O uso do ultra-som na área da saúde é bastante amplo, tanto para o diagnóstico por imagem como para o tratamento de inúmeras afecções (de feridas de pele a tumores malignos). No Programa de Pós-Graduação Interunidades em Bioengenharia há mais de 20 anos são feitas pesquisas sobre a interação do ultra-som com os tecidos biológicos. O presente trabalho objetiva avaliar os campos acústicos gerados pelos aparelhos de ultra-som terapêutico usados no Programa de Pós Graduação Interunidades em Bioengenharia de acordo com a norma NBR-IEC 1689. Para isto foi montado um tanque acústico e um sistema de posicionamento para a avaliação dos aparelhos, bem como foi desenvolvido um software para controle e automação do sistema. Os parâmetros que a norma pede que sejam avaliados e seu respectivo intervalo de tolerância são: potência de saída ('+ OU -' 20%); área de radiação efetiva ('+ OU -' 20%); intensidade efetiva ('+ OU -' 20%); freqüência de trabalho acústica ('+ OU -' 10%); relação de não-uniformidade do feixe ('+ OU -' 30%); intensidade máxima do feixe; tipo de feixe; fator de operação; forma de onda de modulação. Foram avaliados 8 aparelhos, sendo que 3 deles usados no ambulatório da bioengenharia e 5 usados em pesquisa. Para se avaliar os parâmetros dos equipamentos é necessário que eles estejam declarados no equipamento ou em manual que acompanha o equipamento. Na falta destas especificações fez se necessário a proposta de valores de referência para os aparelhos de ultra-som terapêutico da bioengenharia / The use of the ultrasound is quite wide health area, so much for image diagnosis as for the treatment of countless disease (skin wounds to malignant tumors). In the Interunidades Program of Masters degree in Bioengineering during more than 20 years are made researches about the interaction of the ultrasound with the biological tissues. The present work objective is the evaluate the acoustic fields generated by therapeutic ultrasound apparatus used in the Interunidades Program of Masters degree in Bioengineering according with NBR-IEC 1689. In this way, it was set up an acoustic tank and a positioning system for the apparatus, as well as software was developed for control and automation of the system. Parameters required by standard to be measured are presented with the respective tolerance interval: declared potency ('+ OR -' 20%); effective radiation area ('+ OR -' 20%); effective intensity ('+ OR -' 20%); work acoustics frequency ('+ OR -' 10%); non uniformity of the field relationship ('+ OR -' 30%); maximum intensity of the field; field type; operation factor; modulation wave form. There were appraised 8 apparatus, 3 of them are used in clinic of bioengineering and 5 are used in research. To evaluate the equipment parameters it is necessary that they are declared in the equipment or in equipment manual. In the lack of these specifications it is necessary proposal of reference values for the therapeutic ultrasound apparatus of bioengineering

abstract: In these times of increasing industrialization, there arises a need for effective and energy efficient heat transfer/heat exchange devices. The focus nowadays is on identifying various methods and techniques which can aid the process of developing energy efficient devices. One of the most common heat transfer devices is a heat exchanger. Heat exchangers are an essential commodity to any industry and their efficiency can play an important role in making industries energy efficient and reduce the energy losses in the devices, in turn decreasing energy inputs to run the industry. One of the ways in which we can improve the efficiency of heat exchangers is by applying ultrasonic energy to a heat exchanger. This research explores the possibility of introducing the external input of ultrasonic energy to increase the efficiency of the heat exchanger. This increase in efficiency can be estimated by calculating the parameters important for the characterization of a heat exchanger, which are effectiveness (ε) and overall heat transfer coefficient (U). These parameters are calculated for both the non-ultrasound and ultrasound conditions in the heat exchanger. This a preliminary study of ultrasound and its effect on a conventional shell-and-coil heat exchanger. From the data obtained it can be inferred that the increase in effectiveness and overall heat transfer coefficient upon the application of ultrasound is 1% and 6.22% respectively. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

Sound generated by impacting structures is of considerable importance in noise control. Sound is generated by a vibrating structure by inducing pressure fluctuations in the surrounding medium. Impact induced noise is the sound generated by a vibrating structure subjected to motion constraint. In such problems one has to study the vibration behavior of the oscillator, the impact mechanics, and the emanating acoustic field dynamics. A literature review carried out points to the fact that though there has been considerable work on vibration behavior of impact oscillators and the acoustics of impact of rigid masses, there is very little work reported on the sound generated due to vibration and impact. This thesis couples vibration analysis of oscillators undergoing impact with its acoustic behavior. The vibration behavior is nonlinear on account of the impact. Therefore the vibration analysis as well as the resulting acoustic field analysis has to be in the time-domain. This investigation is concerned with the effect of structural dynamics, impact dynamics, and acoustic field boundary conditions, on the sound pressure generated due to vibration and impact. We have considered a single degree of freedom as well as a flexible Euler-Bernoulli beam vibration model. The former is the simplest for studying vibro-acoustic response. The numerical model of the beam is derived using the finite element method resulting in a finite dimensional system with more than one degree of freedom. The dynamics of each degree of freedom are distinct in terms of amplitude and phase and are a function of the nature of linear dependence on other degrees of freedom and the nature of excitation. An impacting beam introduces interesting interactions between the dynamics of the degrees of freedom as a consequence of nonlinearity due to the motion constraint. The impact of the oscillator mass with a barrier is modeled using a simple coefficient of restitution model based on Hertzian contact theory. There is velocity reversal on contact with the barrier. The contact force is finite acting within a finite interval of time. The contact force is assumed to vary in time during the contact interval. This effectively models contact as linearly elastic. The pressure perturbation due to vibration of the oscillator mass is shown equivalent to the pressure perturbation due to an acoustic dipole. The acoustic dipole is placed at the equilibrium position of the vibrating mass. The dipole pressure is then a function of motion of the oscillator. In the case of a single degree of freedom oscillator the dipole axis is along the direction of motion. The sound pressure due to a vibrating beam is modeled as an array of acoustic dipoles placed at the finite element nodes of the beam and stationary at the beam's static equilibrium configuration. The dipole axis is once again aligned with the direction of vibration of the beam that is transverse to the beam neutral axis. Anechoic as well as perfectly reflecting acoustic boundary conditions are simulated in the time-domain. The resulting governing equation of motion of the single degree freedom oscillator as well as the beam are integrated numerically in time to compute its response. The acoustic pressure is shown to be critically dependent on the excitation frequency of the oscillator, dynamic properties of the oscillator, coefficient of restitution of impact and impact dynamics, and acoustic field boundary conditions.

Les systèmes de combustion sont sujets aux instabilités de combustion (IC). Elles résultent d'un couplage constructif entre le taux de dégagement de chaleur instationnaire et des modes acoustiques du système. Les IC peuvent mettre en danger la performance et l'intégrité des systèmes de combustion. Même si ces phénomènes sont connus depuis plus d'un siècle, éviter quelles aient lieux dans les chambres de combustions industrielles reste difficile. Les objectifs de cette thèse sont les suivants : (1) étudier la dynamique des modes acoustiques, (2) analyser la réponse de flamme d'un moteur de fusée à propergol liquide H2/O2 (appelé "BKD"), sujet aux IC, à l'aide de la Simulation aux Grandes Echelles (SGE) et (3) dériver, utiliser et étudier des conditions limites permettant d'imposer des impédances acoustiques complexes en SGE. / Combustion devices are prone to combustion instabilities. They arise from a constructive coupling between the unsteady heat release rate of the flame and the resonant acoustic modes of the entire system. The occurence of such instabilities can pose a threat to both performance and integrity of combustion systems. Although these phenomena have been known for more than a century, avoiding their appearance in industrial engines is still challenging. The objective of this thesis is threefold: (1) study the dynamics of the resonant acoustic modes, (2) investigate the flame response of a liquid rocket engine under unstable conditions using Large Eddy Simulation(LES) and (3) derive, use and study Time Domain Impedance Boundary Conditions (TDIBCs), i.e. boundary conditions modeling complex acoustic impedances.

O uso do ultra-som na área da saúde é bastante amplo, tanto para o diagnóstico por imagem como para o tratamento de inúmeras afecções (de feridas de pele a tumores malignos). No Programa de Pós-Graduação Interunidades em Bioengenharia há mais de 20 anos são feitas pesquisas sobre a interação do ultra-som com os tecidos biológicos. O presente trabalho objetiva avaliar os campos acústicos gerados pelos aparelhos de ultra-som terapêutico usados no Programa de Pós Graduação Interunidades em Bioengenharia de acordo com a norma NBR-IEC 1689. Para isto foi montado um tanque acústico e um sistema de posicionamento para a avaliação dos aparelhos, bem como foi desenvolvido um software para controle e automação do sistema. Os parâmetros que a norma pede que sejam avaliados e seu respectivo intervalo de tolerância são: potência de saída ('+ OU -' 20%); área de radiação efetiva ('+ OU -' 20%); intensidade efetiva ('+ OU -' 20%); freqüência de trabalho acústica ('+ OU -' 10%); relação de não-uniformidade do feixe ('+ OU -' 30%); intensidade máxima do feixe; tipo de feixe; fator de operação; forma de onda de modulação. Foram avaliados 8 aparelhos, sendo que 3 deles usados no ambulatório da bioengenharia e 5 usados em pesquisa. Para se avaliar os parâmetros dos equipamentos é necessário que eles estejam declarados no equipamento ou em manual que acompanha o equipamento. Na falta destas especificações fez se necessário a proposta de valores de referência para os aparelhos de ultra-som terapêutico da bioengenharia / The use of the ultrasound is quite wide health area, so much for image diagnosis as for the treatment of countless disease (skin wounds to malignant tumors). In the Interunidades Program of Masters degree in Bioengineering during more than 20 years are made researches about the interaction of the ultrasound with the biological tissues. The present work objective is the evaluate the acoustic fields generated by therapeutic ultrasound apparatus used in the Interunidades Program of Masters degree in Bioengineering according with NBR-IEC 1689. In this way, it was set up an acoustic tank and a positioning system for the apparatus, as well as software was developed for control and automation of the system. Parameters required by standard to be measured are presented with the respective tolerance interval: declared potency ('+ OR -' 20%); effective radiation area ('+ OR -' 20%); effective intensity ('+ OR -' 20%); work acoustics frequency ('+ OR -' 10%); non uniformity of the field relationship ('+ OR -' 30%); maximum intensity of the field; field type; operation factor; modulation wave form. There were appraised 8 apparatus, 3 of them are used in clinic of bioengineering and 5 are used in research. To evaluate the equipment parameters it is necessary that they are declared in the equipment or in equipment manual. In the lack of these specifications it is necessary proposal of reference values for the therapeutic ultrasound apparatus of bioengineering

Neste trabalho são analisados os campos acústicos gerados por transdutores ultrassônicos planos e circulares, do tipo pistão plano, no modo pulso-eco, trabalhando como emissor e receptor de ondas, com freqüências de 1,6 MHz, 2,25 MHz e 5 MHz. As ondas emitidas por esses transdutores interagem com interfaces denominadas alvos, com diversas geometrias de superfícies, como planas e circulares, planas com cavidade do tipo alvéolo circular, e cone reto, todas compostas de alumínio e imersas em tanque com água. O campo acústico refletido varia de acordo com o tipo de geometria do alvo. Para essas analises foram produzidas e comparadas modelagens do campo acústico no software Matlab, por meio de dois modelos teóricos: método da resposta impulsiva e método da representação discreta. Foram analisados o tempo de computação produzido pelo método numérico com relação a discretização dos elementos de área do transdutor e do alvo, alem da influencia da conversão de modo nas respostas impulsivas simuladas para essas superfícies. Os resultados mostraram uma boa correlação entre os dois métodos teóricos, porem o de representação discreta possibilita o estudo em transdutores com geometria diferente do pistão plano, sem o uso de integrais complexas. As diferenças dos resultados experimentais e teóricos podem ser minimizadas por meio de uma escolha adequada da relação entre a discretização e comprimento de onda (Dx/), em que foi considerado um valor aceitável de erro relativo de 15% para Dx/ 0,68. Foi observado que o uso da conversão de modo na interface refletora influi apenas na amplitude do sinal de eco (atenuação) e não na forma do sinal. / This work deals with acoustic fields generated by ultrasonic broadband transducers as a planar circular piston, operating in pulse-echo mode, with frequencies of 1.6 MHz, 2.25 MHz and 5 MHz. The waves emitted by transducers interact with water-immersed aluminum targets of different geometries such as planar circular surfaces, concave circular cavity on plane surfaces, and right circular conical surfaces. The impulse response and the discrete representation methods were applied to model the echo responses, using the Matlab software. The influence of mode conversion over the simulated impulse responses for these surfaces was analyzed. The results show a good correlation between the two theoretical methods, but the discrete representation enables the study of arbitrary aperture transducers, with no need to solve complex integrals. The computational times of the discrete representation method was analyzed were respect to the spatial discretization of both the transducer aperture and the target. Experimental tests were carried out to validate the simulated results. Differences in experimental and theoretical results can be minimized by an appropriate choice of the discretization/wavelength ratio (Dx / ). A relative error of 15% was considered acceptable for Dx / 0,68. It was observed that the use of mode conversion at the reflected interface modifies only the amplitude of the echo signal (attenuation), but not its shape.

Orientador: Eduardo Tavares Costa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T14:12:14Z (GMT). No. of bitstreams: 1 Kimura_JoaoPauloEiti_M.pdf: 2957897 bytes, checksum: 673b44ecf63cb018401bbbbc71413541 (MD5) Previous issue date: 2007 / Resumo: O diagnóstico médico por ultra-som vem sendo amplamente difundido, tornando se referência em muitos exames clínicos. Por meio das imagens por ultra-som é possível representar a anatomia de tecidos e órgãos de forma não-invasiva, em "tempo real" e sem a utilização de radiação ionizante. A construção de equipamentos de geração de imagens por ultra-som exige um conjunto confiável de circuitos e componentes eletrônicos, de forma a excitar os transdutores ultra-sônicos e também receber os sinais refletidos de forma rápida e robusta. Entretanto, há também a necessidade da utilização de softwares capazes de processar os sinais ultra-sônicos e gerar as imagens de maneira eficiente. Esse trabalho teve como objetivo primário o desenvolvimento de um software código aberto para formação de imagens por ultra-som, empregando técnicas de formação de imagem por ultra-som em "tempo real". O feixe acústico produzido pelos transdutores matriciais do tipo array pode ser defletido e/ou focalizado pela ativação eletrônica dos elementos do transdutor. Dessa forma, como objetivo secundário, foram desenvolvidos circuitos digitais que geram os estímulos com as seqüências de ativação dos elementos transdutores, para que o feixe acústico seja defletido ou focalizado em uma dada distância ou ângulo a partir da face do transdutor matricial. Os circuitos digitais foram criados utilizando FPGA's. O software de geração de imagens bidimensionais por ultra-som, batizado de ImageB, foi desenvolvido em linguagem C++ com Qt Toolkit 4, com estrutura modular, pode ser estendido por meio de plug-ins além de ser multiplataforma e de licença livre. Além dos algoritmos clássicos para conversão do sinal de RF para imagem em escala de cinza, o software incorpora também as técnicas de abertura e focalização sintética (SAFT e SF). O software e o hardware desenvolvidos nesse trabalho foram testados com um transdutor matricial linear de doze elementos, com freqüência central de ressonância de 1MHz. Foi possível observar que os circuitos foram capazes de defletir e focalizar o feixe acústico e o software ImageB foi capaz de gerar imagens dinâmicas de uma estrutura conhecida (phantom de laboratório), trabalhando de forma paralela e integrada com o hardware desenvolvido / Abstract: The ultrasound medical diagnosis has been widely used, becoming a reference in many clinical procedures. Ultrasound imaging makes it possible to represent the anatomy of organs and tissues in a non-invasive, real time way and without using ionizing radiation. The construction of ultrasound imaging systems requires a set of reliable circuits and electronic components, for exciting the ultrasonic transducers and receiving the reflected signals in a fast and robust way. However, one has to use software capable to efficiently process the received ultrasound signals and generate images. This work, as primary objective, aimed at the development of an open-source software for ultrasound image formation, employing techniques for real time ultrasound image formation. The acoustic beam produced by array transducers can be steered and/or focused by electronic activation of the elements of the transducer. As secondary objectives, digital circuits were developed to generate the sequence of activation of the transducer elements in order to steer and focus the acoustic beam electronically over the region of interest at a given distance or angle from the face of the transducer array. These digital circuits were created using FPGA's. The software to generate two-dimensional ultrasound images, ImageB, was developed in C++ with Qt Toolkit 4, has been designed in a modular form, can be extended via plug-ins and is multiplatform and freeware. Besides the traditional algorithms for conversion of the RF signal to grayscale image, the software also incorporates the techniques of aperture and synthetic focus (SAFT and SF). The hardware and software developed in this work were tested using a 1 MHz 12-element array transducer. It was possible to notice that the circuits were capable to steer and focus the acoustic beam and the software ImageB was capable to generate dynamic ultrasound images of a known structure (laboratory phantom), working with the developed hardware in an integrated and parallel way / Mestrado / Engenharia Biomedica / Mestre em Engenharia Elétrica

La caractérisation expérimentale de la réponse vibro-acoustique de panneaux excités par des champs de pression aléatoire est d'un grand intérêt dans le monde de la recherche, aussi bien industrielle qu'académique. Dans le domaine des transports, ce type d'excitation se rencontre par exemple lorsqu'un écoulement turbulent se développe en paroi d'un véhicule en mouvement. Les fluctuations de pression induites par la couche limite turbulente excitent les parois qui rayonnent un bruit à l'intérieur de l'habitacle. La reproduction expérimentale de ces fluctuations de pression nécessite des moyens qui peuvent être très coûteux (i.e, tunnel aérodynamique, essais in situ) et dont il est difficile de maîtriser tous les paramètres physiques. Un second exemple de champ de pression aléatoire est le champ acoustique diffus. Celui-ci est généralement reproduit dans une chambre réverbérante que l'on couple souvent à une chambre anéchoïque par l'intermédiaire de la paroi dont on souhaite étudier l'isolation acoustique. Un champ acoustique est supposé diffus si l'énergie acoustique provient de toutes les directions et l'intensité des ondes incidentes est équiprobable, ce qui n'est jamais le cas en pratique (problème des angles rasants, modes propres en basse fréquence, etc.). Il y a donc un fort intérêt à disposer d'un outil de laboratoire permettant de reproduire l'effet d'excitations aléatoires dans un environnement qui peut être contrôlé. C'est dans ce contexte que s'inscrit cette thèse qui a pour but de développer une méthode expérimentale permettant de caractériser le comportement vibro-acoustique de panneaux sous champ de pression aléatoire tout en se passant des moyens de mesures usuels (soufflerie, chambre réverbérante, essais in situ, etc.). Les approches étudiées dans cette thèse se basent sur la formulation mathématique du problème dans le domaine des nombres d'onde. Celle-ci met en évidence une séparation explicite des contributions de l'excitation via son interspectre de pression pariétale, de celles du comportement vibro-acoustique du panneau via des fonctions appelées "fonctions de sensibilité". Supposant donc que l'interspectre de pression pariétale de l'excitation est connu, il suffit de déterminer expérimentalement ces fonctions de sensibilité, sur le panneau ou dans le milieu acoustique, pour déterminer par post-traitement la réponse du panneau à l'excitation considérée. Deux méthodes permettant de déterminer les fonctions de sensibilité seront étudiées numériquement et validées expérimentalement: la méthode par antenne synthétique et la méthode basée sur le principe de réciprocité. Pour étudier la validité de ces méthodes, on compare leurs résultats à ceux obtenus par des moyens standards sur la base de plusieurs indicateurs vibro-acoustiques. Les méthodes sont validées en considérant les deux types d'excitations évoqués précédemment et pour deux types de panneaux: un panneau académique et un panneau "complexe" issu du domaine aéronautique. / The experimental vibro-acoustic characterization of panels submitted to random pressure fields is of great interest in the industry as well as in research laboratories. For the transport sector, this type of excitation can be found when a turbulent flow develops at the wall of a moving vehicle for example. The pressure fluctuations induced by the turbulent boundary layer excite the panels which radiate a noise inside the cabin. The experimental reproduction of those pressure fluctuations requires test means which can be very costly (i.e., wind tunnel, in situ tests) and whose physical parameters can hardly be controlled. The repeatability of measurements can thereby be questioned which makes it hard to compare different technological solutions. A second example of random pressure field is the diffuse acoustic field. This latter is usually reproduced in a reverberant room which is often coupled with an anechoic chamber by means of the panel whose acoustic insulation is to be tested. A pressure field is assumed to be diffuse if the acoustic energy comes from every direction with an equiprobable intensity of the incident waves. This assumption is never fully reached in practice (lack of grazing incident waves, strong modal behavior of the room at low frequencies, etc.). A laboratory tool which allows reproducing the effect of those random excitations in a controlled environment is therefore of great interest. In this context, this thesis aims at developing an experimental method to characterize the vibro-acoustic behavior of panels under random pressure fields without using the common test means (wind tunnel, reverberant room, in situ tests, etc.). For relevance sake, this approach must compensate for the previously stated issues. The approaches studied in this work are based on the mathematical formulation of the problem in the wavenumber domain. This latter allows an explicit separation of the contributions of the excitation via the wall-pressure cross-spectrum, from those of the vibro-acoustic behavior of the panel via so-called `sensitivity functions'. Assuming the wall-pressure cross-spectrum of the excitation is known, it is only required to experimentally determine those sensitivity functions, on the panel or in the acoustic medium, to determine the response of the panel to the considered excitation by post-processing. Two methods aiming at determining the sensitivity functions will be numerically and experimentally studied: the source scanning technique and the method based on the reciprocity principle. Results obtained with those method are compared to measurements using standard test means to attest the validity of those methods. Several vibro-acoustic indicators will be confronted while considering the two previously mentioned excitations and for two types of panels: an academic panel and a `complex' from the aeronautic sector. This latter shows the applicability of the method in an industrial context.

Este trabalho trata da modelagem de sinais ultrassônicos gerados por transdutores circulares (plano e côncavo) no modo de pulso-eco, inspecionando uma região de interesse predeterminada. Para essa análise, dois modelos da resposta impulsiva de um transdutor piezelétrico foram implementados: um do transdutor circular plano e outro do transdutor circular côncavo focalizado. Este último sendo o modelo proposto pelo autor com uma geometria baseada em anéis concêntricos como elementos de área do emissor. A adição de diversos anéis concêntricos, deslocados ao longo de seu eixo e de raios sucessivamente menores, permitiu calcular o campo acústico, gerado por uma abertura côncava, bem como seu eco refletido. A resposta impulsiva de cada anel resulta da diferença entre as respostas impulsivas calculadas para um emissor circular grande e um pequeno. O modelo implementado para o cálculo dos sinais de eco foi utilizado na varredura de uma região contendo um conjunto de pontos com refletividade acústica igual a 1. A reconstrução da imagem foi feita com esses sinais aplicando-lhes a técnica de regularização de Tikhonov. A qualidade das reconstruções das imagens obtidas foi avaliada e comparada a das imagens convencionais. Dentre as métricas de avaliação das imagens reconstruídas estão a influência na variação da velocidade de propagação da onda acústica no meio, a extensão e a discretização do grid e o parâmetro de regularização alfa. Todas as reconstruções foram analisadas segundo o Erro Médio Quadrático (MSE). Finalmente, ensaios experimentais foram conduzidos para a obtenção de A-scans (imagens em modo de amplitude) os quais foram inseridas no modelo teórico para a reconstrução de imagens e analisadas pelo MSE. / This work deals with the modeling of ultrasonic signals generated by circular transducers (planar and concave pistons) in pulse-echo mode, inspecting a predetermined region of interest (ROI). For this analysis, two models of the impulse response of a transducer were implemented: one using a plane piston transducer and the other, a model proposed by the author of this work, using a concave transducer with concentric rings as elements of the emitting area. The addition of several concentric rings moved along its axis allowed us to calculate the acoustic field generated by a concave opening and the echo reflected from each point in space. The impulse response of each ring represents the difference between the impulse responses calculated for a large circular transmitter and a small one. The model implemented for calculating the echo signals is used to scan a region, within a ROI, containing a set of points with acoustic reflectivity of 1. Simulations of the regions are made with these signals by applying the Tikhonov regularization method. To evaluate the quality of image reconstruction, the images are compared with the conventional images. Among the metrics to evaluate the reconstructed images are the influence of the variation of the acoustic wave propagation in the media, the grid range and discretization and the parameter of regularization alpha. All of the image reconstructions were analyzed through the Mean Square Error (MSE) criterion. Finally, experiments were conducted in order to obtain A-scans which were then re-inserted in the theoretical model to reconstruct and analyze the images.

L'acoustique du conduit vocal est souvent décrite avec de simples modèles ondes planes à une dimension. Cependant, cela n'est pas satisfaisant quand à haute fréquence (à partir d'environ 5 kHz) des variations tridimensionnelles du champ acoustique sont présentes. La théorie acoustique multimodale a été implémentée pour prendre en compte les aspects tridimensionnels de l'acoustique du conduit vocal.Un système expérimental a été conçu pour mesurer avec précision des fonctions de transfert, des champs de pression et des diagrammes de directivité sur des maquettes de conduits vocaux. Les données expérimentales obtenues ont été comparées avec les simulations réalisées avec la théorie implémentée et avec la méthode des éléments finis. Le champ acoustique tridimensionnel et les diagrammes de directivité ont été prédit avec succès par les deux méthodes de simulation. Il a été observé que la propagation de mode acoustique d'ordre supérieur induit des variations tridimensionnelles du champ acoustique, génère des antirésonances et des résonances additionnelles et affecte la directivité du son rayonné de façon significative. L'excentricité de la forme du conduit vocal apparaît comme critique pour l'excitation et la propagation des modes d'ordre supérieur.Il est conclu qu'à haute fréquence (au-delà de 5 kHz), la fonction de transfert du conduit vocal peut avoir des variations significatives dans des intervalles de fréquences petit (de l'ordre de 100 Hz) et dans des régions angulaires restreintes (de l'ordre de 30°) qui nécessitent d'être prise en compte dans les études de la parole qui se focalisent sur les hautes fréquences. / The vocal tract acoustics is often described witha simple one dimensional plane wave approach.However, this is not satisfying when at high frequency(from about 5 kHz) three dimensional variations ofthe acoustic fieldare present. The multimodal acoustic theory has beenimplemented in order to account for the threedimensional aspects ofthe vocal tract acoustics.An experimental setup has been designed to measure accuratelytransfer functions, pressure field maps and directivitypatterns of vocal tract replicas.The experimental data obtained have been compared withsimulations performed with the implemented theory andwith a finite element method.The three dimensional acoustic fields and the directivitypatterns were successfully predicted by both simulationmethods.It has been observed that the propagation of higher orderacoustical modes, induces three dimensional variations ofthe acoustic field, generates anti-resonances andadditional resonances, and significantly affects the directivityof the radiated sound.The eccentricity of thevocal tract shape appears as critical for the excitation and thepropagation of the higher order acoustical modes.It is concluded thatat high frequency (above 5 kHz), the transfer functionof the vocal tract can have significant variationswithin short frequency intervals (of the order of 100Hz) and within small angular regions (of the order of30°) which need to be taken into account inthe studies of speech which focus on high frequencies.