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Design of an acoustic device to measure platelet adherence and aggregationHurley, Bridget Anne 08 1900 (has links)
No description available.
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An ultrasonic image-forming system for ionospheric studies / by N.E HolmesHolmes, Nigel Eric January 1974 (has links)
v, 137 p. : ill., plates ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1974
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An ultrasonic image-forming system for ionospheric studies /Holmes, Nigel Eric. January 1974 (has links) (PDF)
Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics, 1974.
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An investigation into the development of a portable, ultrasonic, density measuring instrumentHulse, Nigel Douglas January 1987 (has links)
Dissertation submitted in compliance with the requirements for the Master's Diploma in Technology: Electrical Engineering (Light Current), Technikon Natal, 1987. / In the gold mining industry, one of the significant physical
properties of the mineral slurry is its density and it is
important to be able to measure this parameter in most
processes.
There are many techniques for determining the density of
fluids, but because of the hostile, abrasive nature of
mineral slurry, very few of these are suitable,
This dissertation describes the deveiopment, construction
and testing of a portable, ultrasonic, density measuring
instrument. The instrument uses an ultrasonic transducer as
the primary measuring element, and system operation is based
on the fact that the driving impedance of the transducer
varies with changes in the physical properties, and hence
the characteristic impedance, of the surrounding medium into
which the ultrasonic energy is being transferred.
The technique may a-Lao be used to measure the relative
concentrations of two liquids in a mixture or emulsion,
provided that the characteristic impedances of the liquids
are sufficiently dissimilar. The electronic circuitry is
fairly straightforward, consisting essentially of an oscillator,
driving circuit for the transducer and a voltage
monitor to provide a d.c. voltage proportional to the
impedance of the transducer, and hence to the density of the
surrounding medium. Most of the research has been concentrated
on the probe design, as the type of transducer, the
type and thickness of facing material and the method of
construction all contribute to the sensitivity of the
instrument. A design of probe assembly has been developed
that may be used for both slurry density measurement and the
measurement of the ratio of aqueous to organic liquids in
emulsion. / M
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Ultrasonic fields in fluids: theoretical prediction using difference equations and three dimensional measurement using optical techniquesDockery, George Daniel January 1983 (has links)
M. S.
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Ultrasonic fields in fluids: theoretical prediction using difference equations and three dimensional measurement using optical techniquesDockery, George Daniel January 1983 (has links)
A technique for calculating bulk ultrasonic fields which uses implicit difference equations to evaluate the parabolic approximation to the Helmholtz equation is described. The parabolic approximation assumes that the field varies much faster in the transverse directions than in the direction of propagation and results in a partial differential equation which is formulated as a pure i initial value problem . Finite difference equation descriptions are derived for one-dimensional, cylindrically symmetric problems and for more general two-dimensional problems. A Fourier stability analysis is performed on the simpler numerical scheme to determine acceptable values for parameters such as the grid spacing and increment step sizes. Several example calculations for each geometry are presented to demonstrate the usefulness of this parabolic-difference equation technique in transducer modeling. Included in these examples are gaussian, rectangular, circular, and concentric ring amplitude distributions, as well as uniform and focused phase distributions. In many cases, qualitative agreement between the numerical results and analytic diffraction theory predictions can be observed.
An experimental system is developed for the detection of acoustic fields in water using a dual beam differential interferometer which is scanned through a large tank. The output from this system is proportional to the average difference in refractive index sampled by the two beams and is effectively integrated along the path of the beams through the specimen. An algorithm is presented which reconstructs a radial profile of the measured field from the integrated data assuming cylindrical symmetry. Raw, averaged, and reconstructed data is given for scans taken in the far-field of a circular, uniform transducer. / M.S.
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Pulsed ultrasonic doppler velocimetry for measurement of velocity profiles in small channels and capplilariesMesser, Matthias 07 September 2005 (has links)
Pulsed ultrasound Doppler velocimetry proved to be capable of measuring velocities accurately (relative error less than 0.5 percent). In this research, the limitations of the method are investigated when measuring:
in channels with a small thickness compared to the transducer diameter,
at low velocities
and in the presence of a flow reversal area.
A review of the fundamentals of pulsed ultrasound Doppler velocimetry reveals that the accuracy of the measured velocity field mainly depends on the shape of the acoustic beam through the flow field and the intensity of the echo from the incident particles where the velocity is being measured. The ultrasonic transducer turned out to be most critical component of the system. Fundamental limitations of the method are identified.
With ultrasonic beam measurements, the beam shape and echo intensity is further investigated. In general, the shape of the ultrasonic beam varies depending on the frequency and diameter of the emitter as well as the characteristics of the acoustic interface that the beam encounters. Moreover, the most promising transducer to measure velocity profiles in small channels is identified. Since the application of pulsed ultrasound Doppler velocimetry often involves the propagation of the ultrasonic burst through Plexiglas, the effect of Plexiglas walls on the measured velocity profile is analyzed and quantified in detail. The transducers ringing effect and the saturation region caused by highly absorbing acoustic interfaces are identified as limitations of the method.
By comparing measurement results in the small rectangular channel to numerically calculated results, further limitations of the method are identified. It was not possible to determine velocities correctly throughout the whole channel at low flow rates, in small geometries and in the flow separation region. A discrepancy between the maximum measured velocity, velocity profile perturbations and incorrect velocity determination at the far channel wall were main shortcomings. Measurement results are improved by changes in the Doppler angle, the flow rate and the particle concentration.
Suggestions to enhance the measurement system, especially its spatial resolution, and to further investigate acoustic wave interactions are made.
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Développement d’un système d’imagerie photoacoustique : Validation sur fantômes et application à l’athérosclérose / Development of a photoacoustic imaging system : Phantom validation and application to atherosclerosisVallet, Maëva 30 September 2015 (has links)
L’imagerie photoacoustique est une nouvelle modalité couplant imagerie optique et échographie. Non invasive, elle permet d’imager des absorbeurs optiques à quelques centimètres de profondeur et avec la résolution de l’échographie. La réception des signaux photoacoustiques se faisant à l’aide d’un échographe clinique, cette modalité hybride vient compléter idéalement l’imagerie ultrasonore en apportant des informations fonctionnelles aux informations structurelles de l’échographie. Ces atouts en font une technique d’imagerie très prometteuse pour la clinique, notamment comme outil de diagnostic précoce. Ce travail de thèse a pour objectif principal la mise en place des outils nécessaires au développement de cette thématique de recherche d’un point de vue expérimental, à des fins cliniques. En particulier, l’apport de l’imagerie photoacoustique pour le diagnostic de plaques d’athérome vulnérables est investigué sur fantômes, grâce à un protocole original. Pour cela un système d’imagerie photoacoustique a été développé et caractérisé à l’aide de fantômes bimodalités élaborés spécifiquement pour les différentes études présentées. Gardant à l’esprit le transfert de cette technique en clinique, un échographe clinique de recherche est utilisé et différentes spécificités du banc nécessaires à l’imagerie in vivo et au diagnostic médical ont été investiguées. Cela implique une amélioration des performances de détection du signal photoacoustique, notamment en termes de sensibilité et de contraste. Pour cela, une nouvelle technologie de sondes ultrasonores est évaluée en la comparant aux sondes actuellement utilisées. De plus, une excitation multispectrale permet l’identification de différents éléments présents dans les tissus. L’aspect temps-réel de l’échographie fait de cette modalité une des plus utilisées pour le diagnostic clinique. Par conséquent, une imagerie photoacoustique voire bimodale en temps réel présente un réel atout pour son transfert clinique. Cette possibilité est investiguée sur le système mis en place au cours de la thèse grâce à un échographe de recherche et une étude sur fantômes. Enfin, une autre contribution de ce travail concerne l’apport de l’imagerie photoacoustique à la caractérisation de la vulnérabilité de la plaque d’athérome. Cette indication de vulnérabilité est obtenue en déterminant la composition de la plaque, en particulier en termes de lipides. L’imagerie photoacoustique, couplée à l’échographie, peut permettre cette identification. Pour étudier cette possibilité, nous nous sommes intéressés à l’artère carotide pour son accessibilité et la place qu’elle occupe dans le diagnostic de la plaque d’athérome en échographie et échographie Doppler. Un protocole original a été élaboré afin d’apporter l’excitation optique au plus près de la carotide. La faisabilité de cette approche est investiguée sur un fantôme conçu spécifiquement pour cette étude et les résultats préliminaires sont présentés. / Photoacoustic (PA) imaging is a new imaging modality coupling ultrasound and optical imaging. This non-invasive technique achieves a penetration depth up to several centimeters with optical contrast and ultrasound resolution. Moreover, since PA signals are detected with a US scanner, PA imaging ideally complete US imaging, adding functional information to the structural ones brought by echography. Therefore PA imaging looks very promising, specifically as a clinical early diagnosis tool. The main objective of this thesis is to set up the required tools to develop the experimental investigation for this research topic and, in particular, to apply it to the diagnosis of vulnerable atheroma plaques. A PA imaging system has been set up and characterized using specifically designed bimodal phantoms. Additional studies have been made to evaluate the suitability of this imaging platform for clinical imaging. For example, in vivo imaging requires better signal detection in terms of contrast and sensitivity, achieved thanks to a new probe technology, and the identification of tissue composition using a multispectral optical excitation. Finally, PA and even PAUS real time imaging is a real asset for medical diagnosis that has been investigated. Another contribution of this work is the use of PA imaging to characterized atheroma plaques vulnerability with the detection of lipids inside these plaques. PA imaging, coupled to echography, can address this need. To study this possibility, the carotid artery has been considered and a new protocol has been elaborated to bring the optical excitation very close to this artery. A feasibility study has been realized on a specific phantom and the preliminary results are presented.
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Modeling and Optimal Design of Annular Array Based Ultrasound Pulse-Echo SystemWAN, Li 18 April 2001 (has links)
The ability to numerically determine the received signal in an ultrasound pulse-echo system is very important for the development of new ultrasound applications, such as tissue characterization, complex object recognition, and identification of surface topology. The output signal from an ultrasound pulse-echo system depends on the transducer geometry, reflector shape, location and orientation, among others, therefore, only by numerical modeling can the output signal for a given measurement configuration be predicted. This thesis concerns about the numerical modeling and optimal design of annular array based ultrasound pulse-echo system for object recognition. Two numerical modeling methods have been implemented and evaluated for calculating received signal in a pulse-echo system. One is the simple, but computationally demanding Huygens Method and the other one is the computationally more efficient Diffraction Response for Extended Area Method (DREAM). The modeling concept is further extended for pulse-echo system with planar annular array. The optimal design of the ultrasound pulse-echo system is based on annular array transducer that gives us the flexibility to create a wide variety of insonifying fields and receiver characteristics. As the first step towards solving the optimization problem for general conditions, the problem of optimally identifying two specific reflectors is investigated. Two optimization methods, the straightforward, but computationally intensive Global Search Method and the efficient Waveform Alignment Method, have been investigated and compared.
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Reflector geometry specific modeling of an annular array based ultrasound pulse-echo systemNadkarni, Aditya 12 September 2007 (has links)
"Abstract Conventional ultrasound imaging systems use array transducers for focusing and beam steering, to improve lateral resolution and permit real-time imaging. This thesis research investigates a different use of array transducers, where the acoustic field and the receiver characteristics are designed such that the energy of the output signal from targets of a specified geometry is maximized. The output signal is the sum of the received signals obtained using all the possible combinations of transducer array elements as transmitter and receiver. This work is based on annular array transducers, but is applicable for any array configuration. The first step is the development of software for the efficient modeling of the wave interaction between transmitted field and target, and between the transducer and receiver field. Using this software, we have calculated the received signal for each combination of an array element as transmitter and the same or another array element as receiver, leading to an N x N received signal matrix for an N element array transducer. A waveform optimization algorithm is then implemented for the purpose of determining the set of delays for the individual array elements, which maximizes the energy of the sum of the received signals. In one implementation of this algorithm, the received signal with the maximum energy is considered as a reference signal, and specific delays are applied to the other signals so that any two signals produce a maximum correlation. This leads to an N x N delay matrix, which, however, is not readily implemented in a practical real-time system, which uses all the elements in an array transducer simultaneously to customize acoustic fields. Hence, the values in this delay matrix are fed into a linear programming optimizer tool to obtain a set of delay values, which makes its implementation practical. The optimized set of delays thus obtained is used to maximize the energy of the received signal for a given transducer and target geometry and hence to enhance the reflectivity of that target. It is also important to check the robustness of the optimized set of delays obtained above, for a given target geometry. Robustness refers to the sensitivity of the optimization to variation in target geometry. This aspect is also evaluated as a part of this thesis work."
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