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Dissertations / Theses on the topic 'CMUT'

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Published: 4 June 2021
Last updated: 16 June 2025

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1

Hochman, Michael. "Investigation of acoustic crosstalk effects in CMUT arrays." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42782.

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Capacitive Micromachined Ultrasonic Transducers (CMUTs) have demonstrated significant potential to advance the state of medical ultrasound imaging beyond the capabilities of the currently employed piezoelectric technology. Because they rely on well-established micro-fabrication techniques, they can achieve complex geometries, densely populated arrays, and tight integration with electronics, all of which are required for advanced intravascular ultrasound (IVUS) applications such as high-frequency or forward-looking catheters. Moreover, they also offer higher bandwidth than their piezoelectric counterparts. Before CMUTs can be effectively used, they must be fully characterized and optimized through experimentation and modeling. Unfortunately, immersed transducer arrays are inherently difficult to simulate due to a phenomenon known as acoustic crosstalk, which refers to the fact that every membrane in an array affects the dynamic behavior of every other membrane in an array as their respective pressure fields interact with one another. In essence, it implies that modeling a single CMUT membrane is not sufficient; the entire array must be modeled for complete accuracy. Finite element models (FEMs) are the most accurate technique for simulating CMUT behavior, but they can become extremely large considering that most CMUT arrays contain hundreds of membranes. This thesis focuses on the development and application of a more efficient model for transducer arrays first introduced by Meynier et al. [1], which provides accuracy comparable to FEM, but with greatly decreased computation time. It models the stiffness of each membrane using a finite difference approximation of thin plate equations. This stiffness is incorporated into a force balance which accounts for effects from the electrostatic actuation, pressure forces from the fluid environment, mass and damping from the membrane, etc. For fluid coupling effects, a Boundary Element Matrix (BEM) is employed that is based on the Green's function for a baffled point source in a semi-infinite fluid. The BEM utilizes the nodal mesh created for the finite difference method, and relates the dynamic displacement of each node to the pressure at every node in the array. Use of the thin plate equations and the BEM implies that the entire CMUT array can be reduced to a 2D nodal mesh, allowing for a drastic improvement in computation time compared with FEM. After the model was developed, it was then validated through comparison with FEM. From these tests, it demonstrated a capability to accurately predict collapse voltage, center frequency, bandwidth, and pressure magnitudes to within 5% difference of FEM simulations. Further validation with experimental results revealed a close correlation with predicted impedance/admittance plots, radiation patterns, frequency responses, and noise current spectrums. More specifically, it accurately predicted how acoustic crosstalk would create sharp peaks and notches in the frequency responses, and enhance side lobes and nulls in the angular radiation pattern. Preliminary design studies with the model were also performed. They revealed that membranes with larger lateral dimensions effectively increased the bandwidth of isolated membranes. They also demonstrated potential for various crosstalk reduction techniques in array design such as disrupting array periodicity, optimizing inter-membrane pitch, and adjusting the number of membranes per element. It is expected that the model developed in this thesis will serve as a useful tool for future iterations of CMUT array optimizations.
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2

McIntosh, James Stuart. "Advances in capacitive micromachined ultrasonic transducer (CMUT) technologies." Thesis, University of Warwick, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396401.

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3

Gurun, Gokce. "Integrated electronics design for high-frequency intravascular ultrasound imaging." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45860.

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Close integration of front-end electronics and the transducer array within the catheter is critical for successful implementation of CMUT-based intravascular ultrasound (IVUS) imaging catheters to enable next generation imaging tools. Therefore, this research developed and implemented custom-designed electronic circuits and systems integrated with an IC compatible transducer technology for realization of miniature IVUS imaging catheters operating at 10-50 MHz frequency range. In one path of this research, an IC is custom designed in a 0.35-um CMOS process to monolithically integrate with a CMUT array (CMUT-on-CMOS) to realize a single-chip, highly-flexible, forward-looking (FL) IVUS imaging system. The amplifiers that are custom-designed achieved transducer thermal-mechanical noise dominated receive performance in a CMUT-on-CMOS implementation. In parallel to the FL-IVUS effort, for realization of a side-looking IVUS catheter based on an annular phased array, a dynamic receive beamformer IC is custom designed also in a 0.35-um CMOS process. Overall, the circuits and systems developed as part of this dissertation form a critical step in the translation of the research on CMUT-based IVUS catheters into real clinical applications for better management of coronary arterial diseases.
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4

Klemm, Markus. "Acoustic Simulation and Characterization of Capacitive Micromachined Ultrasonic Transducers (CMUT)." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-225933.

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Ultrasonic transducers are used in many fields of daily life, e.g. as parking aids or medical devices. To enable their usage also for mass applications small and low- cost transducers with high performance are required. Capacitive, micro-machined ultrasonic transducers (CMUT) offer the potential, for instance, to integrate compact ultrasonic sensor systems into mobile phones or as disposable transducer for diverse medical applications. This work is aimed at providing fundamentals for the future commercialization of CMUTs. It introduces novel methods for the acoustic simulation and characterization of CMUTs, which are still critical steps in the product development process. They allow an easy CMUT cell design for given application requirements. Based on a novel electromechanical model for CMUT elements, the device properties can be determined by impedance measurement already. Finally, an end-of-line test based on the electrical impedance of CMUTs demonstrates their potential for efficient mass production.
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5

Ngo, Sophie. "Dispositf acoustique pour l'isolation galvanique : le CMUT, une voie innovante." Thesis, Tours, 2013. http://www.theses.fr/2013TOUR4027.

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Les dispositifs d’isolation galvanique intégrés au sein des systèmes de commande d’interrupteurs de puissance doivent répondre à une demande accrue en performance, facilité d’intégration et efficacité énergétique. Les transducteurs ultrasonores capacitifs micro-usinés (cMUT : capacitive Micromachined Ultrasonic Transducer), capables d’émettre et de recevoir des ondes ultrasonores, semblent une alternative tout à fait nouvelle à la fonction d’isolation galvanique. Ces travaux de thèse ont pour objectif de démontrer la faisabilité d’un dispositif basé sur la technologie cMUT. Le principe de fonctionnement consiste à transmettre une information grâce à une communication par onde acoustique de volume entre deux réseaux de cMUT placés de part et d’autre d’un substrat. Nous focalisons, en premier lieu, ces travaux sur le processus de fabrication par micro-usinage de surface des cMUT ainsi que les techniques de réalisation des dispositifs en structure double face sur substrat de silicium. L’étude permet d’identifier le collage de substrat comme une solution de fabrication industrialisable. Suite à la réalisation des dispositifs, la caractérisation électro-mécanique des cMUT est une étapeessentielle à la validation de leur fonctionnalité en tant que dispositifs émetteurs. L’étude débute par uneévaluation des propriétés mécaniques du matériau constituant la membrane et qui impactent directementle comportement global des cMUT. Puis, la caractérisation du comportement statique et dynamique descMUT permet d’extraire les paramètres tels que la fréquence de résonance, la tension de collapse etl’efficacité électro-mécanique qui définissent le mode de pilotage d’un tel système.Finalement, la validation du concept de transmission et de détection d’ondes ultrasonores est réaliséegrâce à des mesures de vibrométrie laser Doppler. Les résultats apportent des éléments de réponse quantau mode de propagation des ondes et permettent d’identifier les topologies de meilleure efficacité entransmission acoustique. Enfin, l’intégration du prototype dans l’application de commanded’interrupteur de puissance démontre la faisabilité du concept de transformateur acoustique basé sur latechnologie cMUT<br>Galvanic isolation devices integrated into switch command systems must be able to answer all of the increasing demand for performance, energetic efficiency and integration easiness. The capacitive micro machined ultrasonic transducers (cMUT), able to emit and receive ultrasounds, could be an entirely new alternative to the function of galvanic isolation. This work aims to demonstrate the feasibility of a cMUT-based device. The operating principle consists in transmitting information thanks to a bulk acoustic wave between two cMUT arrays located on both sides of a substrate. We first focus on cMUT surface micromachining fabrication process and techniques of double-side device manufacturing. Our study allows us to identify wafer bonding as a realistic industrial solution. After device fabrication, electro-mechanical of cMUT is an essential step to validate their functionality as ultrasonic emitters. The study starts with the mechanical properties evaluation of the membrane material. These properties directly impact the global behavior of cMUT. Then, the characterization of cMUT static and dynamic behavior allows extracting parameters as resonance frequency, collapsing voltage and electro-mechanical efficiency which define the actuation mode of such a system. Finally, the validation of transmission and reception of ultrasonic waves is evaluated by vibrometer laser Doppler measurements. Results bring elements concerning the waves propagation modes and allow identifying the best acoustical efficiency in regard to the topology. In conclusion, the prototype integration in the application of power switch command demonstrates the feasibility of acoustic transformer concept based on cMUT technology
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6

Bahette, Emilie. "Réalisation et caractérisation de CMUT basse température pour applications d'imagerie médicale." Thesis, Tours, 2014. http://www.theses.fr/2014TOUR4011.

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Les cMUT sont des microsystèmes principalement utilisés pour de l’imagerie médicale. Afin de développer de nouvelles architectures de sondes, intégrer l’électronique de commande devient impératif. Pour y parvenir, la température du procédé de réalisation ne doit pas excéder 400°C. Cela nécessite donc de revoir les procédés et matériaux utilisés. Pour répondre à cette problématique, nous avons utilisé une électrode originale en siliciure de nickel obtenu à 400°C, une couche sacrificielle en nickel et une membrane en nitrure de silicium déposée à 200°C. Des cMUT ont été fabriqués sur un substrat silicium. Ils présentent les caractéristiques souhaitées à savoir une forte fréquence de résonance (16,4MHz), une tension de collapse maitrisée (65V) et un coefficient de couplage électromécanique satisfaisant (0,6). De plus, le procédé développé peut être étendu à d’autres types de substrats<br>CMUTs are innovating microsystems for ultrasonic medical imaging. To develop new array architectures, monolithic integration of integrated circuits is required. In this context, microsystems must be achieved using process temperature limited to 400°C. The main objective of this PhD thesis is the development of alternative processes and materials to replace usual ones done at high temperature. We have developed a nickel silicide bottom electrode at 400°C, a metallic sacrificial layer and a silicon nitride membrane deposited at 200°C. The devices, fabricated on silicon substrates, are functional with a high resonance frequency (16.4MHz), a mastered collapse voltage (65V) and an efficient electromechanical coupling coefficient (0.6). Moreover, this low temperature process was successfully applied on other substrates such as glass
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7

SAUTTO, MARCO. "ANALOG FRONT-END CIRCUITS FOR HIGHLY INTEGRATED ULTRASOUND IMAGING SYSTEMS." Doctoral thesis, Università degli studi di Pavia, 2017. http://hdl.handle.net/11571/1203280.

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Ultrasound imaging is a well-established medical diagnostic technique. Compared with other imaging modalities, such as for example X-ray, ultrasound is harmless to the patient and less expensive while providing real-time imaging capability with adequate resolution for most applications. Piezoelectric materials have dominated the ultrasound transducers technology for a long time but, thanks to the intense research activity in recent years, capacitive micromachined ultrasonic transducers (CMUT) are emerging as a competitive alternative for next generation imaging systems. The objective of the thesis is to analyze the ultrasound system, when a CMUT is used instead of a piezoelectric transducer, to identify and design the best integrated solution to optimize the front-end performance. After giving an overview of the ultrasound system and the Capacitive Micromachined Ultrasonic Transducer (CMUT) in Chapter 1, Chapter 2 presents a thorough comparison between RX amplifier alternatives. The impact on the pulse-echo frequency response and SNR is assessed. The study demonstrates that a capacitive-feedback stage provides a remarkable improvement in the noise-power performance compared to the very popular resistive-feedback amplifier, at the expense of a low-frequency shift of the pulse-echo response, making it suitable for integration of dense CMUT arrays for low and mid-frequency ultrasound imaging applications. Then, Chapter 3 proposes the design of a CMUT front-end circuits comprising a TX driver, T/R switch and RX amplifier. Realized in BCD8-SOI technology from STMicroelectronics, the TX delivers up to 100V pulses, while the RX shows 70dB dynamic range with very low noise at 1mW only power dissipation. Measurement results and imaging experiments are presented and discussed. In Chapter 4, the non-linear behavior of the CMUT is discussed and possible solution proposed. Experimental results demonstrate a significant reduction of the second-harmonic distortion, estimated to be lower than -30 dB, resulting in good linearization for typical nonlinear imaging operation. In addition, Chapter 5 shows a novel amplifier architecture exploiting the regeneration feature of the cross-coupled pair. It will be used as Programmable Gain Amplifier (PGA) in the ultrasound chain. A test-chip in 0.18 μm CMOS provides 15dB to 66dB gain over 50MHz bandwidth. With state-of-the-art noise and linearity performance, a record GBW up to 100GHz is demonstrated with only 420 μW power dissipation.
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8

Xu, Toby Ge. "Material and array design for CMUT based volumetric intravascular and intracardiac ultrasound imaging." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54861.

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Recent advances in medical imaging have greatly improved the success of cardiovascular and intracardiac interventions. This research aims to improve capacitive micromachined ultrasonic transducers (CMUT) based imaging catheters for intravascular ultrasound (IVUS) and intra-cardiac echocardiography (ICE) for 3-D volumetric imaging through integration of high-k thin film material into the CMUT fabrication and array design. CMUT-on-CMOS integration has been recently achieved and initial imaging of ex-vivo samples with adequate dynamic range for IVUS at 20MHz has been demonstrated; however, for imaging in the heart, higher sensitivities are needed for imaging up to 4-5 cm depth at 20MHz and deeper at 10MHz. Consequently, one research goal is to design 10-20MHz CMUT arrays using integrated circuit (IC) compatible micro fabrication techniques and optimizing transducer performance through high-k dielectrics such as hafnium oxide (HfO2). This thin film material is electrically characterized for its dielectric properties and thermal mechanical stress is measured. Experiments on test CMUTs show a +6dB improvement in receive (Rx) sensitivity, and +6dB improvement in transmit sensitivity in (Pa/V) as compared to a CMUT using silicon nitride isolation (SixNy) layer. CMUT-on-CMOS with HfO2 insulation is successfully integrated and images of a pig-artery was successfully obtained with a 40dB dynamic range for 1x1cm2 planes. Experimental demonstration of side looking capability of single chip CMUT on CMOS system based FL dual ring arrays supported by large signal and FEA simulations was presented. The experimental results which are in agreement with simulations show promising results for the viability of using FL-IVUS CMUT-on-CMOS device with dual mode side-forward looking imaging. Three dimensional images were obtained by the CMUT-on-CMOS array for both a front facing wire and 4 wires that are placed perpendicular to the array surface and ~4 mm away laterally. For a novel array design, a dual gap, dual frequency 2D array was designed, fabricated and verified against the large signal model for CMUTs. Three different CMUT element geometries (2 receive, 1 transmit) were designed to achieve ~20MHz and ~40MHz bands respectively in pulse-echo mode. A system level framework for designing CMUT arrays was described that include effects from imaging design requirements, acoustical cross-talk, bandwidths, signal-to-noise (SNR) optimization and considerations from IC limitations for pulse voltage. Electrical impedance measurements and hydrophone measurements comparisons between design and experiment show differences due to inaccuracies in using SixNy homogenous material in simulation compared to fabricated thin-film stacks (HfO2-AlSi-SixNy). It is concluded that for “thin” membranes the effect of stiffness and mass of HfO2 and AlSi (top electrode) cannot be ignored in the simulation. Also, it is understood that aspect ratio (width to height) <10 will have up to 15% error for center frequency predicted in air when the thin-plate approximation is used for modelling the bending stiffness of the CMUT membrane.
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9

Lani, Shane W. "Ultrasonic subwavelength acoustic focusing and imaging using a 2D membrane metamaterial." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54867.

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A metasurface or 2D metamaterial composed of a membrane array can support an interesting acoustic wave field. These waves are evanescent in the direction normal to the array and can propagate in the immersion fluid immediately above the metasurface. These waves are a result of the resonant membranes coupling to the fluid medium and propagate with a group and phase speed lower than that of the bulk waves in the surrounding fluid. This work examines and utilizes these evanescent surface waves using Capacitively Micromachined Ultrasonic Transducers (CMUT) as a specific example. CMUT arrays can generate and detect membrane displacement capacitively, and are shown to support the surface waves capable of subwavelength focusing and imaging. A model is developed that can solve for the modes of the membrane array in addition to transiently modeling the behavior of the array. It is found that the dispersive nature of the waves is dependent on the behavior of the modes of the membrane array. Two-dimensional dispersion analysis of the metasurface shows evidence of four distinct frequency bands of surface wave propagation: isotropic, anisotropic, directional band gap, and complete band gap around the first resonant frequency of the membrane. Some of the frequencies in the partial band gap show concave equifrequency contours capable of negative refraction. The dispersion and modal properties are also examined as to how they are affected by basic array parameters. Potential applications of this wave field are examined in the context of subwavelength focusing and imaging. Several methods of acoustic focusing are used on an array consisting of dense grid of membranes and several membranes spatially removed from the structure. Subwavelength acoustic focusing to a resolution of λ/5 is shown in simulations and verified with experiments. An imaging test is also performed in which a subwavelength defect is localized. This fundamental work in characterizing the waves above the membrane metasurfaces is expected to have impact and implications for transducer design, resonant sensors, 2D acoustic lenses, and subwavelength focusing and imaging.
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10

Gross, Dominique. "Conception et évaluation d'une sonde CMUT mixte dédiée à la thérapie ciblée à guidage ultrasonore." Thesis, Tours, 2015. http://www.theses.fr/2015TOUR3313/document.

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Présentés pour la première fois en 1994, les transducteurs ultrasonores capacitifs micro- usinés, ou CMUTs (Capacitive Micromachined Ultrasonic Transducers), représentent une technologie alternative aux matériaux piézoélectriques pour la transduction électroacoustique. En particulier, leur souplesse de conception et leur haut degré de miniaturisation en font des candidats privilégiés pour le développement de sondes mixtes complexes alliant thérapie et imagerie par ultrasons. C’est dans ce contexte que s’est inscrit ce travail de thèse, dédié au développement d’une première sonde CMUT mixte. Le document débute par une présentation générale de la technologie et du contexte du projet. Puis, le développement est présenté, en commençant par les étapes préliminaires de modélisation numérique jusqu’aux caractérisations les plus avancées du prototype fabriqué. Les résultats démontrent l’intérêt de la technologie pour les applications visées<br>Presented for the first time in 1994, capacitive micromachined ultrasonic transducers (CMUT) are a promising alternative to the piezoelectric technology for electroacoustic transduction. Particularly, their intrinsic design flexibility and miniaturization capability are strong advantages for the manufacturing of high-end Ultrasound-guided Focused Ultrasound (USgFUS) probes. The work presented in this Ph.D. dissertation is devoted to the f irst development of a USgFUS CMUT probe. After a general introduction of the CMUT technology and the context of this research project, the development is reported starting from the preliminary numerical studies to the most advanced characterizations of the fabricated device. The first results demonstrate the benefits of this technology for the targeted applications
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11

Behnamfar, Parisa. "On the design of high-voltage analog front-end circuits for capacitive micromachined ultrasonic transducers (CMUT)." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50469.

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In ultrasound imaging, capacitive micromachined ultrasonic transducer (CMUT) technology has become a promising alternative to conventional piezoelectric- based technology. This work focuses on various aspects of CMUT-based imaging technologies. In the context of CMUT design and integration with associated electronics, flexible and reliable CMUT models that can be seamlessly simulated with the read-out circuits and provide insights in the system-level performance are of great importance. This work proposes a generic Verilog-AMS model for CMUT sensors that takes into account the non-linearities, dynamic behavior and harmonic resonances of the CMUT. This model is able to provide reliable estimations of the pull-in voltage as well as the resonance frequency and the spring softening effect. To improve the signal-to-noise ratio (SNR), integrating the CMUT transducer with the front-end electronics is critical. Design and implementation of a comprehensive analog front-end system in a 0.8μm high-voltage CMOS technology which includes high-voltage and fast-switching transmitters as well as low-power variable-gain receivers is presented. Co-simulation of the front-end electronics and the CMUT model demonstrates full system functionality. Experimental results of the system at the transmit mode confirm the reliability of this co-simulation. An on-chip adaptive biasing unit (ABU) is also included in the design which aims to improve the CMUT receive sensitivity. The ABU consists of a DC-DC converter to generate a range of bias voltage levels and a digital control unit to select the desired voltage. Co- simulation of the ABU with the Verilog-AMS model confirms the increase in the CMUT sensitivity in receive mode. In the context of CMUT super-resolution imaging, we present the design of a transceiver circuit in a 0.35μm high-voltage CMOS technology that supports both the fundamental and asymmetric modes of operation. The transmitter provides high- voltage pulses to the CMUT electrodes. The receiver includes transimpedance analog adders to add the fundamental mode in-phase signals as well as differential amplifiers to combine the out-of-phase signals of the asymmetric modes. Furthermore, low- power variable-gain stages are included to amplify the resulting signals and facilitate interfacing to the ultrasound imaging machine for additional processing and display. The design functionality is confirmed by experimental results.<br>Applied Science, Faculty of<br>Electrical and Computer Engineering, Department of<br>Graduate
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12

Boulmé, Audren. "Conception et caractérisation de sondes cMUT large bande pour l'imagerie conventionnelle et l'évaluation du tissu osseux." Thesis, Tours, 2013. http://www.theses.fr/2013TOUR3319/document.

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Les transducteurs ultrasonores capacitifs micro-usinés (cMUT : capacitive Micromachined Ultrasound Transducers) apparaissent, au vu de leur maturité croissante, comme une alternative de plus en plus viable à la technologie piézoélectrique. Caractérisés par une large bande passante et une large directivité, ces transducteurs sont des solutions intéressantes pour le développement de sondes ultrasonores « exotiques » dont les spécifications sont difficilement atteignables en technologie piézoélectrique. C'est dans ce contexte et fort de l'expérience acquise par notre laboratoire sur cette technologie pendant plus d'une dizaine d'années, que s'est inscrit ce travail de thèse. L'originalité du travail rapporté ici est d'aller de l'analyse du comportement général des barrettes cMUT jusqu'à un exemple précis de conception de sonde cMUT pour l'évaluation du tissu osseux. Des outils de modélisation précis et rapides, basés sur l'introduction de conditions de périodicité, ont été développés. Plusieurs modèles ont ainsi été mis en place afin d'adapter la stratégie de modélisation à la topologie du dispositif cMUT à modéliser : cellule isolée, colonne de cellules, matrice de cellules et élément de barrette. Ces modèles ont permis d'étudier le comportement des éléments de barrette cMUT et d'améliorer notre connaissance sur les mécanismes physiques mis en jeu. De cette façon, l'origine des effets de baffle, problème récurrent du comportement des barrettes cMUT, a clairement été interprété par l'intermédiaire d'une analyse modale. Des solutions ont ainsi été identifiées et proposées afin d'optimiser le comportement des barrettes cMUT, de façon à réduire la présence des effets de baffle et à augmenter leur bande passante. Le développement d'une barrette cMUT dédiée à l'évaluation du tissu osseux est présenté dans sa totalité, afin d'illustrer les différents aspects liés à la conception d'une sonde de cette technologie. Un travail original de caractérisation a été réalisé sur cette barrette, afin d'estimer l'homogénéité inter-cellules à l'échelle de l'élément et l'homogénéité inter-éléments à l'échelle de la barrette. Enfin, une confrontation a été réalisée avec une sonde PZT de même topologie sur plusieurs fantômes osseux. Il a ainsi été démontré que la sonde cMUT permettait la détection d'un plus grand nombre de modes guidés, et par conséquent, une meilleure évaluation du tissu osseux<br>Following recent advances, the capacitive Micromachined Ultrasound Transducers (cMUT) technology seems to be a good alternative to the piezoelectric technology. For specific applications, the requirements and specifications of the probe are sometimes difficult to obtain with the traditional PZT technology. The cMUT technology, with both large bandwidth and angular directivity, can be an interesting way to overcome these limitations. This PhD has been carried out in this context, in a laboratory which has nearly 10 years of experience in the field of cMUT technology. The originality of the work sustained in this PhD is that it covers the cMUT technology, from general aspects dealing of modeling and characterization up to a complete example of cMUT-based probe applied to the assessment of cortical bone. Fast and accurate modeling tools, based on periodicity conditions, have been developed. Several models have been proposed to match the modeling strategy to the topology of the cMUT array : isolated cell, columns of cells, 2-D matrix of cells and array element. These models have been used to analyze the cMUT array behavior and to understand how mutual couplings between cMUTs impact the response of one element. Origins of the baffle effect, well-known as a recurrent problem in cMUT probe, have been explained using an original method based on the normal mode decomposition of the radiated pressure field. Thus, solutions have been identified and tested to optimize the cMUT frequency response, i.e. to increase the bandwidth, and to suppress parasitic disturbances linked to baffle effect in the electroacoustic response. The development of a dedicated cMUT array for the assessment of bone tissue is accurately detailed in the manuscript, including description of the design rules, fabrication steps and packaging procedure. An original characterization work has been carried out in order to check the device homogeneity, first from cell to cell and then from element to element. Finally, a comparison with a PZT probe with the same topology has been performed on bone mimicking phantom. Nice results has been obtained, showing that cMUT probe allows detecting higher number of guided modes in the cortical shell, and consequently, improving the cortical bone assessment
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13

Jeanne, Edgard. "Réalisation et caractérisations électromécaniques de transducteurs ultrasonores capacitifs micro-usines." Thesis, Tours, 2008. http://www.theses.fr/2008TOUR4041.

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Les transducteurs ultrasonores capacitifs micro-usinés peuvent s’adapter à la complexité et à la miniaturisation requise par l’évolution des techniques d’échographie vers l’imagerie intracardiaque ou l’imagerie 3D en temps réel. L’objectif de ce travail de thèse est la réalisation de démonstrateurs pouvant être intégrés dans une sonde cathéter 9Fr pour l’imagerie intracardiaque. Nous proposons, d’évaluer une technologie de micro-usinage de surface a?n de réaliser une architecture reposant sur un couple de membrane en nitrure de silicium faiblement contraint et de couche sacri?cielle en oxyde. Nous abordons la caractérisation électromécanique des transducteurs ultrasonores en proposant une approche mécanique pour la détermination de la tension de collapse et la fréquence de résonance. Di?érentes techniques nous ont permis d’extraire les propriétés mécaniques de la couche structurelle du microsystème. Nous ?nalisons ces travaux sur l’intégration des dispositifs dans la sonde avec un report de connectique sur la face arrière, basée sur des vias traversants et une couche de passivation en nitrure de silicium déposé par PECVD ou de parylène C<br>Capacitive Micromachined Ultrasonic Transducers (cMUTs) based on MEMS technology may ?t the complexity and the miniaturization required by ultrasound probes evolution. The objective of this thesis work is to realize a technological test vehicle which can be easily and directly integrated in a 9Fr catheter probe. This document focuses on a surface micromachining process in order to realize a 450nm thick suspended membrane over a 200nm gap. The process lies on a LPCVD low stress silicon nitride membrane and an oxide sacri?cial layer. The electromechanical characterization of the membrane is performed through laser Doppler vibrometry and optical pro?lometry in order to determine the collapse voltage and the natural frequency of the membranes. Material’s mechanical properties being fundamental in any MEMS prediction behavior, dedicated mechanical test structures were characterized in order to extract silicon nitride mechanical properties. In an integration and a ?ip-chip scheme, a through wafer interconnect technology is proposed. Finally, this document ends on the investigation of PECVD silicon nitride and parylene C as a passivation layer
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14

Vogl, Gregory William. "Nonlinear Dynamics of Circular Plates under Electrical Loadings for Capacitive Micromachined Ultrasonic Transducers (CMUTs)." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/30095.

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We created an analytical reduced-order model (macromodel) for an electrically actuated circular plate with an in-plane residual stress for applications in capacitive micromachined ultrasonic transducers (CMUTs). After establishing the equations governing the plate, we discretized the system by using a Galerkin approach. The distributed-parameter equations were then reduced to a finite system of ordinary-differential equations in time. We solved these equations for the equilibrium states due to a general electric potential and determined the natural frequencies of the axisymmetric modes for the stable deflected position. As expected, the fundamental natural frequency generally decreases as the electric forcing increases, reaching a value of zero at pull-in. However, strain-hardening effects can cause the frequencies to increase with voltage. The macromodel was validated by using data from experiments and simulations performed on silicon-based microelectromechanical systems (MEMS). For example, the pull-in voltages differed by about 1% from values produced by full 3-D MEMS simulations. The macromodel was then used to investigate the response of an electrostatically actuated clamped circular plate to a primary resonance excitation of its first axisymmetric mode. The method of multiple scales was used to derive a semi-analytical expression for the equilibrium amplitude of vibration. The plate was found to always transition from a hardening-type to a softening-type behavior as the DC voltage increases towards pull-in. Because the response of CMUTs is highly influenced by the boundary conditions, an updated reduced-order model was created to account for more realistic boundary conditions. The electrode was still considered to be infinitesimally thin, but the electrode was allowed to have general inner and outer radii. The updated reduced-order model was used to show how sensitive the pull-in voltage is with respect to the boundary conditions. The boundary parameters were extracted by matching the pull-in voltages from the macromodel to those from finite element method (FEM) simulations for CMUTs with varying outer and inner radii. The static behavior of the updated macromodel was validated because the pull-in voltages for the macromodel and FEM simulations were very close to each other and the extracted boundary parameters were physically realistic. A macromodel for CMUTs was then created that includes both the boundary effects and an electrode of finite thickness. Matching conditions ensured the continuity of displacements, slopes, forces, and moments from the composite to the non-composite regime of the CMUT. We attempted to validate this model with results from FEM simulations. In general, the center deflections from the macromodel fell below those from the FEM simulation, especially for relatively high residual stresses, but the first natural frequencies that accompany the deflections were very close to those from the FEM simulations. Furthermore, the forced vibration characteristics also compared well with the macromodel predictions for an experimental case in which the primary resonance curve bends to the right because the CMUT is a hardening-type system. The reduced-order model accounts for geometric nonlinear hardening, residual stresses, and boundary conditions related to the CMUT post, allows for general design variables, and is robust up to the pull-in instability. However, even more general boundary conditions need to be incorporated into the model for it to be a more effective design tool for capacitive micromachined ultrasonic transducers.<br>Ph. D.
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15

Montilla, Leonardo Gabriel. "Advanced Devices for Photoacoustic Imaging to Improve Cancer and Cerebrovascular Medicine." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/312510.

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Recent clinical studies have demonstrated that photoacoustic imaging (PAI) provides important diagnostic information for breast cancer staging. Despite these promising studies, PAI remains an unfeasible option for clinics due to the cost to implement, the required large modification in user conduct and the inflexibility of the hardware to accommodate other applications for the incremental enhancement in diagnostic information. The research described in this dissertation addresses these issues by designing attachments to clinical ultrasound probes and incorporating custom detectors into commercial ultrasound scanners. The ultimate benefit of these handheld devices is to expand the capability of current ultrasound systems and facilitate the translation of PAI to enhance cancer diagnostics and neurosurgical outcomes. Photoacoustic enabling devices (PEDs) were designed as attachments to two clinical ultrasound probes optimized for breast cancer diagnostics. PAI uses pulsed laser excitation to create transient heating (<1°C) and thermoelastic expansion that is detected as an ultrasonic emission. These ultrasonic emissions are remotely sensed to construct noninvasive images with optical contrast at depths much greater than other optical modalities. The PEDs are feasible in terms of cost, user familiarity and flexibility for various applications. Another possible application for PAI is in assisting neurosurgeons treating aneurysms. Aneurysms are often treated by placing a clip to prevent blood flow into the aneurysm. However, this procedure has risks associated with damaging nearby vessels. One of the developed PEDs demonstrated the feasibility to three-dimensionally image tiny microvasculature (<0.3mm) beyond large blood occlusions (>2.4mm) in a phantom model. The capability to use this during surgery would suggest decreasing the risks associated with these treatments. However, clinical ultrasound arrays are not clinically feasible for microsurgical applications due to their bulky size and linear scanning requirements for 3D. Therefore, capacitive micromachined ultrasound transducer (CMUT) two-dimensional arrays compatible with standard ultrasound scanners were used to generate real-time 3D photoacoustic images. Future probes, designed incorporating CMUT arrays, would be relatively simple to fabricate and a convenient upgrade to existing clinical ultrasound equipment. Eventually, a handheld tool with the ability to visualize, in real-time 3D, the desired microvasculature, would assist surgical procedures. The potential implications of PAI devices compatible with standard ultrasound equipment would be a streamlined cost efficient solution for translating photoacoustics into clinical practice. The practitioner could then explore the benefits of the enhanced contrast adjunctive to current ultrasound applications. Clinical availability of PAI could enhance breast cancer diagnostics and cerebrovascular surgical outcomes.
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Vallet, Maëva. "Développement d’un système d’imagerie photoacoustique : Validation sur fantômes et application à l’athérosclérose." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0086/document.

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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<br>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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17

Oliveira, Victor Inacio de. "Estudo de dispositivos CMUTS fabricados com métodos e materiais alternativos para aplicação potencial em ensaios não destrutivos." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3152/tde-11082015-160035/.

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O presente trabalho propõe o estudo de dispositivos CMUTs fabricados através de métodos e materiais alternativos com potencial aplicação em ensaios não destrutivos. O CMUT é constituído por uma membrana condutiva colocada sobre uma cavidade com o fundo metalizado, formando uma estrutura capacitiva. Ondas acústicas incidentes criam uma vibração na membrana que modifica de forma detectável a capacitância do dispositivo (modo de detecção). De modo inverso, é possível aplicar tensão alternada sobre a estrutura do CMUT fazendo com que a membrana vibre gerando ondas acústicas (modo de emissão). Hoje as principais tecnologias utilizadas para detecção e emissão de ondas acústicas utilizam materiais piezelétricos que são de difícil obtenção, possuem baixa integrabilidade e restrições em aplicações em altas temperaturas. O transdutor proposto baseia-se na tecnologia MEMS onde efeitos elétricos e mecânicos são combinados de forma a atender uma determinada aplicação. Os dispositivos MEMS são fabricados por técnicas de microfabricação, o que diminui o custo de produção e possibilita o uso de diversos tipos de materiais. Antes da fabricação dos CMUTs, foram feitas modelagens analíticas e computacionais visando determinar as dimensões ideais dos dispositivos a serem fabricados e também quais materiais seriam melhores se aplicados como membrana. A partir dos resultados da modelagem foi possível determinar que CMUTs com membrana de cobre fossem fabricados. Com os resultados da modelagem foram propostos métodos de fabricação baseados em técnicas de wafer-bonding. Dois materiais foram utilizados para produzir as cavidades, um deles foi o fotorresiste SU-8 e outro uma resina adesiva de secagem rápida, material este não convencional para produção de CMUTs. No primeiro caso, as cavidades foram abertas por processo de fotolitografia, já no segundo foi utilizado um método de corrosão a laser, também não convencional. Diferentes métodos foram utilizados na colagem das membranas, sendo que membranas coladas com resina adesiva e membranas deixadas suspensas sobre as cavidades apresentaram melhores resultados. As caracterizações elétricas e acústicas realizadas nos dispositivos fabricados mostraram que os CMUTs obtidos possuem características capacitivas e podem emitir e receber, comprovando assim seu funcionamento. Isto indica que os roteiros de fabricação propostos são eficientes e que os materiais e métodos utilizados se mostraram adequados. Além disso, a partir das caracterizações acústicas é possível dizer que os CMUTs fabricados podem ser potencialmente aplicados em ensaios não destrutivos, principalmente em análise de vibrações.<br>This thesis proposes the study of CMUT devices produced using alternative methods and materials with potential application in non-destructive analysis. CMUT is composed of a metallized substrate covered with an insulator cavity structure and a conductive membrane on its top, forming a capacitive structure. Incident acoustic waves cause vibration in the membrane modifying their capacitance (detection mode). AC voltage can be applied on the structure of the CMUT causing the membrane to vibrate generating acoustic waves (transmission mode). Today the main technologies used for the detection and emission of acoustic waves use piezoelectric materials that are difficult to obtain, have low integrability and restrictions in high temperature applications. The proposed transducer is based on MEMS technology where electrical and mechanical effects are combined to suit a particular application. MEMS devices are manufactured by microfabrication techniques, which reduce the cost of production and allow the use of various types of materials. Before the fabrication of CMUTs, analytical and computational modeling were made to determine the optimal dimensions of the devices to be manufactured and also what materials would be best if applied as membrane. From the modeling results CMUTs with copper membrane were manufactured. Based on the results of the modeling process, manufacturing methods based on wafer-bonding techniques were proposed. Two materials were used to produce the cavities: one of them was the SU-8 photoresist and the other an acrylic adhesive, an unconventional material for the production of CMUTs. In the first case the cavities were opened by the photolithographic process. In the second method the corrosion laser was used, which is also unconventional. Different methods were used to bond the membranes. The membranes bonded with acrylic adhesive and left suspended over the cavity wells showed better results. The electric and acoustic characterizations performed on fabricated devices showed that CMUTs present capacitive characteristics and can emit and receive acoustic waves, thus proving its operation. This indicates that the proposed manufacturing routes are efficient and that the materials and methods used are appropriate. Moreover, these results show that the manufactured CMUTs may be potentially applied to nondestructive analyses, especially in analyses of vibrations.
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18

Klemm, Markus [Verfasser], Gerald [Akademischer Betreuer] [Gutachter] Gerlach, and Mario [Gutachter] Kupnik. "Acoustic Simulation and Characterization of Capacitive Micromachined Ultrasonic Transducers (CMUT) / Markus Klemm ; Gutachter: Gerald Gerlach, Mario Kupnik ; Betreuer: Gerald Gerlach." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/1137830190/34.

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19

Meynier, Cyril. "Modélisation, conception et caractérisation de transducteurs ultrasonores capacitifs micro-usinés." Thesis, Tours, 2012. http://www.theses.fr/2012TOUR3308/document.

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La transduction électrostatique est utilisée depuis plusieurs décennies dans les fréquences du domaine audible, principalement sous la forme de microphones membranaires. La transposition du même principe de transduction, mais dans un domaine de fréquence au-dessus du MHz, et par l’utilisation de dispositifs micro-usinés, c'est-à-dire produits à l’aide de technologies de photolithographie, a été proposée à partir de la fin des années 1990. Ces transducteurs, désignés sous l’acronyme cMUT (capacitive micromachine ultrasonic transducers), se composent d’un assemblage de transducteurs élémentaires, chacun possédant une partie mobile conventionnellement appelée diaphragme ou membrane, actionnée par la pression électrostatique. Cette thèse s’inscrit dans le développement de transducteurs de ce type destinés au domaine de l’imagerie médicale ultrasonore. Ce secteur d’application utilise actuellement des transducteurs basés sur des céramiques (ou, dans certains cas précis, des polymères) piézoélectriques. Le cMUT est intéressant dans certains sous-domaines d’application des ultrasons médicaux en raison de sa bonne adaptation à une production en grande série, de son intégration plus facile avec des éléments électroniques, de son faible échauffement et de l’absence de matériaux toxiques dans son processus de fabrication. La partie théorique de cette thèse repose sur une approche de modélisation par différences finies. Un modèle basé sur la théorie des plaques minces est développé pour prendre en compte la mécanique du transducteur élémentaire cMUT (c'est-à-dire d’un seul diaphragme). Ce modèle est ensuite complété par l’intégration de l’effet d’un chargement acoustique par un fluide. De façon à modéliser un transducteur entier, il est nécessaire de prendre en compte le couplage acoustique existant entre les différentes membranes. Pour rendre cela possible, un circuit équivalent, permettant de réduire chaque membrane à un système à un seul degré de liberté, est développé. Il est validé en le comparant au modèle de différences finies dans des cas où celui-ci peut être utilisé. Les travaux expérimentaux ont fait appel principalement aux deux techniques de caractérisation suivantes : les mesures d’impédance électrique, et les mesures de déplacement effectuées par interférométrie laser. Ces mesures ont été utilisées dans une double optique. D’une part, dans un objectif de caractérisation, ils ont permis de vérifier la fonctionnalité des dispositifs fabriqués et d’évaluer leurs performances. D’autre part, en comparant différentes configurations entre elles, ils ont rendu possible une validation expérimentale du modèle qui a été mis au point<br>Electro-acoustic transduction based on electrostatic force has a long history in the range of audible frequencies, mainly as membrane-based microphones. Starting in the late 1990’s, it has been proposed to use the same principle in the multi-MHz frequency domain, thanks to micro-machined devices – meaning they’re produced through lithography technology. Such transducers, known as cMUT for capacitive micromachine ultrasonic transducers, are made of an assembly of elementary vertically mobile cells, usually designated as membranes, driven by electrostatic force. This PhD work is part of the development of this kind of transducers designed for medical imaging applications. This area currently uses transducers based on piezoelectric ceramics (or piezoelectric polymers for some peculiar cases). CMUT is an interesting alternative for some subdomains of medical ultrasound applications, due to its volume production ability, its easier integration with electronic elements, its low heat dissipation and the absence of toxic materials
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20

Johansson, Patrick. "Capacitive Micromachined Ultrasonic Transducers for Underwater Applications." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-447067.

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Capacitive micromachined ultrasonic transducers (CMUT:s) are often used in medical imaging and they show some promise as underwater transducers. This thesis collates the available information about how CMUT:s operate, their strengths and weaknesses and investigates their efficiency as an underwater transducer. The accumulated knowledge was channelled into a simulation of a CMUT as a dampened spring system done in MATLAB and Simulink. The simulation investigated the resonance frequency and bandwidth through simulation and compared the results to experimental results from literature.  CMUT:s have good acoustic matching with water making them sensitive, broadband transducers when used under water. Special care must be taken when choosing the CMUT so that materials and designs can fulfil the task for which it is intended, such as the radius of the membrane, the material of the membrane, the insulating layers in or around the CMUT and the height of the air gap inside. CMUT:s are, for the transmission of sound, less capable than existing lead zirconate-titanate-transducers (PZT-transducers). This problem can be somewhat alleviated through operating the CMUT in collapse-mode but care must be taken so that the CMUT is not damaged during this operation. Simulation results and results from literature show that it is possible to simulate CMUT:s with accuracy. By simulating 10 different CMUT:s, using the geometries and material properties of experimentally tested devices and testing for resonance frequency and bandwidth the results were as follows:The average relative error of resonance frequency was found to be -14 %, if outlier results are excluded and the average relative error of bandwidth proved inaccurate at -54 %
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21

Cetin, Ahmet Murat. "Design And Verification Of Diamond Based Capacitive Micromachined Ultrasonic Transducer." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12612960/index.pdf.

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Potential applications such as high intensity focused ultrasound in medical therapeutics require larger output pressures. To offer unprecedented acoustic output pressure in transmit without the limitations, Capacitive Micromachined Ultrasonic Transducer operation modes of collapse and collapse-snapback are introduced in literature. Both operation modes require the membrane to contact the substrate surface, which poses a problem on the durability of the membrane in terms of structural integrity and tribological property. Based on the additional requirements of these modes, diamond is proposed as the ultimate solution to be used as the membrane material. Mechanical, thermal, and electrical properties of diamond are all in favor of its use in the microfabrication of CMUTs. This thesis introduces the design and test results of the first diamond-based CMUTs as an alternative to silicon and silicon nitride based CMUTs. Simulations are performed using Finite Element Methods (FEM) using a commercially available software package, ANSYS. The diamond-based CMUT is operated successfully both in air and immersion for the first time. Fully customizable in-house software is developed to command and control the test setup equipments for current dissertation and future work. Fresnel and Fraunhofer regions of the CMUT are characterized in sunflower oil using a combination of advanced hardware and software. The experimental results of radiation and diffraction for the diamond-based circular CMUT are verified by the theoretical calculations for a circular piston transducer. The results obtained from the first generation diamond-based CMUTs presented the diamond as a promising material for membranes in CMUTs.
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22

Novell, Anthony. "Imagerie de contraste ultrasonore avec transducteurs capacitifs micro-usinés." Phd thesis, Tours, 2011. http://tel.archives-ouvertes.fr/tel-00665141.

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Les produits de contraste ultrasonore constituent un véritable apport pour l'imagerie échographique et sont aujourd'hui utilisés en clinique pour l'évaluation de la perfusion cardiaque ou encore la détection de tumeurs. Depuis quelques années, les transducteurs capacitifs micro-usinés (cMUTs) se présentent comme une alternative intéressante aux transducteurs piézoélectriques classiques et offrent certains avantages comme une large bande passante. Nous proposons dans cette thèse d'évaluer le potentiel de cette technologie pour l'imagerie de contraste. Dans un premier temps, notre étude s'est orientée vers l'adaptation des cMUTs à l'imagerie non linéaire. Ensuite, de nouvelles méthodes de détection de contraste, basées sur le comportement spécifique des microbulles, ont été développées pour exploiter les avantages de la technologie cMUT. Comparés aux méthodes conventionnelles, les résultats obtenus montrent une meilleure visualisation des agents de contraste par rapport aux tissus environnants. L'utilisation de cMUTs améliore l'efficacité de ces méthodes démontrant, ainsi, leur intérêt pour l'imagerie de contraste.
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23

Davis, Lynford O. "Investigation of residual and thermal stress on membrane-based MEMS devices." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0003295.

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24

Chinchilla, Lenin. "Quantitative ultrasound techniques to characterize soft tissue anisotropy." Thesis, Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0154.

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Les techniques quantitatives ultrasonores basées sur la paramétrisation du coefficient de rétrodiffusion (BSC) supposent généralement que le tissu étudié est homogène et isotrope. Cependant, certains tissus tels que les agrégats des globules rouges, le myocarde ou les muscles du biceps présentent des propriétés acoustiques dépendantes de l'angle (BSC et/ou coefficient d'atténuation). L'objectif de cette thèse était d'intégrer l'anisotropie dans l'analyse de la rétrodiffusion tissulaire. Dans un premier temps, un modèle de rétrodiffusion ultrasonore est proposé et évalué numériquement pour caractériser les structures anisotropes des agrégats des globules rouges. Ensuite, une procédure expérimentale a été évaluée pour mesurer l'anisotropie du BSC dans des fantômes des tissus. Plus précisément, une comparaison des performances est effectuée entre une sonde à transducteur ultrasonore micro-usiné capacitif et une sonde piézoélectrique commerciale pour mesurer l'anisotropie de rétrodiffusion en utilisant la stratégie d'imagerie par orientation du faisceau focalisé<br>Quantitative ultrasound techniques based on the parameterization of the backscatter coefficient (BSC) generally assume that the tissue under investigation is homogeneous and isotropic. However, some tissues such as flowing red blood cell (RBC) aggregates, myocardium or bicep muscles exhibit angle-dependent acoustic properties (BSC and/or attenuation coefficient). The objective of this thesis was to incorporate anisotropy in tissue backscatter analysis. First, an ultrasonic backscattering model is proposed and evaluated numerically to characterize the anisotropic structures of RBC aggregates. Then, an experimental procedure was evaluated to measure BSC anisotropy in tissue-mimicking phantoms. More specifically, a performance comparison is carried out between a capacitive micromachined ultrasonic transducer probe and a commercial piezoelectric probe to measure backscatter anisotropy by using the focused beam steering imaging strategy
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Heller, Jacques. "Modélisation et caractérisation de transducteurs ultrasonores capacitifs micro-usinés appliqués à la réalisation de transformateurs pour l'isolation galvanique." Thesis, Tours, 2018. http://www.theses.fr/2018TOUR4009/document.

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Ces travaux présentent l'étude de transformateurs par voie acoustique, basés sur la technologie CMUT (Capacitive Micromachined Ultrasonic Transducer ), visant à développer des composants monolithiques assurant l'isolation électrique au sein de la commande des interrupteurs à semi-conducteurs. S'agissant de microsystèmes électromécaniques, les CMUTs offrent des perspectives intéressantes en terme d'intégrabilité monolithique avec les interrupteurs à semi-conducteurs. L'architecture proposée est constituée de deux transducteurs CMUTs de part et d'autre d'un substrat en silicium. Un outil de modélisation a été développé dans le but de prédire le comportement du transformateur. Des protocoles de mesure du rendement des dispositifs fabriqués ont été mis en place permettant une évaluation quantitative des performances des prototypes (un rendement de 32 % est atteint avec une marge de progression à 60 %). L'exploitation du modèle développé, et validé par les résultats de caractérisation, a permis de mettre en évidence les limites et perspectives d'amélioration de ces dispositifs<br>This work is a study of CMUT (Capacitive Micromachined Ultrasonic Transduer)based acoustical transformers as a step in the development of insulating components in semiconductor switches control chain. CMUT transducers being electromechanical systems (MEMS), their monolithic integration with semiconductor switches is full of interesting perspectives . The proposed architecture consists of two CMUTs layered on each side of a silicon substrate. A computational tool was designed to predict the behaviour of the transformer. Measurement protocols of the power efficiency of the constructed transformers were set up and allowed to quantify the prototypes' performances (A 32 % efficiency is currently reached, with improvements attainable up to 60 %). Exploring the results of the developed model, validated by bench measurements, allowed to determine the current limits of the transformers as well as perspectives of improvement
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Lascaud, Julie. "Elaboration de couches minces atténuantes en silicium poreux : Application aux transducteurs ultrasonores capacitifs micro-usinés." Thesis, Tours, 2017. http://www.theses.fr/2017TOUR4026/document.

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Les transducteurs ultrasonores capacitifs micro-usinés (CMUT) représentent aujourd’hui une réelle alternative aux technologies piézoélectriques dans le domaine de l’imagerie échographique médicale. Au cours des années, les procédés de fabrication des transducteurs se sont enrichis en vue d’améliorer leurs performances. A contrario le choix du substrat, généralement en silicium, a été peu étudié. Il est cependant reconnu que le support contribue à la signature acoustique du dispositif ultrasonore. L’objectif de ces travaux de thèse a été d’intégrer une couche de silicium poreux afin d’absorber une partie des ondes élastiques qui se propagent dans le substrat et interfèrent avec le signal acoustique émis. Nous montrons alors qu’il été possible de réaliser une couche de silicium poreux en face arrière de composants, sur plaquettes 6 pouces, sans dégrader leurs performances. Finalement, par l’intermédiaire de caractérisations acoustiques et des signatures impulsionnelles des transducteurs, nous révélons le potentiel prometteur de ce matériaux pour la réalisation de milieu arrière atténuant dédié à la transduction ultrasonore<br>Capacitive micromachined ultrasonic transducers (CMUT) have emerged as a potential alternative to traditional piezoelectric transducers for ultrasound imaging. Along the years, CMUT processes have been evolved to enhance the device performances. In the meantime, no particular attention was paid on the silicon substrate, even if it is well-known that it could contribute to the transducer efficiency. The aim of this PhD thesis was to use porous silicon as a backing material for ultrasonic transducers to absorb a piece of the acoustic wave propagating in the substrate and which induce crosstalks in the acoustic signal. We show that porous silicon layer can be obtained on the rear side of already processed wafers without any damage on the performances of capacitive micromachined ultrasonic transducers. Finally, by means of acoustic characterizations and the transducer electroacoustic responses, we reveal the potential interest of porous silicon as backing material for ultrasonic transducers
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27

Zahorian, Jaime S. "Fabrication technology and design for CMUTS on CMOS for IVUS catheters." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51730.

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The objective of this research is to develop novel capacitive micromachined ultrasonic transducer (CMUT) arrays for intravascular ultrasonic (IVUS) imaging along with the fabrication processes to allow for monolithic integration of CMUTs with custom CMOS electronics for improved performance. The IVUS imaging arrays include dual-ring arrays for forward-looking volumetric imaging in coronary arteries and annular-ring arrays with dynamic focusing capabilities for side-looking cross sectional imaging applications. Both are capable of integration into an IVUS catheter 1-2 mm in diameter. The research aim of monolithic integration of CMUTs with custom CMOS electronics has been realized mainly through the use of sloped sidewall vias less than 5 µm in diameter, with only one additional masking layer as compared to regular CMUT fabrication. Fabrication of CMUTs has been accomplished with a copper sacrificial layer reducing isolation layers by 50%. Modeling techniques for computational efficient analysis of CMUT arrays were developed for arbitrary geometries and further expanded for use with larger signal analysis. Dual-ring CMUT arrays for forward-looking volumetric imaging have been fabricated with diameters of less than 2 mm with center frequencies at 10 MHz and 20 MHz, respectively, for an imaging range from 1 mm to 1 cm. These arrays, successfully integrated with custom CMOS electronics, have generated 3D volumetric images with only 13 cables necessary. Performance from optimized fabrication has reduced the bias required for a dual-ring array element from 80 V to 42 V and in conjunction with a full electrode transmit array, it was shown that the SNR can be improved by 14 dB. Simulations were shown to be in agreement with experimental characterization indicated transmit surface pressure in excess of 8 MPa. For side-looking IVUS, three versions of annular CMUT arrays with dynamic focusing capabilities have been fabricated for imaging 1 mm to 6 mm in tissue. These arrays are 840 µm in diameter membranes linked to form 8 ring elements with areas that deviate by less than 25 %. Through modeling and simulation undesirable acoustic cross between ring elements was reduced from -13 dB to -22 dB.
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28

Sadat, David. "Simulation of a Capacitive Micromachined Ultrasonic Transducer with a Parylene Membrane and Graphene Electrodes." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5476.

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Medical ultrasound technology accounts for over half of all imaging tests performed worldwide. In comparison to other methods, ultrasonic imaging is more portable and lower cost, and is becoming more accessible to remote regions where traditionally no medical imaging can be done. However, conventional ultrasonic imaging systems still rely on expensive PZT-based ultrasound probes that limit broader applications. In addition, the resolution of PZT based transducers is low due to the limitation in hand-fabrication methods of the piezoelectric ceramics. Capacitive Micromachined Ultrasonic Transducers (CMUTs) appears as an alternative to the piezoelectric (PZT) ceramic based transducer for ultrasound medical imaging. CMUTs show better ultrasound transducer design for batch fabrication, higher axial resolution of images, lower fabrication costs of the elements, ease of fabricating large arrays of cells using MEMS fabrication, and the extremely important potential to monolithically integrate the 2D transducer arrays directly with IC circuits for real-time 3D imaging. Currently most efforts on CMUTs are silicon based. Problems with current silicon-based CMUT designs include low pressure transmission and high-temperature fabrication processes. The pressure output from the silicon based CMUTs cells during transmission are too low when compared to commercially available PZT transducers, resulting in relatively blurry ultrasound images. The fabrication of the silicon-based cells, although easier than PZT transducers, still suffers from inevitable high temperature process and require specialized and expensive equipment. Manufacturing at an elevated temperature hinders the capability of fabricating front end analog processing IC circuits, thus it is difficult to achieve true 3D/4D imaging. Therefore novel low temperature fabrication with a low cost nature is needed. A polymer (Parylene) based CMUTs transducer has been investigated recently at UCF and aims to overcome limitations posted from the silicon based counterparts. This thesis describes the numerical simulation work and proposed fabrication steps of the Parylene based CMUT. The issue of transducer cost and pressure transmission is addressed by proposing the use of low cost and low temperature Chemical Vapor Deposition (CVD) fabrication of Parylene-C as the structural membrane plus graphene for the membrane electrodes. This study focuses mainly on comparing traditional silicon-based CMUT designs against the Parylene-C/Graphene CMUT based transducer, by using MEMS modules in COMSOL. For a fair comparison, single CMUT cells are modeled and held at a constant diameter and the similar operational frequency at the structural center. The numerical CMUT model is characterized for: collapse voltage, membrane deflection profile, center frequency, peak output pressure transmission over the membrane surface, and the sensitivity to the change in electrode surface charge. This study took the unique approaches in defining sensitivity of the CMUT by calculating the membrane response and the change in the electrode surface charge due to an incoming pressure wave. Optimal design has been achieved based on the simulation results. In comparison to silicon based CMUTs, the Parylene/Graphene based CMUT transducer produces 55% more in volume displacement and more than 35% in pressure output. The thesis has also laid out the detailed fabrication processes of the Parylene/Graphene based CMUT transducers. Parylene/Graphene based ultrasonic transducers can find wide applications in both medical imaging and Non destructive evaluation (NDE).<br>ID: 031001393; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Title from PDF title page (viewed May 28, 2013).; Thesis (M.S.M.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 105-113).<br>M.S.M.E.<br>Masters<br>Mechanical and Aerospace Engineering<br>Engineering and Computer Science<br>Mechanical Engineering; Miniature Engineering Systems
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29

Sénégond, Nicolas. "APPROCHE TEMPORELLE DE LA SIMULATION ET DE LA CARACTÉRISATION DES TRANSDUCTEURS ULTRASONORES CAPACITIFS MICRO-USINÉS." Phd thesis, Université François Rabelais - Tours, 2010. http://tel.archives-ouvertes.fr/tel-00738359.

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Les transducteurs ultrasonores capacitifs micro-usinés (cMUT : capacitive Micromachined Ultrasound Transducers) sont aujourd'hui une nouvelle alternative à la transduction d'ondes ultrasonores. En comparaison avec la technologie piézoélectrique, ils offrent de nombreuses potentialités en termes de fiabilité, de production, de miniaturisation et d'intégration, d'une électronique associée mais aussi en termes de performances acoustiques. Les voies d'application de ces dispositifs, dédiés initialement à l'imagerie médicale, sont aujourd'hui étendues à de nombreux domaines tels que la thérapie, les capteurs biochimiques ou encore l'émission paramétrique d'ondes sonores. Néanmoins, leur mise en œuvre n'en est encore qu'à ses balbutiements et la compréhension de leurs comportements à la fois statique et dynamique nécessite d'être approfondie. C'est dans ce cadre que s'inscrit le présent travail de thèse. Ce mémoire adresse deux aspects majeurs de ces micro-systèmes : leur caractérisation mécanique et l'impact de la non-linéarité des forces électrostatiques sur la réponse temporelle. La caractérisation des micro-systèmes, notamment en termes de contraintes initiales et de modules d'élasticité, est une problématique récurrente de ces dispositifs. Dans le contexte des technologies cMUT, fabriquées par procédé de micro-usinage de surface, nous avons souhaité reposer les bases de cette étape de mesure et proposer des méthodes de caractérisation basées sur l'utilisation de dispositifs fonctionnels plutôt que s'appuyer sur des structures dédiées (micro-poutre, ponts, structures rotatives). L'impact de la non-linéarité sur la dynamique dans le fluide d'une cellule, puis d'un réseau de cellules, est ensuite étudié en s'appuyant à la fois sur des mesures d'interférométrie laser et sur un modèle temporel intégrant les effets du fluide. Nous exposons ici une étude à plusieurs échelles, allant de la cellule unitaire du dispositif à la pression rayonnée par un élément de barrette. Une optimisation de l'excitation dans l'objectif de réduire l'effet de la non-linéarité tout en conservant des niveaux de pressions optimum est proposée. En fin, à travers l'étude dynamique effectuée, un nouveau régime de fonctionnement des cMUTs est identifié et vérifié. Celui-ci s'appuie sur l'exploitation du régime forcé dans l'air ou dans l'eau de ces dispositifs pour la génération d'ondes ultrasonores basse-fréquence.
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30

Guldiken, Rasim Oytun. "Dual-electrode capacitive micromachined ultrasonic transducers for medical ultrasound applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/31806.

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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009.<br>Committee Chair: Degertekin, F. Levent; Committee Member: Benkeser, Paul; Committee Member: Berhelot, Yves; Committee Member: Brand, Oliver; Committee Member: Hesketh, Peter. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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31

Hery, Maxime. "Conception et optimisation de transducteurs capacitifs micro-usinés appliqués à l'imagerie ultrasonore." Thesis, Tours, 2019. http://www.theses.fr/2019TOUR4013.

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Les Transducteurs Ultrasonores Capacitifs Micro-usinés (CMUT en anglais) sont étudiés par plusieurs laboratoires internationaux depuis les années 90. Se présentant comme une alternative aux transducteurs traditionnels piézoélectriques, cette technologie inspirée des MEMS (MicroElectroMechanical Systems) a aujourd'hui atteint la maturité suffisante pour voir émerger sa commercialisation. Dans son application historique, l'imagerie médicale, de nombreux acteurs industriels proposent des sondes CMUTs, comme Hitachi, Kolo Medicals ou Butterfly Network pour n'en citer que quelques uns. La recherche autour de ces dispositifs continue néanmoins à travers des études sur la conception, la modélisation, la fabrication ou pour de nouvelles applications. À travers le projet collaboratif TUMAHI (Transducteurs capacitifs Ultrasonores Multi-Application Hautement Intégrés) entre le laboratoire GREMAN et la société VERMON S.A, deux axes d'optimisation ont été étudiés. Le premier objectif consistait à créer et valider expérimentalement une stratégie de conception d'éléments CMUTs pour optimiser la réponse électroacoustique sur la bande passante ou la sensibilité. La principale contrainte était de définir des degrés de liberté et des paramètres fixes pour fabriquer des barrettes CMUTs pour diverses applications et fréquences de travail sur un même wafer. Par l'intermédiaire d'un dispositif centré à 10 MHz pour de l'imagerie médicale, nous avons fait varier les tailles de membranes pour posséder une configuration Large Bande et une configuration Sensible. Une campagne de mesures de pression a été effectuée avec les sondes complètes et prêtes à l'emploi pour valider les critères de conception établis. L'analyse poussée a néanmoins souligné que la démarche de conception pour une sonde CMUT la plus efficace était d'optimiser la fréquence de résonance du premier mode de rayonnement pour qu'elle coïncide avec la fréquence de travail désirée. La seconde étude était focalisée sur la couche de passivation, couche de protection pour les éléments CMUTs traditionnellement conçue en polymère silicone, et visait à implémenter son impact dans les outils de modélisation avec un nouveau modèle de couplage CMUT / matériau viscoélastique. Une fonction de Green en trois dimensions a été utilisée en définissant des équivalences entre propriétés élastiques et viscoélastiques et validée théoriquement avec des problèmes de Lamb 2D et 3D complémentaires. Une confrontation avec des résultats expérimentaux a été engagée en créant une série d'huiles avec des viscosités variables et en excitant des colonnes CMUTs découplées électriquement pour viser un mode de rayonnement plus sensible aux propriétés de cisaillement du milieu. L'influence de la viscosité a été identifiée à travers la variation de la fréquence centrale et du facteur de qualité sur l'impédance électrique mesurée et simulée, posant la base d'une étude de viabilité de la technologie CMUT pour un capteur sensible viscoélastique. La considération de la couche de passivation a permis de retrouver un comportement équivalent à la réalité mais nécessite une base de données complète sur les propriétés viscoélastiques des matériaux dans le domaine ultrasonore pour être présente dans les étapes de conception d'un transducteur CMUT<br>Capacitive Micromachined Ultrasonic Transducers (CMUT) have been studied by several international laboratories since the 1990s. Presenting itself as an alternative to traditional piezoelectric transducers, this MEMS (MicroElectroMechanical Systems) inspired technology has now reached the maturity needed for commercialization. In its historic application, medical imaging, many industrial actors propose CMUT probes, such as Hotachi, Kolo Medicals or Butterfly Network to name a few. However, research on these devices continues through studies on design, modeling, manufacturing or for new applications. Through the collaborative project TUMAHI (Highly Integrated Multi-Application capacitive Ultrasonic Transducers) between the GREMAN laboratory and VERMON S.A, two areas of optimization were carried out. The first objective was to create and experimentally validate a CMUT element design strategy to optimize electroacoustic response over bandwidth or sensitivity. The main constraint was to define degrees of freedom and fixed parameters to manufacture CMUTs for various applications and working frequency on a single wafer. Through a 10 MHz centered device for medical imaging, we have varied the size of membranes to have a Broadband and Sensitive configuration. A pressure measurement campaign was carried out with complete and ready-to-use probes to validate the established design criteria. However, the in-depth analysis emphasized that the design approach for the most effective CMUT probe was to optimize the resonance frequency of the first radiation mode to coincide with the desired working frequency. The second study focused on the passivation layer, a protective layer for CMUT elements traditionally designed in silicone polymer, and aimed to implement its impact in modeling tools with a new CMUT / viscoelastic material coupling model. A three-dimensional Green function was used by defining equivalences between elastic and viscoelastic properties and theoretically validated with complementary 2D and 3D Lamb problems. A confrontation with experimental results was initiated by creating a series of oils with variable viscosities and by exciting electrically decoupled CMUT columns to target a more sensitive radiation mode to the shear properties of the medium. The influence of viscosity was identified through the variation of the central frequency and quality factor on the measured and simulated electrical impedance, providing the basis for a viability study of CMUT technology for a viscoelastic sensitive sensor. The consideration of the passivation layer has enabled the retrieval of equivalent behavior to reality but requires a complete database on the viscoelastic properties of materials in the ultrasonic domain to be present in the design steps of a CMUT transducer
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32

Hurtz, Melanie. "ADAM15/PTK6/cMET interplay : promotors of prostate cancer progression." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/107830/.

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ADAM15 is a transmembrane metalloproteinase involved in disease progression and aggressiveness in prostate cancer (PCa). ADAM15 is composed of an extracellular domain, a transmembrane region and an intracellular domain, the latter being subject to splicing due to alternative use of exons 19 to 21. The splice variants that will be subject in this study are ADAM15-A, ADAM15-B, ADAM15-C, ADAM15-D and ADAM15-E. Previously, ADAM15 splice variant A and B were reported to associate with the PCa promotor PTK6 and the cMET adaptor protein Grb2. In order to understand the underlying mechanisms for the contribution of ADAM15 to disease progression in PCa, ADAM15 A-E splice variants, overexpressed in LNCaP and PC3 PCa cells, were biochemically and functionally characterized. Overexpression of ADAM15-A in PC3 led to enhanced invasion upon HGF treatment, which could be reverted by cMET inhibitor treatment. In addition, ADAM15-induced invasion was dependent on its proteolytic activity. Moreover, PC3 cells expressing proteolytically active ADAM15 showed more MMP2 activity compared to cells with the proteolytically inactive ADAM15 mutant in cell supernatants. In contrast to the aggressive, androgen independent PC3, androgen dependent LNCaP cells did not show any response to HGF treatment upon ADAM15 A-E overexpression. All ADAM15 splice variants were found in a complex with PTK6, which could be disrupted upon cMET inhibition in PC3. Strikingly, ADAM15 was found in a complex with cMET/Gab1/Grb2/PTK6. cMET inhibition led to complex loss of cMET/Gab1/PTK6, however, Grb2 remained in complex with ADAM15 regardless of treatment. Unlike cMET, PTK6 activity was not needed for formation of the ADAM15 complex. Analysis of the ADAM15 splice profile in prostate cancer patients and comparison with healthy prostate tissue revealed a significant overexpression of all ADAM15 splice variants. In summary, we show for the first time that ADAM15 is found in a complex with cMET/Gab1/Grb2/PTK6, and importantly, that, this complex formation is dependent on the cMET/HGF axis in PC3 PCa cells. Moreover, we found that proteolytically active ADAM15 resulted in enhanced invasion upon HGF treatment in PC3s. Our data suggest an important role for ADAM15 in prostate cancer disease progression.
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33

Brattan, Daniel Keith. "Aspects of hydrodynamics in AdS/CMT." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/6370/.

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Condensed matter theory is the study of systems at finite density. In this thesis we will attempt to argue that gauge-gravity dualities can give deep and meaningful insights into the behaviour of strongly coupled condensed matter systems. The first three chapters will be a review of material already available in literature. Chapter 1 will introduce holography and the AdS-CFT correspondence. Particularly, in this chapter, the technique for the extraction of diffusion constants for charge and shear stress-energy-momentum fluctuations in a field theory with a holographic dual will be demonstrated. Chapter 2 will summarise relevant literature on the relativistic fluid-gravity correspondence. In the first half of the chapter it will be shown how to calculate the transport coefficients and Navier-Stokes equations for a suitable thermal field theory. The second half of chapter 2 will then be dedicated to extracting the transport coefficients for a strongly coupled field theory dual to a Reissner-Nordstrøm AdS spacetime. In chapter 3 a scaling of the metric and gauge field found in chapter 2 will be taken such that the boundary field theory admits Galilean, as opposed to relativistic, symmetry. Consequently, the governing hydrodynamic equations will be the non-relativistic, incompressible Navier-Stokes. Chapters 4 and 5 represent novel work. In chapter 4 the transport coefficients for a particular strongly coupled thermal field theory with underlying Schrodinger symmetry will be extracted from a charged, asymptotically Schrodinger spacetime. The governing hydrodynamic equations will be compressible with non-relativistic symmetry as opposed to those found via the scaling limit of chapter 3. In chapter 5 we show how knowledge of the transport coefficients of a thermal field theory can be used as a test-bed for numerical methods to explore beyond the hydrodynamic (long wavelength and low frequency) regime. With this in mind we consider Reissner-Nordstrøm AdS4 and determine the two point correlators at arbitrary frequency and momentum. Finally in chapter 6 we summarise the work discussed in this thesis and speculate about further applications of hydrodynamic techniques to strongly coupled condensed matter theories.
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34

Šoulák, Petr. "Aplikace CMT Advanced v průmyslové praxi." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-401050.

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In presented diploma thesis is studied problematics of welding of high strength steels. This work also describes arc welding in protective atmosphere CMT Advanced. In experimental part of this work is CMT Advanced method compared with conventional arc welding in protective atmosphere in shortcut mode used for welding of Hardox 450 and Weldox 700 E. Comparing of mechanical properties of weld material are realized via transverse tensile testing and measuring of microhardness. Macrostructure and microstructure of weld was evaluated too. In the last part of this thesis is a brief economical assessment of both studied methods.
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35

You, Wei. "Exploring multiple-mode vibrations of capacitive micromachined ultrasonic transducers (CMUTs)." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44222.

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Capacitive Micromachined Ultrasonic Transducers (CMUTs) are considered advantageous over piezoelectric transducers for ultrasound imaging for the high bandwidth, ease of integration with electronics and miniaturization. Research efforts over the past two decades have been focusing on manufacturing and system integration of CMUTs to achieve comparable and better performance than the piezoelectric counterparts, while the uniqueness of the CMUT structure and physics is barely exploited. This thesis explores the complex behavior of CMUTs from a mode superposition perspective, and demonstrates imaging applications using CMUTs' multi-modal operation. The operation of CMUTs is first analytically modeled as a coupled electro-mechano-acoustical system using plate vibration theory. As the simplest case, the first symmetric and asymmetric modes of vibration can be excited simultaneously via asymmetric electrostatic actuation, resulting in a vibration profile with a shifted center. Finite element modeling (FEM) is used to verify the theoretical calculation, and an equivalent circuit consisting of two sub-circuits for the symmetric and asymmetric vibration modes is built to show the possibility of fast simulation of complex CMUT array behavior. Experimental characterization of fabricated CMUT chips show that asymmetric vibration can be achieved with multi-electrode CMUTs. Two imaging applications using the multi-modal operation of CMUTs are proposed. The first concept, tiltable transducers, explores the benefits of orienting each transducer element toward the focal point to concentrate the acoustic energy and reduce grating lobes and side lobes. Imaging simulation shows the grating lobes can be reduced by 20dB while the main lobe energy is preserved. FEM simulation demonstrates that CMUTs capable of asymmetric vibration can be a viable candidate as tiltable transducers with careful design of the cell dimension and central frequency. The second imaging application takes advantage of the ringing response of a CMUT to off-axis acoustic sources to achieve super-resolution imaging with low computational cost. The differential responses across all CMUT cells form a more decorrelated pattern than the regular average responses, which leads to better estimation performance of the proposed super-resolution algorithm. While only preliminary experimental results for the proposed applications are presented, the multi-modal operation concept shows potential in improving several aspects of ultrasound imaging.
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36

Cao, Xue Wen. "Acoustic output pressure enhancement for CMUTs using Helmholtz resonance principle." Thesis, University of Macau, 2015. http://umaclib3.umac.mo/record=b3335757.

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37

Halepoto, Imtiaz Ali. "Scheduling and flow control in CMT-SCTP." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/210189.

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38

Jiskra, Milan. "Porovnání CMT TWIN s ostatními MIG/MAG procesy." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231134.

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The development of welding technology is constantly going forward mainly due to the reduction of production costs and the costs of additional straightening of weldments due to the welding distortion. Therefore, the leading producers of welding machine are coming with new methods and technologies. One of the innovations is also the tandem technology CMT Twin from the company Fronius. The experiment carried out in the diploma thesis confirmed that this is a very cost effective process. The CMT Twin is from the point of view of production costs of the weld cheaper variant and bring less heat into the material compared with conventional welding. Application equipment CMT Twin requires industrial robot, so the method is predestined for the series up to mass production. The CMT Twin finds application, for example in the automotive and shipbuilding industry.
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39

Albon, Helen. "What factors influence CMHT staff estimations of work-readiness in their clients?" Thesis, University of London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542327.

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40

Arroyo, Torres Elmer Jesús. "Hernioplastia Lichtenstein en el Centro Médico Naval "CMST". Experiencia de 5 años." Bachelor's thesis, Universidad Nacional Mayor de San Marcos, 2004. https://hdl.handle.net/20.500.12672/1887.

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Desde 1988 hasta la actualidad, la técnica de Lichtenstein (1) ha sido, sin duda ,la de mayor aceptación a nivel mundial; sin presentar hasta el momento un pico de descenso en su utilización y sin las complicaciones asociadas a las técnicas laparoscópicas que actualmente cobran muchos adeptos. La técnica de Lichtenstein ha demostrado su eficacia al ser aplicable para todo tipo de hernias en el orificio miopectíneo de Fruchaud, similar principio utilizado en las hernioplastías laparoscópicas; pero con la ventaja de ser aplicable a todo tipo de hernias inguinales y reproducible en centros hospitalarios de formación quirúrgica (2), y no presentar complicaciones reporatadas y costos tan elevados con la laparoscópica (3) En el Centro Médico Naval “CMST”, uno de los principales centros de referencia en el área quirúrgica en nuestro país, dicha técnica se viene reproduciendo desde hace más de 5 años, sin contar aún con un estudio retrospectivo que nos oriente hacia los beneficios obtenidos en comparación con las técnicas clásicas convencionales ni con las nuevas técnicas laparoscópicas de abordaje transabdominal (6,11,26,33) y extraperitoneal (3) Los resultados recogidos en la bibliografía, tras reparación de una hernia inguinal primaria sin empleo de material protésico son variables, dependiendo de la técnica realizada,(3,8), así como de la experiencia del cirujano, con tasas de recidiva que oscilan entre 1% y el 10% (9,10,38). Se considera que la principal causa de estos resultados es la aproximación de tejidos bajo tensión. Por ello han surgido técnicas que incluyen la colocación de prótesis sintéticas (malla) (4,5,49,16) sobre el defecto, dentro de ellas está la técnica de Lichtenstein con baja tasa de recidiva (menor al 1%) (7). Sin embargo no previene ni trata a las hernias femorales (tipo III C), tampoco protege totalmente el área defectuosa principal (preperitoneal).<br>Tesis de segunda especialidad
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41

Manger, Stefanie Verfasser], Margarete [Akademischer Betreuer] Schön, Inga [Gutachter] [Zerr, and Marios-Nikos [Gutachter] Psychogios. "cMRT-Auffälligkeiten und Symptomatik bei CJK-Patienten - Gibt es eine Korrelation zwischen cMRT-Veränderungen und der klinischen Symptomatik / Stefanie Manger ; Gutachter: Inga Zerr, Marios-Nikos Psychogios ; Betreuer: Margarete Schön." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://d-nb.info/1159375534/34.

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42

Fitzmaurice, Silas James. "Blast retrofit design of CMU walls using polymer sheets." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4569.

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Thesis (M.S.)--University of Missouri-Columbia, 2006.<br>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) Includes bibliographical references.
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43

Jeckel, Pauline [Verfasser]. "Die Rezeptortyrosinkinase cMet reguliert die mTOR-abhängige Gephyrinclusterung an inhibitorischen Synapsen / Pauline Jeckel." Tübingen : Universitätsbibliothek Tübingen, 2021. http://d-nb.info/1228858209/34.

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44

Satir, Sarp. "Modeling and optimization of capacitive micromachined ultrasonic transducers." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54303.

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The objective of this research is to develop large signal modeling and optimization methods for Capacitive Micromachined Ultrasonic Transducers (CMUTs), especially when they are used in an array configuration. General modeling and optimization methods that cover a large domain of CMUT designs are crucial, as many membrane and array geometry combinations are possible using existing microfabrication technologies. Currently, large signal modeling methods for CMUTs are not well established and nonlinear imaging techniques utilizing linear piezoelectric transducers are not applicable to CMUTs because of their strong nonlinearity. In this work, the nonlinear CMUT behavior is studied, and a feedback linearization method is proposed to reduce the CMUT nonlinearity. This method is shown to improve the CMUT performance for continuous wave applications, such as high-intensity focused ultrasound or harmonic imaging, where transducer linearity is crucial. In the second part of this dissertation, a large signal model is developed that is capable of transient modeling of CMUT arrays with arbitrary electrical terminations. The developed model is suitable for iterative design optimization of CMUTs and CMUT based imaging systems with arbitrary membrane and array geometries for a variety of applications. Finally, a novel multi-pulse method for nonlinear tissue and contrast agent imaging with CMUTs is presented. It is shown that the nonlinear content can be successfully extracted from echo signals in a CMUT based imaging system using a multiple pulse scheme. The proposed method is independent of the CMUT geometry and valid for large signal operation. Experimental results verifying the developed large signal CMUT array model, proposed gap feedback and multi-pulse techniques are also presented.
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45

GEREN, REBECCA. "CALCULATING FIRE-RESISTANCE RATINGS OF CONCRETE MASONRY UNIT (CMU) WALLS." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/618764.

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This paper serves as a statement accompanying a capstone project for a degree in Information: Science and Technology. It details the work that went into creating the web page dedicated to helping specifications and codes writers to calculate fire resistance ratings of concrete masonry unit (CMU) walls. It briefly examines what a CMU wall is and the calculations that are involved in calculating fire-resistance ratings. The paper delves into how the site itself works, what the user can expect to see when first accessing the page and how to follow the steps in order to get the correct output. Without getting too technical, the paper also describes the four programming languages that were involved with coding the web page and what they handle in accordance with the page’s design and implementation. Finally, the paper concludes with an appendix containing the URL that will lead the reader to the web calculator and provides some practice problems that will allow the reader to test the calculator’s abilities.
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46

Paroissien, Simon. "Simulation numérique d’un assemblage métal / composite thermoplastique par CMT pins." Thesis, Ecole centrale de Nantes, 2016. http://www.theses.fr/2016ECDN0001/document.

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Une méthode est proposée pour la modélisation d’unassemblage multimatériaux innovant visant des applicationsdans l’allègement structurel des véhicules. Dans cetassemblage une partie composite thermoplastique, est fixée àune plaque acier texturée par la technologie CMT pins.L’interface est particulièrement complexe et non linéaire : unereprésentation fine du comportement local serait extrêmementpénalisante en temps de calcul. Dans cette optique il a étéchoisi d’orienter la méthodologie vers une modélisation la plussimple possible tout en conservant de bons résultats globaux.Pour ce faire, en s’inspirant de l’état de l’art existant sur lesmultimatériaux, une campagne expérimentale a été menée surdes éprouvettes longitudinales à double recouvrement afin decaractériser cette interface. Une fois les mécanismes locauxinvestigués, deux modèles sont proposés. Le premiernumérique basé sur la méthode des éléments finis etl’introduction d’éléments cohésifs nous permet de valider leshypothèses de modélisation tout en quantifiant la répartitiondes efforts entre les picots. Le deuxième se base sur le calcullocal d’un Volume Élémentaire Représentatif pour établiranalytiquement la loi de comportement de l’interface. Cette loiest ensuite introduite sous la forme d’un ressort non linéaire ausein d’un modèle numérique simplifié de l’éprouvette. Pourfinir ces approches sont appliquées au cas d’étude industriel etles résultats sont validés par une deuxième campagneexpérimentale<br>A method is proposed to simulate an innovative multimaterialassembly which has applications in structural lightweight forvehicles. In this assembly, a thermoplastic composite part isfixed on a steel plate, textured by the CMT pins technology.This is an especially complex and nonlinear interface: a finerepresentation of local behaviour would be extremely costlyfor calculation. So, it has been chosen to investigate a model assimple as possible which still demonstrates accurate globalresults.An experimental campaign on double lap shear specimen,inspired by existing state of the art on multimaterial has beenset up to characterize this interface. Once local mechanismshave been understood, two models are proposed and compared.The first is numerical and based on finite elements method andcohesive elements. It allows us to validate the modelhypotheses while describing the effort repartition between thepins. The second one is based on a Representative VolumeElement. It establishes analytically the behaviour law of theinterface. This law is then inserted inside a simplifiednumerical model of the specimen by means of a nonlinearspring. To conclude, these approaches are applied to theindustrial case of study and the result have been validated by asecond experimental campaign
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47

Legros, Mathieu. "Transducteurs capacitifs micro-usinés pour l'imagerie échographique." Thesis, Tours, 2013. http://www.theses.fr/2013TOUR3306.

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La conception des sondes ultrasonores pour l’imagerie médicale est traditionnellement basée sur l’utilisation de matériaux piézoélectriques. Depuis quelques années, est apparue la technologie des CMUTs, (Capacitive Micromachined Ultrasonic Transducers). Ces microsystèmes électromécaniques se présentent comme une alternative attractive à la piézoélectricité, offrant la possibilité d’explorer de nouveaux designs de sonde, et d’expérimenter de nouveaux modes d’imagerie. Ce travail s’inscrit dans une dynamique de développement et d’évaluation des sondes CMUTs, de la modélisation à la démonstration par l’image. Des transducteurs multi-éléments CMUTs ont ainsi été conçus, et des prototypes de sondes d’échographie finalisés ont pu être réalisés, ce en adaptant les développements à la transduction capacitive et aux systèmes d’imagerie conventionnels. Leurs comportements électroacoustiques et acoustiques ont été étudiés et comparés à des sondes standards. Finalement, des démonstrations par l’image ont été apportées, et les points forts de cette technologie pour l’imagerie médicale ont pu être établis<br>Fabrication of ultrasound probes for medical imaging conventionally exploits piezoelectric based materials. CMUTs technology (Capacitive Micromachined Ultrasonic Transducers) has emerged about a decade ago. These electromechanical micro-systems are presented as an alternative transduction mode, and gives new opportunities for probe design and novel imaging techniques. This dissertation aims to develop and review CMUTs probes for ultrasound imaging, from modeling to imaging demonstration. Multi-elements transducers with CMUT technology have been thus developed, and ultrasound probes were successfully achieved. Developments have been carried out, taking care of both capacitive transduction and standard ultrasound systems. Electro-acoustic and acoustic behavior were evaluated and compared to the state of the art piezoelectric probes. Finally, quantitative imaging assessments have been performed and have pointed out the strengths of CMUT technology for ultrasound imaging
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48

Ma, Nicholas. "Modeling and evaluation of multi-core multithreading processor architectures in SystemC." Thesis, Kingston, Ont. : [s.n.], 2007. http://hdl.handle.net/1974/510.

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49

Kwiatkowska, Aneta, Sebastien Didier, Shannon Fortin, et al. "The small GTPase RhoG mediates glioblastoma cell invasion." BioMed Central, 2012. http://hdl.handle.net/10150/610207.

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BACKGROUND:The invasion of glioblastoma cells into regions of the normal brain is a critical factor that limits current therapies for malignant astrocytomas. Previous work has identified roles for the Rho family guanine nucleotide exchange factors Trio and Vav3 in glioblastoma invasion. Both Trio and Vav3 act on the small GTPase RhoG. We therefore examined the role of RhoG in the invasive behavior of glioblastoma cells.RESULTS:We found that siRNA-mediated depletion of RhoG strongly inhibits invasion of glioblastoma cells through brain slices ex vivo. In addition, depletion of RhoG has a marginal effect on glioblastoma cell proliferation, but significantly inhibits glioblastoma cell survival in colony formation assays. We also observed that RhoG is activated by both HGF and EGF, two factors that are thought to be clinically relevant drivers of glioblastoma invasive behavior, and that RhoG is overexpressed in human glioblastoma tumors versus non-neoplastic brain. In search of a mechanism for the contribution of RhoG to the malignant behavior of glioblastoma cells, we found that depletion of RhoG strongly inhibits activation of the Rac1 GTPase by both HGF and EGF. In line with this observation, we also show that RhoG contributes to the formation of lamellipodia and invadopodia, two functions that have been shown to be Rac1-dependent.CONCLUSIONS:Our functional analysis of RhoG in the context of glioblastoma revealed a critical role for RhoG in tumor cell invasion and survival. These results suggest that targeting RhoG-mediated signaling presents a novel avenue for glioblastoma therapy.
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50

Corral, Carla Maria Fernandes. "Partilhando olhares : perspectivas da arte na educação de jovens e adultos do CMET Paulo Freire." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2005. http://hdl.handle.net/10183/5069.

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Esta dissertação aborda os sentidos produzidos nas aulas de Artes Visuais para jovens e adultos das Totalidades Iniciais do Centro Municipal de Educação dos Trabalhadores Paulo Freire (CMET Paulo Freire), centro de educação de jovens e adultos vinculado à Secretaria Municipal de Educação de Porto Alegre. O trabalho insere-se na temática da arte e educação de jovens e adultos. A pesquisa foi realizada ao longo do ano de 2004. Paulo Freire, Alberto Melucci, Miguel Arroyo, João Francisco Duarte Jr., Fayga Ostrower, Ernest Fischer, Louis Porcher, A.J.Greimas, entre outros, foram fontes teórico-inspiradoras. A metodologia utilizada está apoiada em entrevistas individuais, na esfera das histórias de vida, das entrevistas coletivas e do diário de campo. As histórias de vida contam um pouco de como foi e como é a vida de duas idosas alunas do CMET, ilustrando quem são os adultos idosos que lá freqüentam as aulas. Nas entrevistas coletivas, três categorias foram encontradas: papel do professor, importância das aulas de arte, fazer arte. Cada uma dessas categorias expressa o olhar que o aluno tem sobre as aulas de Artes Visuais, o que lhe é significativo, o que lhe chama atenção. São muitos os sentidos produzidos nas aulas de Artes Visuais: o tempo interno de cada um, a possibilidade de fazer arte, o cotidiano desses sujeitos de pesquisa, modificado seja pelas trocas entre pares, com professora e com familiares, seja por fazerem coisas que nunca imaginaram fazer. Os sujeitos perceberam-se seresfazedores que, com o resultado de seu fazer, tornam-se seres-sabedores-de-beleza. Os alunos foram fazer aula de Artes Visuais e encontraram, talvez, outros sentidos para si mesmos, para a vida. Sentidos produzidos para além das aulas.
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