear MOKE pump-probe experiments show that transient laser-induced release of the magnetoelastic strains lead to the excitation of GHz L and S acoustic waves. These results are the first experimental observation of picosecond shear acoustic wave excitation by laser-induced demagnetostriction mechanism. Second, the interaction of an optically generated L acoustic pulse with the magnetization of a Terfenol thin film is reported. Arrival of the picosecond strain wave alters a change of its magnetization and leads to acoustic mode conversion, which is another pathway of shear acoustic wave generation. The frequency bandwidth of the generated acoustic pulses matches the demagnetization timescale and lies in the range of several hundreds of GHz, close to 1 THz
16
Martinez, Garcia Jairo Andres. "A Novel Ultrasonic Method to Quantify Bolt Tension". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4145.
Testo completoAbstract (sommario):
The threaded fasteners are one of the most versatile methods for assembly of structural components. For example, in bridges large bolts are used to fix base columns and small bolts are used to support access ladders. Naturally not all bolts are critical for the operation of the structure. Fasteners loaded with small forces and present in large quantities do not receive the same treatment as the critical bolts. Typical maintenance operations such tension measurements, internal stress checking or monitoring of crack development are not practical due to cost and time constrains. Although failure of a single non-critical fastener is not a significant threat to the structure's stability, massive malfunction may cause structural problem such as insufficient stiffness or excessive vibrations.
The health of bolted joints is defined by a single parameter: the clamping force (CF). The CF is the force that holds the elements of the joint together. If the CF is too low, separation and bolt fatigue may occur. On the other hand, excessive CF may produce damages in the structural members such as excessive distortion or breakage. The CF is generated by the superposition of the individual tension of the bolts. The bolt tension, also referred as bolt preload, is the actual force that is stretching the bolt body. Maintaining the appropriate tension in bolts ensures a proper CF and hence a good health of the joint.
In this thesis, a novel methodology for estimating the tension in bolts using surface acoustic waves (SAWs) is investigated. The tension is estimated by using the reflection of SAWs created by the bolt head interference. Increments in the bolt tension raise the points of interaction between the waves and the bolt head (real area of contact), and hence the position of the reflective boundaries. The variations are estimated using the "conventional linear synthetic array" imaging technique. A singular transducer is actuated from predefined positions to produce an array of signals that are subsequently arranged and added to construct an acoustic image.
Three sets of experiment are presented in this research for validating the proposed concept: tension estimation of a ¼ inch stainless steel bolt, a ½ inch stainless steel bolt and ¼ inch grade 8 bolt. Acoustic images of the surface of the clamped plate illustrate a clear trend in the position of the reflective boundary when torque is changed. In all cases, the torque increments increase the real area of contact and therefore the position of the reflective boundary. As expected, the real area of contact grew from the bolt head center to the perimeter, which causes an effect of apparent movement of the boundary. This research proves the potential of the ultrasonic imaging methodology to measure applied tension. The result showed that the system can be used to successfully inspect tension in bolts of ½ and ¼ inches. The methodology investigated in this thesis is the first steps towards the development of bolt tension sensor based on surface acoustic waves.
17
Partan, James Willard. "Analysis of acoustic communication channel characterization data in the surf zone". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/86872.
Testo completoAbstract (sommario):
Thesis (S.M. in Electrical Engineering)--Joint Program in Oceanography and Oceanographic Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2000.Includes bibliographical references (leaves 64-65).
by James Willard Partan.
S.M.in Electrical Engineering
18
Tan, Lin. "Development of micro-acoustic devices with applications of viscous effects". Diss., Online access via UMI:, 2006.
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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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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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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.
Testo completoAbstract (sommario):
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.
22
Sen, Rahul. "Acoustic scattering by discontinuities in waveguides". Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/81021.
Testo completoAbstract (sommario):
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.
23
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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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.
Testo completoAbstract (sommario):
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.
25
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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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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Damani, Shishir. "Excitation of Acoustic Surface Waves by Turbulence". Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/104742.
Testo completoAbstract (sommario):
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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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.
Testo completoAbstract (sommario):
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.
29
Ash, Benjamin James. "Locally resonant metamaterial for surface acoustic waves". Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34380.
Testo completoAbstract (sommario):
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.
30
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.
Testo completoAbstract (sommario):
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.
31
Pendergraft, Karen Anne. "Frequency dependent acoustic transmission in nonuniform materials". Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43265.
Testo completoAbstract (sommario):
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
32
Hong, Stanley Seokjong 1977. "Surface acoustic wave optical modulation". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86715.
Testo completoAbstract (sommario):
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (leaves 50-54).
by Stanley Seokjong Hong.
M.Eng.
33
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.
Testo completo
34
Oudich, Mourad. "Contribution à l'étude des cristaux phononiques à résonance locale dans les régimes sonique et hypersonique : approches théorique et expérimentale". Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10065/document.
Testo completoAbstract (sommario):
Dans le cadre de cette thèse, nous nous sommes intéressés d'abord au mécanisme de résonance locale en développant différents modèles théoriques pour l'étude de nouveaux cristaux phononiques à résonance locale (CPRL) en plaque dont l'élément principal et l'élastomère (silicone rubber). Le mode opératoire de ce mécanisme a été étudié et les ouvertures des bandes interdites ont été interprétées théoriquement ainsi que les phénomènes physiques mis en jeu. La mise en évidence expérimentale de la bande interdite a été réalisée par la fabrication et la caractérisation de structures CPRL et une parfaite concordance a été constatée entre les résultats théoriques et expérimentaux. Une étude des phénomènes de guidage a permis par ailleurs de montrer la possibilité du confinement et de la transmission d'un seul mode élastique au niveau d'un CPRL. Dans un second temps, nous avons montré que les propriétés d'un CPRL peuvent être reproduites dans le régime hypersonique. En effet, par le biais de la mise en place d'un nouveau modèle théorique et en proposant un nouveau CPRL à ondes de surface à base de films de diamant, nous avons pu montrer que ce type de cristal peut faire l'objet d'applications potentielles à des fins de guidage et de démultiplexage et ainsi initier la conception de nouveaux dispositifs miniaturisés à ondes de surface destinés aux systèmes de télécommunications (>GHz)In this PhD work, we focused our interest on the theoretical and experimental study of locally resonant phononic crystals (LRPC) operating in sonic and hypersonic regimes. We first developed numerical models to understand the dispersion behaviour of elastic waves in those plate-type LRPC in which the silicone rubber plays a key role. We showed that with such structure, we can understand clearly how the local resonance (LR) mechanism operates to give rise to opening of low frequency BG two orders of magnitude that the one allowed by Bragg diffusion. The physics behind such structures was also figured out by means of theoretical models. An experimental study was then undertaken by manufacturing a new LRPC plate which has been characterized in terms of elastic behaviour and BG investigation. A perfect concordance was demonstrated between the theoretical an experimental results by evidencing a 2kHz BG opening using a 6mm diameter rubber stub and 1cm periodicity. In addition, waveguiding phenomena was investigated in those structures and showed the possibility of guiding of only one defect mode unlike conventional PCs in which many defects modes are generated. A second part of this study was dealt with LR mechanism in hypersonic regime. Using a new numerical and theoretical approach, we were able to show the BG opening and waveguiding for surface acoustic waves (SAW) in a LRPC composed of metallic stubs arranged on a diamond semi-infinite substrate. The added value of LR in such frequency regime remains in its ability to select only one guided mode due to the longer involved wavelengths. Such structures can then be suitable for filtering and demultiplexing applications
35
Naseer, Shahid Mohammad. "Shaping surface acoustic waves for cardiac tissue engineering". Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7740/.
Testo completoAbstract (sommario):
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.
36
Lin, Yiqiang Farouk Bakhtier. "Acoustic wave induced convection and transport in gases under normal and micro-gravity conditions /". Philadelphia, Pa. : Drexel University, 2007. http://hdl.handle.net/1860/1795.
Testo completo
37
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.
Testo completo
38
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.
Testo completoAbstract (sommario):
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.
39
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.
Testo completoAbstract (sommario):
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.
40
Hay, Robert Russell. "Digitally-tunable surface acoustic wave resonator". [Boise, Idaho] : Boise State University, 2009. http://scholarworks.boisestate.edu/td/58/.
Testo completo
41
McNeil, Robert Peter Gordon. "Surface acoustic wave quantum electronic devices". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610718.
Testo completo
42
Kaplan, Emrah. "Surface acoustic wave enhanced electroanalytical sensors". Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6557/.
Testo completoAbstract (sommario):
In the last decade, miniaturised “lab-on-a-chip” (LOC) devices have attracted significant interest in academia and industry. LOC sensors for electrochemical analysis now commonly reach picomolar in sensitivities, using only microliter-sized samples. One of the major drawbacks of this platform is the diffusion layer that appears as a limiting factor for the sensitivity level. In this thesis, a new technique was developed to enhance the sensitivity of electroanalytical sensors by increasing the mass transfer in the medium. The final device design was to be used for early detection of cancer diseases which causes bleeding in the digestive system. The diagnostic device was proposed to give reliable and repeatable results by additional modifications on its design. The sensitivity enhanced-sensor model was achieved by combining the surface acoustic wave (SAW) technology with the electroanalytical sensing platform. The technique was practically tested on a diagnostic device model and a biosensing platform. A novel, substrate (TMB) based label-free Hb sensing method is developed and tested. Moreover, the technique was further developed by changing the sensing process. Instead of forming the sensitive layer on the electrodes it was localised on polystyrene wells by a rapid one-step process. Results showed that the use of acoustic streaming, generated by SAW, increases the current flow and improves the sensitivity of amperometric sensors by a factor of 6 while only requiring microliter scale sample volumes. The heating and streaming induced by the SAW removes the small random contributions made by the natural convection and temperature variation which complicate the measurements. Therefore, the method offers stabilised conditions for more reliable and repeatable measurements. The label-free detection technique proved to be giving relevant data, according to the hemoglobin concentration. It has fewer steps than ELISA and has only one antibody. Therefore, it is quick and the cross-reactivity of the second antibody is eliminated from the system. The additional modifications made on the technique decreased the time to prepare the sensing platform because the passivation steps (i.e., pegylation), prior to structuring a sensitive layer were ignored. This avoidance also increased the reliability and repeatability of the measurements.
43
Millo, Florian. "Coupling of spin waves with surface acoustic waves for high frequency devices". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST156.
Testo completoAbstract (sommario):
Les appareils de radiofréquence (RF) jouent un rôle important dans notre vie quotidienne. Ces appareils utilisent les ondes acoustiques de surface (SAW) - ondes acoustiques se déplaçant à la surface d'un solide déformé - pour effectuer des opérations complexes de filtrage des signaux, de détection, et de circuits hyperfréquences. Pour fonctionner à des fréquences supérieures à 3,7 GHz, les dispositifs SAW doivent surmonter deux limitations : 1) l'absence d'accordabilité du dispositif et 2) l'absence de SAW non réciproques. L'hypothèse centrale de cette thèse conciste à surmonter ces limitations : Le couplage des ondes acoustiques de surface (SAW) avec les ondes de spin (SW) peut être un moyen de surmonter l'absence d'accordabilité et de non-réciprocité dans les dispositifs SAW correctement conçus. Les SW sont des excitations magnétiques qui présentent une propagation anisotrope et une non réciprocité. Dans ce manuscrit, nous étudions l'interaction SAW-SW dans des hétérostructures composées de films de CoFeB déposés sur le substrat piézoélectrique de pointe LiNbO₃ pour des dispositifs SAW à haute fréquence. Nous donnons une brève introduction à la physique micromagnétique et élastomagnétique, y compris la description de deux mécanismes, magnétoélastique et magnétorotation, que nous mettons en œuvre pour comprendre l'interaction SAW-SW. Dans l'hétérostructure CoFeB / LiNbO₃, nous avons mis en évidence une symétrie d'ordre 2 du couplage SAW-SW différente de celle de la littérature d'une symétrie d'ordre 4. Nous avons ajusté les résultats expérimentaux en calculant la puissance absorbée dans le film magnétique. Nous en avons déduit que cette symétrie d'ordre 2 pouvait s'expliquer par l'anisotropie uniaxiale du film magnétique. Nous avons également étudié les SW dans des systèmes à fort contraste d'aimantation tels que les antiferromagnétiques synthétiques (SAF). Dans les SAF, certaines orientations de propagation des SW leur permettent d'être fortement non-réciproques et induisent en outre un flux d'énergie unidirectionnel dans le système. Nous avons fourni des mesures magnéto-optiques et électriques, mais aussi des simulations théoriques et micromagnétiques pour comprendre mieux les dynamiques de SW dans le SAF. Enfin, nous donnons des perspectives pour la prochaine génération de dispositifs SAW en exploitant les formalismes présentés dans ce manuscritRadio-frequency (RF) devices play an important role in our everyday life. RF devices use surface acoustic waves (SAW) -- acoustic waves traveling on the surface of a deformed solid -- to perform complex signal filtering operations, sensing, and microwave circuitry. To operate at higher frequencies than 3.7 GHz, SAW devices must overcome two limitations: 1) the absence of device tunability and 2) the absence of non-reciprocal SAWs. Overcoming these limitations comprises this thesis's central hypothesis: Coupling surface acoustic waves (SAW) with spin waves (SW) may be a route to overcome the absence of tunability and non-reciprocity in properly designed SAW devices. SWs are elementary magnetic excitations exhibiting anisotropic propagation and non-reciprocity. In this manuscript, we study the SAW-SW coupling in heterostructures comprised of CoFeB films deposited on top of the state-of-art piezoelectric substrate LiNbO₃ for high frequency SAW devices. We give a brief introduction of micromagnetic and elastomagnetic physics, including the description of two mechanisms, magnetoelastic and magnetorotation, that we implement to understand the SAW-SW interaction. In the heterostructure CoFeB / LiNbO₃ we evidenced a 2-fold symmetry of SAW-SW coupling different from the 4-fold symmetry given in literature. We fit experimental results by calculating the absorbed power in the magnetic film. We deduced that a posible reason to this 2-fold symmetry is the uniaxial anisotropy within the magnetic film. We investigated also SWs in systems with high magnetization contrast such as synthetic antiferromagnets (SAF). In SAF, certain propagation orientations of SWs allowed them to be highly non-reciprocal and furthemore inducing a unidirectional flow of energy in the system. We provide magneto-optical, electrical measurements but also theoretical and micromagnetic simulation to understand the SW dynamics in SAF. Last but not least, we give perspectives for the next generation of SAW devices exploiting the results gven in this manuscript
44
Kenny, Thomas Donald. "Identification of High-Velocity Pseudo-surface Acoustic Wave Substrate Orientations and Modeling of Surface Acoustic Wave Structures". Fogler Library, University of Maine, 2011. http://www.library.umaine.edu/theses/pdf/KennyT2011.pdf.
Testo completo
45
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.
Testo completo
46
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.
Testo completo
47
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.
Testo completo
48
Gizeli, Electra. "New acoustic wave sensor geometries". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282004.
Testo completo
49
Thorn, Adam Leslie. "Electron dynamics in surface acoustic wave devices". Thesis, University of Cambridge, 2009. https://www.repository.cam.ac.uk/handle/1810/224176.
Testo completoAbstract (sommario):
Gallium arsenide is piezoelectric, so it is possible to generate coupled mechanical and electrical surface acoustic waves (SAWs) by applying a high-frequency voltage to a transducer on the surface of GaAs. By combining SAWs with existing low-dimensional nanostructures one can create a series of dynamic quantum dots corresponding to the minima of the travelling electric wave, and each dot carries a single electron at the SAW velocity (~ 2800 m/s). These devices may be of use in developing future quantum information processors, and also offer an ideal environment for probing the quantum mechanical behaviour of single electrons. This thesis describes a numerical and theoretical study of the dynamics ofan electron in a range of geometries. The numerical techniques for solving thetime-dependent Schrödinger equation with an arbitrary time-dependent potential will be described in Chapter 2, and then applied in Chapter 3 to calculate the transmission of an electron through an Aharonov-Bohm (AB) ring. It will be seen that an important property of the techniques used in this thesis is that they can be easily adapted to study realistic geometries, and we will see features in the AB oscillations which do not arise in simplified analytic descriptions. In Chapter 4, we will then study a device consisting of two parallel SAW channels separated by a controllable tunnelling barrier. We will use numerical simulations to investigate the effect of electric and magnetic fields upon the electron dynamics, and develop an analytic model to explain the simulation results. From the model, it will be apparent that it is possible to use this device to rotatethe state of the electron to an arbitrary superposition of the first two eigenstates. We then introduce coherent and squeezed states in Chapter 5, which are ex-cited states of the quantum harmonic oscillator. Coherent and squeezed electronicstates may be of use in quantum information processing, and could also arise dueto unwanted perturbations in a SAW device. We will discuss how these statescan be controllably generated in a SAW device, and also discuss how they couldthen be detected. In Chapter 6 we describe how to use the motion of a SAW to create a rapidly-changing potential in the frame of the electron, leading to a nonadiabatic excita-tion. The nonadiabatically-excited state oscillates from side to side within a 1Dchannel on a few-picosecond timescale, and this motion can be probed by placing a tunnelling barrier at one side of the channel. Numerical simulations will beperformed to show how this motion can be controlled, and the simulation resultswill be seen to be in good agreement with recent experimental work performed by colleagues. Finally, we will show that this device can be used to measure the initial state of an electron which is an arbitrary superposition of the first twoeigenstates.
50
Astley, Michael Robert. "Surface-acoustic-wave-defined dynamic quantum dots". Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/261973.
Testo completoAbstract (sommario):
The strain associated with a surface acoustic wave (SAW) propagating across a piezoelectric medium creates a travelling electric potential. Gallium Arsenide is such a piezoelectric material, and so SAWs can be used with existing semiconductor technologies for creating complex low-dimensional nanostructures. A SAW travelling along an empty quasi-one-dimensional channel creates a series of dynamic quantum dots which can transport electrons at the SAW velocity (∼ 2800 ms−1 ), allowing high-frequency operations to be carried out on the electron without the need for fast pulsed-gate techniques. Such dynamic quantum dot devices can provide valuable insights into fundamental physical phenomena and could have technological applications in quantum information processing. This thesis details investigations into SAW-defined dynamic quantum dot devices. Chapter 1 introduces the scientific background to the experiments described in this thesis; Chapter 2 provides details of the processing and measurement techniques used to perform these experiments. Chapter 3 consists of a study into the effect that reflections have on the acousto-electric current generated in a SAW channel. Reflections create a modulation to the channel entrance potential which is critical in determining the magnitude of the acousto-electric current. As the frequency of the SAW is varied, a particular reflection creates a periodic interference with the main SAW driving the current which can be observed in the Fourier transform of the acousto-electric current’s frequency dependence. The period of these oscillations is directly related to the distance which the reflection has travelled relative to the main SAW, which allows the principle reflection mechanisms to be characterised. Reflections persisted on a SAW device for large amounts of time, giving rise to much of the “noise” seen in the frequency dependence, and the pattern of reflections was found to be chaotic. Chapters 4-8 show the results obtained with a device where two SAW channels were linked by a tunnel barrier. This device allowed quantum mechanical tunnelling of electrons from the dynamic quantum dots to be observed over a subnanosecond timescale. Chapter 5 describes how the escape rates of the electrons from dynamic quantum dots can be measured using a rate equation analysis, and these rates are fit to a simple tunnelling model to derive the addition energies of the dynamic quantum dots. In Chapter 6 the tunnelling current was found to contain low-visibility oscillations, which cannot be explained by simple models. It is thought that these oscillations are caused by the non-adiabatic time-evolution of the electron wave function when the tunnel barrier is lowered suddenly. Chapter 7 shows how a crosstalk current through a short constriction is sensitive to local potential changes in an analogous manner to a quantum point contact, and how this effect can be used to detect the occupation of dynamic quantum dots in a nearby SAW channel. Chapter 8 collects some minor observations which have been made whilst studying the tunnel barrier device. In Chapter 9 I present the conclusions of the experiments presented in this thesis, and provide some ideas for future directions this work may take.