Cette thèse s’intéresse à la modélisation dynamique d’une pile à combustible (PàC) PEM en vue de son utilisation en électronique de puissance. Un modèle statique basé sur une expression de la tension en fonction du courant débité est tout d’abord présenté. Le modèle dynamique est élaboré ensuite. Il est montré que l’impédance électrochimique de diffusion-convection (Zd) s’apparente à une ligne de transmission de type RC. Une discrétisation en un nombre fini d’éléments a été effectuée. Afin d’obtenir un modèle simple, deux branches RC différentes sont considérées pour l’impédance Zd auxquelles sont ajoutées la capacité de double couche, les résistances de transfert et de la membrane. Ce modèle est validé sur deux PàC de 500 W et 5 kW sur une gamme de fréquence 5 mHz à 2 kHz, lors d’échelons de courant et lors du débit sur un hacheur élévateur. Il est montré que l’utilisation du découpage haute fréquence du convertisseur permet un diagnostic de l’état d’humidification de la membrane / This thesis deals with dynamic modelling of a proton exchange membrane fuel cell (PEMFC) with a view to integrate it into power electronics environment. Firstly a static model based on an expression that links current and voltage is presented. The dynamic model is then obtained. It is shown that the electrochemical diffusion-convection impedance (Zd) is similar to a RC transmission line. A discretization on a short number of elements is carried out. In order to obtain a simple model, two different RC branches for Zd impedance, a double layer capacitor, a transfer resistance, and a membrane resistance are considered. This modelling is validated on two 500 W and 5 kW PEMFC, for frequencies varying from 5 mHz to 2 kHz. The model is validated for both fuel cells during current step responses and operation with a boost converter. In this case it is shown how the high frequency switching of the converter can be used to obtain a diagnostic on the humidification state of the membrane

Cette thèse porte sur la conception et la réalisation de micros capteurs à électrodes interdigitées pour la caractérisation des milieux biologiques dans la gamme de fréquences : 100 kHz - 10 MHz. L'objectif principal de ce travail est l’optimisation géométrique de la structure d’un capteur à électrodes interdigitées afin d’élargir la plage fréquentielle de mesure en réduisant les effets de polarisation. Le premier chapitre synthétise les données fondamentales relatives au comportement électrique des tissus biologiques ainsi que leurs propriétés électriques notamment en basses fréquences. Le deuxième chapitre concerne une approche théorique pour l’optimisation du capteur pour élargir la bande de fréquence utile de mesure ; ce chapitre recommande également une nouvelle méthode pour déterminer les paramètres de la double couche à la surface en contact entre les électrodes et le milieu biologique. Dans le troisième chapitre nous proposons une modélisation tridimensionnelle du système d’électrodes chargé par un modèle du milieu biologique sous le logiciel ConventorWare®. Les résultats de simulation sont discutés. Les résultats obtenus nous permettent d’évaluer l'influence des paramètres géométriques de la structure interdigitée du capteur ainsi que les propriétés diélectriques du milieu sur l’impédance bioélectrique. Les facteurs d’influence en fonction de la fréquence sont ainsi maîtrisés lors de la conception d’u capteur interdigité destiné à la mesure de bioimpédance. Dans le quatrième chapitre, les dispositifs ainsi que la conception et la fabrication des composants développés au cours de cette thèse sont décrits. Dans le dernier chapitre, les mesures expérimentales effectuées avec de très faibles volumes de différentes solutions (solutions étalons, sang humain) par cinq micros capteurs à électrodes interdigitées. Les mesures sur les échantillons ainsi que la validation des théories d’optimisation ont été élaborées et discutées. Enfin nous avons comparé nos résultats à des valeurs publiées dans la littérature et nous avons justifié expérimentalement la théorie d’optimisation développée. / This thesis focuses on the design and realization of interdigitated sensors for the electrical characterization of the biological medium within the frequency range: 100 kHz - 10 MHz. The main objective of this thesis is to optimize the geometry of the sensor structure according to the specificities of the interdigitated electrodes structure. This optimization leads to widen the measurement frequency range by reducing the effects of polarization at low frequency. The first chapter synthesizes the basics and fundamentals relative to the electric behavior of biological tissues as well as to their electric properties. The second chapter concerns a theoretical approach for the optimization of the sensor to widen the useful frequency band of measurement; this chapter also presents a new method to determine the parameters of the double layer at the contact interface between the electrodes and the biological medium. A three-dimensional modelling of the system, the electrodes being loaded with a biological medium, is implemented using ConventorWare® software and the results discussed in the third chapter. The results obtained allow us to evaluate the influence of the geometrical parameters of the interdigitated structure of the sensor as well as the dielectric properties of the medium on the bioelectric impedance. In the fourth chapter, the devices developed during this thesis are described. The design and the manufacturing of components are presented. The last chapter deals with the experimental measurements obtained with very small volumes of the different solutions (standard solutions, human blood) using five micro sensors that we built in the laboratory. The measurements as well as the validation of the theoretical approach are discussed. Finally we have compared our results with published values in the literature and validated our experimental and theoretical approaches developed in this work.

A redução de peso é uma questão tecnológica fundamental para a indústria aeroespacial, uma vez que diminui o consumo de combustível, resultando em redução de custos e contribuindo para a redução da emissão de gases de efeito estufa. Devido à relação favorável entre resistência mecânica e peso, as ligas de alumínio de elevada resistência mecânica contribuem favoravelmente para este aspecto. Entretanto, como estas ligas são dificilmente soldáveis pelos processos tradicionais envolvendo fusão, o procedimento de junção utilizado em aeronaves é a rebitagem, resultando em ganho de peso. O processo de soldagem por fricção (friction stir welding -FSW), desenvolvido no início dos anos noventa pelo The Welding Institute (TWI) do Reino Unido, se constituiu em um grande avanço para a soldagem das ligas de alumínio utilizadas na indústria aeroespacial, pois permite a produção de soldas mais confiáveis e virtualmente livres de defeitos. Entretanto, o aquecimento das peças e a deformação mecânica durante a FSW geram zonas com diferentes características microestruturais que, de acordo com a literatura, apresentam resistências à corrosão diferentes. Por oferecerem elevada resolução lateral, as técnicas eletroquímicas locais são úteis para elucidar as diferenças de reatividade local de eletrodos heterogêneos, como no caso de metais soldados. No presente trabalho técnicas eletroquímicas locais foram empregadas para caracterização da resistência à corrosão em meio contendo cloreto das diferentes zonas geradas pela soldagem de topo da liga de alumínio 2024-T3 por FSW, comparando-a com a exibida pelo metal base. O estudo foi complementado com a caracterização microestrutural destas regiões e também por ensaios macroscópicos de corrosão. Os resultados dos procedimentos de caracterização microestrutural confirmaram que a FSW provoca modificações na microestrutura das regiões afetadas pelo processo, principalmente no que concerne à distribuição das nanopartículas precipitadas durante o envelhecimento natural da liga. Por sua vez, os resultados dos ensaios macroscópicos de corrosão e eletroquímicos locais mostraram-se concordantes na determinação da região mais sensível à corrosão, que foi verificada como sendo as zonas termicamente afetada (Heat Affected Zone - HAZ) e termomecanicamente afetada (Thermomechanically Affected Zone - TMAZ) do lado do avanço da ferramenta de soldagem, mostrando também que as regiões afetadas pelo processo de soldagem apresentam resistência à corrosão inferior à do metal base. Através do uso da espectroscopia de impedância eletroquímica local (Local Electrochemical Impedance Spectroscopy - LEIS) foi evidenciado que o acoplamento galvânico entre as diferentes zonas geradas durante o processo de soldagem não desempenha um papel relevante na aceleração do processo corrosivo, o que está em desacordo com os resultados publicados em diversos estudos realizados com esta liga soldada por FSW. O trabalho apresenta ainda uma contribuição teórica original demonstrando que medidas de ângulo de contato e de espectroscopia de impedância eletroquímica em uma gota séssil podem ser usadas simultaneamente para a determinação da capacitância da dupla camada elétrica. As previsões do modelo teórico foram confirmadas tanto através de resultados obtidos com um sistema modelo como também em determinações realizadas nas diferentes regiões geradas pela soldagem por FSW da liga 2024-T3. / Weight reduction is a fundamental technological issue for the aerospace industry, as it decreases the fuel consumption, resulting in reduced both costs and greenhouse gases emission. Due to the favorable relation between strength and weight, high strength aluminum alloys favorably contribute to this aspect, but they remain difficult to weld by conventional processes involving fusion, and, therefore, the junction procedure used in aircraft is riveting, resulting in weight gain. The friction stir welding (FSW) process, developed in the early nineties by the \"The Welding Institute\" (TWI), United Kingdom, is a major breakthrough for the welding of aluminum alloys as it allows the production of more reliable and virtually defect-free welds. However, the heating of the parts and the mechanical deformation during FSW generate zones with different microstructures with different corrosion resistances. As they offer high lateral resolution, local electrochemical techniques are useful for elucidating differences in local reactivity of heterogeneous electrodes, as the case of welded metals. In the present work, local electrochemical techniques were employed to characterize the corrosion resistance in chloride environment of the different zones generated by butt welding the 2024-T3 aluminum alloy by FSW, and to compare this response with that displayed by the base metal. The study was complemented with the microstructural characterization of these regions and also by macroscopic corrosion tests. The results of the microstructural characterization confirmed that FSW causes changes in the microstructure of the regions affected by the process, especially with regard to the distribution of the precipitated nanoparticles during the natural aging of the alloy. The results of the macroscopic corrosion and of the local electrochemical tests showed good agreement in the determination of the most sensitive regions to corrosion, which were found to be the heat affected (HAZ) and the thermomechanically affected (TMAZ) zones of the advancing side of the weld tool. They also showed that the regions affected by the welding procedure have a lower corrosion resistance than the base metal. By using Local Electrochemical Impedance Spectroscopy (LEIS), it was shown that the galvanic coupling between the different areas generated during the welding process does not need to be taken into account in the description of the corrosion process, which is at odds with the results published in several studies of this alloy welded by FSW. The work also present an original theoretical contribution, demonstrating that contact-angle measurements and electrochemical impedance spectroscopy in a sessile drop can be used simultaneously to determine the capacity of the interface. The theoretical model predictions were confirmed by the experimental results obtained both with a model system and in the different regions generated by FSW of aluminum alloy 2024-T3.

Devido às dificuldades encontradas excessivas variabilidades de água no organismo do lactente, considera-se a análise vetorial de impedância bioelétrica (BIVA) um método propício para avaliação da composição corporal. Trata-se de um método que não faz nenhuma pressuposição sobre valores da composição corporal, podendo ser controlado por seus próprios valores, independente de equações ou modelos. Os objetivos deste estudo foram descrever valores de referência e criar curvas de BIVA para lactentes saudáveis de 30 a 90 dias de vida e descrever valores de normalidade de ângulo de fase em lactentes a termo, sadios e adequados para a idade gestacional de 30 a 90 dias de idade, além de comparar os dados de BIVA entre os sexos e entre os existentes na literatura para neonatos e lactentes jovens, com os obtidos neste estudo. Este estudo descritivo transversal avaliou 150 lactentes do Centro Médico Social Comunitário Vila Lobato de Ribeirão Preto - SP - Brasil. Foram coletados dos lactentes os dados antropométricos e a impedância bioelétrica (aparelho de monofrequência RJL System ® modelo Quantum II - 800 ?A e 50 KHz). Usando distribuição bivariável normal de resistência e reactância por comprimento (R/H e Xc/H) do lactente, respectivamente, foram calculados e assim confeccionados os gráficos RXc com os intervalos de tolerância de 95, 75, 50% do valor vetorial da impedância por meio do BIVA Software 2002. Foram avaliados 150 lactentes (48,6% do sexo feminino), nascidos a termo, adequados para idade gestacional e em aleitamento materno exclusivo. A idade média foi 56,4 (± 23,1) dias. O peso médio encontrado foi de 5038,5g (± 902,4), sendo maior no sexo masculino (p = 0,001). Quanto ao comprimento corporal, a média foi 56,0 cm (± 0,03), sendo maior no sexo masculino (p = 0,001). As médias de R (±DP) foram 521,2 (± 52,1); 519,4 (± 53,4) e 523,0 (± 51,1) ?, e para Xc foram 39,2 (± 5,3); 38,6 (± 5,5) e 39,7 (± 4,9) ?, respectivamente para todos os lactentes, e separados por sexo (meninos e meninas), não havendo diferença entre os sexos (p = 0,6) e (p = 0,1). Em relação ao ângulo de fase, encontrou-se o valor de normalidade de 4,3° (± 0,7°) para todos os lactentes, 4,3° (± 0,6°) para os do sexo masculino e 4,4° (± 0,5°) para os do sexo feminino, não havendo diferença estatisticamente significativa (p = 0,3). Para a análise vetorial de lactentes de 30 a 90 dias de idade, devem ser utilizados os valores de referência específicos para esta faixa etária e sexo, pois estes se apresentaram diferentes dos descritos na literatura. Com o modelo de estudo BIVA torna-se possível a comparação direta do vetor medido na criança pequena ou com necessidade de cuidados especiais com os intervalos de tolerância de referência de lactentes saudáveis, permitindo uma avaliação qualitativa da composição corporal e sem erro de predição das fórmulas. Com os valores de ângulo de fase caracterizados no presente estudo para lactentes brasileiros saudáveis, de 30 a 90 dias de idade, dados de pacientes críticos podem ser comparados, sendo útil durante a internação e acompanhamento de pacientes graves. / Bioelectrical impedance vectorial analysis (BIVA) can be considered a favorable method for evaluation of the body composition, due to the difficulties in the early life and excessive variability of the amount of water in the organism of the infants. It is a method that doesn\'t make any presumption on values of the body composition, which can be controlled by their own values, with no need for validation based on gold standards, not depending on equations or models. The aims of the study are to establish reference values creating BIVA curves, and to establish reference values for phase angle in term infants, healthy and appropriate-forgestational age (AGA), from 30 to 90 days of life. This study still intend to compare the data of BIVA between genders, among newborns and young infants, presented in the literature, and the ones obtained in this study. This transversal cohort study assessed healthy infants of a Community Centre for Social Medicine Vila Lobato, located in Ribeirão Preto, São Paulo, Brazil. Data of infants, anthropometry and bioelectrical impedance were collected (singlefrequency - RJL System ® model Quantum II - 800 ?A and 50 KHz). Using bivariate normal distribution of R/H and Xc/H (resistance and reactance for infants length, respectively), graphs RXc with the 95, 75 and 50% tolerance intervals of the vectorial value of the impedance, were made through BIVA Software 2002. 150 infants were studied (48,6% girls), term, AGA, exclusively breastfed. The average age was 56,4 (± 23,1) days, average weight was 5038,5g, higher in girls (p = 0,001), and the average length was 56,0 cm (± 0,03), higher in girls (p = 0,001). The values of R (± SD) were 521,2 (± 52,1); 519,4 (± 53,4) and 523,0 (± 51,1) ? and for Xc were 39,2 (± 5,3); 38,6 (± 5,5) e 39,7 (± 4,9) ?, respectively for all the infants, and boys and girls, with no difference between the genders (p = 0,6) and (p = 0,1). Regarding to the phase angle, we found normal value of 4,3° (± 0,7°) for all the infants, 4,3° (± 0,6°) for male and 4,4° (± 0,5°) for female, without statistical difference (p = 0,36). For Bioelectrical Impedance Vector analysis of infants from 30 to 90 days of life, it would be interesting to use specific reference values for this age group and gender. BIVA model makes possible the direct comparison of the measured vector of the small children; still makes it possible for children needing special care, using the tolerance reference values of healthy infants. This comparison allows us a qualitative assessment of the body composition, with no need of equations. With the values of phase angle characterized in the present study for healthy Brazilian infants, from 30 to 90 days of life, critical patients data can be compared, being useful during the hospitalization due to severe illness.

The impedance response of silicon carbide whisker-alumina composites is investigated utilizing novel stereological techniques along with a microstructural simulation. The stereological techniques developed allow for a measurement of the trivariate length, radius and orientation distribution of whiskers in the composite from measurements made on two-dimensional sectioning planes. The measured distributions are then utilized in a Monte Carlo simulation that predicts connectivity in the composite for a given volume fraction. It is assumed in the simulation that connectivity factors dominate the electrical response, not interfacial phenomena. The results of the simulation are compared with impedance spectra taken from real samples, and conclusions are drawn regarding the nature of the impedance response.

This thesis reports the analysis of the rectangular shaped defected ground structure (RS-DGS) and the application of the structure on some microwave devices. DGS is analyzed in terms of its superior properties, which enables the designers to easily realize many kind of microwave devices which are impossible to achieve with the standard applications. Within the scope of this thesis, the focus is on the rectangular shaped DGS and its characteristic properties. The basic slow wave and high impedance characteristics are utilized in the design of some microwave devices. The design is carried on at the two different frequency bands: X-band and Ka band, centering at 10 GHz and 35 GHz, respectively. Finally, using the high impedance property and the coupling between the defects, a wide band 1 : 4 beam forming network is designed and implemented at 10 GHz.

Series-fed printed slot antenna arrays excited by microstrip lines are low profile, easy to manufacture, low cost structures that found use in applications that doesn&rsquo / t require high power levels with having advantage of easy integration with microwave front-end circuitry. In this thesis, design and analysis of microstrip line fed slot antenna arrays are investigated. First an equivalent circuit model that ignores mutual coupling effects between slots is studied. A 6-element array is designed by using this equivalent circuit model. From the measurement and electromagnetic simulation results of this array, it is concluded that mutual coupling effects should be considered in order to achieve a successful design that meets the design specifications related to the main beam direction and sidelobe levels of the antenna. Next, an improved equivalent circuit model proposed for stripline fed slot antenna arrays is studied. It is observed that, the mutual coupling effects are incorporated into the equivalent model through the utilization of active impedance concept. Finally, the design equations proposed in the improved equivalent circuit model are derived for the microstrip line fed slot antenna array structure. To demonstrate the validity and the accuracy of the derived design equations, results obtained by the proposed analysis method are compared with simulation and measurement results. It is concluded that the proposed method successfully predicts the radiation pattern of the array by including the mutual coupling effects.

Current environmental and energy sustainability trends have instigated considerable interest in alternative energy technologies that exhibit reduced dependence on fossil fuels. The advantages of such a direction are two-fold: reduced greenhouse gas emissions (notably CO2) and improved energy sustainability. Fuel cells are recognized as a potential technology that achieves both of these goals. However, improvements to fuel cell power density and stability must be realized to make them economically competitive with traditional, fossil-based technologies. The work in this dissertation is largely focused on the use of analytical tools for the study of transport processes in three fuel cell systems toward improvement of fuel cell performance. Polymer electrolyte membrane fuel cells (PEMFCs) are fueled by hydrogen and oxygen to generate electrical current. Microbial fuel cells (MFCs) use bacteria to degrade carbon compounds, such as those found in wastewaters, and simultaneously generate an electric current. Enzyme fuel cells (EFCs) operate similarly to PEMFCs but replace precious metal catalysts, such as platinum, with biologically-derived enzymes. The use of enzymes also allows EFCs to utilize simple carbon compounds as fuel. The operation of all three fuel cell systems involves different modes of ion and electron transport and can be affected negatively by transport limitations. Electrochemical impedance spectroscopy (EIS) was used in this work to study the distribution of transport resistances in all three fuel cell systems. The results of EIS were used to better understand the transport resistances that limited fuel cell power output. By using this technique, experimental conditions (including operating conditions, construction, and materials) were identified to develop fuel cells with greater power output and longevity. In addition to EIS, neutron imaging was employed to quantify the distribution of water in PEMFCs and EFCs. Water content is an integral aspect of providing optimal power output from both fuel cell systems. Neutron imaging contributed to developing an explanation for the loss of water observed in an operating EFC despite conditions designed to mitigate water loss. The findings of this dissertation contribute to the improvement of fuel cell technology in an effort to make these energy devices more economically viable.

Made available in DSpace on 2014-06-11T19:30:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-01-08Bitstream added on 2014-06-13T18:40:52Z : No. of bitstreams: 1 baptista_fg_dr_ilha.pdf: 1105245 bytes, checksum: d9df8c940603a26591e01168eaac4aaa (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A técnica da impedância eletromecânica (E/M) tem sido amplamente pesquisada para o desenvolvimento de sistemas de SHM (Structural Health Monitoring – monitoramento de integridade estrutural) em diversas aplicações. Embora existam muitos trabalhos que indiquem a eficiência e a viabilidade dessa técnica, alguns problemas práticos em aplicações reais ainda precisam ser investigados. A medição da impedância elétrica, etapa básica da técnica, geralmente é realizada por instrumentos comerciais volumosos, pesados e de alto custo, características proibitivas para muitas aplicações. A seleção da faixa de frequência em que a impedância deve ser medida para assegurar boa sensibilidade ao dano é feita por métodos de tentativa e erro ou por metodologias que utilizam dados medidos em uma quantidade considerável de testes. Além disso, o dimensionamento dos transdutores é feito sem um embasamento teórico, independentemente das características da estrutura monitorada. Neste trabalho é proposto um sistema de medição de impedância elétrica rápido, versátil e de baixo custo que substitui com eficiência os instrumentos comerciais. A partir de um circuito eletromecânico equivalente, o efeito de carregamento do transdutor devido à estrutura monitorada foi analisado. A análise do efeito de carregamento permite dimensionar corretamente o transdutor de acordo com a estrutura monitorada e assegurar um bom desempenho do sistema. O circuito eletromecânico também foi utilizado para determinar, teoricamente, as faixas de frequência em que o transdutor tem boa sensibilidade e auxiliar na seleção da faixa de frequência adequada para a detecção de danos estruturais. Todas as metodologias propostas foram verificadas através de experimentos em estruturas de alumínio e houve uma boa concordância entre os resultados teóricos e experimentais / The electromechanical (E/M) impedance technique has been widely studied for the development of Structural Health Monitoring (SHM) systems in various applications. Although there are many studies indicating the effectiveness and feasibility of this technique, some practical issues in real applications yet should be investigated. The electrical impedance measurement, basic stage of the technique, is usually performed by bulky, heavy and expensive instruments; these features are prohibitive for many applications. The selection of the frequency range in which the electrical impedance must be measured to ensure good sensitivity for damage detection is performed by trial and error methods or by methodologies that use measured data in a considerable amount of tests. Furthermore, the design of the transducer is done without theoretical basis, regardless the characteristics of the host structure. In this work, a fast, versatile and low-cost electrical impedance measurement system was developed; the proposed system successfully replaces the conventional instruments. From an equivalent electromechanical circuit, the transducer loading effect due to the host structure was analyzed. The analysis of the loading effect allows the correct design of the transducer according to the host structure for ensure a good performance of the system. The electromechanical circuit was also used to theoretically determine the frequency ranges in which the transducer has good sensitivity and assist in the selection of the suitable frequency range for structural damage detection. All proposed methodologies were validated by experimental tests on aluminum structures and there was a good match between the theoretical and practical results

La réduction des nuisances sonores induites par les aéronefs civils autour des grands aéroports est devenue un enjeu sociétal important. Pour réduire le bruit propulsif de soufflante, devenu prépondérant au cours des dernières années avec l'avènement de turboréacteurs à double flux, les constructeurs sont amenés à généraliser l'utilisation de matériaux absorbants acoustiques (également appelés « liners »). Ce sujet de thèse s'inscrit dans le cadre de l'amélioration des outils CAA relativement à la prévision numérique de ces matériaux absorbants. Cette modélisation soulève plusieurs interrogations, liées à divers aspects tels que le type d'écoulement mis en jeu (inhomogénéités, couche limite, etc.), les niveaux acoustiques en présence (effets de non linéarité), les effets de diffraction induits par les ruptures d'impédance, etc. Cette étude consiste donc à valider et à améliorer la condition limite d'impédance, implémentée dans le solveur CAA sAbrinA.v0, développé par l'Onera. Des développements théoriques sont d'abord consacrés à la modélisation de l'impédance dans le domaine temporel, et conduisent à une discussion sur la généralisation de cette modélisation. Le travail consiste ensuite à simuler plusieurs cas tests canoniques de l'absorption du bruit par un revêtement acoustique, lesquels sont validés par confrontation avec d'autres résultats analytiques et/ou expérimentaux. Ce travail fournit de nouvelles connaissances sur la façon dont les matériaux absorbants acoustiques peuvent être modélisés et simulés de manière précise dans le cadre d'une approche CAA dans le domaine temporel. / The reduction of acoustic emission induced by civil aircraft around major airports has become an important societal issue. To reduce the fan noise, induced by the engines, which has become preponderant over the past years with the advent of turbofan engines, manufacturers are led to generalize the employment of acoustic absorbing materials (or acoustic “liners”). The present thesis is related to the numerical prediction of such absorbing materials, in the context of time-domain CAA (Computational AeroAcoustics) methods. Such modeling raises several key questions, which are related to various aspects such as the type of flow involved (boundary layers effects, etc.), the sound levels considered (non-linear phenomena), the diffraction effects induced by ruptures of impedance, etc. The present study then consists in validating and improving the time-domain impedance boundary condition implemented in Onera’s structured CAA solver (named sAbrinA.v0). Theoretical developments are first devoted to the modeling of impedance in the time-domain, and lead to a discussion on the generalization of this modeling. The work then consists in CAA-simulating several canonical tests of noise absorption by acoustic liners. Outputs are compared against experimental and/or analytical results, delivering new insight in the way noise absorption materials can be accurately modeled and simulated using time-domain CAA-approaches.