Cochlear implants are devices, which are implanted into the cochlea to aid hearing via stimulation of the cochlear nerve. For this study, we were interested in understanding the age-related changes in the impedances of the electrodes implanted with a cochlear implant system. The impedances of the electrodes reflect the integrity of the implanted system in the inner ear, and the efficiency of transmission of information from the externally worn device to the implanted system. Thus, monitoring cochlear impedances is important for the patient's rehabilitation. Our hypothesis was that cochlear implant impedances would decrease as an effect of age. Current systems record the impedances via a telemetry system when the patient’s cochlear implant is connected to the programming software. This data is saved within the system and can be retrieved and de-identified within the software. In our investigation, we collected the de-identified impedance data from this system to understand the effects of age. This data was collected from the ETSU Audiology Clinic at the Nave Center. The de-identified data was reviewed and sorted between 3 different age brackets. Data was averaged and compared between age brackets and electrodes. Overall, we found in this study that there are no significant differences between age brackets when comparing cochlear implant impedances across the different electrodes. The slight differences between impedances across electrodes and age brackets could be due to many contributing factors, however, the differences were not considered statistically significant. This study could indicate future directions for further research including, comparing impedance differences between male and female subjects, longitudinal case studies, and comparing across implant manufacturers and device type.

De manière classique, une caractérisation large signal des amplificateurs de puissance s'effectue en présence d'un signal sinusoïdal CW dans le but de fournir aux concepteurs les informations nécessaires permettant un compromis entre puissance de sortie et rendement en puissance ajoutée. Cependant, Dans les systèmes de communications modernes, les amplificateurs de puissance sont soumis à des signaux de plus en plus complexes (modulations numériques) pour lesquels la linéarité est un critère capital supplémentaire pour les performances globales de ces systèmes. Il est donc indispensable de disposer d'outils de caractérisation fonctionnelle permettant de mesurer l'ensemble de ces critères en présence de ces signaux complexes afin de rendre compte au mieux du comportement du dispositif sous test en le plaçant dans ses conditions réelles de fonctionnement. Ce mémoire présente l'étude et la mise en oeuvre d'un banc de caractérisation fonctionnelle de type "load-pull" pour la mesure de l'ensemble des critères de puissance, rendement et linéarité en présence de tous types de signaux (CW, CW-pulsés, GMSK, QPSK, QAM, etc.). L'ENST dispose d'un banc de mesure "source-pull" et "load-pull" multi-harmonique capable d'optimiser la puissance de sortie et le rendement en puissance ajoutée en mode CW. Ce banc est constitué de réflectomètres six-portes, pour la mesure des impédances et des puissances. Afin de permettre l'utilisation de signaux modulés nous avons implémenté des détecteurs de puissance rapides bas coût à base de diodes Schottky non polarisées pour la détection de puissance au niveau des jonctions six-portes. Pour l'optimisation de la linéarité en plus, nous avons ajouté des modules de contrôle des impédances basses fréquences en entrée et en sortie du composant à tester. Un transistor de puissance MESFET a été testé à la fréquence 1.575 GHz en présence d'un signal modulé QPSK de largeur 1.25 MHz et d'un signal bi-porteuses séparées de 800 kHz pour une polarisation de type A et AB. L'ensemble des mesures effectuées permet d'aboutir aux trois principales conclusions montionnées ci-dessous. Premièrement, les contours "load-pull" d'iso-puissances, d'iso-rendement, d'iso-ACPR et d'iso-produits d'intermodulation d'ordre 3 et 5 montrent que les conditions optimales de puissance, de rendement et de linéarité sont différentes d'où la nécessité de trouver des compromis entre les différents critères. D'autre part, ces résultats montrent qu'il existe une forte corrélation entre l'ACPR et le produit d'intermodulation d'ordre 3 en classe A mais pas en classe AB. De toute façon, quel que soit le degré de corrélation, il apparaît difficile de prédire l'ACPR à partir de la connaissance des produits d'intermodulation. Deuxièmement, l'effet des impédances de source BF n'est notable qu'en classe AB dans la zone de saturation. Cet effet se fait sentir uniquement sur la linéarité (variation de 5 dB pour l'ACPR). Finalement, l'effet des impédances de charge BF apparaît quelle que soit la classe de fonctionnement avec évidemment un effet très prononcé pour les classes fortement non-linéaire comme la classe AB pour laquelle on a observé des variations de 5 à 20 dB pour l'ACPR sur toute la dynamique de mesure. Notons que l'impédance optimale n'est pas obligatoirement un court-circuit, et que cette impédance optimale n'est pas toujours l'impédance minimisant la dissymétrie. Par ailleurs, ces impédances ont également une grande influence sur le rendement (variation observée de 10 points) et sur la puissance de sortie (variation de 1 dB).

[pt] O objetivo deste trabalho é apresentar o slotline como uma linha de transmissão alternativa para microcircuitos integrados de microondas. Ênfase especial foi dada ao dimensionamento desta estrutura e à  sensibilidade dos parâmetros da linha às variações das características do substrato dielétrico e da realização da mesma. Inicia-se o trabalho com o estudo de métodos de análise do stoline. Comparações são feitas entre eles de forma evidenciar as vantagens e limitações de cada um. A isto corresponde o capí­tulo 1. O segundo capí­tulo é dedicado às equações de dimensionamento em substrato isotrópico. Estende-se, então, o estudo aos substratos anisotrópicos. Ainda neste capí­tulo apresenta-se uma análise detalhada da sensibilidade às tolerâncias dos parâmetros da linha. Fecha-se o capí­tulo 2 com uma discussão pertinente às dimensões da caixa em que serã montado o circuito. Considerando-se os modos guiados e a intensidade dos campos dentro do contorno compreendido. No terceiro capí­tulo a linha microstrip é estudada, dado à  necessidade de sua caracterização para o dimensionamento de transições microstrip-slotline em substratos iso/anisotrópicos, discutidas no capí­tulo 4. neste, são estudados os principais tipos de transição de coaxial para slotline e de microstrip para slotline. As transições duplas, microstrip-slotline-microstrip, são também estudadas, sendo proposto um método de otimização para a transição dupla com dois estubes. No quinto capí­tulo são dados exemplos de algumas aplicações de slotlines, continuando-se o trabalho com a descrição de um programa de computados para dimensionamento, otimização e análise de linhas e transições microstrip-slotline; capí­tulo 6. encerrando-se o trabalho, os pontos relevantes são destacados e sugestões são dadas para uma eventual continuação deste estudo. As contribuições originais do autor, pertinentes, são apresentadas nos apêndices I e II. / [en] This work presents the slotline as an alternative MIC`s transmission line. Special emphasis was given to the slotline design and to the effect of tolerances in various parameters on the performance of the slotline, using sensitivity analysis. The first chapter discusses some previously reported methods of analysis, using a compative approach. The second chapter deals with the desing equations of this kind of transmission line on iso/anisotropic substrate, and the sensibility analysis. Enclosure effects on the electric field configuration are also considered. Chapter 3 presents the characterization of microstrip lines which was necessary to the study of the microstrip- slotine transition. The most usual types of transitions from slotline to coaxial line and to microstrip are studied in the fourth chapter. Especial attention is given to the two-stub microstrip-slotline transition. Optimization methods for broadband desing of single and double transitions are proposed and some practical results are presented. Some of the circuit applications of slotline are discussed in the fifth chapter. The discussion is limited to those slotline circuits which either have some advantages over corresponding microstrip configuration or which are possible anly with slotlines. A powerful synthesis/analysis/optimization software is described in chapter 6. Chapter 7 presents a comprehensive conclusion to the work and points out the author`s original contributions.

Two separate problems are to be investigated in this thesis. The first problem is the propagation of waves through a short rod (or slug) of viscoelastic material. The second problem is the study of impact of a short viscoelastic rod (or slug) on a stationary semi-infinite viscoelastic. rod. The viscoelastic materials are modelled as standard linear solids which involve 3 material parameters and the motion is treated. as one-dimensional. For the first study, a viscoelastic slug is placed between two semi-infinite elastic rods and a wave initiated in the first rod is transmitted through the slug into the second rod. The objective is to relate the transmitted signal to the material parameters of the slug. We solve the governing system of partial differential equations using the Laplace transform and we examine the propagating velocity discontinuity using discontinuity analysis and the limit theorem of the Laplace transform. We then approximate the solution of the propagating disturbance using the regular perturbation method. We invert the Laplace transformed solution numerically to obtain the transmitted signal for several viscosity time constants and ratios of acoustic impedances. We compare the results obtained using the above techniques. In the second problem, we first model the impact and solve the governing system of partial differential equations in the Laplace transform domain. Then we examine the propagating stress and velocity discontinuities using discontinuity analysis. We approximate the solutions of the propagating stress and velocity using the regular and multiple scales perturbation methods. In this problem, we first consider the slug is elastic and the rod is viscoelastic. Secondly, we consider the slug is viscoelastic and the rod is elastic and thirdly, we consider both materials are viscoelastic. Numerically we invert the Laplace transformed solutions for the interface stress and interface velocity for several viscosity time constants and ratios of acoustic impedances to determine whether the slug and the rod part company or remain in contact. Then we compare the results obtained using the discontinuity analysis, regular and multiple scales perturbation methods.

The automotive sector finds itself undergoing a significant and substantial transformation, propelled by the pronounced proliferation of electric vehicles (EVs) and autonomous driving technologies. As the industry proactively adapts to embrace this, an increasingly pressing demand becomes evident for higher performance, reliability, sustainability, and speed. Semiconductor packages emerge as primary catalysts within this ongoing revolution, positioned squarely at the forefront to assume a critical and indispensable function in facilitating the realization of these fundamental objectives. Commercial vehicle manufacturers are taking steps to respond to these demands for sustainability and speed, the driving force in facilitating this being the shift from Si IGBTs to SiC MOSFETs. Silicon Carbide is an increasingly popular choice in inverter module fabrication for electric vehicle applications owing to its inherent characteristics such as reduced on resistance, higher blocking voltage, and higher temperature stability that enable high power density, increased efficiency, and speeds. This work focuses on developing and fabricating a high-density 1.7 kV, 300 A SiC MOSFET half-bridge power module tailored for a 280-320 kW, 2-level inverter configuration. Co-designed with the busbar and gate driver, the custom power module stresses efficient heat dissipation, minimized parasitic inductance, and a compact footprint. Key target parameters to achieve optimal performance include a Rdson below 20 mΩ, Rthjc under 0.2 K/W and a switching time below 20 ns. The proposed module features a double-sided cooling sandwiched structure, an integrated thermistor for health and degradation monitoring, and incorporates three Wolfspeed 3rd generation 1.7 kV, 18 mΩ devices per switch position. The simulated power loop inductance is 14.5 nH, the simulated parasitic resistance is 0.265 m, and the simulated junction-to-case thermal resistance is 0.12182 ℃/W. To keep the die temperature below 150 ℃, a cooling coefficient of 5500 W/m2 is necessary. / Master of Science / The automotive sector is in the midst of a major transformation, propelled by the noticeable spread of electric vehicles (EVs) and autonomous driving technologies. As the industry actively evolves to accommodate this, an increasingly pressing demand becomes apparent for higher performance, reliability, sustainability, and speed. Semiconductor packages are at the forefront of this transformation, playing a crucial role in achieving these goals. Commercial vehicle makers are taking steps to respond to these demands for sustainability and speed, the driving force for this being the shift from Si IGBTs to SiC MOSFETs. Silicon Carbide is an increasingly popular choice in inverter module fabrication for electric vehicle applications owing to its inherent characteristics such as reduced resistance, higher blocking voltage, and higher temperature stability that enable high power density, increased efficiency, and speeds. This study focuses on creating a compact and efficient power module for commercial electric vehicle applications. The designed module is capable of handling high power levels while remaining compact, thus prioritizing power density. This is carefully designed to ensure it cools down effectively, minimizes unnecessary energy losses, and has a small footprint. Certain key features, such as its commutation speed, current carrying capacity, and thermal and mechanical limitations, were also studied. A temperature sensor was incorporated to monitor its health and performance over time. Simulations were performed to validate that this module performs well in terms of its resistances in the electrical conduction path and the oath of heat dissipation.

To support the study of potential utilization of the emerging silicon carbide (SiC) devices, two SiC active switches, namely 1.2 kV, 5 A SiC JFET manufactured by SiCED, and 1.2 kV, 20 A SiC MOSFET by CREE, have been investigated systematically in this thesis. The static and switching characteristics of the two switches have firstly been characterized to get the basic device information. Specific issues in the respective characterization process have been explored and discussed. Many of the characterization procedures presented are generic, so that they can be applied to the study of any future SiC unipolar active switches. Based on the characterization data, different modeling procedures have also been introduced for the two SiC devices. Considerations and measures about model improvement have been investigated and discussed, such as predicting the MOSFET transfer characteristics under high drain-source bias from switching waveforms. Both models have been verified by comparing simulation waveforms with the experimental results. imitations of each model have been explained as well. In order to capture the parasitic ringing in the very fast switching transients, a modeling methodology has also been proposed considering the circuit parasitics, with which a device-package combined simulation can be conducted to reproduce the detailed switching waveforms during the commutation process. This simulation, however, is inadequate to provide deep insights into the physics behind the ringing. Therefore a parametric study has also been conducted about the influence of parasitic impedances on the device's high-speed switching behavior. The main contributors to the parasitic oscillations have been identified to be the switching loop inductance and the device output junction capacitances. The effects of different parasitic components on the device stresses, switching energies, as well as electromagnetic interference (EMI) have all been thoroughly analyzed, whose results exhibit that the parasitic ringing fundamentally does not increase the switching loss but worsens the device stresses and EMI radiation. Based on the parametric study results, this thesis finally compares the difference of SiC JFET and MOSFET in their respective switching behavior, comes up with the concept of device switching speed limit under circuit parasitics, and establishes a general design guideline for high-speed switching circuits on device selection and layout optimization. / Master of Science

A distância e o tempo de viagem são elementos de importância para a avaliação do acesso aos serviços de saúde, esta é uma questão que para a população do campo tem uma importância especial devido às particularidades geográficas do espaço rural. A presente pesquisa tem como objetivo desenvolver uma metodologia de mapeamento da rede de rodovias rurais com indicações de impedâncias de viagem, utilizando-se para isso dos Sistemas de Informação Geográfica (SIG) e tendo em vista a otimização do traslado da população rural aos serviços de saúde. A orientação teórica se apóia no conceito de distância na Geografia e em concepções sobre a medida da acessibilidade e mobilidade espacial. Faz-se uma ampla observação das abordagens e metodologias voltadas ao estudo da acessibilidade geográfica das populações rurais aos serviços de saúde, sobretudo, as que tratam de fatores espaciais e fazem uso dos SIG. Dados relativos às classes de rodovias rurais, declividade da paisagem, sinuosidade, visibilidade e uso da terra, são considerados na composição de uma síntese de impedâncias. A avaliação toma como parâmetro o tempo de viagem por veículo automotor e as medidas se fazem com base na rede rodoviária ponderada por impedâncias. A população rural e as unidades de atendimento à saúde são os referencias para a avaliação da acessibilidade geográfica. A metodologia foi aplicada à Microrregião de Registro (SP) e os resultados indicam que a velocidade nos percursos muda de acordo com os atributos associados às rodovias, sendo as estradas locais nãopavimentadas as que apresentam maior variabilidade para a geração de condições ótimas de viagem. A distribuição espacial dos serviços de saúde reflete na acessibilidade geográfica e algumas regiões são mais penalizadas no acesso aos serviços hospitalares. O modelo aqui apresentado orienta à montagem de um SIG para a análise da acessibilidade da população rural aos postos de saúde e hospitais e atende a duas principais aplicações: (i) o apoio ao planejamento da viagem da população rural aos postos de atendimento à saúde; (ii) e auxílio em facilitar o acesso da população rural às consultas e atendimento de ocorrências emergenciais, pela aplicação de recursos de análise de rede, tais como: caminho mínimo, matriz de origens-destinos e área de serviço. Ambas as aplicações poderão resultar num melhoramento do planejamento das áreas de influencia dos centros de saúde na região rural. / Distance and travel time are important parameters in the evaluation of access to health services. For the population living in the countryside, this has become a significant issue due to geographical particularities of rural areas. The objective of this work is the development of a GIS-based methodology for the mapping of rural road networks and the determination of travel impedances in order to optimize the travel time of the rural population to health care facilities. The theoretical orientation is based on the concept of geographical distance and on the conception of the extent of accessibility and mobility. A general overview is given of approaches and methodologies which study the geographical accessibility of health services facilities by the rural population with particular consideration of those which deal with spatial factors and make use of GIS (Geographic Information System). Data on rural roads classes, slope, sinuosity, visibility and land use are considered in the composition of the impedances synthesis. The evaluation uses the travel time by car as a parameter, and the quantifications are based on the road network with velocities adjusted by the impedances. This way, network distances, velocity and the travel time are the criteria for the evaluation of the geographical accessibility to health care facilities by the rural population. The methodology was applied to the Region of Registro (SP), and the results indicate that the velocity on the particular road sections changes depending on the attributes associated with the road classes with the observation that unpaved roads represent the worst conditions for establishing optimum travel conditions. The distribution of health service facilities is reflected in the geographical accessibility, and some regions are highly penalized regarding access to hospital services. The model presented here points out methods for the installation of a GIS for the analysis of the accessibility of health care facilities by the rural population with respect to the following applications: (i) support of the rural population when planning journeys to health care facilities; (ii) improved access to medical examination and emergency assistance by analysis of the network, i.e., by determining the minimum traveling distance, the origin-destination matrix and the service areas of the health care facilities. Both applications may improve covering and planning rural health service facilities.

A distância e o tempo de viagem são elementos de importância para a avaliação do acesso aos serviços de saúde, esta é uma questão que para a população do campo tem uma importância especial devido às particularidades geográficas do espaço rural. A presente pesquisa tem como objetivo desenvolver uma metodologia de mapeamento da rede de rodovias rurais com indicações de impedâncias de viagem, utilizando-se para isso dos Sistemas de Informação Geográfica (SIG) e tendo em vista a otimização do traslado da população rural aos serviços de saúde. A orientação teórica se apóia no conceito de distância na Geografia e em concepções sobre a medida da acessibilidade e mobilidade espacial. Faz-se uma ampla observação das abordagens e metodologias voltadas ao estudo da acessibilidade geográfica das populações rurais aos serviços de saúde, sobretudo, as que tratam de fatores espaciais e fazem uso dos SIG. Dados relativos às classes de rodovias rurais, declividade da paisagem, sinuosidade, visibilidade e uso da terra, são considerados na composição de uma síntese de impedâncias. A avaliação toma como parâmetro o tempo de viagem por veículo automotor e as medidas se fazem com base na rede rodoviária ponderada por impedâncias. A população rural e as unidades de atendimento à saúde são os referencias para a avaliação da acessibilidade geográfica. A metodologia foi aplicada à Microrregião de Registro (SP) e os resultados indicam que a velocidade nos percursos muda de acordo com os atributos associados às rodovias, sendo as estradas locais nãopavimentadas as que apresentam maior variabilidade para a geração de condições ótimas de viagem. A distribuição espacial dos serviços de saúde reflete na acessibilidade geográfica e algumas regiões são mais penalizadas no acesso aos serviços hospitalares. O modelo aqui apresentado orienta à montagem de um SIG para a análise da acessibilidade da população rural aos postos de saúde e hospitais e atende a duas principais aplicações: (i) o apoio ao planejamento da viagem da população rural aos postos de atendimento à saúde; (ii) e auxílio em facilitar o acesso da população rural às consultas e atendimento de ocorrências emergenciais, pela aplicação de recursos de análise de rede, tais como: caminho mínimo, matriz de origens-destinos e área de serviço. Ambas as aplicações poderão resultar num melhoramento do planejamento das áreas de influencia dos centros de saúde na região rural. / Distance and travel time are important parameters in the evaluation of access to health services. For the population living in the countryside, this has become a significant issue due to geographical particularities of rural areas. The objective of this work is the development of a GIS-based methodology for the mapping of rural road networks and the determination of travel impedances in order to optimize the travel time of the rural population to health care facilities. The theoretical orientation is based on the concept of geographical distance and on the conception of the extent of accessibility and mobility. A general overview is given of approaches and methodologies which study the geographical accessibility of health services facilities by the rural population with particular consideration of those which deal with spatial factors and make use of GIS (Geographic Information System). Data on rural roads classes, slope, sinuosity, visibility and land use are considered in the composition of the impedances synthesis. The evaluation uses the travel time by car as a parameter, and the quantifications are based on the road network with velocities adjusted by the impedances. This way, network distances, velocity and the travel time are the criteria for the evaluation of the geographical accessibility to health care facilities by the rural population. The methodology was applied to the Region of Registro (SP), and the results indicate that the velocity on the particular road sections changes depending on the attributes associated with the road classes with the observation that unpaved roads represent the worst conditions for establishing optimum travel conditions. The distribution of health service facilities is reflected in the geographical accessibility, and some regions are highly penalized regarding access to hospital services. The model presented here points out methods for the installation of a GIS for the analysis of the accessibility of health care facilities by the rural population with respect to the following applications: (i) support of the rural population when planning journeys to health care facilities; (ii) improved access to medical examination and emergency assistance by analysis of the network, i.e., by determining the minimum traveling distance, the origin-destination matrix and the service areas of the health care facilities. Both applications may improve covering and planning rural health service facilities.

One of the many challenges in radio astronomy is the ability to make accurate measurements quickly. In recent years engineers and astronomers have begun implementing phased array feeds (PAFs) as a way to negate the long observation times required by single antenna feeds. Unfortunately, large mutual coupling and other loss terms result in low sensitivity, restricting PAF usefulness in on dish observation. This thesis addresses several ways to reduce mutual coupling and maximize sensitivity for PAFs in radio astronomy. Antenna design of this magnitude requires accurate modeling capabilities. To this end, electromagnetic software models and low loss component designs are verified and validated with measured data. This process required the construction of a 50 Ω matched dipole and measurements on a network analyzer at Brigham Young University. The design and optimization of several single and dual polarization hexagonal grid arrays of 19 and 38 elements respectively are also described. Model figures of merit are compared with measurements taken on the 20-Meter dish at the National Radio Astronomy Observatory (NRAO) in Green Bank, WV and the 300 meter dish at the Arecibo Observatory in Arecibo, PR. Although some unexplained discrepancies exist between measured and model datasets, the dual pol cryocooled kite array described boasts the highest PAF sensitivity ever measured.

Research institutions around the globe are developing phased array feed (PAF) systems for wide-field L-band radio astronomical observations. PAFs offer faster survey speeds and larger fields of view than standard single-pixel feeds, which enable rapid sky surveys and significantly increased scientific capability. Because deep space astronomical signals are inherently weak, PAF systems must meet stringent noise and sensitivity requirements. Meeting these requirements requires detailed modeling of the phased array itself as well as the reflector it is mounted on. This thesis details a novel approach to dual-pol PAF design that models the array and reflector as a complete system in order to achieve a more optimal sensitivity and system noise temperature. The design and construction of two arrays designed using this technique is discussed. The implementation of a data acquisition system to receive data from the first of these arrays is also detailed. Polarization state information plays an important role in understanding cosmological processes for many deep space sources. Because of phase and gain imbalances in the LNAs and receiver chains calibration is required for accurate measurement of polarization by phased array feeds. As a result accurate polarimetric calibration techniques are essential for many observations. Existing polarimetric calibration methods are based on assumptions about the form of the system Mueller matrix that limit the generality of the method or require long observations of a polarized source which is time-consuming for multiple PAF beams. This thesis introduces a more efficient method of calibration that uses only three snapshot observations of bright astronomical calibrator sources, one unpolarized and two partially polarized. The design of an engineering array for the Green Bank Telescope is discussed. Measured results from a prototype element are presented along with simulated on-reflector results for the full array. Simulations predict that the array will be the highest sensitivity dual pol feed built by the Radio Astronomy Systems group at Brigham Young University to date.