Neste trabalho foi investigado o processo de relaxação em copolímeros metacrilicos funcionalizados com o grupo cromóforo 4-[N-etil-N-(2-hidroxietil)]amino-2\'-cloro-4\'nitro-azobenzeno (MMADRI3). Os copolímeros sintetizados foram caracterizados por espectrofotometria de visível e infravermelho, calorimetria diferencial de varredura, análise termogravimétrica e elipsometria. O triodo de corona foi utilizado para induzir a orientação dos cromóforos dipolares a temperaturas próximas da transição vítrea. Os valores do coeficiente eletroóptico linear r13 de filmes obtidos por derramento de solução podem alcançar 14 pm/V em amostras funcionalizadas com 43%de cromóforo.O efeito piezoelétricoé significativo para amostras contendo 4% de cromóforo sendo a sua origem atribuída à carga espacial. A relaxação orientacional dos cromóforos foi estudada medindo-se o decaimento do coeficiente eletroóptico e a relaxação dielétrica a diferentes temperaturas. O processo de relaxação foi interpretado utilizando a equação de Kohlraush-Williams-Watts (KWW) aplicada aos domínios do tempo e da freqüência. O tempo de relaxação característico &#964 e o parâmetro b da equação de KWW foram obtidos como função da temperatura desde a temperatura ambiente até acima da temperatura de transição vítrea. O parâmetro b à temperatura de transição vítrea aproxima-se de 0,6 valor que é atribuído a forças de curto alcance. As medidas dielétricas revelaram duas bandas de relaxação &#946 e &#945 respectivamente a baixas e a altas temperaturas. A relaxação a está relacionada com a transição vítrea e à desorientação dos cromóforos. A dependência de &#964 foi fundamentada nas equações de Arrhenius e de Vogel-Fulcher-Tarmnann-Hesse (VFTH), respectivamente a baixas e a altas temperaturas. Os parâmetros de VFTH encontram-se próximos dos considerados universais. O comportamento de &#964 em toda a gama de temperaturas, foi explicado pela equação de Adam-Gibbs, usando-se os parâmetros de VFTH. O resfriamento a taxas lentas após o processo de polarização aumenta substancialmente o tempo de relaxação e a sua energia de ativação. Os expoentes m e n do modelo de Dissado-Hill baseado na interação de multicorpos foram obtidos em função da temperatura. Os valores do parâmetro n ficam dentro do esperado pela teoria / The relaxation process of side-chain methacrylate copolymers functionalized with the nonlinear optical azo chromophore 4-[Nethyl-N-(2-hydroxyethyl)]-amino-2\'-chloro-4-nitroazobenzene (MMADR13) was investigated. The copolymers synthesized were characterized by visible and infrared spectrophotometry, differential scanning calorimetry, thermogravimetric analysis and ellipsometry. The corona triode was employed to induce the orientation of the dipolar chromophore at a temperature near the glass transition. The linear eletrooptic coefficient r13 of cast fllms can reach values as high as 14 pm/V in samples with 43% of chromophore contento The piezoeletric effect attributed to space charge was only significant in the lowest chromophore content samples (4%). Electrostriction was shown to affect to some extent the quadratic electrooptic measurements. The chromophore relaxation at different temperatures was investigated by both electrooptic decay and dielectric measurements. The relaxation process was interpreted using the Kohlraush-Williams-Watts (KWW) equation both in the time and frequency domains. From the KWW equation the characteristic relaxation time &#964 and the stretching parameter b were obtained from room temperature to temperatures above the glass transition. Near the glass transition b is ca 0.6 which is characteristic of short range interactions. Dielectric measurements revealed two relaxation bands, &#946 and &#945, at low and high temperatures, respectively. The &#945 relaxation was attributed to the glass transition and to the 10ss of chromophore orientational order. The temperature behavior of &#964 was interpreted by the Arrhenius and Vogel-Fulcher-Tammann-Hesse (VFTH) equations. at low and high temperatures. respectivelly. The VFTH parameters lie close to the so-called universal values. In addition the overall temperature dependence was explained by the Adam-Gibbs equation using the VFTH parameters. Using a small cooling rate after corona poling increases substantially the relaxation time and the activation energy .The power law exponents m and n. from Dissado-Hill manybody interactions model were obtained as a function of temperature. The n values are in the range of expected values for the many-body interactions model

Orientador: João Carlos Silos Moraes / Banca: José de Los Santos Guerra / Banca: Roberto Luiz Moreira / Resumo: Na caracterização das propriedades ópticas em materiais, a determinação dos parâmetros ópticos como o índice de refração (n) e o coeficiente de extinção (k) são fundamentais. A análise da dispersão dos parâmetros ópticos com a freqüência fornece informações do comportamento da polarização do material com a radiação e as relações de Kramers-Kronig representam uma ferramenta básica de estudo. Neste trabalho, o principal objetivo é determinar parâmetros ópticos (n e k) e dielétricos do sistema vítreo telureto ((20-x)Li2O-xWO3-80TeO2) através da análise de espectro infravermelho pelas relações de Kramers-Kronig. Para tanto, amostras de vidro na composição x = 0, 5, 10 e 15 %mol foram sintetizadas no laboratório do grupo Vidros e Cerâmicas. As amostras foram polidas opticamente e seus espectros de refletância foram obtidos nos espectrômetros Bomem DA8 e Nexus 670 da Nicolet, na região entre 40 e 4000 cm-1. Os espectros obtidos apresentam picos de reflexão característicos observados em outros sistemas vítreos telureto, o que permitiu identificar as bandas vibracionais. As constantes ópticas foram obtidas utilizando as relações de Kramers-Kronig. Para todas as composições estudadas foi observado um aumento no índice de refração quando se aumentou a quantidade de WO3. Do espectro obtido para a constante dielétrica foi possível determinar as freqüências correspondentes aos modos ópticos transversais e longitudinais. As freqüências obtidas se ajustam com aquelas obtidas pelo modelo analítico dos quatro parâmetros semi-quânticos da constante dielétrica, principalmente para a região acima de 500 cm-1. / Abstract: In the study of optical and dielectric properties of materials, the determination of complex indices of refraction and complex dielectric function is fundamental. The analysis of the dispersion of the optical parameters with the frequency provides information about the behavior of the polarization of the material with the radiation, and the Kramers-Kronig relations represent a basic tool of the study. In this work, the main objective was to determine the optical (n and k) and dielectric parameters of a tellurite glasses system ((20-x)Li2O-xWO3-80TeO2) through the infrared spectrum analysis by Kramers-Kronig dispersion relations. For this, glass samples with x=0, 5, 10, and 15 %mol were prepared at the laboratory of Glasses and Ceramics group. The glass samples were polished and their reflectance spectra were obtained in the Bomem DA8 and Nicolet Nexus 670 spectrometers, in the spectral range of 40 to 4000 cm-1. The obtained spectra present allowed us to assign the vibrational bands. The optical and dielectric constants were obtained by the Kramers-Kronig method. For all studied glass compositions an increase was observed in the real part of refractive index when the WO3 content is increased. From de obtained dielectric function it was possible to extract transversal and longitudinal optical phonons frequencies. The frequencies agree with those obtained by the four-parameter semiquantum model, mainly for the region above 500 cm-1. / Mestre

Neste trabalho foi investigado o processo de relaxação em copolímeros metacrilicos funcionalizados com o grupo cromóforo 4-[N-etil-N-(2-hidroxietil)]amino-2\'-cloro-4\'nitro-azobenzeno (MMADRI3). Os copolímeros sintetizados foram caracterizados por espectrofotometria de visível e infravermelho, calorimetria diferencial de varredura, análise termogravimétrica e elipsometria. O triodo de corona foi utilizado para induzir a orientação dos cromóforos dipolares a temperaturas próximas da transição vítrea. Os valores do coeficiente eletroóptico linear r13 de filmes obtidos por derramento de solução podem alcançar 14 pm/V em amostras funcionalizadas com 43%de cromóforo.O efeito piezoelétricoé significativo para amostras contendo 4% de cromóforo sendo a sua origem atribuída à carga espacial. A relaxação orientacional dos cromóforos foi estudada medindo-se o decaimento do coeficiente eletroóptico e a relaxação dielétrica a diferentes temperaturas. O processo de relaxação foi interpretado utilizando a equação de Kohlraush-Williams-Watts (KWW) aplicada aos domínios do tempo e da freqüência. O tempo de relaxação característico &#964 e o parâmetro b da equação de KWW foram obtidos como função da temperatura desde a temperatura ambiente até acima da temperatura de transição vítrea. O parâmetro b à temperatura de transição vítrea aproxima-se de 0,6 valor que é atribuído a forças de curto alcance. As medidas dielétricas revelaram duas bandas de relaxação &#946 e &#945 respectivamente a baixas e a altas temperaturas. A relaxação a está relacionada com a transição vítrea e à desorientação dos cromóforos. A dependência de &#964 foi fundamentada nas equações de Arrhenius e de Vogel-Fulcher-Tarmnann-Hesse (VFTH), respectivamente a baixas e a altas temperaturas. Os parâmetros de VFTH encontram-se próximos dos considerados universais. O comportamento de &#964 em toda a gama de temperaturas, foi explicado pela equação de Adam-Gibbs, usando-se os parâmetros de VFTH. O resfriamento a taxas lentas após o processo de polarização aumenta substancialmente o tempo de relaxação e a sua energia de ativação. Os expoentes m e n do modelo de Dissado-Hill baseado na interação de multicorpos foram obtidos em função da temperatura. Os valores do parâmetro n ficam dentro do esperado pela teoria / The relaxation process of side-chain methacrylate copolymers functionalized with the nonlinear optical azo chromophore 4-[Nethyl-N-(2-hydroxyethyl)]-amino-2\'-chloro-4-nitroazobenzene (MMADR13) was investigated. The copolymers synthesized were characterized by visible and infrared spectrophotometry, differential scanning calorimetry, thermogravimetric analysis and ellipsometry. The corona triode was employed to induce the orientation of the dipolar chromophore at a temperature near the glass transition. The linear eletrooptic coefficient r13 of cast fllms can reach values as high as 14 pm/V in samples with 43% of chromophore contento The piezoeletric effect attributed to space charge was only significant in the lowest chromophore content samples (4%). Electrostriction was shown to affect to some extent the quadratic electrooptic measurements. The chromophore relaxation at different temperatures was investigated by both electrooptic decay and dielectric measurements. The relaxation process was interpreted using the Kohlraush-Williams-Watts (KWW) equation both in the time and frequency domains. From the KWW equation the characteristic relaxation time &#964 and the stretching parameter b were obtained from room temperature to temperatures above the glass transition. Near the glass transition b is ca 0.6 which is characteristic of short range interactions. Dielectric measurements revealed two relaxation bands, &#946 and &#945, at low and high temperatures, respectively. The &#945 relaxation was attributed to the glass transition and to the 10ss of chromophore orientational order. The temperature behavior of &#964 was interpreted by the Arrhenius and Vogel-Fulcher-Tammann-Hesse (VFTH) equations. at low and high temperatures. respectivelly. The VFTH parameters lie close to the so-called universal values. In addition the overall temperature dependence was explained by the Adam-Gibbs equation using the VFTH parameters. Using a small cooling rate after corona poling increases substantially the relaxation time and the activation energy .The power law exponents m and n. from Dissado-Hill manybody interactions model were obtained as a function of temperature. The n values are in the range of expected values for the many-body interactions model

L’analyse de la stabilité de formulations est primordiale dans de multiples secteurs industriels : pharmaceutique, cosmétique, agroalimentaire… Il existe donc de nombreuses techniques permettant de caractériser la stabilité de solutions colloïdales. Les méthodes les plus communément utilisées reposent sur l’analyse par diffraction de la lumière, comme le Turbiscan, développé par la société Formulaction, qui est un instrument de référence dans ce domaine. Cependant, de par leur principe de mesure, ces techniques ne sont pas suffisamment sensibles pour l’analyse d’échantillons fortement absorbants. Les autres méthodes existantes – l’analyse par ultrasons, par rayons X… - sont quant à elles complexes, requièrent la connaissance de propriétés difficilement accessibles, voire sont insensibles de par leur principe physique aux produits à base de noir de carbone, qui constituent la majeure partie du marché des produits dits noirs. Il existe donc un besoin concernant une méthode de mesure simple et non-intrusive qui permette d’étudier la stabilité de dispersions fortement absorbantes. Nous présentons dans ce manuscrit une nouvelle méthode de caractérisation, basée sur l’interaction entre les ondes électromagnétiques hyperfréquences et la dispersion fluidique à l’étude. Dans un premier temps, une modélisation des capteurs ainsi que de l’interaction entre ondes hyperfréquences et liquide est présentée, afin de comprendre les mécanismes de fonctionnement du système développé et d’en optimiser la sensibilité. Par la suite, nous avons corroboré les résultats de modélisation par des simulations hyperfréquences démontrant la sensibilité de la technique à une variation de permittivité effective du liquide, et par extension à une variation de fraction volumique. Forts de ces résultats, l’intégration du système de mesure complet comportant quatre capteurs a été réalisée puis le fonctionnement de la technique a été validé par mesures de solutions colloïdales modèles. Enfin, le système de mesure a été testé sur diverses dispersions plus complexes, permettant ainsi de valider la capacité de la technique hyperfréquence à caractériser la stabilité des solutions colloïdales, et par extension la stabilité de solutions colloïdales fortement absorbantes. / Stability analysis of formulations is essential in several industrial fields: pharmaceutical, cosmetics, agri-food… Therefore, many technics were developed to characterize the stability of colloidal suspensions. The most commonly used ones are based on light diffraction analysis, such as the Turbiscan developed by Formulaction, which is a reference instrument in the field. Nevertheless, because of the measurement principle, those techniques are not suitable for the analysis of highly absorbing samples. There are several other methods – acoustic measurements, X-rays diffraction spectrometry… - to analyse absorbing samples but they are complex, require a good knowledge of the sample properties or even are not sensitive to carbon based products, due to their physical principle, which constitute the larger part of the black products market. Therefore, there is a need for a new measurement method, simple and non-intrusive, that allows to study highly absorbing solutions stability. In this manuscript, we present a new characterization method, based on the interaction between microwaves and the fluidic dispersion under study. In a first time, a modelling of the sensors and the interactions between microwaves and the liquid will be presented, to understand the working of the developed system and to optimize it. Thereafter, we will corroborate the modelling results with microwave simulations, to demonstrate the sensitivity of the method to a variation of the effective permittivity of the liquid, and so to a variation of the volume fraction. Based on those results, the integration of the whole system, with the four sensors, will be realised and the functioning of the system will be validated by measuring reference colloidal suspensions. Finally, the measurement system will be tested on several complex suspensions, to validate the ability of the microwave method to characterise the stability of colloidal suspensions, and by extension of highly absorbing colloidal suspensions.

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-03-28Bitstream added on 2014-06-13T19:53:24Z : No. of bitstreams: 1 santos_afs_me_ilha.pdf: 529659 bytes, checksum: add7c6495e005e9cdef13e0ca3baf349 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Na caracterização das propriedades ópticas em materiais, a determinação dos parâmetros ópticos como o índice de refração (n) e o coeficiente de extinção (k) são fundamentais. A análise da dispersão dos parâmetros ópticos com a freqüência fornece informações do comportamento da polarização do material com a radiação e as relações de Kramers-Kronig representam uma ferramenta básica de estudo. Neste trabalho, o principal objetivo é determinar parâmetros ópticos (n e k) e dielétricos do sistema vítreo telureto ((20-x)Li2O-xWO3-80TeO2) através da análise de espectro infravermelho pelas relações de Kramers-Kronig. Para tanto, amostras de vidro na composição x = 0, 5, 10 e 15 %mol foram sintetizadas no laboratório do grupo Vidros e Cerâmicas. As amostras foram polidas opticamente e seus espectros de refletância foram obtidos nos espectrômetros Bomem DA8 e Nexus 670 da Nicolet, na região entre 40 e 4000 cm-1. Os espectros obtidos apresentam picos de reflexão característicos observados em outros sistemas vítreos telureto, o que permitiu identificar as bandas vibracionais. As constantes ópticas foram obtidas utilizando as relações de Kramers-Kronig. Para todas as composições estudadas foi observado um aumento no índice de refração quando se aumentou a quantidade de WO3. Do espectro obtido para a constante dielétrica foi possível determinar as freqüências correspondentes aos modos ópticos transversais e longitudinais. As freqüências obtidas se ajustam com aquelas obtidas pelo modelo analítico dos quatro parâmetros semi-quânticos da constante dielétrica, principalmente para a região acima de 500 cm-1. / In the study of optical and dielectric properties of materials, the determination of complex indices of refraction and complex dielectric function is fundamental. The analysis of the dispersion of the optical parameters with the frequency provides information about the behavior of the polarization of the material with the radiation, and the Kramers-Kronig relations represent a basic tool of the study. In this work, the main objective was to determine the optical (n and k) and dielectric parameters of a tellurite glasses system ((20-x)Li2O-xWO3-80TeO2) through the infrared spectrum analysis by Kramers-Kronig dispersion relations. For this, glass samples with x=0, 5, 10, and 15 %mol were prepared at the laboratory of Glasses and Ceramics group. The glass samples were polished and their reflectance spectra were obtained in the Bomem DA8 and Nicolet Nexus 670 spectrometers, in the spectral range of 40 to 4000 cm-1. The obtained spectra present allowed us to assign the vibrational bands. The optical and dielectric constants were obtained by the Kramers-Kronig method. For all studied glass compositions an increase was observed in the real part of refractive index when the WO3 content is increased. From de obtained dielectric function it was possible to extract transversal and longitudinal optical phonons frequencies. The frequencies agree with those obtained by the four-parameter semiquantum model, mainly for the region above 500 cm-1.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Barium Titanate (BaTiO3 BT) based Ceramic materials have a wide industrial application as Multilayer Ceramic Capacitors (MLCCs) mainly due to its high dielectric constant and good capacitance stability with the temperature change, however this material also presents some limitations, for example, oxidation of low cost electrodes. Several ways of BT modifications have been proposed in Literature, as example, the use of different synthesis methods and the doping with different ions. Therefore, the present work had as objectives the synthesis, sintering and electrical characterization of the BaTiO3 and Ba0.77Ca0.23TiO3 (Barium Calcium Titanate) ceramics. The Sol Gel Proteic method was used to powder synthesis, in this method, coconut water is employed as polymeric agent instead of the conventional alcoxide precursors. The characterization was done using the differential thermal analysis, thermogravimetry, x-ray powder diffraction, scanning electron microscopy and impedance spectroscopy techniques. Both, the calcined powders at 1100 °C and the sintered ceramics at 1350 °C presented single crystalline phase, with good microstructural homogeneity and relative density higher than 90%. The sintered ceramics presented a dielectric constant value at room temperature of 1200 (BT) and 680 (BCT), and dielectric loss of 4,8% (BT) and 1,8% (BCT). Besides, the BCT ceramics presented a Curie temperature on average 14 °C above that observed in Literature. Finally, the activation energies of the conductive process of the grain an grain boundary regions were evaluated following two distinct methods using: i) the Brick-layer model; and ii) the average relaxation frequency of each ceramic region, grain and grain boundary. The obtained values by the two methods are in accordance with them and suggest that the dominant conduction mechanism occurs by oxygen vacancy diffusion created still during the sintering process. / Materiais cerâmicos a base de titanato de bário (BaTiO3 BT Barium Titanate ) possuem uma larga aplicação industrial como Capacitores Cerâmicos Multicamadas (MLCCs Multi layers ceramic capacitors ) devido, principalmente, a sua alta constante dielétrica e boa estabilidade da capacitância com a variação da temperatura, porém esse material apresenta também algumas limitações, como por exemplo, a oxidação de eletrodos de baixo custo. Diversas modificações no BT têm sido sugeridas na literatura, como a utilização de diferentes métodos de síntese e a dopagem com diferentes íons. Dessa forma, o presente trabalho objetivou a síntese, a sinterização e a caracterização elétrica de cerâmicas de BaTiO3 e Ba0.77Ca0.23TiO3 (Titanato de Bário e Cálcio BCT Barium Calcium Titanate ). Para a síntese dos pós foi utilizado o método sol-gel proteico, neste método, a água de coco é utilizada como agente polimérico, ao invés dos alcóxidos convencionais. Para a caracterização das amostras foram utilizadas as técnicas de análise térmica diferencial, termogravimetria, difração de raios X, microscopia eletrônica de varredura e espectroscopia de impedância. Os pós calcinados a 1100°C bem como as cerâmicas sinterizadas a 1350°C e apresentaram fase cristalina única, com boa homogeneidade microestrutural e densidade relativa superior a 90%. O valor da constante dielétrica à temperatura ambiente foi de 1200 para o BT e 680 para o BCT com perda dielétrica de 4,8% e 1,8%, respectivamente. Além disso, as cerâmicas de BCT apresentaram uma temperatura de Curie em média 14 °C acima dos valores observados na Literatura. Por ultimo, as energias de ativação dos processos condutivos nas regiões de grão e de contorno de grão foram obtidas seguindo dois procedimentos distintos: i) utilizando o modelo de brick-layer; e ii) utilizando a frequência de relaxação média de cada região da cerâmica, grão e contorno de grão. Os valores obtidos pelos dois métodos concordaram entre si e sugerem que o mecanismo de condução dominante ocorre por vacâncias de O2- formadas ainda durante o processo de sinterização.

Résumé / Abstract

Dans le secteur de l'agroalimentaire, l'utilisation de la RFID permet d'améliorer la sécurité des produits alimentaires tout en assurant une meilleure traçabilité et un meilleur suivi des produits. Le travail de cette thèse était principalement réalisé dans le cadre d’un projet en coopération avec plusieurs partenaires académiques et industriels dans le secteur fromager où l’objectif principal du projet était de maitriser l’ensemble des étapes de fabrication par un parfait suivi de la traçabilité des produits et un pilotage précis de l’affinage. Le travail réalisé dans cette thèse s'inscrit dans ce contexte et a comme objectif le développement de tags RFID UHF adaptés aux contraintes des produits alimentaires en assurant une double fonction: une fonction de traçabilité à identification unitaire, et ensuite une fonction de détection du degré de maturation de l'aliment par mesure indirecte de ses propriétés électromagnétiques et physico-chimiques.La première étape du projet était la caractérisation des paramètres électromagnétiques des produits alimentaires durant l’affinage afin de réaliser une conception appropriée de l'antenne du tag. En radiofréquences, c'est principalement le substrat qui dicte les propriétés électromagnétiques des composants, notamment la taille des antennes et leur diagramme de rayonnement. La connaissance de ces propriétés est indispensable afin de répondre aux exigences industrielles et d'intégrer dans de bonnes conditions les systèmes dans l'environnement applicatif. En plus, une étude de corrélation est réalisée entre la variation des propriétés diélectriques et celle des propriétés chimiques durant la période d’affinage des produits. Cette étude aide à comprendre la différence entre les différents produits et permet de déterminer les paramètres principaux à suivre durant l’affinage pour la conception du tag capteur.La deuxième étape était la conception des tags identifiants pour la traçabilité des produits alimentaires durant la procédure de fabrication. L’objectif principal est de réaliser un tag identifiant avec une performance qui répond aux besoins des fabricants dans le secteur fromager concernant la taille, la mémoire et la distance de lecture du tag tout en respectant les normes de santé au niveau d’emballage du tag ainsi que le substrat utilisé. Plusieurs configurations de tag RFID UHF étaient réalisées et testées dans un environnement industriel où les résultats obtenus montrent l’efficacité d’utiliser un système de RFID pour automatiser la traçabilité des produits dans le secteur fromager.La troisième étape concerne la conception des tags capteurs pour suivre le degré d’affinage des produits pendant la période de maturation. Une première solution, basée sur l’exploitation de l’effet de variation des propriétés diélectriques sur la distance de lecture de tag, montre un manque de performance due aux faibles variations ainsi qu’aux difficultés de mesure dans un environnement réel. Une deuxième solution basée sur la mesure de taux de dégagement des gaz durant l’affinage montre la possibilité d’estimer le degré d’affinage. Par contre, la puissance d’activation de capteur et le coût élevé ne permettent pas d’adopter cette solution. Finalement, deux solutions alternatives étaient réalisées pour mesurer l’augmentation du taux d’échapement des gaz d’une manière indirecte. La première configuration de tag capteur est basée sur le suivi du changement de dimensions du produit en utilisant un capteur résistif. D’autre part, la deuxième configuration de tag capteur est basée sur le suivi de changement de pression dans l’emballage du produit dû à la production de gaz. Les résultats obtenus montrent que ces deux configurations de tag RFID capteur peuvent offrir des solutions simples et efficaces pour le pilotage de l’affinage des produits alimentaires. / In the food sector, the use of RFID makes it possible to improve the safety of food while ensuring better traceability and better monitoring of products. The work of the thesis was mainly carried out within the framework of a project in cooperation with several academic and industrial partners in the cheese sector where the main objective of the project is to develop UHF RFID tags adapted to the constraints of food products by ensuring a dual function: a traceability function with unitary identification, and then a sensing function of cheese maturation by indirect measurement of its electromagnetic and physicochemical properties.The first step of the project was the characterization of the electromagnetic parameters of food products during ripening in order to achieve an appropriate design of the tag antenna. Knowledge of these properties is essential to meet industrial requirements and to integrate systems in right conditions. Also, a correlation study is carried out between the variation of the dielectric properties and that of the chemical properties during the period of cheese ripening. This study helps to understand the difference between cheese types and allows determining the main parameters to follow during cheese maturation for the design of the sensor tag.The second step was the design of identification tags for the traceability of food products during the manufacturing process. The primary objective is to create a UHF RFID tag with a performance that meets the needs of manufacturers in the cheese sector regarding the size, memory and reading distance while respecting the health standards at the packaging level as well as the substrate used. Several UHF RFID tag configurations were realized and tested in an industrial environment where the results obtained show the effectiveness of using an RFID system to automate the traceability of products in the cheese sector.The third step is the design of sensor tags to track the degree of maturation of products during the ripening period. A first solution, based on the exploitation of the effect of variation of the dielectric properties on the tag reading distance, shows a lack of performance due to the small variations as well as the difficulties of measurement in a real environment. A second solution based on the analysis of gas evolution rate shows the possibility of estimating the degree of cheese maturation. However, the sensor activation power and the high cost represent significant challenges and thus it was difficult to adopt this solution. Finally, two alternative solutions to measure the effect of gas evolution were presented. The idea is based on monitoring other parameters varying due to the increase of gas release during cheese maturation. The first sensor tag configuration traces the variation of product dimension due to maturation using a resistive sensor. On the other hand, the second sensor tag configuration measures the change of pressure inside the product packaging due to gas production. The results obtained show that these two sensor RFID tag configurations can offer simple and practical solutions for controlling the cheese ripening process.

Abstract The main objective of this thesis was to research and develop a sensitive characterization method for dielectric powdery substances which could be utilized in various industrial and research fields. With modern electromagnetic simulation tools and the presented experimental measurements, the characterization of dielectric powders using an indirectly coupled open-ended coaxial cavity resonator operating in TEM mode at 4.5 GHz was found to have potential. The modelling and the experimental measurement results of commonly used dielectric powders revealed that, from the nine classical mixing rules, it was possible to derive reliable inclusion permittivity values when using the properties of the perturbed resonator and the Bruggeman symmetric and the Looyenga mixing theories. In addition, the determination accuracy of the inclusion permittivity was found to be greatly improved with the correction factor included into the previously presented permittivity equation of the quarter wave coaxial resonator. Determination of the dielectric losses was found to be reliable when using the differences between the perturbed and unperturbed resonator and the general mixing model equation. The sensitivity of the characterization method was researched with both humidity exposed and surfactant treated modified SiO2, Al2O3 and ZrO2 powders. Experimental results showed that the effect of adsorbed water on the particles was most pronounced when measuring the dielectric losses of the inclusions. Furthermore, a clear correlation with the theory of the general mixing model was found. Thus, in addition to the changed dielectric properties between dry and humidity exposed powders, it was also possible to determine the moisture content with reasonable accuracy. This correlated well with the traditional, mass based, determination. Stearic acid coating of the particles induced only a small change in inclusion permittivity but a notable change in dielectric losses. Unlike the cases with the larger particle sized SiO2 and Al2O3, the dielectric loss of ZrO2 inclusions, with stearic acid coating, was decreased significantly from 6.2 × 10-3 to 3.8 × 10-3. When characterizing magnesium and calcium titanate composite powders, with CaTiO3 molar ratios of 0.0, 0.02, 0.05 and 0.1, the method was found to have good sensitivity and accuracy. Additions of CaTiO3 exhibited a clear increase in net inclusion permittivities from 13.4 up to 14.9 and in dielectric loss tangents from 7.1 × 10-3 up to 8.5 × 10-3. In addition, a good correlation was found in the theoretical determination of the CaTiO3 molar ratios using the resonator measurement results and the general mixing model. The characterization method was proved to be capable of measuring the dielectric properties and detecting even very slight changes in the powders. Thus, the method could be utilized in various types of powdery material characterization, for example, in the analysis and quality control of different composite powders. / Tiivistelmä Väitöstyön päätavoitteena oli tutkia ja kehittää herkkä jauhemaisten eristemateriaalien karakterisointimenetelmä, jota voitaisiin hyödyntää usealla teollisuuden ja tutkimuksen alueella. Hyödyntäen nykyaikaisia sähkömagnetiikan simulointityökaluja sekä kokeellisia mittauksia, havaittiin TEM -moodissa 4,5 GHz taajuudella toimivan avoimen epäsuorasti kytketyn koaksiaalionteloresonaattorin soveltuvan karakterisoimaan eristejauheita. Sähkömagneettinenmallinnus yhdessä yleisesti käytettyjen eristejauheiden kokeellisten mittausten kanssa osoitti, että partikkelin permittiivisyysarvot voitiin johtaa luotettavasti. Tällöin käytettiin näytemateriaalilla täytetyn resonaattorin ominaisuuksia, sekä yhdeksästä vertaillusta klassisesta sekoitusyhtälöstä Bruggeman symmetristä ja Looyengan sekoitusteorioita. Tämän lisäksi tarkkuutta voitiin parantaa huomattavasti lisäämällä korjauskerroin aikaisemmin julkaistuun neljännesaalto-koaksiaaliresonaattorin permittiivisyyden määrittävään yhtälöön. Eristehäviöiden määrittäminen havaittiin luotettavaksi, kun käytettiin mitattavalla materiaalilla muutetun ja tyhjän resonaattorin ominaisuuksien eroja, sekä general mixing model -yhtälöä. Karakterisointimenetelmän herkkyys tutkittiin ilmankosteudelle altistetuilla, sekä pintakäsittelyllä muutetuilla SiO2, Al2O3 ja ZrO2 -jauheilla. Mittaustulokset osoittivat, että partikkelin pinnalle adsorpoituneen veden vaikutus oli kaikkein korostunein, kun mitattiin partikkelien eristehäviöitä. Tämän lisäksi havaittiin myös selkeä korrelaatio general mixing model -teorian kanssa. Näin ollen muuttuneiden eristeominaisuuksien määritysten lisäksi voitiin määrittää jauheen kosteussisältö riittävällä tarkkuudella. Tulokset korreloivat hyvin perinteisen massaeroihin perustuvan määrittämisen kanssa. Partikkelien pinnoitus steariinihapolla aiheutti ainoastaan pienen muutoksen permittiivisyyteen mutta merkittävän muutoksen eristehäviöihin. Toisin kuin suuremman partikkelikoon SiO2:lla ja Al2O3:lla ZrO2 -partikkelin eristehäviö laski huomattavasti steariinihappopinnoituksen jälkeen, 6,2 × 10-3:sta 3,8 × 10-3:een. Karakterisoitaessa magnesium- ja kalsiumtitanaattikomposiittijauheita käyttämällä CaTiO3 -moolisuhteita 0,0, 0,02, 0,05 ja 0,1 menetelmällä havaittiin olevan hyvä herkkyys ja tarkkuus mitattavan materiaalin muutoksille. CaTiO3 -määrän lisäykset aiheuttivat selkeän nousun partikkelien kokonaispermittiivisyyksissä, joka kasvoi 13,4:sta 14,9:ään, sekä häviötangentissa, joka kasvoi 7,1 × 10-3:sta aina 8,5 × 10-3:een. Tämän lisäksi resonaattorin mitattuihin ominaisuuksiin sekä general mixing model -yhtälöön perustuvan teoreettisen määrityksen havaittin korreloivan hyvin CaTiO3 -moolisuhteisiin. Karakterisointimenetelmän osoitettiin soveltuvan eristeominaisuuksien mittaukseen sekä havaitsemaan jopa erittäin pienet muutokset jauheiden eristeominaisuuksissa. Menetelmää voitaisiin hyödyntää usean tyyppisissä jauhemateriaalien ominaisuuksien määrityksissä, kuten esimerkiksi erilaisten komposiittijauheiden analysoinnissa ja laaduntarkkailussa.

Cette thèse s’intéresse à la caractérisation de couches diélectriques et magnétiques de structures multicouches par cavité résonante microonde. Les matériaux multicouches ont des propriétés électromagnétiques spécifiques et sont utilisés dans beaucoup de secteurs industriels, par exemple, dans les radiocommunications. La caractérisation électromagnétique reste une priorité pour la compréhension des caractéristiques de propagation des ondes électromagnétiques dans ces milieux. Dans ce travail de thèse nous proposons une nouvelle approche expérimentale pour déterminer les propriétés diélectriques effectives d’une structure multicouches en fonction des propriétés et de l’épaisseur de chacune des couches. En particulier, nous appliquons les expressions de permittivités issues de la méthode des perturbations utilisée en cavité résonante au cas d’un échantillon rectangulaire bicouche. L’analyse théorique établie a montré qu’une expression de simple proportionnalité reliant les propriétés diélectriques moyennes d’un matériau bicouche avec les propriétés diélectriques relatives et les épaisseurs des couches constituantes peut être obtenue. Cette méthode a été appliquée avec succès sur différents matériaux bicouches. En particulier, elle a permis la caractérisation d’une couche de YIG d’épaisseur très mince (19.6 μm) déposée par pulvérisation cathodique sur un substrat d’alumine en connaissant l’épaisseur et les propriétés diélectriques du substrat. La comparaison avec les résultats expérimentaux a révélé un bon accord entre théorie et mesure. L’analyse de l’incertitude associée au calcul de la permittivité par la méthode a montré une bonne sensibilité. Enfin, nous donnons les courbes de variation de la perméabilité effective mesurée pour un empilement bicouche avec une couche mince de YIG / This thesis aimed at characterizing the dielectric and magnetic layers of multilayer structures by using the technique of microwave resonant cavity. Multilayer structures have specific electromagnetic properties and are becoming increasingly important in many industrial domains, such as in radio-communication systems. The electromagnetic characterization remains a priority for understanding the characteristics of electromagnetic wave propagation in such environments. The thesis proposed a new experimental approach to determine the effective dielectric properties in a bilayer structure as a function of the characteristics and thickness of each specific layer. In particular, we apply the expressions of permittivities derived from the perturbations method which are used in resonant cavities in case of a bilayer rectangular sample. The established theoretical analysis leads us to propose a new expression of simple proportionality describing a relationship between the mean dielectric properties of a bilayer material and the relative dielectric properties and thickness of the constituent layers. The presented method has been successfully applied to different bilayer materials. Particularly, it allowed the characterization of a very thin layer (YIG layer) of thickness 19.6 microns deposited by cathodic sputtering on an alumina substrate by knowing the thickness and dielectric properties of this substrate. The comparison with the experimental results revealed good agreement between theory and measurement. The analysis of the uncertainty associated to the calculation of the permittivity by the presented method showed good sensitivity. Finally, we provide the curves of variation of the effective permeability measured for a bilayer stack