Chronic liver diseases are the eighth leading cause of death in Brazil and a major public health problem in the world. Liver biopsy is the best available reference standard for evaluating and classifying stages of liver diseases, but it presents limitations and complications that are common in invasive methods. In recent years, elasticity imaging methods have been the focus of intense research activity with the ability to measure mechanical properties of soft tissues in a non-invasive way. Shear wave elastography is one of the most promising methods because it enables to quantitatively assess tissue elasticity. However, the current depth range of shear wave elastography impedes its application in obese patients, which have a great risk of developing liver disease. The aim of this study is to investigate the use of shear wave elastography in deeper tissues using a two-dimensional ultrasound transducer array. An efficient transducer array arrangement was simulated, fabricated and characterized. The results show that the proposed transducer configuration presents enhanced transmitting capabilities for generating tissue displacement in deeper tissues. In addition, numerical simulations were performed in order to track the tissue deformation and reconstruct its elastic properties. / Doenças crônicas do fígado são a oitava causa de morte no Brasil e um dos principais problemas de saúde pública do mundo. A biópsia do fígado é o melhor padrão de referência disponível para avaliação e classificação dos estágios das doenças hepáticas, mas apresenta limitações e complicações que são comuns nos métodos invasivos. Nos últimos anos, métodos de imagem por elasticidade têm sido o foco de intensa atividade de pesquisa, pois têm a capacidade de medir propriedades mecânicas dos tecidos moles de maneira não invasiva. A elastografia por ondas de cisalhamento é um dos métodos mais promissores, pois permite avaliar quantitativamente a elasticidade do tecido. No entanto, a atual faixa de profundidade da elastografia por ondas de cisalhamento impede sua aplicação em pacientes obesos, que apresentam grande risco de desenvolver doença hepática. O objetivo deste estudo é investigar o uso da elastografia por onda de cisalhamento em tecidos mais profundos usando um transdutor de ultrassom bidimensional. Uma configuração eficiente de transdutores matriciais foi simulada, fabricada e caracterizada. Os resultados mostram que o transdutor proposto possui capacidade de transmissão melhorada para gerar deslocamento em tecidos profundos. Além disso, simulações numéricas foram realizadas para monitorar a deformação do tecido e reconstruir suas propriedades elásticas.

This work consists in the development and design of an energy harvesting device to supply power to the new generation pacemakers, miniaturized leadless implants without battery placed directly in heart chambers. After analyzing different mechanical energy sources in the cardiac environment and associated energy harvesting mechanisms, a concept based on regular blood pressure variation stood out: an implant with a flexible packaging that transmits blood forces to an internal transducer. Advantages compared to traditional inertial scavengers are mainly: greater power density, adaptability to heartbeat frequency changes and miniaturization potential. Ultra-flexible 10-µm thin metal bellows have been designed, fabricated and tested. These prototypes acting as implant packaging that deforms under blood pressure actuation have validated the proposed harvesting concept. A new type of electrostatic transducer (3D multi-layer out-of-plane overlap structure with interdigitated combs) has been introduced and fully analyzed. Promising numerical results and associated fabrication processes are presented. Also, large stroke optimized piezoelectric spiral transducers including their complex electrodes patterns have been studied through a design analysis, numerical simulations, prototype fabrication and experimental testing. Apower density of 3 µJ/cm3/cycle has been experimentally achieved. With further addressed developments, the proposed device should provide enough energy to power autonomously and virtually perpetually the next generation of pacemakers.

Surface Acoustic Waves (SAW) fall under a special category of elastic waves that need a material medium to propagate. The energy of these waves is confined to a limited depth below the surface over which they propagate, and their amplitudes decay with increasing depth. As a consequence of their being a surface phenomenon, they are easily accessible for transduction. Due to this reason, a lot of research has been carried out in the area, which has resulted in two very popular applications of SAW - SAW devices and in Non-Destructive Testing and Evaluation. A major restriction of SAW devices is that the SAW need a piezoelectric medium for generation, propagation and reception. This thesis reports the attempt made to overcome this restriction and utilize the SAW on non-piezoelectric substrates for sensing capabilities. The velocity of the SAW is known to be dependent purely on the material properties, specifically the elastic constants and material density. This dependence is the motivation for the sensor system developed in the present work. Information on the survey of the methods suitable for the generation and reception of SAW on non-piezoelectric substrates has been included in the thesis. This is followed by the theoretical and practical details of the method chosen for the present work - the point source/point receiver method. Advantages of this method include a simple and inexpensive fabrication procedure, easy customizability and the absence of restrictions due to directivity of the SAW generated. The transducers consist of a conically shaped PZT element attached to a backing material. When the piezoelectric material on the transmitter side is electrically excited, they undergo mechanical oscillations. When coupled to the surface of a solid, the oscillations are transferred onto the solid, which then acts as a point source for SAW. At the receiver, placed at a distance from the source on the same side, the received mechanical oscillations are converted into an electrical signal as a consequence of the direct piezoelectric effect. The details of the fabrication and preliminary trials conducted on metallic as well as non-metallic samples are given. Various applications have been envisaged for this relatively simple sensor system. One of them is in the field of pressure sensing. Experiments have been carried out to employ the acoustoelastic property of a flexible diaphragm made of silicone rubber sheet to measure pressure. The diaphragm, when exposed to a pressure on one side, experiences a varying strain field on the surface. The velocity of SAW generated on the stressed surface varies in accordance with the applied stress, and the consequent strain field generated. To verify the acoustoelastic phenomenon in silicone rubber, SAW velocities have been measured in longitudinal and transverse directions with respect to that of the applied tensile strain. Similar measurements are carried out with a pressure variant inducing the strain. The non-invasive nature of this setup lends it to be used for in situ measurement of pressure. The second application is in the field of elastography. Traditional methods of diagnosis to detect the presence of sub-epidermal lesions, some tumors of the breast, liver and prostate, intensity of skin irritation etc have been mainly by palpation. The sensor system developed in this work enables to overcome the restrictive usage and occasional failure to detect minute abnormal symptoms. In vitro trials have been conducted on tissue phantoms made out of poly (vinyl alcohol) (PVA-C) samples of varying stiffnesses. The results obtained and a discussion on the same are presented.

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.

Made available in DSpace on 2014-06-11T19:31:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-01-14Bitstream added on 2014-06-13T18:42:30Z : No. of bitstreams: 1 rossi_sr_dr_ilha.pdf: 2325960 bytes, checksum: 7ef7ad22ede243a4f480a84cc0e63023 (MD5) / Universidad Nacional de Asuncion / Atualmente, as redes de transdutores inteligentes desempenham um papel de importância vital em sistemas de Medição e Controle Distribuído. Nesse contexto, o Padrão IEEE 1451 para interfaceamento de transdutores inteligentes tem como objetivo simplificar a conectividade de transdutores em ambientes de rede, fornecendo, para tal fim, um conjunto de interfaces padronizadas, aumentando a flexibilidade dos sistemas de instrumentação distribuída. Neste trabalho descreve-se a implementação de um nó de rede em conformidade com o padrão IEEE 1451. O nó foi completamente desenvolvido através do emprego de ferramentas padronizadas e sistemas abertos. O nó é composto por um Processador de Aplicação com Capacidade de Operar em Rede (NCAP), com base no padrão IEEE 1451.1 e um Módulo de Interface para Transdutores Inteligentes (STIM), em conformidade com o padrão IEEE 1451.2. A parte física do NCAP foi implementada através dos recursos de um Computador Pessoal (PC) e de um Dispositivo Lógico Programável (PLD) de uso geral. A parte lógica do NCAP foi desenvolvida através da tecnologia Java. O STIM foi implementado com dispositivos lógicos programáveis versáteis, de uso geral, e sua funcionalidade foi integralmente descrita em linguagem de descrição de hardware. O conjunto NCAP-STIM foi conectado a uma rede de área local, sob o modelo de comunicação cliente-servidor, sendo que várias aplicações clientes podem acessar as informações dos transdutores conectados ao STIM, através da rede, via intermediação do NCAP. O emprego de ferramentas padronizadas e abertas no desenvolvimento total do sistema IEEE 1451 é uma das contribuições mais importantes do presente trabalho. No entanto, há várias contribuições pontuais como: a maneira de descrever as Informações de Transdutores em Formato Eletrônico (TEDS), a implementação... . / Nowadays, smart transducer networks play an essential role in distributed measurement and control systems. In this context, the IEEE 1451 smart transducer interface standards aimed to simplify transducer connectivity, providing a set of common interfaces for connecting transducers in a networked fashion, increasing the flexibility of distributed instrumentation systems. In this work the implementation of a network node according to the IEEE 1451 standard is introduced. The node has been fully developed using open and standardized tools. A Network Capable Application Processor (NCAP) according to the IEEE 1451.1 Standard and a Smart Transducer Interface Module (STIM) comprises the node. The physical part of the NCAP has been implemented using the resources of a Personal Computer (PC) and a general-purpose Programmable Logic Device (PLD). The logical part of the NCAP has been developed using Java technology. The STIM module was implemented with versatile, general-purpose Programmable Logic Devices. STIM functionality has been fully developed in hardware description language. A network node (STIM-NCAP) was connected in a client-server modelbased local area network. Many client applications can access STIM transducers information, through the network with the NCAP as an intermediary. One of the most important contributions of this work is the employment of open and standardized tools for implementing the IEEE 1451 network node. However, there are many specific contributions such as: Transducer Electronic Data Sheet (TEDS’s) description method, programmable logic-based Protocol Manager implementation that allows the use of the parallel port without any modification, the employment of low-cost PLDs for implementing the STIM and the Protocol Manager, and Java-based NCAP software development. Through the implementation of the IEEE Standard, industries... (Complete abstract, click electronic address below).

Ressonância Magnética (RM) é uma técnica bastante versátil, pois é utilizada em muitas áreas de pesquisa, como biologia, física, química, engenharia e medicina. Apesar disso, constitui-se uma desvantagem o alto custo do equipamento e suas restrições físicas para alguns experimentos. Para reduzir essas desvantagens, o grupo de pesquisadores do CIERMag está desenvolvendo um equipamento de RMN multipropósito e, para complementá-lo, este trabalho vem desenvolver um subsistema non-real-time que gerencia os dispositivos periféricos de um experimento. Foi proposta uma rede de dispositivos que é controlada por um Raspberry Pi como elemento central, o qual está conectado ao terminal computadorizado do sistema através de uma rede local (Local Area Network - LAN) via Ethernet e conectado aos dispositivos periféricos via Serial Peripheral Interface (SPI). Com o objetivo de ser possível gerenciar qualquer tipo de dispositivo, foi desenvolvido um conjunto de parâmetros baseado no Transducer Electronic Data Sheet (TEDS), definido no padrão IEEE 1451, de modo que cada dispositivo, normalmente um transdutor, possui seu próprio. Foram elaboradas duas interfaces de software: uma desenvolvida em Python e a outra uma interface web HTML. Ambas as interfaces possuem as mesmas funcionalidades: editor e gerenciador de TEDS, visualização gráfica de medidas dos sensores e interface para os atuadores. / Magnetic Resonance (MR) is a very versatile technique, since it is used in many research areas such as biology, physics, chemistry, engineering and medicine. Despite this, the cost of the equipment and its physical restrictions in some experiments constitute a serious drawback. To minimize these problems, the CIERMag research team is developing multipurpose MR equipment and, to complement this equipment, this work develops a non-real-time subsystem that manages the peripheral devices of the experiment. It was proposed a network of devices controlled by a Raspberry Pi as its central element, which is connected to the terminal computer of the system. The protocol adopted for this was Ethernet via Local Area Network (LAN); communication with peripheral transducers was performed with the Serial Peripheral Interface (SPI). With the objective to be able to manage any type of device, we created parameter sets based on Transducer Electronic Data Sheet (TEDS), defined in the IEEE 1451 standard, so each device, normally a transducer, has its own parameter set. We created two software interfaces: one developed with Python and the other is a HTML web interface. Both have the same functionalities: a TEDS editor and manager, a graphical visualization of sensor measurements and also an actuator interface.

Submitted by (edna.saturno@ufrpe.br) on 2016-10-14T12:17:11Z No. of bitstreams: 1 Leopoldo Mayer de Freitas Neto.pdf: 829417 bytes, checksum: 20a0e805e8a2d62a9b139566d0ef9786 (MD5) / Made available in DSpace on 2016-10-14T12:17:11Z (GMT). No. of bitstreams: 1 Leopoldo Mayer de Freitas Neto.pdf: 829417 bytes, checksum: 20a0e805e8a2d62a9b139566d0ef9786 (MD5) Previous issue date: 2010-02-15 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / In this work, divided into three experiments, the aim was to verify the possibility to diagnose the pregnancy of does and ewes by different pathway access and diagnose the fetuses sex originated by natural mating and transfer of fresh and cryopreserved embryos. The examinations were carried out using an ultrasound scanner equipped with a linear transducer (6.0 and 8.0 MHz) used by transrectal and transabdominal via and a microconvex endocavitary (5.0 and 7.5 MHz) transducer used by transvaginal via. In the first experiment was verified the viability of the ultrasound examination by transretal, transabdominal and transvaginal via to diagnose pregnancy in goats (n = 240) and ewes (n = 320) at days 30th, 45th, 60th and 75th. In does and ewes the ultrasound examination was faster (P < 0.05) on days 30th and 45th of pregnancy, however by transabdominal via was faster on day 60th and 75th. In both species the time of pregnancy diagnose was greater (P < 0.05) on day 30th than the others days while this time was smallest (P < 0.05) at day 75th than day 45th and 60th. Independent of the examination via and the day of pregnancy the average time to diagnose the pregnancy was shorter (P < 0.05) in does than in ewes. Independing of the specie and the day of pregnancy the average time to diagnose the pregnancy by transrectal via was shorter (P < 0.05) than the other vias and the transvaginal via was shorter (P < 0.05) than the transabdominal one. In the second experiment, in order to improve the sexing of Boer fetuses (n = 123) by transrectal ultrasonography, the aim was to identify the migration period of the genital tubercle and its later differentiation into genital structures in fetuses derived from natural mating (TI) and fetus from fresh (TII), frozen (TIII) and vitrified (TIV) embryo transfer collected 7 days after breeding. Migration of the genital tubercle occurred earlier (P < 0.05) in TI (45.21 ± 3.31 days) than in TII (48.50 ± 3.70 days), TIII (48.93 ± 3.61 days) and TIV (48.85 ± 3.23 days). The visualization of the scrotum, prepuce and vulva occurred earlier (P < 0.05) in TI (51.20 ± 2.56; 50.35 ± 1.59; 49.75 ± 1.73 days) than in TII (53.25 ± 2.02; 53.37 ± 1.92; 51.76 ± 2.10 days),TIII (53.37 ± 1.92; 52.31 ± 2.00; 51 ± 78 ± 2.22 days) and TIV (54.06±1.75; 52.46 ± 1.95; 51.91 ± 2.06 days). In the third experiment, in order to improve fetal sexing by ultrasonography in Dorper ewe breed (n = 130), the objective was to identifythe migration period of the genital tubercle and the period of the visualization of external genital structures in fetuses derived from natural mating (TI) and from fresh (TII), frozen (TIII) and vitrified (TIV) embryos transfer collected 7 days after breeding. Migration of the genital tubercle occurred earlier (P < 0.05) in TI (42.21±2.86 days) than in TII (43.98±3.00 days), TIII (44.97±1.83 days) and TIV (44.58±1.97days). The visualization of scrotal bag, prepuce and vulva occurred, respectively, earlier (P < 0.05) in TI (45.22±1.25; 45.95±1.53; 45.01±.103 days) than in TII (48.91±1.92; 48.52±1.41; 47.41±1.41 days), TIII (49.97±1.08; 49.18±2.00; 47.64±1.82 days) and TIV(50.12±1.66; 49.27±1.1.61; 47.93±1.92 days). The results allow to conclude that the pregnancy diagnose may be performed by transrectal, transabdominal and transvaginal via, as well as, that is faster by transrectal via and hat the time for diagnosing is shorterin advanced pregnancy and in goat specie. Is also possible to conclude, taking into consideration the final position of the genital tubercle, that goat fetal sexing can be done from the 55th day onward in fetuses produced by natural mating and from the 60th day onward in fetuses derived from cryopreserved embryos. It can also be concluded that, real-time ultrasonography is a reliable tool for fetal sex determination in sheep after Day 50 of pregnancy taking into account both the location of the genital tubercle and the identification of external genital structures. In ovine species the fetal sexing can be done from the 50th day onward in fetuses produced by natural mating and from the 55th day onward in fetuses derived from cryopreserved embryos. Finally is possible to conclude that real-time ultrasonography is a reliable tool for early pregnancy diagnose in small ruminant as well as that to identify the sex on the first 60 days of pregnancy. / Com este trabalho, dividido em três experimentos, objetivou-se verificar a possibilidade de realizar o diagnóstico de prenhez em cabras e ovelhas por diferentes vias de acesso e sexar fetos originados de monta natural e da transferência de embriões frescos e criopreservados. Os exames foram realizados com um aparelho de ultrassom equipado com um transdutor linear (6,0 e 8,0 MHz) utilizado pelas vias transretal e transabdominal e outro microconvexo (5,0 e 7,5 MHz) endocavitário utilizado por via transvaginal. No primeiro experimento verificou-se a viabilidade do exame ultrassonográfico pelas vias transretal, transabdominal e transvaginal para diagnosticar a gestação de cabras (n = 240) e ovelhas (n = 320) no 30o, 45o, 60o e 75o dia. Nas cabras e ovelhas, o exame ultrassonográfico pela via transretal foi mais rápido (P < 0, 05) no 30o e no 45o dia da gestação, mas, pela via transabdominal foi mais rápido no 60o e no 75o dia. Em ambas as espécies, a duração do diagnóstico de gestação foi maior (P < 0,05) no 30o dia do que nos demais, enquanto que a duração do diagnóstico no 75o dia foi menor (P < 0,05) do que no 45o e 60o. Independentemente da via de exame e do dia da gestação, o tempo médio para diagnosticar a gestação foi menor (P < 0,05) nas cabras do que nas ovelhas. Independentemente da espécie e do dia da gestação, o tempo médio para diagnosticar a gestação pela via transretal foi menor (P < 0,05) do que as demais e o da transvaginal foi menor (P < 0,05) do que o da via transabdominal. No segundo experimento, com a finalidade de aperfeiçoar a sexagem de fetos (n = 123) caprinos da raça Boer por via transretal, procurou-se identificar o período de migração do tubérculo genital e sua diferenciação nas estruturas da genitália de fetos derivados de monta natural (TI) e da transferência de embriões frescos (TII), congelados (TIII) e vitrificados (TIV) colhidos 7 dias após a cobertura. A migração do tubérculo genital ocorreu mais cedo (P < 0,05) no TI (42,21±2,86 dias) do que no TII (43,98±3,00 dias), TIII (44,97±1,83 dias) e no TIV (44,58±1,97 dias). A visibilização da bolsa escrotal, prepúcio e vulva ocorreu precocemente (P < 0,05) no TI (45,22±1,25; 45,95±1,53;45,01±1,03 dias) do que no TII (53,25 ± 2,02; 53,37 ± 1,92; 51,76 ± 2,10 dias), TIII (53,25 ± 2,02; 53,37 ± 1,92; 51.76 ± 2,10 dias) e TIV (54,06±1,75; 52,46 ± 1,95;51,91 ± 2,06 dias). No terceiro experimento, com o propósito de aperfeiçoar a sexagem de fetos (n = 130) ovinos da raça Dorper por via transretal, procurou-se identificar o período de migração do tubérculo genital e sua diferenciação nas estruturas da genitália de fetos derivados de monta natural (TI) e da transferência de embriões frescos (TII), congelados (TIII) e vitrificados (TIV) colhidos 7 dias após a cobertura. A migração do tubérculo genital ocorreu mais cedo (P < 0,05) no TI (45,21 ± 3,31 dias) do que no TII (48,50 ± 3,70 dias), TIII (48.50 ± 3.70 dias) e no TIV (48,85 ± 3,23 dias). A visibilização da bolsa escrotal, prepúcio e vulva ocorreu precocemente (P < 0,05) no TI (51,20 ± 2,56; 50,35 ± 1,59; 49,75 ± 1,73 dias) do que no TII (53,25 ± 2,02; 53,37 ± 1,92; 51,76 ± 2,10 dias), TIII (53,25 ± 2,02; 53,37 ± 1,92; 51.76 ± 2,10 dias) e TIV (54,06±1,75; 52,46 ± 1,95; 51,91 ± 2,06 dias). Os resultados permitem concluir que o diagnóstico de gestação pode ser realizado pelas vias transretal, transabdominal etransvaginal, bem como que é mais rápido pela via transretal, na gestação avançada e na espécie caprina. É também permissível concluir que, com base no posicionamento final do tubérculo genital, é recomendável sexar fetos caprinos provenientes de monta natural somente a partir do 55o dia de prenhez e a partir do 60o dia naqueles derivados da transferência de embriões frescos e criopreservados. Nos ovinos a sexagem fetal já pode ser efetuada a partir do 50o dia de prenhez nos fetos oriundos de monta natural e a partir do 55o dia naqueles originados da transferência de embriões frescos e criopreservados. Ainda é possível concluir que a ultrassonografia em tempo real é uma ferramenta importante para diagnosticar precocemente a prenhez nos pequenos ruminantes, assim como identificar o sexo fetal nos primeiros 60 dias de gestação

Chronic liver diseases are the eighth leading cause of death in Brazil and a major public health problem in the world. Liver biopsy is the best available reference standard for evaluating and classifying stages of liver diseases, but it presents limitations and complications that are common in invasive methods. In recent years, elasticity imaging methods have been the focus of intense research activity with the ability to measure mechanical properties of soft tissues in a non-invasive way. Shear wave elastography is one of the most promising methods because it enables to quantitatively assess tissue elasticity. However, the current depth range of shear wave elastography impedes its application in obese patients, which have a great risk of developing liver disease. The aim of this study is to investigate the use of shear wave elastography in deeper tissues using a two-dimensional ultrasound transducer array. An efficient transducer array arrangement was simulated, fabricated and characterized. The results show that the proposed transducer configuration presents enhanced transmitting capabilities for generating tissue displacement in deeper tissues. In addition, numerical simulations were performed in order to track the tissue deformation and reconstruct its elastic properties. / Doenças crônicas do fígado são a oitava causa de morte no Brasil e um dos principais problemas de saúde pública do mundo. A biópsia do fígado é o melhor padrão de referência disponível para avaliação e classificação dos estágios das doenças hepáticas, mas apresenta limitações e complicações que são comuns nos métodos invasivos. Nos últimos anos, métodos de imagem por elasticidade têm sido o foco de intensa atividade de pesquisa, pois têm a capacidade de medir propriedades mecânicas dos tecidos moles de maneira não invasiva. A elastografia por ondas de cisalhamento é um dos métodos mais promissores, pois permite avaliar quantitativamente a elasticidade do tecido. No entanto, a atual faixa de profundidade da elastografia por ondas de cisalhamento impede sua aplicação em pacientes obesos, que apresentam grande risco de desenvolver doença hepática. O objetivo deste estudo é investigar o uso da elastografia por onda de cisalhamento em tecidos mais profundos usando um transdutor de ultrassom bidimensional. Uma configuração eficiente de transdutores matriciais foi simulada, fabricada e caracterizada. Os resultados mostram que o transdutor proposto possui capacidade de transmissão melhorada para gerar deslocamento em tecidos profundos. Além disso, simulações numéricas foram realizadas para monitorar a deformação do tecido e reconstruir suas propriedades elásticas.

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 paper discusses basic issues of micromachined ultrasonic transducers, including their design and fabrication. First, the acoustic fundamentals of ultrasonic transducers are introduced, and relevant simulation methods are illustrated. Following these topics, important aspects of silicon micromachining are presented. Based on this knowledge, two distinctive micromachining processes for transducer fabrication are proposed. One of them, the bulk process, has been proved to be successful, whereas for the second one, a surface process, some improvements are still needed. Besides these works, an innovative direct bonding technology is also developed. This technology constitutes the basis of the bulk process. Of course, it can also be used for the packaging of other MEMS devices.