L’imagerie photoacoustique est une nouvelle modalité couplant imagerie optique et échographie. Non invasive, elle permet d’imager des absorbeurs optiques à quelques centimètres de profondeur et avec la résolution de l’échographie. La réception des signaux photoacoustiques se faisant à l’aide d’un échographe clinique, cette modalité hybride vient compléter idéalement l’imagerie ultrasonore en apportant des informations fonctionnelles aux informations structurelles de l’échographie. Ces atouts en font une technique d’imagerie très prometteuse pour la clinique, notamment comme outil de diagnostic précoce. Ce travail de thèse a pour objectif principal la mise en place des outils nécessaires au développement de cette thématique de recherche d’un point de vue expérimental, à des fins cliniques. En particulier, l’apport de l’imagerie photoacoustique pour le diagnostic de plaques d’athérome vulnérables est investigué sur fantômes, grâce à un protocole original. Pour cela un système d’imagerie photoacoustique a été développé et caractérisé à l’aide de fantômes bimodalités élaborés spécifiquement pour les différentes études présentées. Gardant à l’esprit le transfert de cette technique en clinique, un échographe clinique de recherche est utilisé et différentes spécificités du banc nécessaires à l’imagerie in vivo et au diagnostic médical ont été investiguées. Cela implique une amélioration des performances de détection du signal photoacoustique, notamment en termes de sensibilité et de contraste. Pour cela, une nouvelle technologie de sondes ultrasonores est évaluée en la comparant aux sondes actuellement utilisées. De plus, une excitation multispectrale permet l’identification de différents éléments présents dans les tissus. L’aspect temps-réel de l’échographie fait de cette modalité une des plus utilisées pour le diagnostic clinique. Par conséquent, une imagerie photoacoustique voire bimodale en temps réel présente un réel atout pour son transfert clinique. Cette possibilité est investiguée sur le système mis en place au cours de la thèse grâce à un échographe de recherche et une étude sur fantômes. Enfin, une autre contribution de ce travail concerne l’apport de l’imagerie photoacoustique à la caractérisation de la vulnérabilité de la plaque d’athérome. Cette indication de vulnérabilité est obtenue en déterminant la composition de la plaque, en particulier en termes de lipides. L’imagerie photoacoustique, couplée à l’échographie, peut permettre cette identification. Pour étudier cette possibilité, nous nous sommes intéressés à l’artère carotide pour son accessibilité et la place qu’elle occupe dans le diagnostic de la plaque d’athérome en échographie et échographie Doppler. Un protocole original a été élaboré afin d’apporter l’excitation optique au plus près de la carotide. La faisabilité de cette approche est investiguée sur un fantôme conçu spécifiquement pour cette étude et les résultats préliminaires sont présentés. / Photoacoustic (PA) imaging is a new imaging modality coupling ultrasound and optical imaging. This non-invasive technique achieves a penetration depth up to several centimeters with optical contrast and ultrasound resolution. Moreover, since PA signals are detected with a US scanner, PA imaging ideally complete US imaging, adding functional information to the structural ones brought by echography. Therefore PA imaging looks very promising, specifically as a clinical early diagnosis tool. The main objective of this thesis is to set up the required tools to develop the experimental investigation for this research topic and, in particular, to apply it to the diagnosis of vulnerable atheroma plaques. A PA imaging system has been set up and characterized using specifically designed bimodal phantoms. Additional studies have been made to evaluate the suitability of this imaging platform for clinical imaging. For example, in vivo imaging requires better signal detection in terms of contrast and sensitivity, achieved thanks to a new probe technology, and the identification of tissue composition using a multispectral optical excitation. Finally, PA and even PAUS real time imaging is a real asset for medical diagnosis that has been investigated. Another contribution of this work is the use of PA imaging to characterized atheroma plaques vulnerability with the detection of lipids inside these plaques. PA imaging, coupled to echography, can address this need. To study this possibility, the carotid artery has been considered and a new protocol has been elaborated to bring the optical excitation very close to this artery. A feasibility study has been realized on a specific phantom and the preliminary results are presented.

The ability to numerically determine the received signal in an ultrasound pulse-echo system is very important for the development of new ultrasound applications, such as tissue characterization, complex object recognition, and identification of surface topology. The output signal from an ultrasound pulse-echo system depends on the transducer geometry, reflector shape, location and orientation, among others, therefore, only by numerical modeling can the output signal for a given measurement configuration be predicted. This thesis concerns about the numerical modeling and optimal design of annular array based ultrasound pulse-echo system for object recognition. Two numerical modeling methods have been implemented and evaluated for calculating received signal in a pulse-echo system. One is the simple, but computationally demanding Huygens Method and the other one is the computationally more efficient Diffraction Response for Extended Area Method (DREAM). The modeling concept is further extended for pulse-echo system with planar annular array. The optimal design of the ultrasound pulse-echo system is based on annular array transducer that gives us the flexibility to create a wide variety of insonifying fields and receiver characteristics. As the first step towards solving the optimization problem for general conditions, the problem of optimally identifying two specific reflectors is investigated. Two optimization methods, the straightforward, but computationally intensive Global Search Method and the efficient Waveform Alignment Method, have been investigated and compared.

"Abstract Conventional ultrasound imaging systems use array transducers for focusing and beam steering, to improve lateral resolution and permit real-time imaging. This thesis research investigates a different use of array transducers, where the acoustic field and the receiver characteristics are designed such that the energy of the output signal from targets of a specified geometry is maximized. The output signal is the sum of the received signals obtained using all the possible combinations of transducer array elements as transmitter and receiver. This work is based on annular array transducers, but is applicable for any array configuration. The first step is the development of software for the efficient modeling of the wave interaction between transmitted field and target, and between the transducer and receiver field. Using this software, we have calculated the received signal for each combination of an array element as transmitter and the same or another array element as receiver, leading to an N x N received signal matrix for an N element array transducer. A waveform optimization algorithm is then implemented for the purpose of determining the set of delays for the individual array elements, which maximizes the energy of the sum of the received signals. In one implementation of this algorithm, the received signal with the maximum energy is considered as a reference signal, and specific delays are applied to the other signals so that any two signals produce a maximum correlation. This leads to an N x N delay matrix, which, however, is not readily implemented in a practical real-time system, which uses all the elements in an array transducer simultaneously to customize acoustic fields. Hence, the values in this delay matrix are fed into a linear programming optimizer tool to obtain a set of delay values, which makes its implementation practical. The optimized set of delays thus obtained is used to maximize the energy of the received signal for a given transducer and target geometry and hence to enhance the reflectivity of that target. It is also important to check the robustness of the optimized set of delays obtained above, for a given target geometry. Robustness refers to the sensitivity of the optimization to variation in target geometry. This aspect is also evaluated as a part of this thesis work."

This thesis presents the development and microfabrication of capacitive micromachined ultrasonic transducers (CMUT) with diamond membranes for the first time in the literature. Although silicon and silicon nitride (Si3N4) membranes have been generally used as the membrane material in CMUTs. These membrane materials have moderate properties that can cause damage during the operation of CMUTs. In this thesis, a new material for the membrane is introduced for CMUTs. Diamond has exceptional potential in the area of micro-nano technologies due to unrivalled stiffness and hardness, excellent tribological performance, highly tailorable and stable surface chemistry, high thermal conductivity and low thermal expansion, high acoustic velocity of propagating waves, and biocompatibility. Based on these excellent material properties, diamond is employed in the new generation CMUT structures for more robust and reliable operations. The microfabrication process of CMUT has been generally performed with either sacrificial release process or wafer bonding technique. High yield and low cost features of wafer bonding process makes it preferable for CMUT devices. In this thesis, plasma-activated direct wafer bonding process was developed for the microfabrication of 16-element 1-D CMUT arrays with diamond membranes. They were designed to operate at different resonance frequencies in the range of 1 MHz and 10 MHz with different cell diameters (120, 88, 72, 54, 44 &mu / m) and element spacing (250, 375 &mu / m). 1-D CMUT array devices can be used for focusing ultrasound applications. The electronic circuit for 1-D CMUT devices with diamond membranes was designed and implemented on PCB for the ultrasound focusing experiment. This electronic circuit generates continuous or burst AC signals of &plusmn / 15 V with different and adjustable phase shifting options at 3 MHz frequency. 16 elements of 72 &mu / m 1-D CMUT array were successfully tested. Fully functional 7 elements of 1-D CMUT array are focused at an axial distance of 5.81 mm on the normal to the CMUT center plane. The CMUT array was excited using 10 Vp&minus / p with 10 cycles sinusoidal signals at 3 MHz. The microfabrication process and focusing ultrasound of 1-D CMUT devices with diamond membranes are done successfully in this thesis.

Capacitive Micromachined Ultrasonic Transducers (CMUTs) have been introduced as a viable alternative to piezoelectric transducers in medical ultrasound imaging in the last decade. CMUTs are especially suitable for applications requiring small size such as catheter based cardiovascular applications. Despite these advantages and their broad bandwidth, earlier studies indicated that the overall sensitivity of CMUTs need to be improved to match piezoelectric transducers. This dissertation addresses this issue by introducing the dual-electrode CMUT concept. Dual electrode configuration takes advantage of leveraged bending in electrostatic actuators to increase both the pressure output and receive sensitivity of the CMUTs. Static and dynamic finite element based models are developed to model the behavior of dual-electrode CMUTs. The devices are then successfully fabricated and characterized. Experiments illustrate that the pulse echo performance is increased by more than 15dB with dual-electrode CMUTs as compared to single electrode conventional CMUT. Further device optimization is explored via membrane shape adjustment by adding a center mass to the design. Electromechanical coupling coefficient (kc2) is investigated as a figure of merit to evaluate performance improvement with non-uniform/uniform membrane dual-electrode CMUTs. When the center mass is added to the design, the optimized non-uniform membrane increases the electromechanical coupling coefficient from 0.24 to 0.85 while increasing one-way 3dB fractional bandwidth from 80% to 140% and reducing the DC bias requirement from 160V to 132V. The results of this modeling study are successfully verified by experiments. With this membrane shape adjustment, significant performance improvement (nearly 20dB) is achieved with the dual-electrode CMUT structure that enables the CMUT performance to exceed that of piezoelectric transducers for many applications.

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.

Health monitoring of aeronautic structures and human beings is becoming crucial because of the human safety issues. In this thesis integrated (IUTs) and flexible ultrasonic transducers (FUTs) have been developed using a sol-gel spray piezoelectric film fabrication technology. IUTs can be fabricated directly onto the structures with curved surfaces even on-site. FUTs were made using membrane substrates of thickness less than 75 mum. In-situ monitoring of AI airframe thickness was carried out and the thickness measurement accuracy was better than 36 mum and 41 mum for IUT and FUT, respectively. The thickness of the ice on top of the AI airframe was also measured. Two crucial piezoelectric constants d33 and d31 of the composite film were measured with laser interferometer and optical coherence tomography system, respectively. Pulse and breath of a human being were also monitored using flexible piezoelectric membrane sensors. In addition, bones in human body were observed using FUTs as well and their performance is comparable to that of commercial ultrasonic transducers.

Orientador: Eduardo Tavares Costa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-14T01:45:18Z (GMT). No. of bitstreams: 1 SalinetJunior_JoaoLoures_M.pdf: 5974402 bytes, checksum: d82e2a2b0c6f65d111327247ff86a1e4 (MD5) Previous issue date: 2009 / Resumo: Os equipamentos de imagem por ultra-som associam diferentes técnicas e provêm informações não só das estruturas anatômicas como também do estado funcional dos diversos sistemas, em tempo real, com excelente qualidade de imagem. Isto se deve ao desenvolvimento de transdutores cada vez mais aprimorados e, ainda, da utilização de eletrônica digital, analógica e mista com microprocessadores, processadores digitais de sinais (DSPs - digital signal processors) e lógica programável (FPGAs - field programmable gate arrays) cada vez mais rápidos e potentes, aliados à utilização de novas técnicas de processamento digital de sinais e de imagens. O presente trabalho teve como objetivo o desenvolvimento de circuitos de acionamento de elementos cerâmicos de transdutores matriciais. Estes circuitos são responsáveis pela geração e recepção de ondas ultra-sônicas e foram desenvolvidos utilizando técnicas de projetos específicos de placas de circuito impresso de alta freqüência e multicamadas. Foram utilizados componentes SMD (surface-mounted devices) para redução do tamanho do hardware. O sistema é formado por um circuito de controle, uma placa de interligação, uma fonte de alimentação com 10 níveis de tensão, e duas placas de circuito impresso (PCI) contendo os circuitos de transmissão e de recepção (4 canais) para transdutores de ultra-som matriciais. No circuito de controle foi utilizada a linguagem de descrição de hardware VHDL. Este circuito de controle é capaz de executar a variação de largura de pulso, taxa de repetição e defasagem de acionamento dos elementos do transdutor matricial para focalização e deflexão do feixe acústico. Os circuitos de transmissão geram pulsos de até +65V e são disparados pelos pulsos digitais do circuito de controle (mínimo de 20ns de largura). Os circuitos de proteção são eficientes atenuando os pulsos de alta tensão na entrada do circuito de recepção e permitindo a passagem dos ecos. Os circuitos de recepção são formados por circuitos integrados de tecnologia mista (analógico e digital) com faixa de passagem de 100 MHz, baixo ruído e ganho máximo de 70dB. Este ganho pode ser configurado através dos três estágios de amplificação independentes do componente utilizado (LNA, VCA e PGA). O sistema foi testado em laboratório e apresentou desempenho adequado, mostrando-se versátil, permitindo seu uso com transdutores matriciais e mostrando-se interessante ferramenta para laboratórios de ensino e pesquisa em ultra-som. / Abstract: Ultrasound image equipments associate different techniques to provide not only anatomical but also functional information of body parts and organs in real time and with excellent image quality. This is due to great advances in transducer technology and also to digital and analog electronics with the use of microcomputers, digital signal processors (DSPs) and field programmable gate arrays (FPGAs) even faster and powerful, allied to new digital signal and image processing techniques. The objective of the present work was the development and construction of circuits to actuate on piezoelectric ceramic transducer arrays. The circuits are able to generate and receive ultrasound waves and were developed with techniques for high frequency multilayer printed circuit boards. In order to reduce hardware size it was used surface mounted devices (SMD). The system consists of a control circuit, a interconnection board, power supply (10 different voltage), two four channel printed circuit boards with the transmission and reception circuits to be used with transducer arrays. It was used VHDL for hardware description language and the control circuit defines pulse width, repetition rate and temporal phasing for activation of each element of the transducer array enabling focusing and ultrasound beam in different directions. The transmission circuits generate pulses up to +65V that are triggered by the control circuit (20 ns minimum pulse width). The protection circuit is very efficient avoiding high tension electrical surges. The reception circuits have mixed technologies (analog and digital integrated circuits) with 100 MHz bandwidth , low noise and up to 70 dB gain. This gain can be programmed through 3 independent amplification stages (LNA, VCA and PGA). The system has been tested in laboratory and presented adequate performance, being versatile and allowing its use with array transducers becoming an interesting tool for education and research purposes. / Mestrado / Engenharia Biomedica / Mestre em Engenharia Elétrica

Orientador: Vera Lucia da Silveira Nantes Button / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-04T03:25:15Z (GMT). No. of bitstreams: 1 Duarte_MauricioGomes_M.pdf: 2754469 bytes, checksum: 075905e730585b96c40637855bee28c3 (MD5) Previous issue date: 2003 / Resumo: o objetivo deste trabalho foi aprimorar o processo de apodização de discos de cerâmica piezoelétrica utilizado no LUS (Laboratório de Ultra-Som, DEB/FEEC e CEB, UNlCAMP), buscando estabelecer uma melhor relação entre tempo de aplicação do campo elétrico e a temperatura do banho de óleo isolante usado no processo. A apodização das cerâmicas piezoelétricas é utilizada para reduzir a difração no campo acústico gerado por transdutores de ultra-som, como já foi comprovado no LUS em trabalhos anteriores. Buscou-se reduzir o tempo de aplicação do campo elétrico através do ensaio de temperaturas diferentes do óleo mineral que banha o disco cerâmico e verificando em quais ensaios foi obtida uma boa apodização. Foram utilizadas cerâmicas piezoelétricas PZT-5A de 12,7mm de diâmetro, com 0,885mm (EDO Acoustics) e lmm (APCI) de espessura. O campo elétrico aplicado foi de 2kV/mm de espessura de cerâmica, e um eletrodo esférico de 5mm de raio foi usado para formatar o campo elétrico de apodização. Foram utilizados dois tipos de óleo mineral: o Nujol, que acima de 160°C evapora rapidamente e o óleo da CooperPower, que permitiu utilizar temperaturas até 250°C, com pouca evaporação. Os discos cerâmicos apodizados para os quais o coeficiente eletromecânico do modo espessura, kt, resultou em valores acima de 0,37, foram considerados bem apodizados. O óleo isolante foi aquecido a temperaturas diferentes entre 120°C e 250°C e o campo elétrico foi aplicado por períodos de 2 minutos até 4 horas e 30 minutos (tempo necessário para a temperatura do óleo resfriar até 25°C). Este estudo também incluiu a avaliação do efeito de sucessivas despolarizações e repolarlzações nos modos de vibração da cerâmica piezoelétrica. Os resultados confirmaram que, usando temperaturas mais altas (acima de 200°C), o campo elétrico precisa ser aplicado durante um período menor. Apodizações que utilizaram temperatura igual a 160°C, só mostraram acoplamentos bons quando o campo permaneceu aplicado enquanto o óleo resfriava até 25°C. Apodizações em que o óleo foi aquecido a temperaturas inferiores a 160°C não apresentaram bons resultados, independentemente do tempo de aplicação do campo elétrico. Os resultados também mostraram que o efeito de aplicar o campo elétrico ainda antes do óleo ser aquecido foi um aumento do acoplamento eletromecânico obtido, comparando com o resultado de um processo de apodização semelhante, mas em que o campo elétrico só foi aplicado depois do aquecimento do óleo. O mesmo efeito não foi observado com as apodizações em que utilizou-se a temperatura mais alta possível, 250°C, usando o óleo mineral da Copper Power. Concluiu-se que, usando a temperatura igual a 250°C, foi possível reduzir o tempo de aplicação do campo elétrico de apodização, com resultados satisfatórios, de mais de 4 horas para apenas 2 minutos. No entanto, o processo que utiliza uma dada relação tempo de aplicação do campo/temperatura do óleo, e que apodiza satisfatoriamente uma cerâmica com lmm de espessura, pode resultar na polarização convencional (linear) de uma cerâmica mais fina, como a cerâmica com espessura igual a O,885mm. Algumas das cerâmicas apodizadas foram usadas para construir transdutores de ultra-som. Os campos acústicos gerados pelos transdutores construidos foram mapeados, confirmando o aumento da profundidade do campo acústico, como conseqüência da redução da difração acústica, obtida a partir da apodização da polarização das cerâmicas piezoelétricas / Abstract: The objective of this work was to optimize the process of apodization of piezoelectric ceramics disks, looking for the better relation between the insulating oil bath temperature and the smaIlest period of time through which the poling field must be applied. The apodization of the piezoelectric ceramic is performed to reduce the diffraction in the acoustic field generated by ultrasonic transducers. We looked for the best initial temperature of the insulating mineral oil that surrounds the piezoelectric ceramic, and how long the poling electric field must be applied to the ceramic to achieve a good apodization. We used 12.7mm diameter, 0.885mm and lmm thickness PZT-5A ceramic disks. The non-uniform poling electric field (2kV/mm) has been shaped by a 5mm radius spherica1 electrode. The apodized ceramic disks which showed piezoelectric coupling coefficient values larger than 0.37, were considered well apodizated. We used oil temperatures from 120°C to above 200°C and the electric field was applied for periods of at least 2 minutes to up to 4 hours and third minutes (until the oil temperature cooled down to 25°C). This study a1so inc1uded the ceramic disk evaluation after successive depolarizations and repolarizations. The results showed that using higher temperatures (above 200°C) we needed to apply the poling field for a shorter time. Temperature equa1160°C was efficient on1y ifthe poling field was applied until the oil was cooled down to 25°C (4 hours and thirty minutes). The results also showed that if the poling electric field was applied to the piezoelectric ceramic even before the oil was heated, we obtained larger piezoelectric coupling coefficients, compared to the poling processes where the electric field was applied to the ceramic on1y afier the oil was heated. This was not necessary if we used higher temperatures (250°C). We concluded that using higher temperatures (250°C) it was possible to reduce the apodization process, with good results, from more than 4 hours to on1y 2 minutes. Ultrasound transducers were built; their acoustic fields were mapped in a water tank, and the results confirmed the increasing of the depth of the acoustic field, as consequence of the acoustic difraction reduction / Mestrado / Engenharia Biomedica / Mestre em Engenharia Elétrica

Orientadores: Sandra Lucia Cruz, João Alexandre Ferreira da Rocha Pereira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-07T19:03:10Z (GMT). No. of bitstreams: 1 Pavan_AndreMauricio_M.pdf: 4399374 bytes, checksum: d76e0e55472d41a43569b1e700a1a749 (MD5) Previous issue date: 2005 / Resumo: Vasos de pressão são equipamentos muito importantes numa indústria, sendo responsáveis por armazenar gases, líquidos e outros fluidos a altas pressões. Um pequeno vazamento nesses vasos pode ser muito perigoso, gerando poluição, explosão e perda financeira para a indústria. Por isso, é imprescindível uma rápida e eficaz detecção da ocorrência de qualquer vazamento. Este trabalho descreve o desenvolvimento e teste de uma técnica de detecção de vazamentos de gás em vasos de pressão, baseada na análise da pressão no interior do vaso e doruído sonoro gerado pelo vazamento. Na montagem experimental utilizou-se um vaso de pressão com capacidade 34,5 litros, operando com ar. A pressão no interior do vaso variou de 1 a 7 kgf/cm2. Vazamentos de diversas magnitudes foram simulados através de um orifício, instalado lateralmente no vaso, cujo diâmetro variou de 0,1 a 4,0 mm. Vazamentos foram detectados quando o vaso de pressão operava em batelada e também quando havia alimentação contínua de ar para o vaso. Para a detecção de vazamentos foi utilizado um microfone e um programa, em linguagem C, que faz a aquisição on-line, através de uma placa ADA, dos sinais provenientes de um transdutor de pressão conectado ao vaso e do microfone instalado no interior do vaso. O circuito elétrico que compatibiliza o sinal proveniente do microfone com aquele compreendido pela placa ADA foi desenvolvido no laboratório e apresenta duas etapas. Na primeira o sinal alternado é amplificado e na segunda o sinal passa por filtros passa banda de 1kHz, 5kHz e 9kHz gerando três sinais contínuos em diferentes faixas de freqüência. Os resultados obtidos mostraram que é possível detectar vazamentos através da detecção e análise dos ruídos sonoros gerados por vazamentos em vasos de pressão, mesmo quando a variação na pressão interna do vaso não é significativa. A resposta em freqüência do sinal do vazamento variou com a magnitude do vazamento e com as diferentes condições de pressão no interior do vaso. O sistema desenvolvido mostrou que pode ser uma ferramenta confiável para a supervisão de vasos de pressão / Abstract: Pressure vessels are very important equipment in the industry, being responsible for storing gases, liquids and other fluids at high pressures. A small leakage on them can be very dangerous, generating pollution, explosion and also financials losses to the industry. For those reasons, it is essential to have a fast and efficient leakage detection system. This work describes a leak detection technique of gas based on the analysis of the pressure in the vessel and the noise generated by the leak. An experimental apparatus was set up using a 34.5 liters pressure vessel, fitted with a system to simulate sudden leakage through small orifices. Compressed air was used in the leakage experiments and the pressure in the vessel varied between 1 and 7 kgf/cm2. Leaks of various magnitudes were simulated through orifices with sizes varying between 0.1 and 4 mm in diameter. Leaks were detected when the vessel operated with a batch of air and also when the vessel was continuously fed with air. The leak detection system used a microphone and a software, written in C language, for data acquisition through an ADA converter of the signals generated by a pressure transducer installed in the vessel and by the microphone which was placed inside the vessel. An electric circuit was developed to process the noise captured by microphone and had two different stages:- on the first, the signal was only amplified and, on the second stage, the signal was filtered through three band pass filters, centered in 1kHz, 5kHz and 9kHz each one, generating three continuous signals in different frequencies. The experimental results show that it is possible to detect leaks based on the detection and analysis of sound noises generated by leak occurrence in pressure vessels even when yht pressure in the vessel does not change significantly. The analysis of the signal amplitude for different frequencies shows that the leakage noise signal changes with the leakage size and pressure in the vessel. The developed system shows to be a very reliable tool for safety supervision of pressure vessels / Mestrado / Sistema de Processos Quimicos e Informatica / Mestre em Engenharia Química