Le contrôle non destructif par ondes guidées générées et détectées par des transducteurs ultrasonores à couplage par air, présente deux avantages majeurs. Le premier réside dans la capacité des ondes guidées à transporter l’information sur la qualité du milieu sur une grande distance. De plus, l’absence d’un milieu de couplage liquide entre les capteurs et le milieu à tester, rend le contrôle plus commode. Ce travail consiste d’abord à développer un procédé de simulation numérique qui prend en considération de nombreux paramètres du système de contrôle. Dans une optique de réduire le nombre de degrés de liberté, un modèle hybride a été développé qui consiste en une combinaison entre un modèle analytique basé sur l’intégrale de Kirchhoff pour la propagation des ultrasons dans l’air et un modèle éléments finis de la propagation des ondes guidées dans le matériau. La mesure des caractéristiques du transducteur à couplage par air (efficacité de l’émetteur et sensibilité du récepteur) permet, d’une part, de calculer la valeur exacte de la pression dans l’air et les valeurs exactes des champs de contraintes et de déplacements dans la structure, pour une tension et une fréquence d’excitation, et d’autre part, de remonter à la tension électrique aux bornes de ce récepteur pour une pression rayonnée par le matériau. Par suite, cette caractérisation rend possible la comparaison entre les prédictions numériques de la réponse (en niveau de tension) du système et les mesures expérimentales correspondantes. A la lumière du modèle numérique développé, une optimisation des paramètres du système de contrôle (angle, fréquence,diamètre, direction de propagation, champ proche et champ lointain) a été effectuée pour améliorer la pureté des modes guidés par le matériau. Une manipulation expérimentale, basée sur un transducteur à couplage par air pour l’émission et une sonde laser pour la réception, a été alors mise en place pour valider quelques prédictions numériques. Ensuite, on a étudié l’interaction des ondes guidées ultrasonores avec des défauts de type délaminage enfouis dans une plaque composite à symétrie quadratique. Pour cela, on a analysé la sensibilité des deux modes fondamentaux A0 et S0 au délaminage en terme de détectabilité. En parallèle, on a traité un problème inverse qui consiste à dimensionner un délaminage par le calcul du spectre fréquentiel du coefficient de réflexion. Enfin, on a mis en évidence le potentiel des transducteurs à couplage par air à ausculter des pièces aéronautiques impactées. / Non-destructive testing (NDT) using guided waves generated and detected by air-coupled ultrasonic transducers have two main advantages. First, this non-contact technique without coupled medium allows obvious convenience of use. Moreover, the ability of guided waves to carry information about medium quality over long distance. In this context, a numerical model has been developed, which takes into account many parameters of the control system. In order to reduce the number of degrees of freedom, a hybrid model has been developed which consists of a combination between an analytical model, based on the Kirchhoff integral for the propagation of ultrasound in air and a finite element model for the propagation of guided waves in the material. The measured characteristics (efficiency and sensitivity) of two air-coupled transducers allow the prediction of the accurate values of the pressure of bulk waves generated in air and the measurement of the pressure of the radiated field in air by guided waves propagating in a structure. This process enables the comparison between predicted and measured guided waves modes. Based on the hybrid model, an optimization of the parameters of the control system (angle, frequency, diameter, direction of propagation, near and far field) was performed to improve the purity of guided modes along the material plate. To validate some numerical predictions, an aircoupled ultrasonic transducer is used and oriented at a specific angle chosen for generating one specific Lambmode guided along a composite plate sample, and a laser probe measures the normal velocity at different locations on the surface of the plate. Then, the interaction of ultrasonic guided waves with delamination in acomposite plate was studied. In particular, the sensitivity of the two fundamental modes A0 and S0 was analyzed in order to predict the detectability of the defect. In parallel, the inverse problem is solved and the defect size is quantified by calculating the spectrum of the reflection coefficient. Finally, the potential of air-coupled transducers to examine an aircraft structure, has been demonstrated.

La détection de gaz potentiellement dangereux représente une problématique d’actualité pour la protectiondes personnes mais aussi un enjeu d’avenir pour le stockage des énergies renouvelables. Les outils desimulations développés au sein du Département Temps-Fréquence de l’Institut FEMTO-ST, associés aux outilstechnologiques proposés par la centrale MIMENTO ont permis la mise au point de capteurs SAW apportantdes réponses à ces problématiques. Ces derniers fondés sur les propriétés des ondes de Love ont ainsi permis ladétection du monoxyde de carbone dans la gamme du ppm. De même, la mesure de concentration d’hydrogènede l’ordre du pourcent a pu être réalisée par le biais de dispositifs s’appuyant sur les ondes Rayleigh. Les effortsfournis pour l’optimisation des dispositifs électro-acoustiques ont aboutis à la réalisation de lignes à retard surquartz affchant des pertes d’insertion de 16 dB. La limitation de ces pertes, généralement de l’ordre de 25 dB à30 dB sur quartz, augmente les potentialités de nos capteurs en terme d’autonomie et de fonctionnalisation desurface. La connaissance des phénomènes physiques gouvernant leur fonctionnement représente, à notre sens,la base de leur développement futur. De cette idée découle notre démarche d’identification et de compréhensionde ces derniers par le biais des différentes techniques de caractérisations et d’analyses disponible au sein denotre l’institut. Des pistes, telles que le recours à un alliage métallique pour la fonctionnalisation des surfacessensibles et la mise en œuvre d’une méthode de séparation des puces limitant les perturbations du signal directdes dispositifs électro-acoustiques, ont été explorées et ont permis d’améliorer la réponse des capteurs. Lepotentiel des composants à ondes élastiques guidée pour la détection de grandeurs chimiques en phase gazeusea pu être établi sur la base des résultats expérimentaux obtenus au cours de cette thèse. Dans la continuité decette dernière, deux projets de recherche (P-AIR et SMARTY) visant le contrôle de la qualité de l’air en milieuurbain ont d’ors et déjà été engagés. / The detection of hazardous gas is a topical issue for the protection of persons. Besides, it represents a challenge linked to the storage of renewable energy. Simulation tools developed within the Time and Frequency Department attached to the FEMTO-ST Institute together with technological facilities available at MIMENTO center have enabled the development of SAW sensors providing answers to these issues. These Love wave’sbased sensors properties have enabled the detection of carbon monoxide in the ppm range. Similarly, hydrogen concentrations of the percent order has been measured by mean of Rayleigh wave’s based sensors. The efforts to optimize electro-acoustic devices have led to achieve delay lines built on quartz with insertion losses of 16 dB.Usually around 25 dB to 30 dB, the reduction of the insertion losses improves the potential of these sensorsin terms of autonomy and surface functionalization. Knowledge of the physical phenomena governing theoperation of these sensors represent the basis of their future development. Thus, different characterization and analysis techniques available in our institute have been carried out to reveal these phenomena. From there, the functionalization of sensor’s sensitives surfaces with metallic alloys and implementation of a chip separation method limiting the disturbance of the direct signal of the electro-acoustic devices, have been explored to improve the performance of the sensors. Based on the experimental results obtained in this thesis, the potential of elastic guided wave’s sensors applied to the detection of chemical quantities in gas phase can be established.In continuation of this study, two projects (P-AIR and SMARTY) dedicated to the control of the urban air quality have already been engaged.

[pt] A acoustoelasticidade estuda a variação da velocidade de ondas elásticas em corpos sujeitos a um estado de tensão inicial. A teoria da acoustoelasticidade consiste-se de um relação não-linear entre tensão e deformação que rege a resposta dinâmica de uma onda elástica sobreposta à pré deformação inicial. A teoria da acoustoelasticidade aplicada a ondas guiadas é um ramo de estudo extremamente novo. Seu desenvolvimento teórico para ondas de Lamb foi concluída em 2012, o que permitiu o cálculo da variação da velocidade em função da tensão. Ondas de Lamb são ondas elástica que propagam-se em placas de faces paralelas obedecendo às condições de contorno nas superfícies. Essas ondas são a princípio dispersivas. Modelagem por elementos finitos (MEF) é uma ferramenta útil para a análise das ondas ultrassônicas. A fim de abordar o efeito acoustoelástico utilizando método de elementos finitos pode-se utilizar as constantes elásticas eficazes. Por meio dessas é possível montar um tensor de rigidez anisotrópico equivalente, que por sua vez pode ser utilizado como a entrada de rigidez do material em softwares comerciais. O processo de inversão temporal é um método bem conhecido para a obtenção de ondas acústicas focalizadas no tempo e no espaço. No caso de ondas de Lamb, o uso de sinais de inversão temporal compensa a dispersão de cada modo de propagação, recomprime e focaliza a onda na posição de leitura. Nesta tese, o novo ramo da acoustoelasticidade em ondas de Lamb foi analisado e seu estado da arte revisado. A possibilidade de utilizar constantes elásticas eficazes para determinação da dependência da velocidade com a tensão e os erros nesta aproximação foram investigados. O uso do programa de elementos finitos Ansysr foi validado para propagação de ondas de Lamb monomodo em uma placa submetida a tração uniaxial. Em seguida, simulações de propagação de ondas de Lamb multimodais acoustoelásticas foram realizadas através do software e o efeito da carregamento na focalização foi analisado numericamente. Finalmente, experimentos foram realizadas em uma placa de alumínio carregada longitudinalmente. A viabilidade e limitações da utilização das características de focalização por inversão temporal a fim de medir a tensão são apontadas. / [en] The acoustoelasticity studies the variation of the elastic waves velocity in bodies subject to an initial stress state. The acoustoelastic theory consists of non-linear relationship between stress and strain that rules the dynamic response superimposed to the initial pre-deformation. The acoustoelastic theory applied to guided waves is a very new branch of study. The theoretical development of this theory for Lamb waves was completed in 2012, which enabled the calculation of velocity variation as a function of stress. Lamb waves are elastic waves that propagate in plates obeying the boundary conditions on the surface. These waves are a priori dispersive. Finite Element Method (FEM) is an useful tool for ultrasonic waves propagation analysis. In order to address the acoustoelastic effect employing FEM one can use the effective elastic constants. By these effective constants it is possible to assemble an equivalent anisotropic stiffness tensor, which can be the material stiffness input in commercial software. The time reversal process is a well-known method for obtaining focused acoustic waves in both time and space. In the case of Lamb waves, the use of time-reversed signals compensates the dispersion of each propagation mode, recompressing the wave and producing a focused signal at the reception position. In this thesis the new branch of acoustoelasticity for Lamb waves is thoroughly analyzed and its state of the art is reviewed. The possibility of using effective elastic constants for determination of the velocity dependence on stress and the errors in this approximation are investigated. The use of FEM in Ansysr is validated for single mode under uniaxial tensile stress. Then, the simulations of wideband multi-mode acoustoelastic Lamb waves is carried out in the numerical software, the time-reversal focusing ability is verified and the effect of uniaxial load on the focus is investigated. Finally, experiments were performed in an aluminum plate longitudinally loaded. The feasibility of using the time reversal focus characteristics in order to measure the strain is concluded and its limitations are pointed out.

TM-(transverse magnetic)guided waves, propagating in a lossless, nonmagnetic three-layer structure (substrate-film-cladding) are studied. Two types of the dielectric permittivities (I and II) are analyzed. All three media of the waveguide with the permittivity of type I are assumed to exhibit a local Kerr-like tensorial nonlinearity. Maxwell's equations in this case are reduced to an exact differential equation leading to a first integral, relating two electric field components so that one component can be eliminated. The other one can be found by integration. Combination of the first integral with the boundary conditions leads to an exact analytical dispersion relations (expressed in terms of integrals) establishing a link between the parameters of the problem (in particular, thickness of the film, the propagation constant of the travelling wave, the electric field components at the interface substrate-film). The film thickness and the propagation constant satisfying the dispersion relation (by given electric field component at the boundary substrate-film)are associated to the possible modes travelling through the waveguide. Numerical evaluation of the corresponding power flow derived using of Maxwell' equations and the first integral processes straightforwardly, without known wave solutions at first. The waveguide with the permittivity of type II consists of the film with the dielectric function depending on the field intensity (Kerr-type nonlinearity) as well as on the transverse coordinate (spatially varying permittivity) situated between the linear, isotropic substrate and cladding. The problem in this case is reduced to a system of two integral equations. Using the Banach fixed-point theorem it is shown that the solutions of Maxwell's equations exist in form of a uniformly convergent sequence of iterations. The conditions of the Banach fixed-point theorem are derived and used to estimate the quality of the approximation. The exact dispersion relation is derived. Results of numerical evaluation of the dispersion relation and field solutions are presented in the first approximation. Solutions of the dispersion relation, the field components and the power flow obtained using the method for the permittivity I are compared with these found using an integral equation approach (the permittivity II but without the coordinate dependence) - the consistency is remarkably good. The proposed methods seem to be applicable to permittivities more general as considered.

The reflection and transmission of an electromagnetic TE-polarized plane wave at a dielectric film between two linear semi-infinite media (substrate and cladding) is considered. All media are assumed to be homogeneous in x- and z- direction, isotropic, and non-magnetic. The permittivity of the film is assumed to be characterized by a continuously differentiable function of the transverse coordinate and the field. To obtain solutions of Maxwell´s equations that satisfy the boundary conditions the problem is reduced to a Helmholtz equation, which is transformed to a Volterra integral equation for the field intensity inside the film. The Volterra equation is solved by iteration subject to the appropriate boundary conditions. The (iteration) solutions for the linear case and for the nonlinear case are expressed in terms of a uniformly convergent series and a uniformly convergent sequence, respectively. The uniform convergence is proved using the Banach Fixed-Point Theorem. The condition for its applicability leads to a condition for the parameters of the problem. By iterating the Volterra equation an approximate solution for the intensity inside the film is presented. The mathematical basis of the procedure is outlined in detail. Using an approximate solution, the phase function,the phase shifts on reflection and transmission, the reflectivity and the absorptance are determined.Further iterations of the Volterra equation are possible.Semianalytical and numerical examples illustrate the main features of the approach. The method is succesfully applied to different permittivity functions (real, complex, Kerr-like and saturable nonlinear). The agreement between the approximate analytical solutions and numerical solutions is satisfactory. It seems that the method proposed can serve as a means to optimize certain parameters of the problem (material and/or geometrical) for particular purposes.

Un système SHM par ondes guidées a pour but d'évaluer l'intégrité d'une grande variété de structures fines, telles que les fuselages d'avions, les tuyaux, les réservoirs, etc. Un tel système est basé sur un réseau de capteurs piézoélectriques pour l'excitation et la mesure des ondes guidées. Cette méthode de SHM par ondes guidées est prometteuse pour l'inspection de structures de grande taille, ces ondes se propageant sur de grandes distances avec peu d'atténuation, tout en étant sensibles aux défauts surfaciques et subsurfaciques.Cette thèse présente les travaux menés dans le but de développer un système de SHM par ondes guidées capable de détecter, localiser et dimensionner efficacement les défauts dans des structures aéronautiques assimilables à des plaques, en matériaux composites ou en aluminium. Des simulations et des méthodes d'apprentissage sont utilisées pour déterminer les caractéristiques principales des ondes guidées propagées, notamment les vitesses de phase et de groupe ainsi que la fonction de Green 3D. Celles-ci sont ensuite utilisées pour traiter les signaux des ondes guidées afin de produire des images représentant l'intégrité des structures étudiées. Ce travail comprend également une étude approfondie des algorithmes d'imagerie DAS, MV et Excitelet, les plus prometteurs parmi ceux de la littérature, une évaluation de leurs performances par analyse statistique sur une grande base de données de résultats de simulations d'imagerie par ondes guidées et propose une méthode d'imagerie parcimonieuse.Alors que la détection et la localisation des défauts à partir de l'analyse des images est aisée, le dimensionnement du défaut est un problème plus complexe en raison de sa forte dimensionnalité et de sa non-linéarité. Il est démontré que ce problème peut être résolu par des méthodes d'apprentissage automatique sur une grande base de données de résultats de simulations d'imagerie par ondes guidées. Ces méthodes d'imagerie nécessitent cependant une référence, mesurée sur la structure dans un état supposé sain. Elles sont efficaces dans des conditions opérationnelles stationnaires mais sont sensibles aux variations de l'environnement et notamment aux fluctuations de température.Ce travail présente donc l'étude de la robustesse face aux effets thermiques des méthodes d'imagerie par ondes guidées et propose un modèle de détection de défauts capable d'analyser des résultats d'imagerie détériorés. Plusieurs techniques de compensation des effets thermiques sont étudiées et des améliorations sont proposées. Leur efficacité est validée pour les plaques d'aluminium mais des améliorations supplémentaires sont nécessaires pour les étendre aux plaques de composites. / A guided wave-based structural health monitoring (SHM) system aims at determining the integrity of a wide variety of plate-like structures, including aircraft fuselages, pipes, tanks etc. It relies on a sparse array of piezoelectric transducers for guided waves (GWs) excitation and sensing. With a number of benefits, these waves are standing out among other methods as a promising method for the inspection of large structures. They can propagate on significant distances with small attenuation while being sensitive to surface and subsurface defects.This thesis presents studies conducted with the purpose of developing such a GWs-based SHM system that is capable of efficient defect detection, localization and sizing aeronautical plate-like structures made of aluminum and composite materials. Simulation and data-driven approaches are presented for determining principal characteristics of propagating GWs, namely modal group and phase velocities, 3D Green's functions etc. in structures of interest. They are then used for GWs signals processing in order to compute images representing the integrity of studied structures. This work also provides a comprehensive overview of DAS, MV and Excitelet defect imaging algorithms, determines their performance using statistical analysis of an extensive dataset of simulated guided waves imaging (GWI) results and proposes a method for sparse defect imaging.While defect detection and localization are straightforward from the image analysis, the defect sizing is a more complex problem due to its high dimensionality and non-linearity. It is demonstrated that this problem can be solved by means of machine learning methods, relying on an extensive database of simulated GWI results. Aforementioned defect imaging methods are baseline demanding. They are efficient under stationary operational conditions but vulnerable to environmental variations, especially to the temperature fluctuation.Finally, this work presents studies on the robustness of GWI methods against thermal effects, and a defect detection model capable of analyzing deteriorated GWI results is proposed. Different techniques for thermal effects compensation are reviewed, and improvements are proposed. Their effectiveness is validated for aluminum plates but further improvements are required to translate these techniques to composite plates.

[pt] A avaliação não destrutiva ultrassônica é de extrema importância na indústria de óleo e gás, principalmente para ativos e estruturas sujeitos a condições que aceleram os mecanismos de falha. Apesar de amplamente difundidos, os métodos ultrassônicos não destrutivos dependem de uma força de trabalho especializada, sendo, portanto, suscetíveis a erros e demorados. Nesse contexto, métodos de reconhecimento de padrões, como o aprendizado de máquina, se encaixam convenientemente para solucionar os desafios da tarefa. Assim, este trabalho tem como objetivo a aplicação de técnicas de inteligência artificial para abordar a interpretação de dados adquiridos por meio de avaliação não destrutiva ultrassônica no contexto da indústria de óleo e gás. Para tanto, esta dissertação envolve três estudos de caso. Primeiramente, sinais de ondas guiadas ultrassônicas são usados para classificar os defeitos presentes em juntas soldadas de compósito termoplástico. Os resultados mostraram que, ao usar atributos extraídos com modelos autoregressivos, a acurácia do modelo de aprendizado de máquina melhora em pelo menos 72,5 por cento. Em segundo lugar, dados ultrassônicos em formato de imagens são usados para construir um sistema de diagnóstico de solda automático. A estrutura proposta resultou em um modelo computacionalmente eficiente, capaz de realizar classificações com acurácia superior à 99 por cento. Por fim, dados obtidos por simulação numérica foram usados para criar um modelo de aprendizado profundo visando estimar a severidade de defeitos semelhantes à corrosão em dutos. Resultados de R2 superiores a 0,99 foram alcançados. / [en] Ultrasonic non-destructive evaluation is of extreme importance in the oil and gas industry, especially for assets and structures subjected to conditions that accelerate failure mechanisms. Despite being widely spread, ultrasonic non-destructive methods depend on a specialized workforce, thus being errorprone and time-consuming. In this context, pattern recognition methods, like machine learning, fit conveniently to solve the challenges of the task. Hence, this work aims at applying artificial intelligence techniques to address the interpretation of data acquired through ultrasonic non-destructive evaluation in the context of the oil and gas industry. For that purpose, this dissertation involves three case studies. Firstly, ultrasonic guided wave signals are used to classify defects present in welded thermoplastic composite joints. Results have shown that, when using features extracted with autoregressive models, the accuracy of the machine learning model improves by at least 72.5 percent. Secondly, ultrasonic image data is used to construct an automatic weld diagnostic system. The proposed framework resulted in a lightweight model capable of performing classification with over 99 percent accuracy. Finally, simulation data was used to create a deep learning model for estimating the severity of corrosion-like defects in pipelines. R2 results superior to 0.99 were achieved.

[pt] Recentemente, ondas guiadas por ultrassom têm mostrado grande potencial para ensaios não destrutivos e monitoramento de integridade estrutural (SHM) em um cenário de avaliação de danos. As medições obtidas por meio de ondas elásticas são particularmente úteis devido a sua capacidade de se propagarem em diferentes materiais, como meios sólidos e fluidos e, também, a capacidade de abrangerem áreas amplas. Ao possuir suficientes medições oriundas de ondas guiadas, técnicas avançadas baseadas em dados, como aprendizado de máquina, podem ser aplicadas ao problema, tornando o procedimento de avaliação de danos ainda mais poderoso e robusto. Com base nessas circunstâncias, o presente trabalho trata da aplicação de modelos de aprendizado de máquina para fornecer inferências de avaliação de falhas baseadas em informações de ondas guiadas por ultrassom. Dois principais estudos de caso são abordados. Primeiramente, uma placa de polímero reforçado com fibra de carbono (PRFC) é avaliada, utilizando dados da literatura de sinais de onda guiada do tipo Lamb na detecção de defeitos pontuais. Os resultados demonstraram que uma abordagem que utiliza um sinal de referência foi capaz de obter excelentes acurácias ao usar a extração de características baseadas em técnicas de identificação de sistemas. Em um segundo momento, defeitos semelhantes à corrosão em uma placa de alumínio são classificados de acordo com sua gravidade. A metodologia é auxiliada por um esquema de separação de modos em sinais de ondas guiadas do tipo SH pré-adquiridos. Os resultados obtidos mostraram que a adoção da separação de modos pode, de fato, melhorar os resultados do aprendizado de máquina. / [en] Recently ultrasonic guided waves have shown great potential for nondestructive testing and structural health monitoring (SHM) in a damage evaluation scenario. Measurements utilizing elastic waves are particularly useful due to their capability to propagate in different materials such as solid and fluid bounded media, and, also, the ability to cover broad areas. When enough guided waves measurements are available and advanced data-driven techniques such as machine learning can be applied to the problem, the damage evaluation procedure becomes then even more powerful and robust. Based on these circumstances, the present work deals with the application of machine learning models to provide fault evaluation inferences based on ultrasonic guided waves information. Two main case studies are tackled in the mentioned subject. Firstly, a carbon fiber reinforced polymer (CFRP) plate is assessed using open data of Lamb guided wave signals in the detection of dot type defects. Results demonstrated that a baseline dependent approach can obtain excellent results when using system identification feature extraction. Secondly, corrosion-like defects in an aluminium plate are classified according to their severity. The methodology is assisted by a mode separation scheme of SH guided waves signals of pre-acquired data. Results have shown that the adoption of mode separation can in fact improve the machine learning results.

Monitoring the mechanical integrity of critical structures is extremely important, as mechanical defects can potentially have adverse impacts on their safe operability throughout their service life. Structural defects can be detected by using active structural health monitoring (SHM) approaches, in which a given structure is excited with harmonic mechanical waves generated by actuators. The response of the structure is then collected using sensor(s) and is analyzed for possible defects, with various active SHM approaches available for analyzing the response of a structure to single- or multi-frequency harmonic excitations. In order to identify the appropriate excitation frequency, however, the majority of such methods require a priori knowledge of the characteristics of the defects under consideration. This makes the whole enterprise of detecting structural defects logically circular, as there is usually limited a priori information about the characteristics and the locations of defects that are yet to be detected. Furthermore, the majority of SHM techniques rely on sensors for response collection, with the very same sensors also prone to structural damage. The Surface Response to Excitation (SuRE) method is a broadband frequency method that has high sensitivity to different types of defects, but it requires a baseline. In this study, initially, theoretical justification was provided for the validity of the SuRE method and it was implemented for detection of internal and external defects in pipes. Then, the Comprehensive Heterodyne Effect Based Inspection (CHEBI) method was developed based on the SuRE method to eliminate the need for any baseline. Unlike traditional approaches, the CHEBI method requires no a priori knowledge of defect characteristics for the selection of the excitation frequency. In addition, the proposed heterodyne effect-based approach constitutes the very first sensor-less smart monitoring technique, in which the emergence of mechanical defect(s) triggers an audible alarm in the structure with the defect. Finally, a novel compact phased array (CPA) method was developed for locating defects using only three transducers. The CPA approach provides an image of most probable defected areas in the structure in three steps. The techniques developed in this study were used to detect and/or locate different types of mechanical damages in structures with various geometries.

O presente trabalho objetiva um estudo de aplicação do Método dos Elementos de Contorno à análise de problemas de propagação de ondas eletromagnéticas. O Método baseia-se numa formulação integral que elimina todas as operações de integração em domínio, restando apenas as de contorno. Inicialmente faz-se um estudo dos fundamentos teóricos do método, apresentando-o de forma genérica e encaminhando sua aplicação à equação de Helmholtz. Os procedimentos computacionais desenvolvidos para a implementação do método viabilizam a solução eficiente de problemas de interesse, envolvendo diferentes meios com ou sem perdas. São apresentados resultados de simulações realizadas que confirmam a aplicabilidade do método, permitindo também uma análise de seu desempenho através da variação de parâmetros, como, por exemplo, número de elementos na discretização e função de interpolação. / This work deals with a study of application of the Boundary Element Method (BEM) directed to electromagnetic guided wave propagation. This method relies on an integral formulation that does not need any domain integration. Only boundary integrations have to be performed. The work begins with a study of the theoretical foundations of the method, presenting its general formulation and then directing it to Helmholtz’s equation solution. Developed computational procedures allow efficient application of the method to real problems with more than one medium, with or without losses. Simulations results are presented which confirm the applicability of the method and allow the analysis of its performance through parameters variation as, for example, the number of discretized elements and interpolation function.