Les squats et les head-checks sont des défauts générés par l’endommagement des rails dû à la fatigue de contact de roulement, ils sont localisés à la surface du champignon du rail. La possibilité de les détecter en modes statique et dynamique lorsque leur profondeur se situe sous le seuil critique de 5 mm, constitue un challenge important pour l’industrie ferroviaire. Les méthodes d’inspection existantes ne permettent pas de les déceler avec certitude. L’objectif de ce travail a été de développer des méthodes alternatives pour l’inspection automatique du rail permettant de détecter ces défauts superficiels. Nous montrons que les méthodes sans contact : Ultrasons-Laser et EMATs (transducteurs électromagnétiques) sont très performantes pour la détection des défauts définis précédemment en utilisant des ondes acoustiques de surface, notamment dans le cas d’un contrôle dynamique. Cette étude présente les deux méthodes utilisées pour la génération et la détection des ondes de Rayleigh. Des essais sont effectués en modes statique et dynamique. Les résultats obtenus montrent la faisabilité des méthodes de contrôle non destructives envisagées pour la détection de squats et de head-checks de différentes profondeurs. Les essais EMAT se sont notamment révélés satisfaisants pour des vitesses importantes de déplacement de l’échantillon. / Squats and head-checks are a form of near surface rolling contact fatigue damage found in rail heads. The ability to detect these defects in static and dynamic modes when their depth is under the critical threshold of 5 mm represents a major challenge for the rail industry. Conventional inspection methods do not allow their detection with certainty. Therefore, the aim of this work was to develop alternative methods for automatic rail inspection leading to open cracks detection. We show that non-contact methods: Laser-Ultrasonics and electromagnetic transducers (EMAT) are very efficient for the detection of the previously defined defects using surface acoustic waves, particularly in the case of a dynamic control. This study presents two methods for the generation and detection of Rayleigh waves. Static and dynamic tests are performed. The experimental results show the feasibility of the envisaged methods for the detection of squats and head-checks of different depths. Especially, the EMAT tests were satisfactory for high speeds displacement of the sample.

In recent years, the desperate need for reliable clean and relatively small power demand has emerged for edge-of-grid or off-grid regions to keep pace with development demands. A salient technology that has gained much attention for this purpose is the Small Modular Reactors, i.e., SMRs. SMRs differ from conventional Nuclear Power Plants (NPPs) in many aspects, specifically the enclosing structure of the reactor. The burial depth of the SMR structure is expected to reach great depths. For example, the substructure depth reaches 30 m in the SMR design proposed by NuScale (NuScale Power, 2020). Consequently, seismic analysis of deeply embedded structures with a relatively small footprint has been identified as one of the challenges to the safe implementation of SMR technology (DIS-16-04, 2016). Such structures are expected to be more sensitive to surface wave propagation and the seismic interaction with nearby substructures and nonstructural elements such as pipelines. This dissertation develops analytical and numerical methods to analyze the seismic earth pressure exerted on the SMR substructure by considering the effects of seismic surface waves, structure-soil-structure interaction (SSSI), and the interaction with nearby pipelines. The three-dimensional wave propagation theory is employed in the analysis. Solutions for the earth pressure induced by Rayleigh waves are obtained for substructures deeply embedded into homogeneous or multilayered soil profiles. In addition, the effect of thin soil layer (stiff or soft) soils in a soil profile is investigated in the presence of Rayleigh waves. Furthermore, additional earth pressure due to SSSI is examined, and a simplified procedure is proposed based on the three-dimensional wave propagation theory and a guided flow chart to track seismic wave interference. The SSSI analysis yields solutions for the optimal distance between substructures corresponding to the minimum SSSI in new designs. The interaction between substructures and nearby pipelines is explored numerically using the Spectral Element Method. SPECFEM2D software is adopted to perform the analysis, where the three-dimensional wave propagation is successfully implemented. Based on the analysis for pipelines with different configurations, general conclusions are drawn regarding the additional earth pressure on substructures and pipelines based on a comprehensive parametric study of various parameters. In addition, this research also provides an approach to determine the backfill configuration and the selection of backfill materials, which could minimize the seismic amplitudes transmitted to substructures. / Thesis / Doctor of Philosophy (PhD) / Small Modular Reactors (SMRs) are the cornerstone of recent developments in the nuclear industry. However, the SMRs technology faces several safety-related challenges, which includes the earthquake hazards related to the large embedment depth of the enclosing structure. In particular, the major concerns are about the risks related to seismic surface waves as well as the seismic interaction between nearby structural and non-structural elements (e.g., pipelines). The thesis addressed these major concerns by developing analytical and numerical methods to complement the analysis for the integrity of SMRs with sufficient seismic resistance. The solutions are verified and benchmarked using data in the literature. Future researches are suggested to further improve seismic analysis of SMRs.

This research investigates the modeling of randomly distributed surface-breaking microcracks and their effects on higher harmonic generation in Rayleigh surface waves. The modeling is based on micromechanical considerations of rough surface contact. The nonlinear behavior of a single microcrack is described by a hyperelastic effective stress-strain relationship. Finite element simulations of nonlinear wave propagation in a solid with distributed microcracks are performed. The evolution of fundamental and second harmonic amplitudes along the propagation distance is studied and the acoustic nonlinearity parameter is calculated. The results show that the nonlinearity parameter increases with crack density and root mean square roughness of the crack faces. While, for a dilute concentration of microcracks, the increase in acoustic nonlinearity is proportional to the crack density, this is not valid for higher crack densities, as the microcracks start to interact. Finally, it is shown that odd higher harmonic generation in Rayleigh surface waves due to sliding crack faces introduces a friction nonlinearity.

Os métodos de ondas superficiais com ênfase nas ondas Rayleigh foram utilizados como o núcleo desse trabalho de Doutorado. Inicialmente, as ondas Rayleigh foram modeladas permitindo o estudo de sensibilidade de suas curvas de dispersão sob diferentes configurações de parâmetros físicos representando diversos modelos de camadas, em que pôde ser observado parâmetros com maior e menor sensibilidade e também alguns efeitos provocados por baixas razões de Poisson. Além disso, na fase de inversão dos dados a modelagem das ondas Rayleigh foi utilizada para a construção da função objeto, que agregada ao método de mínimos quadrados, a partir do método de Levenberg-Marquardt, permitiu a implementação de um algoritmo de busca local responsável pela inversão de dados das ondas superficiais. Por se tratar de um procedimento de busca local, o algoritmo de inversão foi complementado por uma etapa de pré-inversão com a geração de um modelo inicial para que o procedimento de inversão fosse mais rápido e eficiente. Visando uma eficiência ainda maior do procedimento de inversão, principalmente em modelos de camadas com inversão de velocidades, foi implementado um algoritmo de pós-inversão baseado em um procedimento de tentativa e erro minimizando os valores relativos da raiz quadrada do erro quadrático médio (REQMr) da inversão dos dados. Mais de 50 modelos de camadas foram utilizados para testar a modelagem, a pré-inversão, inversão e pós-inversão dos dados permitindo o ajuste preciso de parâmetros matemáticos e físicos presentes nos diversos scripts implementados em Matlab. Antes de inverter os dados adquiridos em campo, os mesmos precisaram ser tratados na etapa de processamento de dados, cujo objetivo principal é a extração da curva de dispersão originada devido às ondas superficiais. Para isso, foram implementadas, também em Matlab, três metodologias de processamento com abordagens matemáticas distintas. Essas metodologias foram testadas e avaliadas com dados sintéticos e reais em que foi possível constatar as virtudes e deficiências de cada metodologia estudada, bem como as limitações provocadas pela discretização dos dados de campo. Por último, as etapas de processamento, pré-inversão, inversão e pós-inversão dos dados foram unificadas para formar um programa de tratamento de dados de ondas superficiais (Rayleigh). Ele foi utilizado em dados reais originados pelo estudo de um problema geológico na Bacia de Taubaté em que foi possível mapear os contatos geológicos ao longo dos pontos de aquisição sísmica e compará-los a um modelo inicial existente baseado em observações geomorfológicas da área de estudos, mapa geológico da região e informações geológicas globais e locais dos movimentos tectônicos na região. As informações geofísicas associadas às geológicas permitiram a geração de um perfil analítico da região de estudos com duas interpretações geológicas confirmando a suspeita de neotectônica na região em que os contatos geológicos entre os depósitos Terciários e Quaternários foram identificados e se encaixaram no modelo inicial de hemi-graben com mergulho para Sudeste. / The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical information associated with geological information allowed the generation of an analytical profile of the study region with two geological interpretation confirming the suspect of neotectonic movements in the region wherein the geological contacts between the quaternary and tertiary deposits were identified and they agreed with the initial model of a hemi-graben with dip to Southeast.

Os métodos de ondas superficiais com ênfase nas ondas Rayleigh foram utilizados como o núcleo desse trabalho de Doutorado. Inicialmente, as ondas Rayleigh foram modeladas permitindo o estudo de sensibilidade de suas curvas de dispersão sob diferentes configurações de parâmetros físicos representando diversos modelos de camadas, em que pôde ser observado parâmetros com maior e menor sensibilidade e também alguns efeitos provocados por baixas razões de Poisson. Além disso, na fase de inversão dos dados a modelagem das ondas Rayleigh foi utilizada para a construção da função objeto, que agregada ao método de mínimos quadrados, a partir do método de Levenberg-Marquardt, permitiu a implementação de um algoritmo de busca local responsável pela inversão de dados das ondas superficiais. Por se tratar de um procedimento de busca local, o algoritmo de inversão foi complementado por uma etapa de pré-inversão com a geração de um modelo inicial para que o procedimento de inversão fosse mais rápido e eficiente. Visando uma eficiência ainda maior do procedimento de inversão, principalmente em modelos de camadas com inversão de velocidades, foi implementado um algoritmo de pós-inversão baseado em um procedimento de tentativa e erro minimizando os valores relativos da raiz quadrada do erro quadrático médio (REQMr) da inversão dos dados. Mais de 50 modelos de camadas foram utilizados para testar a modelagem, a pré-inversão, inversão e pós-inversão dos dados permitindo o ajuste preciso de parâmetros matemáticos e físicos presentes nos diversos scripts implementados em Matlab. Antes de inverter os dados adquiridos em campo, os mesmos precisaram ser tratados na etapa de processamento de dados, cujo objetivo principal é a extração da curva de dispersão originada devido às ondas superficiais. Para isso, foram implementadas, também em Matlab, três metodologias de processamento com abordagens matemáticas distintas. Essas metodologias foram testadas e avaliadas com dados sintéticos e reais em que foi possível constatar as virtudes e deficiências de cada metodologia estudada, bem como as limitações provocadas pela discretização dos dados de campo. Por último, as etapas de processamento, pré-inversão, inversão e pós-inversão dos dados foram unificadas para formar um programa de tratamento de dados de ondas superficiais (Rayleigh). Ele foi utilizado em dados reais originados pelo estudo de um problema geológico na Bacia de Taubaté em que foi possível mapear os contatos geológicos ao longo dos pontos de aquisição sísmica e compará-los a um modelo inicial existente baseado em observações geomorfológicas da área de estudos, mapa geológico da região e informações geológicas globais e locais dos movimentos tectônicos na região. As informações geofísicas associadas às geológicas permitiram a geração de um perfil analítico da região de estudos com duas interpretações geológicas confirmando a suspeita de neotectônica na região em que os contatos geológicos entre os depósitos Terciários e Quaternários foram identificados e se encaixaram no modelo inicial de hemi-graben com mergulho para Sudeste. / The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical information associated with geological information allowed the generation of an analytical profile of the study region with two geological interpretation confirming the suspect of neotectonic movements in the region wherein the geological contacts between the quaternary and tertiary deposits were identified and they agreed with the initial model of a hemi-graben with dip to Southeast.

Cette thèse nous a permis de produire des cartes de vitesse de groupe du mode fondamental des ondes de Rayleigh, en utilisant les séismes et les corrélations du bruit sismique ambiant. En plus de la méthode moindres carrées amortis, nous avons adapté la nouvelle méthode d’inversion, SOLA-Backus-Gilbert dans un contexte régional. À courte période, les cartes de vitesse de groupe présentent des vitesses rapides pour la croûte océanique et des vitesses lentes pour la croûte continentale. Pour les périodes intermédiaires, le bassin de Taoudeni se caractérise par de faibles vitesses par rapport au reste du craton ouest africain en raison de l’épaisseur de la couche sédimentaire. A longue périodes, les racines des dorsales Man-Leo et Reguibat sont caractérisées par des vitesses rapides, montrant une lithosphère froide et épaisse sous le craton, tandis que nous avons trouvé des vitesses de groupe lentes sous les zones de ceinture mobile panafricaine indiquant une lithosphère mince. / This thesis allowed us to produce group velocity maps of the fundamental mode of Rayleigh waves, using both earthquakes and seismic ambient noise correlation. In this study, in addition to the damped least squares method, we adapted for the very first time a new inversion method, called SOLA-Backus-Gilbert in regional context. At short periods, the group velocities maps exhibit fast velocities for the oceanic crust and slow velocities for the continental crust. For the intermediate periods, the Taoudeni Basin is characterized by low velocities compared to the rest of the west african craton due to the thickness of the sedimentary layer. Over long periods, the roots of the Man-Leo and Reguibat shields are characterized by fast velocities, showing a cold and thick lithosphere under the craton, while we found slow group velocities under the Pan-African orogenic belts zones indicating a thin lithosphere.

Cold rolled carbon steel 1018C is widely used in pressurized fuel pipelines. For those structures, stress corrosion cracking (SCC) can pose a significant problem because cracks initiate late in the lifetime and often unexpectedly, but grow fast once they get started. To ensure a safe operation, it is crucial that any damage can be detected before the structural stability is reduced by large cracks. In the early stages of SCC, microstructural changes occur which increase the acoustic nonlinearity of the material. Therefore, an initially monochromatic Rayleigh wave is distorted and measurable higher harmonics are generated. Different levels of stress corrosion cracking is induced in five specimens. For each specimen, nonlinear ultrasonic measurements are performed before and after inducing the damage. For the measurements, oil coupled wedge transducers are used to generate and detect tone burst Rayleigh wave signals. The amplitudes of the received fundamental and second harmonic waves are measured at varying propagation distances to obtain a measure for the acoustic nonlinearity of the material. The results show a damage-dependent increase in nonlinearity for early stages of damage, indicating the suitability for this nonlinear ultrasonic method to detect stress corrosion cracking before structural failure.

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.

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.

Orientador: Jacobus W. Swart / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-04T18:27:49Z (GMT). No. of bitstreams: 1 Alcantara_GlaucioPedrode_M.pdf: 1079087 bytes, checksum: afc69d32771f7a3060b934cb3fcabca4 (MD5) Previous issue date: 2005 / Resumo: Este trabalho de dissertação apresenta o estudo e projeto dos elementos que compõem um sensor de gases baseado na tecnologia de Onda Acústica de Superfície (SAW), tais como, o oscilador colpitts SAW e um ressonador SAW de uma porta, os quais estão na malha de realimentação de um amplificador. Foi realizado também a deposição de diferentes espessuras de filme fino de TiO2 sobre o sensor, a fim de se estudar o efeito da atenuação da SAW na fronteira entre o cristal e o filme. É mostrado que atenuação da SAW acontece no filme na fina camada de aproximadamente 500 angstroms de espessura. A dependência de espessura com a mudança de freqüência e com fator Q do oscilador SAW e ressonador são apresentados, bem como a ssensitividade de massa do ressonador SAW para o filme de TiO2. Um modelo de oscilador SAW usando 2 caminhos acústicos, de melhor sensitividade que aquele de modo simples, foi estudado e proposto / Abstract: This thesis presents the study and design of the elements which compose a gas sensor based on Surface Acoustic Wave technology, such as, SAW Colpitts oscillator and the SAW one-port resonator that are presents in the feedback loop of an amplifier. It was done deposition of TiO2 thin film different thickness on the sensor, in order to study the effect of SAW attenuation on the border between the crystal and the film. It is shown that SAW attenuation takes place in the film in thin layer of about 500 angstroms thickness. Thickness dependence of frequency shift and Q-factor of SAW oscillator and resonator, as well as, the mass sensitivity of SAW resonator to TiO2 film are presented. The model of SAW oscillator which uses two acoustic paths, has been studied and proposed. / Mestrado / Mestre em Engenharia Elétrica