Orientadores: Eduardo Tavares Costa, Rosana Almada Bassani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-19T01:08:15Z (GMT). No. of bitstreams: 1 Buiochi_ElaineBelassiano_D.pdf: 9610613 bytes, checksum: 5fefa9e6cf5eaf8478c002d7ab57dc23 (MD5) Previous issue date: 2011 / Resumo: No ultrassom diagnóstico faz-se uso de ondas acústicas de baixa intensidade para investigar os tecidos biológicos, sendo uma técnica não invasiva. Ondas ultrassônicas de maior intensidade podem alterar as características do tecido, e isto é de interesse para aplicações terapêuticas, nas quais a ocorrência de efeitos biológicos é, até certo ponto, desejável. Com relação à cardiologia, o uso do ultrassom diagnóstico é bem estabelecido, enquanto há um potencial inexplorado para aplicações terapêuticas. Soma-se a isso o fato de que os tratamentos disponíveis para as arritmias com estimulação elétrica são limitados por sérias complicações, incluindo infecção sistêmica, choques desnecessários, potencial para pró-arritmia, falha em estimular e, até mesmo, morte. O ultrassom pode se mostrar uma alternativa atraente à estimulação elétrica, porém há poucos estudos sobre a possibilidade de aplicação do ultrassom para o tratamento de arritmias. O objetivo deste estudo foi desenvolver transdutores ultrassônicos de potência e usá-los para investigar conjuntos de parâmetros acústicos capazes de interferir na atividade cardíaca, sem provocar danos teciduais, buscando possíveis aplicações terapêuticas do ultrassom em cardiologia. Os parâmetros acústicos variados foram frequência de ressonância, modo de operação, frequência de repetição de pulso, e pressão de saída. Dois dos sete transdutores construídos se mostraram mais eficientes e, portanto, foram calibrados e usados nos experimentos biológicos. Em experimentos preliminares realizados em corações isolados de ratos Wistar, foi observada geração esporádica de arritmia usando-se o transdutor de 65 kHz, e aumento da frequência espontânea, acompanhada por redução da força de contração do miocárdio, usando-se o transdutor de 1MHz em exposição contínua prolongada. Em estudos in vivo, dez ratos Sprague-Dawley foram anestesiados com isoflurano e expostos a uma seqüência terapêutica de ultrassom, e outros cinco ratos foram usados como grupo controle. A estimulação ultrassônica consistiu de bursts de 1MHz, ciclo de trabalho de 1%, pico de pressão negativa de 3MPa (ISPTA=3W/cm2), e freqüência de repetição de pulso variável e decrescente. O ultrassom transtorácico exerceu efeito cronotrópico negativo, uma vez que foi capaz de reduzir a freqüência cardíaca em 19% logo ao final do período de estimulação. Os efeitos duraram, no mínimo, 15 minutos, sem aparente prejuízo hemodinâmico, que foi monitorado principalmente por meio da medição da fração de ejeção. Trata-se de um fenômeno promissor para o tratamento de taquiarritmias. O regime de exposição utilizado excluiu efeitos térmicos, de forma que o efeito observado foi provavelmente resultante de mecanismos não-térmicos, possivelmente da força da radiação. A variação na frequência de repetição de pulso parece ter sido a chave para a indução do efeito em questão, uma vez que experimentos realizados com frequências de repetição constantes não resultaram em tal efeito / Abstract: Diagnostic ultrasound consists of application of low intensity acoustic waves to noninvasively investigate biological tissues. Higher ultrasound intensities may alter tissue characteristics, and this is of interest for therapeutic applications, when the occurrence of bioeffects is - to a certain extent - desirable. The use of diagnostic ultrasound in Cardiology is well established, although there is an unexplored potential for therapeutic applications. The currently available treatments of arrhythmias by electrical stimulation are limited by serious complications, including systemic infection, inappropriate shock delivery, proarrhythmia, failure to pace and to defibrillate, and even death. Ultrasound can be an interesting alternative for electrical stimulation, but there are only a few studies that investigate the possibility of applying ultrasound for treating arrhythmias. The objective of this study was to develop power ultrasonic transducers to be applied to the investigation of sets of acoustical parameters able to interfere with the cardiac activity without causing tissue damage, thus aiming at potential therapeutic applications of ultrasound in cardiology. The acoustical parameters investigated were resonance frequency, operation mode, pulse repetition frequency, and output pressure. The two most efficient out of the seven transducers built were calibrated and used in biological experiments. In preliminary experiments conducted on isolated hearts from Wistar rats, arrhythmia was esporadically observed at the onset of ultrasound application using the 65kHz transducer, whereas an increase in spontanous beating rate accompanied by a reduction in the force developed by the myocardium occurred during continuous, prolonged exposure using the 1MHz transducer. In in vivo studies, ten Sprague-Dawley rats were anesthetized with isoflurane and exposed to a sequence of therapeutic ultrasound, and other five rats were used as a control group. The ultrasonic stimulation consisted of 1-MHz bursts of 1% duty cycle, 3 MPa peak negative pressure (ISPTA=3W/cm2), and decreasingly variable pulse repetition frequencies. Transthoracic ultrasound application was able to promote a negative chronotropic effect, decreasing the heart rate by 19% just after stimulation ceased. The effect lasted at least 15 minutes, without apparent alteration of pumping function, which was monitored mainly by evaluation of the ejection fraction. This phenomenon is promising for treating tachyarrhythmias. The insonification scheme used in this study excluded thermal effects, so the observed effect seems to have resulted from nonthermal mechanisms, possibly from radiation force. The variation in the pulse repetition frequency seems to be the key element for induction of the described effect, because the latter was not observed for constant repetition rates / Doutorado / Engenharia Biomedica / Doutor em Engenharia Elétrica

This thesis presents the design and analysis for development of a Capacitive Micromachined Ultrasonic Transducer (CMUT), a novel sensor and actuator, aimed at replacing the conventional piezoelectric transducers for air-coupled ultrasonic imaging applications. These CMUTs are fabricated using the silicon micromachining technology wherein all fabrication is done on the surface of a silicon wafer by means of thin-film depositions, patterning with photolithography and etching. The main emphasis of this study is on developing analytical models that serve as effective design tools for the development of these devices. A desirable goal of such study is to create reasonable mathematical models, obtain analytical solutions, wherever possible, for various measures of transducer performance and provide design aids. A logical start is the lumped parameter modeling wherein the explicit dependence of the physical parameters on the spatial extent of the device is ignored. The system lumped parameters, such as the equivalent stiffness, the equivalent mass, and the equivalent damping are extracted from reasonable analytical or numerical models and subsequently used in the static and dynamic analysis of the device. Useful predictions are made with regard to the key transducer parameters, such as, the pull-in voltage, the static deflection, the dynamic response and the acoustic field produced. The modeling work presented embodies two main objectives: (i) it serves to provide direction in the design phase, and, (ii) it serves to aid in the extraction of critical parameters which affect the device behavior. Comparison of the results with the more rigorous FEM simulations as well as with those present in the existing literature assure that the developed models are accurate enough to serve as useful design tools. The distributed parameter modeling is presented next. Analysis of MEMS devices which rely on electrostatic actuation is complicated due to the fact that the structural deformations alter the electrostatic forces, which redistribute and modify the applied loads. Hence, it becomes imperative to consider the electro-elastic coupling aspect in the design of these devices. An approximate analytical solution for the static deflection of a thin, clamped circular plate caused by electrostatic forces which are inherently nonlinear, is presented. The model is based on the Kirchhoff-Love assumptions that the plate is thin and the deflections and slopes are small. The classical thin-plate theory is adequate when the ratio of the diameter to thickness of the plate is very large, a situation commonly prevalent in many MEMS devices, especially the CMUTs. This theory is used to determine the static deflection of the CMUT membrane due to a DC bias voltage. The thin-plate electro-elastic equation is solved using the Galerkin weighted residual technique under the assumption that the deflections are small in comparison to the thickness of the plate. The results obtained are compared to those obtained from ANSYS simulations and an excellent agreement is observed between the two. The pull-in voltage predicted by our model is close to the value predicted by ANSYS simulations. A simple analytical formula, which gives fairly accurate results (to within 3% of the value predicted by ANSYS simulations) for determination of the pull-in voltage, is also presented. As stated, this formula accounts for the elastic deflection of the membrane due to the coupled interaction with the electrostatic field. The effect of vacuum sealing the backside cavity of a CMUT is investigated in some detail. The presence or absence of air inside the cavity has a marked effect upon the system parameters, such as the natural frequency and the pull-in voltage. The possibility of using sealed CMUT cavities with air inside at ambient pressure is explored. In order to estimate the transducer loss due to the presence of air in the sealed cavity, the squeeze film forces resulting from the compression of the trapped air film are evaluated. Towards this end, the linearized Reynolds equation is solved in conjunction with the appropriate boundary conditions, taking the flexure of the membrane into account. From this analysis, it is concluded that, for a sealed CMUT cavity, the presence of air does not cause any squeeze film damping even when the flexure of the membrane is taken into account (the case of a rigid plate is already known). Although the emphasis of the study undertaken here is not on the physical realization of a working CMUT, a single cell as well as a linear array based on the design presented here, were fabricated (in a foundry elsewhere) in order to verify some of the most fundamental device parameters from experimental measurements. The fabricated devices have been characterized for their resonant frequency, quality factor, and structural integrity. These tests were conducted using the laser Doppler vibrometer and the Focused Ion Beam milling. Having investigated thoroughly the behavior of a single cell, we proceed to demonstrate how these cells can be arranged optimally in the form of an array to provide a comprehensive ultrasonic imaging system. A thorough analysis of the requirements for the array architecture is undertaken to determine the optimal configuration. The design constraints that need to be taken into account for CMUT arrays, especially for NDE applications, are presented. The main issue of designing an array consisting of a large number of CMUT cells required for producing a pressure wave of sufficient strength which is detectable upon reflection from the desired location even after suffering severe attenuation resulting from propagation in various media is addressed. A scalable annular array architecture of CMUT cells is recommended based on the analysis carried out.

This thesis describes the development and applications of an extension of DWS which enables the recovery of ‘localized’ mechanical properties, in a specified region of a complex jelly-like object which is inhomogeneous, marked out by the focal volume of an ultrasound transducer, also called the region-of-interest (ROI). Introduction of the sinusoidal forcing creates a sinusoidal phase variation in the detected light in a DWS experiment which modulates the measured intensity autocorrelation, g2 (τ ). Decay in the modulation depth with τ is used to recover the visco-elastic spectrum of the material in the ROI. En route to this, growth of the mean-squared dis- placement (MSD) with time is extracted from the modulation depth decay, which was verified first by the usual DWS experimental data from an homogeneous object with properties matching those in the ROI of the inhomogeneous object and then those obtained by solving the generalized Langevin equation (GLE) modelling the dynamics of a typical scattering centre in the ROI. A region-specific visco-elastic spectral map was obtained by scanning the inhomogeneous object by the ultrasound focal volume. Further, the resonant modes of the vibrating ROI were measured by locating the peaks of the modulation depth variation in g2(τ ) with respect to the ultrasound frequency. These resonant modes were made use of to recover elasticity of the material of the object in the ROI. Using a similar strategy, it was also shown that flow in pipe can be detected and flow rate computed by ‘tagging’ the photons passing through the pipe with a focussed ultrasound beam. It is demonstrated, both through experiments and simulations that the ultrasound-assisted technique devel- oped is better suited to both detect and quantitatively assess flow in a background of Brownian dynamics than the usual DWS. In particular, the MSD of particles in the flow, which shows forth a super-diffusive dynamics with MSD growing following τ α with α < 2, is captured over larger intervals of τ than was possible using existing methods. On the theoretical front, the main contribution is the derivation of the GLE, with multiplicative noise modulating the interaction ‘spring constant’. The noise is derived as an average effect of the micropolar rotations suffered by the ‘bath’ particles on the ‘system’ particle modelled. It has been shown that the ‘local’ dynamics of the system particle is nontrivially influenced by the dynamics, both translation and rotation, of ‘nonlocal’ bath particles.

No description available.

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. / 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.