SuperNEC is a method of moments (MoM) electromagnetic eld solver based on the Numerical Electromagnetics Code (NEC). Much of the simulation time can be attributed to the lling of the impedance matrix, which is performed at each frequency point of interest. Impedance matrix interpolation methods have been implemented in SuperNEC to reduce the computational time required to ll the impedance matrix [Z]. Elements in [Z] vary predictably over frequency and can be approximated by a second order polynomial. A second improved method is implemented where the dominant frequency variation term is removed prior to calculating the tting function. A method of determining the optimum sample range relative to simulation range and maximum interaction distance has been developed. Given the correct choice of sample range the mean error in the MoM solution is less than 10% over the frequency range and the input impedance can be reproduced with good agreement over a wide bandwith. Improvement in the simulation e ciency of 1.7 times can be expected if su cient frequency points are of interest to account for the computational time required to sample the matrix and determine tting function coe cients. This method has been applied to a dipole antenna, an LPDA and a horn antenna. To increase the simulation bandwidth and retain an acceptable level of accuracy, the bandwidth is split into multiple sub-bands.

Neste trabalho desenvolveu-se desenvolver uma versão sem linearizações do método D-bar para Tomografia por Impedância Elétrica (TIE). O problema inverso de TIE é não-linear e mal-posto. O algoritmo baseia-se na prova de existência e unicidade de Adrian Nachman [Ann. of Math. 143 (1996)] para domínios com distribuição de condutividade duas vezes diferenciáveis. O método faz uso de uma Transformada de Fourier não-linear chamada scattering transform, e o caráter mal-posto do Problema Inverso torna-se evidente no cálculo desta transformada, mais especificamente na determinação das soluções Complex Geometrical Optics (CGO). Atuais implementações práticas do método D-bar para padrões trigonométricos tem aproximado os valores na fronteira das soluções CGO por seu comportamento assintótico no cálculo da scattering transform, o que constitue uma linearização nesta etapa específica do método. Neste trabalho calcula-se a scattering transform a partir das soluções exponencialmente crescentes, o que implica calcular as funções Green de Faddeev, com o objetivo de encontrar imagens com maior resolução espacial e precisão nos valores de condutividade por ter resolvido o problema não-linear de forma completa. Dados de simulação numérica e experimentais usando padrões de injeção pula eletrodos e trigonométricos foram usados na avaliação do método. As imagens obtidas apresentam comportamento diferente em função do padrão de injeção utilizado. Do cálculo completo da transformada scattering resultam imagens com melhor resolução espacial. As imagens reconstruídas a partir de padrões de injeção trigonométricos apresentam também melhor resolução espacial comparadas as imagens reconstruídas a partir de padrões por pares, separados por três eletrodos. / This work proposes to develop a version of the D-bar method linearization for Electrical Impedance Tomography (EIT). The inverse problem of EIT is both nonlinear and very ill-posed. The version of the D-bar method implemented here is based on the existence and uniqueness proof of Adrian Nachman [Ann. of Math. 143 (1996)]. The method relies on the use of a nonlinear Fourier transform called the scattering transform, and the inherent ill-posedness of the inverse conductivity problem becomes evident in the computation of the scattering transform, more specifically in the determination of the Complex Geometrical Optics (CGO) solutions. Current practical implementations of the D-bar method using trigonometric patterns have replaced the boundary values of the CGO solutions by their asymptotic behavior in the calculation of the scattering transform, which is a linearization in this particular step of the overall method. This work proposes to calculate the scattering transform from exponentially growing solutions, which implies the calculation of the Faddeev Greens function, with the goal of obtaining images with higher resolution and accuracy in the conductivity values because the full nonlinear problem is solved. Numerical and experimental data using pairwise and trigonometric current injection patterns were used to evaluate the performance of the method. Better spatial resolution is obtained from the complete computation of the scattering transform. Reconstructed images from trigonometric current patterns also show better spatial resolution compared to pairwise current injection patterns, skipping three electrodes.

O projeto tem como proposito estudar o comportamento elétrico da microestrutura e interface de tungstato de prata e do tungstato de prata com nanoparticulas de prata focando em uma possível aplicação como dispositivo eletrônico. Os rods de α-Ag2WO4 foram sintetizadas utilizando o método hidrotermal assistido por microondas e posteriormente submetidas a um feixe de elétrons fazendo com que os íons de prata Ag+, dentro do bulk do cristal, sejam reduzidos e migrem para a superfície do material crescendo as partículas metálicas. A nucleação desses filamentos podem ser visualizado ao vivo e in situ acompanhando as imagens de MEV-FEG da matrix do material. A fase do material, posições atômicas e o entendimento da distrorção da rede foi confirmada pela difratometria de raio-X com o refinamento Rietveld. O material foi caracterizado, estruturalmente, pelas técnicas de espectroscopia Raman e infravermelho, na qual consegue entender quais são as ligações a curto alcance que os átomos estão fazendo. Foi estudado o seu comportamento eletrônico e espectroscópico, por medidas de espectroscopia de UV-Vis-NIR determinando o valor de bandgap do material. Por meio das medidas de XPS foi possível comparar o a pureza e o o grau de oxidação da superfície. E finalmente, foram realizadas medidas de espectroscopia de impedância e condutividade elétrica em regime DC do material não-irradiado e irradiado para com o feixe de elétrons para se entender o mecanismo de condução elétrica. Pelas curvas de impedância, é possível perceber que as amostras irradiadas possuem uma resistência maior causada pelos defeitos gerados dentro da estrutura dificultando a mobilidade dentro do cristal. Foi possível notar pelas medidas elétricas, que a formação dessa superfície com o nanoparticulas altera o o contato entre os cristais do material, apresenta um desvio da linearidade, essa a fase no contorno estaria permitindo a migração dos portadores de carga nos limites dos cristais de tungstato. / This project have to aim study the electrical conduction behavior of silver tungsten and silver tungsten with Ag nanoparticles microstructures and interface on focus in a possible application in electronic device. The rods of α-Ag2WO4 were synthetized using a microwave assisted method and then target by a electron beam, making the Ag+ ions inside of the crystal, reduce and go out to surface material as nanoparticles of Ag0 metallic. This growth can be view in situ by MEV-FEG. The phase of material, atomic position and structure distortion was confirmed by DRX pattern with Rietveld refinement. The material was structural characterized for Raman and infrared spectroscopy, which could be understood what bonds at short range the atoms was doing. The electronic behavior was study by UV-Vis-NIR spectroscopy for determine the bandgap. XPS measurements were performed to compare the purity of the surface and the degree of oxidation. Finally, the samples non-irradiated and irradiated were characterized electrical with impedance spectroscopy and electrical conductivity in DC to understand the electrical conduction mechanism. For the impedance curves, it was possible to notice that the samples irradiated have a higher resistance caused by the bulk defects difficult the mobility inside de crystal. Can be observed by electrical measures, that the formation of this surface with nanoparticles modify the contact between the crystal, showing a leak of linearity, this phase in the boundary could allow the migration of the charge transport.

Eletrólitos sólidos cerâmicos de ZrO2:8% mol Y2O3 foram preparados com pós de três origens: pó comercial fabricado pela Nissan (Japão), pó obtido por coprecipitação dos hidróxidos no IPEN e pó obtido por mistura de óxidos (utilizando-se ZrO2 produzido na Usina de Zircônio do IPEN e Y2O3 (USA) de pureza superior a 99,9%). Esses materiais de partida foram analisados pelas seguintes técnicas: fluorescência de raios X para a determinação dos teores de ítrio, difração de raios X para a determinação das fases, sedimentação para a determinação da distribuição do tamanho de partículas, adsorsão gasosa (BET) para a determinação da área de superfície específica e microscopia eletrônica de transmissão para a determinação do tamanho médio de partícula. Amostras compactadas foram analisadas por dilatometria para avaliar os estágios de sinterização. As amostras sinterizadas foram caracterizadas por difração de raios X para análise de fases e microscopia eletrônica de varredura para análise da morfologia dos grãos. Análises por espectroscopia de impedância foram feitas para acompanhar o envelhecimento térmico dos eletrólitos sólidos de zircônia-ítria a 600 ºC, temperatura de trabalho do sensor permanente de oxigênio, e para estudar a sua cinética de sinterização. Os principais resultados mostram que o envelhecimento térmico a 600 ºC diminui a resposta (fem) do sensor nas primeiras 100 h até um valor estável. Além disso, os estudos de sinterização por espectroscopia de impedância permitiram encontrar correlações entre parâmetros elétricos, a cinética de sinterização e os mecanismos de crescimento de grão. / ZrO2:8 mol %Y2O3 solid electrolyte ceramic pellets have been prepared with powders of three different origins: a Nissan (Japan) commercial powder, a powder obtained by the coprecipitation technique at IPEN, and the mixing of powder oxides (ZrO2 produced at a Pilot Plant at IPEN and 99.9% pure Y2O3 of USA origin). These starting powders have been analysed by the following techniques: X-ray fluorescence for yttrium content, X-ray diffraction for structural phase content, sedimentation for particle size distribution, gas adsorption (BET) for surface area determination, and transmission electron microscopy for average particle size determination. Pressed ceramic pellets have been analysed by dilatometry to evaluate the sintering stages. Sintered pellets have been characterized by X-ray diffraction for phase analysis and scanning electron microscopy for grain morphology analysis. Impedance spectroscopy analysis have been carried out to follow thermal ageing of zirconia-yttria solid electrolyte at 600 ºC, the working temperature of permanent oxygen sensor, and to study sintering kinetics. The main results show that ageing at 600 ºC decreases the emf sensor response in the first 100 h to a steady value. Moreover, sintering studies by impedance spectroscopy allowed for finding correlations between electrical parameters, sintering kinetics and grain growth mechanisms.

Propõe-se um novo método D-bar de Tomografia por Impedância Elétrica (TIE) para obter, simultaneamente, a condutividade e a permitividade de um domínio 2-D. O algoritmo direto baseia-se na prova de existência e unicidade do artigo de E. Francini [1]. A caracterização de tecidos biológicos é fortemente facilitada a partir do conhecimento de suas propriedades elétricas. Particularmente, nas aplicações médicas de TIE há grande interesse na permitividade, uma vez que, vários autores tem apresentado critérios para distinguir patologias baseados nesta propriedade, um exemplo constitui a determinação de presença ou ausência de sangue em líquidos acumulados no pulmão. Realizam-se testes com dados simulados numericamente e experimentais com o propósito de verificar e entender as propriedades, capacidades e limitações do algoritmo implementado. No caso dos testes numéricos, é desenvolvido um programa que resolve o problema direto da admitividade, o qual permite calcular conjuntos de dados de voltagem numéricos. São simulados dados aplicando padrões de corrente trigonométricos e por pares. As soluções exponencialmente crescentes do problema inverso são parte essencial do algoritmo e devem ser decompostas nas bases dos padrões de injeção de corrente. A compreensão da natureza destas decomposições para padrões de injeção trigonométricos e por pares, levou ao estabelecimento de especificações no projeto de um sistema de TIE para este algoritmo. Os resultados encorajadores numéricos e experimentais obtidos nas reconstruções de condutividade e permitividade, quanto à resolução espacial e às magnitudes, indicam que o algoritmo é promissor para uso clínico. / This work proposes a new D-bar method of Electrical Impedance Tomography (EIT) for reconstructing the conductivity and permittivity simultaneously in a 2-D domain. The direct algorithm presented is based on the existence and uniqueness proof by E. Francini [1]. Biological tissue characterization is strongly facilitated by the knowledge of its electric properties. In EIT medical applications there is great interest in the permittivity as an additional property for distinguishing pathologies. For instance, the determination of presence or absence of blood in fluid accumulation in the lung. Numerical and experimental data tests are carried out in order to verify and understand the properties, capabilities and limitations of the implemented algorithm. A numerical phantom to solve the forward admittivity problem is developed which allows to simulate voltage data sets. Trigonometric and pairwise injection current patterns are applied. Exponentially growing solutions of the inverse problem are a key part of the algorithm, which have to be expanded in terms of the current patterns. Understanding the nature of these expansions for trigonometric and pairwise injection current patterns leads to a set of specifications in the design of an EIT system for this algorithm. The encouraging numerical and experimental results obtained in conductivity and permittivity reconstructions, regarding the magnitude and spatial resolution, indicate that the algorithm is promising for clinical use.

by Leung, Kowk-wa. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 207-211). / Dedication / Acknowledgements / CHAPTER / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 2. --- ANALYSIS OF A PROBE-FED HEMISPHERICAL DR ANTENNA --- p.13 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Problem Formulation --- p.14 / Chapter 2.3 --- Single Cavity Mode Approximation --- p.33 / Chapter 2.3.1 --- Evaluation of Input Impedance --- p.33 / Chapter 2.3.2 --- Measured and Computed Results --- p.36 / Chapter 2.4 --- Rigorous Moment Method Solution --- p.47 / Chapter 2.4.1 --- Efficient Evaluation of GEz --- p.47 / Chapter 2.4.2 --- Moment Method Formulation for Input Impedance --- p.51 / Chapter 2.4.3 --- Evaluation of Z-matrix --- p.56 / Chapter 2.4.4 --- Evaluation of V-matrix --- p.62 / Chapter 2.4.5 --- Convergence Checks --- p.65 / Chapter 2.4.6 --- Measured and Computed Results --- p.91 / Chapter 2.4.7 --- Conclusion --- p.113 / Chapter 2.5 --- Theoretical Single Cavity Mode Radiation Patterns --- p.114 / Chapter 2.6 --- Conclusion --- p.117 / Chapter 3. --- ANALYSIS OF APERTURE COUPLED HEMISPHERICAL DR ANTENNA --- p.118 / Chapter 3.1 --- Introduction --- p.118 / Chapter 3.2 --- Problem Formulation --- p.120 / Chapter 3.3 --- Moment Method Solution --- p.133 / Chapter 3.4 --- Magnetic Field Green's Function of DR Antenna --- p.138 / Chapter 3.5 --- Efficient Evaluations of Antenna Green's Function and Yamn --- p.150 / Chapter 3.5.1 --- Modal Green's function of DR Antenna --- p.150 / Chapter 3.5.2 --- Evaluation of Yamn --- p.153 / Chapter 3.6 --- Single Cavity Mode Approximation --- p.155 / Chapter 3.6.1 --- Evaluation of Input Impedance --- p.155 / Chapter 3.6.2 --- Measured and Computed Results --- p.157 / Chapter 3.6.3 --- Conclusion --- p.165 / Chapter 3.7 --- Exact Modal Solution --- p.166 / Chapter 3.7.1 --- Convergence Checks --- p.166 / Chapter 3.7.2 --- Measured and Computed Results --- p.166 / Chapter 3.7.3 --- Conclusion --- p.187 / Chapter 3.8 --- Conclusion --- p.188 / Chapter 4. --- CONCLUSION --- p.189 / APPENDIX A PROOF OF EQUATION (2-16) --- p.192 / APPENDIX B DERIVATION OF EQUATION (2-43) --- p.193 / APPENDIX C DERIVATION OF EQUATION (2-44) --- p.196 / APPENDIX D PROPAGATION CONSTANT OF FIELDS INSIDE MICROSTRIPLINE --- p.198 / APPENDIX E NUMERICAL TECHNIQUE OF SPECTRAL DOMAIN INTEGRAL --- p.200 / APPENDIX F EXPERIMENTAL SET-UP FOR PROBE- FED DR ANTENNA MEASUREMENT --- p.203 / APPENDIX G EXPERIMENTAL SET-UP FOR APERTURE- COUPLED DR ANTENNA MEASUREMENT --- p.205 / REFERENCES --- p.207 / LIST OF PUBLICATIONS PRODUCED DURING THE STUDY A-l / INTERNATIONAL AWARD OBTAINED DURING THE STUDY B-l

by Ye Jian. / Abstract in English and Chinese. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves [140-147]). / ABSTRACT --- p.i / ACKNOWLEDGEMENTS --- p.v / LIST OF ABBREVIATIONS --- p.vi / TABLE OF CONTENTS / Chapter CHAPTER 1 --- Introduction / Chapter 1.1 --- What is the EBI technique --- p.1-1 / Chapter 1.2 --- Applications of the EBI technique --- p.1-2 / Chapter 1.3 --- The electrical impedance rheopneumography-an overview --- p.1-4 / Chapter 1.4 --- Goal of the work --- p.1-6 / Chapter 1.5 --- Main contributions of the work --- p.1-9 / Chapter 1.6 --- Organization of the thesis --- p.1-9 / Chapter CHAPTER 2 --- Principles of the EBI technique and physiological background of the rheopneumogram / Chapter 2.1 --- Tissue impedance and origins of impedance change --- p.2-1 / Chapter 2.1.1 --- Impedance of living organs --- p.2-1 / Chapter 2.1.2 --- Origins of impedance change --- p.2-2 / Chapter 2.2 --- The data acquisition system (DAS) --- p.2-3 / Chapter 2.2.1 --- Impedance detector --- p.2-3 / Chapter 2.2.2 --- Constant current source and safety consideration --- p.2-4 / Chapter 2.2.3 --- Computer interface --- p.2-5 / Chapter 2.3 --- Electrode systems --- p.2-6 / Chapter 2.3.1 --- Two-/four-electrode systems --- p.2-6 / Chapter 2.3.2 --- Geselowitz lead field theory --- p.2-6 / Chapter 2.3.3 --- Comparisons between the two-/four-electrode systems --- p.2-7 / Chapter 2.4 --- The human cardiovascular system --- p.2-8 / Chapter 2.4.1 --- System operation --- p.2-8 / Chapter 2.4.2 --- Pulmonary hemodynamics --- p.2-9 / Chapter 2.5 --- Physiological background of EIR waveform --- p.2-12 / Chapter 2.6 --- EIR wave morphology and pathological factors --- p.2-13 / Chapter 2.6.1 --- Variations in the a-wave --- p.2-13 / Chapter 2.6.2 --- Variations in the Z-wave --- p.2-14 / Chapter 2.6.3 --- Variations in the C-wave --- p.2-14 / Chapter CHAPTER 3 --- THE COMPOSITION OF IMPEDANCE SIGNAL / Chapter 3.1 --- Introduction --- p.3-1 / Chapter 3.1.1 --- Origins of the TIS --- p.3-1 / Chapter 3.1.2 --- EIR measurement and electrode position --- p.3-2 / Chapter 3.1.3 --- Optimal EIR measurement --- p.3-3 / Chapter 3.2 --- Current path in an inhomogeneous medium --- p.3-4 / Chapter 3.3 --- Numerical model --- p.3-5 / Chapter 3.3.1 --- 2D Model --- p.3-5 / Chapter 3.3.2 --- Tissue resistivity --- p.3-6 / Chapter 3.4 --- Calculation of the potential distribution --- p.3-7 / Chapter 3.5 --- Results --- p.3-9 / Chapter 3.5.1 --- Computer simulations --- p.3-9 / Chapter 3.5.2 --- Experimental results --- p.3-13 / Chapter 3.6 --- Discussions --- p.3-14 / Chapter 3.7 --- Conclusion --- p.3-16 / Chapter 3.8 --- Note on publications --- p.3-17 / Chapter CHAPTER 4 --- ON-LINE RESPIRATORY ARTEFACT REMOVAL VIA ADAPTIVE TECHNIQUE / Chapter 4.1 --- Introduction --- p.4-1 / Chapter 4.2 --- Analysis of the TIS --- p.4-3 / Chapter 4.3 --- Modified adaptive noise canceller --- p.4-7 / Chapter 4.3.1 --- Principle of the ANC method --- p.4-8 / Chapter 4.3.2 --- LMS algorithm --- p.4-8 / Chapter 4.3.3 --- MANC method --- p.4-9 / Chapter 4.3.4 --- Results --- p.4-10 / Chapter 4.4 --- Adaptive moving averager --- p.4-15 / Chapter 4.4.1 --- Modified moving averager --- p.4-15 / Chapter 4.4.2 --- Respiratory artefact elimination with adaptive MMA --- p.4-16 / Chapter 4.4.3 --- Performance of the adaptive MMA filter --- p.4-16 / Chapter 4.4.4 --- Results --- p.4-18 / Chapter 4.5 --- Adaptive FIR filter Design --- p.4-22 / Chapter 4.5.1 --- Introduction --- p.4-22 / Chapter 4.5.2 --- Adaptive FIR filter --- p.4-23 / Chapter 4.5.3 --- Results and discussions --- p.4-24 / Chapter 4.6 --- Simultaneously monitoring respiratory and pulmonary circulation- An application of TIS --- p.4-30 / Chapter 4.7 --- Comparisons of the proposed filter schemes --- p.4-33 / Chapter 4.7.1 --- Performance of the filters --- p.4-33 / Chapter 4.7.2 --- Computational complexity and reduced schemes --- p.4-34 / Chapter 4.8 --- Conclusions --- p.4-37 / Chapter 4.9 --- Notes on publications --- p.4-37 / Chapter CHAPTER 5 --- MODELING ANALYSIS OF THE RHEOPNEUMOGRAM / Chapter 5.1 --- Introduction --- p.5-1 / Chapter 5.2 --- Pulmonary circulation modeling --- p.5-2 / Chapter 5.3 --- Model deduction --- p.5-4 / Chapter 5.3.1 --- Pressure-flow in arteries and veins --- p.5-4 / Chapter 5.3.2 --- The two-chamber model and the EIR model --- p.5-5 / Chapter 5.4 --- Parameter estimation --- p.5-8 / Chapter 5.4.1 --- The fitting function and the parameter equations --- p.5-8 / Chapter 5.4.2 --- Curve fitting --- p.5-10 / Chapter 5.4.3 --- Solution of the parameter equations --- p.5-11 / Chapter 5.5 --- Study of the model parameter sensitivity --- p.5-12 / Chapter 5.6 --- Results --- p.5-13 / Chapter 5.7 --- Conclusion --- p.5-17 / Chapter 5.8 --- Notes on publications --- p.5-17 / Chapter CHAPTER 6 --- ANIMAL EXPERIMENTS AND CLINICAL OBSERVATIONS / Chapter 6.1 --- Introduction --- p.6-1 / Chapter 6.2 --- Animal experiments --- p.6-2 / Chapter 6.2.1 --- Methods --- p.6-2 / Chapter 6.2.2 --- Occlusion of the right pulmonary arterial blood flow --- p.6-3 / Chapter 6.2.3 --- Reflection waves in rheopneumogram --- p.6-4 / Chapter 6.3 --- Clinical observations --- p.6-4 / Chapter 6.3.1 --- Mitral valve stenosis --- p.6-5 / Chapter 6.3.2 --- Obstructive emphysema --- p.6-7 / Chapter 6.4 --- Conclusion remarks --- p.6-8 / Chapter 6.5 --- Notes on publications --- p.6-9 / Chapter CHAPTER 7 --- RECAPITULATION AND TOPICS FOR FUTURE INVESTIGATION / Chapter 7.1 --- Recapitulation --- p.7-1 / Chapter 7.2 --- Conclusions --- p.7-3 / Chapter 7.3 --- Topics for future investigation --- p.7-4 / Chapter 7.4 --- Applications of the EIR technique --- p.7-5 / REFERENCES / APPENDICES / Chapter A. --- A circuit diagram of the four-electrode system --- p.A-l / Chapter B. --- NISA/EMAG (A SOFTWARE PACKAGE OF FEM) --- p.A-2 / Chapter C. --- LMS algorithm --- p.A-3 / Chapter D. --- Curve fitting --- p.A-5 / Chapter E. --- List of publications --- p.A-8

Este trabalho consiste em utilizar a técnica de Espectroscopia de Impedância Eletroquímica (EIE) na investigação da cinética de diferentes materiais eletrocatalíticos. O modelo de eletrodos porosos se apresenta como uma forma bastante promissora no tratamento das respostas em freqüência dos ADEs. Uma vez estabelecida a aplicação do modelo, pode-se chegar à obtenção de informações cinéticas importantes durante a análise de vários fatores que ocorrem no sistema em questão, sendo possível então, confirmar resultados obtidos por outras técnicas. Foram investigados eletrodos do tipo ADEs de composição Ti/Ru0,3Ti(0,7-x)SnxO2 (x = 0; 0,3 e 0,7), investigando o efeito da eletrodeposição de Pt na superfície do ADE de Ti/Ru0,3Ti0,7O2, a fim de comparar os resultados obtidos por EIE (ac) com o estudo cinético realizado por curvas de polarização de Tafel (dc) em meio ácido. Além destes realizou-se a investigação dos ânodos, aplicáveis a células a combustível de etanol (DEFCs), de composição: Ti/Pt, Ti/Pt:Ru (80:20), Ti/Pt:Sn (80:20) e Ti/Pt:Ru:Sn (80:10:10) em meio ácido e também de etanol, utilizando-se a EIE como elemento de diagnóstico da atividade da composição do ânodo. Os resultados de EIE confirmam que, o aumento da concentração de SnO2 na composição dos ADEs, favorece a formação de oxigênio, como o apresentado na literatura, por outras técnicas eletroquímicas. A linha de transmissão de um canal apresentou valores satisfatórios dos seus elementos, coerentes com os valores apresentados na literatura, quanto utilizada a técnica da EIE. Foi observado também que adição de Pt na composição do ADE Ti/Ru0,3Ti0,7O2 melhorou a eficiência do material, apresentando menores valores de resistência à transferência de carga, A resistência de transferência de carga (Rtc) diminui à medida que se aumenta o potencial, no sentido da RDO. Analisando-se aos valores de potencial em função das curvas de polarização de Tafel e EIE, pode-se concluir então que existe um relação entre o comportamento ac e dc do sistema. Nos estudos de materiais aplicados a DEFCs, confirmam os resultados que a introdução de Sn melhora a atividade para a oxidação do etanol. A composição Ti/Pt:Sn(80:20) apresentou os melhores resultados nos testes de EIE, obtendo-se valores menores de resistência a transferência de carga, concordando com os resultados obtidos no estudo de célula a combustível. / This work consists in using Electrochemical Impedance Spectroscopy (EIS) in the research of various electrocatalytic materials. The porous electrode model is a very promising approach to treat the frequency responses of Dimensionally Stable Anodes (DSA®). Once the application of the model is established, it is possible to obtain important kinetic information while various factors occurring in the system are analyzed. This allows confirmation results obtained by other techniques. Electrodes of the DSA® type with composition Ti/Ru 0,3Ti(0,7-x)SnxO2 (x=0; 0,3 e 0,7) were investigated. In order to compare the results obtained for DSA® Ti/Ru 0,3Ti0,7O2 electrodes by EIS (ac) with the kinetic studies by Tafel (dc) polarization curves performed in acid environment. Additionally, an investigation of the anodes, applicable to Direct Oxidation of Ethanol Fuel Cells (DEFCs), with composition Ti/Pt, Ti/Pt:Ru (80:20), Ti/Pt:Sn (80:20) and Ti/Pt:Ru:Sn (80:10:10) in acid environment and also in ethanol was carried out, using EIS as a diagnosis element for the activity of the anode composition. The EIS results confirmed that increasing concentration of SnO2 in the DSA® composition enhances oxygen formation, as reported in the literature, for other electrochemical techniques. The EIS technique revealed that the transmission line of one canal provided satisfactory data for its elements, in agreement with literature data. Pt addition to the DSA® Ti/Ru 0,3Ti0,7O2 improved the material efficiency, giving smaller resistance values for charge transfer. The resistance of the charge transfer (Rtc) lowered with increasing potential, in the direction of RDO. Analysing the potential values as a function of the Tafel polarization curves and EIS, it is possible to conclude that there is a relationship between the ac and dc behaviors of the system. In the studies of materials applicable to DEFCs it was confirmed that Sn improves the activity for ethanol oxidation. The composition Ti/Pt:Sn (80:20) led to the best results in EIS tests, revealing lower resistance values in the charge transfer, in agreement with results obtained in the study of fuel cells.

Eletrólitos sólidos cerâmicos de ZrO2:8% mol Y2O3 foram preparados com pós de três origens: pó comercial fabricado pela Nissan (Japão), pó obtido por coprecipitação dos hidróxidos no IPEN e pó obtido por mistura de óxidos (utilizando-se ZrO2 produzido na Usina de Zircônio do IPEN e Y2O3 (USA) de pureza superior a 99,9%). Esses materiais de partida foram analisados pelas seguintes técnicas: fluorescência de raios X para a determinação dos teores de ítrio, difração de raios X para a determinação das fases, sedimentação para a determinação da distribuição do tamanho de partículas, adsorsão gasosa (BET) para a determinação da área de superfície específica e microscopia eletrônica de transmissão para a determinação do tamanho médio de partícula. Amostras compactadas foram analisadas por dilatometria para avaliar os estágios de sinterização. As amostras sinterizadas foram caracterizadas por difração de raios X para análise de fases e microscopia eletrônica de varredura para análise da morfologia dos grãos. Análises por espectroscopia de impedância foram feitas para acompanhar o envelhecimento térmico dos eletrólitos sólidos de zircônia-ítria a 600 ºC, temperatura de trabalho do sensor permanente de oxigênio, e para estudar a sua cinética de sinterização. Os principais resultados mostram que o envelhecimento térmico a 600 ºC diminui a resposta (fem) do sensor nas primeiras 100 h até um valor estável. Além disso, os estudos de sinterização por espectroscopia de impedância permitiram encontrar correlações entre parâmetros elétricos, a cinética de sinterização e os mecanismos de crescimento de grão. / ZrO2:8 mol %Y2O3 solid electrolyte ceramic pellets have been prepared with powders of three different origins: a Nissan (Japan) commercial powder, a powder obtained by the coprecipitation technique at IPEN, and the mixing of powder oxides (ZrO2 produced at a Pilot Plant at IPEN and 99.9% pure Y2O3 of USA origin). These starting powders have been analysed by the following techniques: X-ray fluorescence for yttrium content, X-ray diffraction for structural phase content, sedimentation for particle size distribution, gas adsorption (BET) for surface area determination, and transmission electron microscopy for average particle size determination. Pressed ceramic pellets have been analysed by dilatometry to evaluate the sintering stages. Sintered pellets have been characterized by X-ray diffraction for phase analysis and scanning electron microscopy for grain morphology analysis. Impedance spectroscopy analysis have been carried out to follow thermal ageing of zirconia-yttria solid electrolyte at 600 ºC, the working temperature of permanent oxygen sensor, and to study sintering kinetics. The main results show that ageing at 600 ºC decreases the emf sensor response in the first 100 h to a steady value. Moreover, sintering studies by impedance spectroscopy allowed for finding correlations between electrical parameters, sintering kinetics and grain growth mechanisms.

Detection of DNA by electrochemical impedance spectroscopy (EIS) has been reported by many authors and assays have been developed using lab setups. However, as for most detection assay methods there are issues to address to enable the development for the sensor market: Long time-to-result & high complexity for labelled assays and a lack of sensitivity and reproducibility for label-free assays. This work considers two different approaches to address the issues of time-to-result and assay complexity. The first part presents work on achieving rapid sequence-specific electrochemical detection of DNA hybridisation to complementary DNA on an electrode surface. To accomplish assay sensitivity to low DNA target concentrations, a signal amplification strategy is often necessary. One approach is to couple an enzyme to the hybridised target molecules and to deposit insoluble dyes in the subsequent enzymatic reaction, which enhances sensitivity through an increase in the impedance signal in presence of a redox mediator. The time typically taken for this process (20 – 40 min) precludes the use outside lab setups. Therefore, a protocol for sensitive detection in the presence of redox mediator is demonstrated on a practical timescale required for use in sensor applications. Based on these results a model for the fundamental understanding of the amplification reaction is presented which explains the retention of sensitivity at these enhanced timescales. This also enabled further optimisation of the assay for application in single base pair mismatch detection in biologically relevant sequences. Moreover, direct detection of the precipitate formation is demonstrated which enables real-time measurement of the enzymatic reaction without redox agent addition and with enhanced mismatch discrimination. The second part investigates the possibility to detect DNA non-sequence-specifically by non-Faradaic means. This approach aims at reducing assay complexity by establishing whether it is possible to sense the presence of polymeric DNA in solution by measuring changes in the properties of the electrochemical double layer without DNA surface hybridisation. In a sensor setup this approach could be linked to a polymerase chain reaction (PCR) to discriminate polymer from nucleotide monomer and thereby enable PCR progress to be monitored. In this work the response in the electrochemical double layer at the interface of blocked metal electrodes and solutions containing DNA are studied by means of EIS. Blocking layers were applied to the electrode surface to prevent unspecific adsorption of molecules and ions to the metal surface whilst preserving the sensitivity to detection of changes in the double layer. The characteristics of surface blocking layers on disposable electrodes are studied as they are key to understand the double layer properties at a blocked surface. A number of self-assembled monolayers are compared with respect to their temperature stability and their blocking characteristics at different potentials and ion concentrations. This established the basis to study the effect of the presence of, initially, a model polyelectrolyte and, ultimately, DNA on the double layer. Polyelectrolyte detection is successfully shown for the model polyelectrolyte, polyacrylic acid. DNA detection was more challenging and possible causes for deviation from the polyacrylic acid response are discussed.