It is essential to always track maximum power from photovoltaic (PV) sources. Failure to track the global maximum power point under partial shading conditions is one of the major reasons that lead to significant power losses. Several maximum power point tracking methods have been proposed to deal with this problem. However, none of them were able to effectively identify the occurrence of partial shading. With the facility of Matlab modelling and simulation as well as the aid of a constructed solar emulator, the power-voltage characteristics of a PV panel under uniform and non-uniform irradiance conditions have been studied and some useful conclusions have been identified from observation. Based on these conclusions, a novel maximum power point tracking algorithm has been proposed, which is capable of identifying the occurrence of partial shading hence determining the need for a global scan over the operation range of PV panels for the true maximum power point. In the meantime, the effect of PV dynamics, due to the capacitance of PV cells, on maximum power point trackers has been investigated and some initial results and suggestions have been presented in this work.

Orientador: Paulo Roberto Bueno / Coorientador: Flávio Cesar Bedatty Fernandes / Banca: Hideko Yamanaka / Banca: Marina Ribeiro Batistuti / Resumo: Desde a primeira descrição de biossensor reportada por Clark e Lyons em 1962, houve um extenso trabalho no desenvolvimento e aprimoramento de novas técnicas de biossensoriamento para detecção de biomarcadores com relevância médica. Destaca-se nesse processo o estudo de superfície de eletrodos, pois esse influencia diretamente em aspectos como; sensibilidade, estabilidade e qualidade do sinal. Portanto, este projeto consiste em avaliar comparativamente três superfícies de eletrodos baseadas em nanoestruturas contendo nanopartículas de azul da Prússia, funcionando com sonda redox do sistema, e materiais carbonáceos (como óxido de grafeno e nanotubos de carbono) para aplicação em biossensores. Foram avaliados aspectos como composição, características capacitivas redox e estabilidade de sinal. A técnica de análise utilizada é a espectroscopia de capacitância eletroquímica (ECE) que apresenta vantagens como não usar amplificadores de sinal (sondas redox) em solução, configuração esta, importante para métodos de diagnóstico point-of-care. Das superfícies analisadas, a composta por nanopartículas de azul da Prússia e óxido de grafeno (PBNP+GO) apresentou os melhores parâmetros de estabilidade e compatibilidade com os aspectos teóricos da técnica de ECE, sendo então selecionada para realização de testes de biossensoriamento que, através da funcionalização da superfície com anticorpos Anti-IL-6, detectaram seletivamente a presença do biomarcador IL-6. / Abstract: Since the first description of biosensor reported by Clark and Lyons in 1962, numerous works related to the development and enhancement of novel medical biosensing techniques have been published. In that context, it must be highlighted the study of electrode surfaces as it has direct influence in aspects like; sensitivity, stability and signal quality. Therefore, this project aims to evaluate three electrode surfaces based on nanostructures with Prussian blue nanoparticles, as redox probe, and carbonaceous materials (like graphene oxide and carbon nanotubes) and their application in biosensors. It was evaluated aspects like composition, redox capacitive characteristics and signal stability. The electrochemical capacitance spectroscopy technique (ECE) was used as it offers several advantages like no need of signal amplifiers (redox probes) in solution and, then, making this technique more adequate for point-of-care diagnosis. Among the analysed surfaces, the one composed by Prussian blue nanoparticles and graphene oxide (PBNP+GO) was identified as the best surface in terms of stability and compatibility to the theoretical aspects of ECE. Therefore, that structure was selected to further biosensing essays, by functionalizing the surface with Anti-IL-6 antibodies, that indicated the selective detection of the IL-6 biomarker. / Mestre

Os efeitos do campo elétrico, que surgem pela aplicação de uma voltagem no contato Schottky, na estrutura eletrônica de heteroestruturas semicondutoras utilizadas nos recentes transistores de efeito de campo (FET) e numa super-rede finita são simulados numericamente. Estas heteroestruturas apresentam poços quânticos bidimensionais e camadas que podem estar tensionadas pela diferença entre os parâmetros de rede cristalinos. Através de um procedimento numérico auto-consistente várias grandezas físicas são estudadas, os auto-estados e as densidades eletrônicas nas sub-bandas são calculadas. A variação destas grandezas é associada à capacitância e à transcondutância intrínseca, em função da voltagem no gate. Os resultados da simulação são comparados aos dados experimentais. Este procedimento possibilita a compreensão dos fenômenos quânticos envolvidos com a previsão de certas características de dispositivos sem a necessidade prévia de sua produção e testes / Eletric field effects on the electronic characteristics of semiconductor heterostructures used in recent field effect transistors (FETs) and in a finite superlattice are numerically simulated. This field is due to a voltage bias applied on a Schottky contact. These heterostructures have two-dimensional quantum wells and layers wich can be stressed due to different lattice parameters of the materials involved. Through a numerical self-consistent procedure, many physical quantities are studied, such as the eigen-states and the electronic densities at the sub-bands. The changes in such quantities are associated to the capacitance and to the intrinsic transconductance as a function of the gate voltage. The results are compared to experimental data. This procedure allows the comprehension of the quantum phenomena involved and the prediction of device characteristics, without the need to fabricate and test it

Le sujet de cette thèse concerne le transport en alternatif à basse fréquence dans les états de bords de l'effet Hall quantique. L'objet d'étude est la partie imaginaire de l'admittance, inductive ou capacitive, des échantillons de Hall. Dans un gaz d'électrons bidimensionnel, le transport à très basse température sous champ magnétique quantifiant, se fait dans des canaux de bord unidimensionnels. Ces canaux ont une capacité quantique propre et sont par ailleurs couplés par l'interaction électrostatique.Nos échantillons sont fabriqués à partir d'hétérojonctions GaAlAs/GaAs et n'ont pas de grille pour n'exhiber que leur propriétés capacitives intrinsèques. Deux topologies sont étudiées dans cette thèse : les barres de Hall et les Corbinos, de géométrie circulaire. La topologie permet de distinguer 2 comportements dans le transport en alternatif.Sont d'abord présentées les mesures à l'impédancemètre de la partie imaginaire de l'impédance et les spectres de réactance, pour les barres de Hall en fonction de la fréquence. Nous utilisons des mesures 3 points ou bien 2 points, mais toujours en 4 fils, et révélons la nature inductive des état de bords. Nous montrons que l'inductance est inversement proportionnelle à la densité d'état, comme le prévoit le calcul de l'inductance quantique d'un canal 1D. Le formalisme de Buttiker permet en outre de comprendre cette dépendance en terme de capacité mutuelle des états de bords.Nous mesurons également la partie imaginaire de l'admittance et traçons les spectres de susceptance des Corbinos, qui s'avèrent être des capacités parfaites. Nos résultats s'interprètent en faisant intervenir la capacité quantique des états de bords.Enfin, nous montrons que l'effet Hall dans un échantillon type barre, peut être vu comme l'effet d'apparition d'une inductance, et ceci même à haute température. Cette inductance cinétique est le résultat de l'augmentation du temps de dissipation de l'énergie sur les phonons, avec le champ magnétique. / In a two dimensional electron gas, low energy transport in presence of a magnetic field occurs in chiral 1D channels located on the edges of the sample. In the Buttiker’s description of a.c. quantum transport, the “emittance” determines the amplitude of the imaginary part of the admittance, whose sign and physical meaning are determined by the topology: in the case of an Hall bar the emittance is an inductance, while it is a capacitance in the case of a corbino sample.Emittance is related to the density of states and to the drift velocity of carriers. So quantum capacitances and inductances give access to the velocity of the charge carriers through the transit time/dwell time of charges in the quantum circuit.We performed systematic studies on samples with different topologies : Hall bars and Corbino disks. Our samples have no gate, which makes us able to observe the inner properties of the quantum states. We have measured the ac admittance of quantum Hall samples using standard electrical techniques in the [0.1-100] kHz frequency range, at low temperature under high magnetic field.We measured kinetic inductances of Hall bars with three contacts and showed the perfect inductive nature of edge states. We measured quantum capacitances of Corbino disks as well. In both topologies we observed the close relation between the emittance and the density of states. We show also the proportionality between the emittance and the length of the circuit. We obtain the transit time of electrons through the device, and finally the drift velocity on edge states.At high temperature we still observe an inductive behavior of Hall bars, induced by increase of energy relaxation time with magnetic field.

Electrical capacitance tomography (ECT) is a technology that images the dielectric permittivity distribution of materials under test. ECT has been used as a tool for process monitoring in particular for two-phase flow measurement. These applications mainly focus on the dielectric samples, whose conductivity is negligibly small. This thesis studies ECT imaging with conductivity considerations. The conductive materials will affect the capacitance measurements and introduce difficulties in the ECT image reconstruction. This thesis presents solutions based on ECT to image material of different values of conductivity in different practical process or monitoring scenarios: the conductivity within materials under test is considered to be higher than 10^6 S/m, or less than 10 S/m. This work consists of the following innovative steps. (i) Through an ECT monitoring, floating (i.e., electrically non-grounded) metallic samples are imaged as dielectric illusions and the analysis of capacitance measurements over the conductors is delivered. (ii) Magnetic induction tomography (MIT) is firstly used for locating grounded metallic samples, thereafter as an assistant method to guide ECT to image the dielectric components. (iii) In low conductivity case MIT, as an indicator of conductive material again, helps ECT to solve multiphase flow problems. (iv) The multi-frequency complex ECT measurement provides a potential method to improve the ECT imaging ability for both conductive and dielectric materials. The first three ideas have been testified by both simulated and experimental results, while the fourth part is simulation-based results only on current stage.

O crescimento de pontos quânticos a partir do descasamento dos parâmetros de rede tem sido alvo de intensos estudos nos últimos dez anos. Conhecer as propriedades eletrônicas destes materiais é chave para a engenharia de sistemas quânticos. O objetivo deste trabalho é estudar as propriedades eletrônicas de pontos quânticos (QD) de InAS1-x Px enterrados em GaAs, através de Espectroscopia de Capacitância (CV). A Espectroscopia CV é uma técnica que permite determinar os estados eletrônicos e a distribuição de cargas do sistema. As amostras de InAS1-x Px foram crescidas por MOCVD (Low-Pressure Metalorganic Chemical Vapor Deposition) sobre um substrato de GaAs:Cr (001). A estrutura das amostras é do tipo MIS (Metal-Isolante-Semicondutor) com um contato traseiro do tipo n. As medidas de capacitância foram feitas a 4,2 K para diferentes valores de freqüência e campo magnético. A partir da dispersão dos estados confinados com o campo magnético aplicado perpendicular ao plano dos pontos quânticos, pode-se determinar, &#9690, a freqüência natural do sistema. A partir de &#9690, determinou-se &#87470, o comprimento característico da função de onda. A concordância entre os valores de &#87470 com as dimensões laterais dos pontos quânticos obtidos por microscopia eletrônica de transmissão (TEM) é boa. Finalmente, através das medidas de espectroscopia CV pode-se separar os efeitos de confinamento lateral e vertical, permitindo um melhor entendimento dos espectros de fotoluminescência (PL), assim como os detalhes da forma dos QD obtidos por TEM. / The growth of quantum dots in the Stranski-Krastranov mode has been subject of intense investigation in the last decade. Knowing the electronics properties of these materials is key for performing quantum systems engineering. The objective of this work is to study the quantum dots (QD) electronic properties of the InAS1-x Px embedded in GaAs. The study was done by capacitance spectroscopy (CV), which is an experimental tool that allows the evaluation of the electronic states and the charge distribution of a given quantum device. The samples of InAS1-x Px were grown by Low-Pressure Metalorganic Chemical Vapor Deposition on GaAs:Cr (001) substrates. They consist of metalinsulator-semiconductor structures with an n-type back contact. The measurements were performed at 4.2 K for different values of frequencies and magnetic field. From the confined states dispersion as a function of the applied magnetic field, perpendicular to the QD plane, the system natural frequency, &#9690, was determined. From the &#9690, we could determine the wave function characteristic length, &#87470. The concordance between the &#87470, values and the lateral sizes obtained by Transmission Electronic Microscopy (TEM) is good. Finally, by CV spectroscopy we could separate the lateral and vertical confinement effects, leading to a more complete understanding of the Photoluminescence (PL) spectra, as well as the details of the QD shape obtained by TEM.

The process industry is concerned with the processing of crude resources into other products. Such crudes consist of multiphase components that introduce major challenges to the operators; hence the need for efficient instrumentations that address such challenges is highly desirable. One major need is an early deposit detection system that detects deposit before it builds-up in a pipeline or equipment to prevent any possible hazard. Another critical requirement is the need to continuously monitor the flow and deduce the flow rate of every individual phase in order to study and analyse the produced product. Hence, in order to ensure safety, increase profits, optimize production and ensure production quality, the multiphase flow must be adequately monitored and controlled. This thesis demonstrated the efficiency of novel ECT algorithms for early deposit detection and multiphase flow measurement in order to measure the flow rate of all separate phases. This thesis focuses on developments in ECT image reconstruction specifically the inverse solutions and is divided into three main studies where they all build up to complete each other. In the first study, ECT is used for the first time with a narrowband pass filter to focus on targeted locations in a pipe where dielectric contaminants are expected to deposit in order to enhance the resolution of the produced images. The experimental results showed that different deposit regimes and accumulated fine deposits could be detected with high resolution. The second study allowed a better understanding of how conductive material could be imaged using a conventional ECT device and how state of the art algorithms such as iterative total variation regularisation method and the level set method could enhance this application. Also, absolute ECT imaging is presented for the first time where the level set algorithm uses only one set of ECT measurement data. This study gives a novel solution for detecting conductive deposits as well as paves the way to use the new level set algorithm for multiphase flow measurement. In the third study, the novel narrowband level set algorithm was modified to image multiphase media in order to correctly determine the number, location and concentration of the present phases. The innovative absolute ECT imaging using level set method is tested with high contrast and low contrast multiphase data, which adds more to the challenge.

Structural fire protection is an integral component of shipboard fire safety. There are national and international regulations that delineate requirements for the insulation placed throughout ships. The attachments that penetrate the insulation for hanging wires and pipes can disrupt the integrity of the division, and cause a failure to adhere to the regulations. This problem will be analyzed by using a simplified lumped capacitance model and ANSYS FLUENT CFD. A standard time-temperature fire curve is applied to the fire side of the enclosure. The thermal conductivity of the insulation and steel are made to be temperature dependent. The density of the air of the non-fire side is then approximated using the Boussinesq approximation for lower temperature differences and the incompressible ideal gas law for higher temperature differences. Different attachments of varying surface areas and volumes are exposed to the standard time-temperature fire curve and their heat transfer capabilities are analyzed.

In this work, a multi dimensional RF MEMS variable capacitor that utilizes electrostatic actuation is designed and fabricated on a 425um thick silicon substrate. Electrostatic actuation is preferred over other actuation mechanisms due to low power consumption. The RF MEMS variable capacitor is designed in a CPW topology, with multiple beams supported (1 - 7 beams) on a single pedestal. The varactors are fabricated using surface micromachining techniques. A 1um thick silicon monoxide (Er - 6) is used as a dielectric layer for the varactor. The movable membrane is suspended on a 2.5um thick electroplated gold pedestal. The capacitance between the membrane and the bottom electrode increases as the bias voltage between the membrane and the bottom electrode is increased, eventually causing the membrane to snap down at the actuation voltage. For the varactors designed herein, the actuation voltage is approximately 30 - 90V. Full-wave electromagnetic simulations are performed from 1 - 25GHz to accurately predict the frequency response of the varactors. The EM simulations and the measurement results compare favorably. A series RLC equivalent circuit is used to model the varactor and used to extract the parasitics associated with the capacitor by optimizing the model with the measurement results. The measured capacitance ratio is approximately 12:1 with a tuning range from 0.5 - 6pF. Furthermore, the measured S-parameter data is used to extract the unloaded Q of the varactor (at 1GHz) and is found to be 234 in the up state and 27 in the down state. An improved anodic bonding technique to bond high resistivity Si substrate and low alkali borax glass substrate that finds potential application towards packaging of MEMS varactors is investigated. To facilitate the packaging of the varactors the temperature is maintained at 400°C. The bonding time is approximately 7min at an applied voltage of 1KV.

<p>This thesis work investigates the effects of crosstalk on on-chip interconnects. We use optimal repeater insertion as a reference and derive analytical expressions for signal latency, maximum data-rate and power consumption. Through calculations and simulations we show that despite large uncertainties in arrival time of a signal that is subject to crosstalk, we are able to make predictions about the maximum data-rate on a bus. We also show that data-rates can exceed the classical limit of the latency inverted by using wave pipelining. To increase the data-rate, we can increase the number of repeaters to a limit, at the cost of additional latency and power. Savings in power consumption can be achieved by using fewer repeaters, paying in latency and data-rate. Through fewer repeaters, the top metal layer shows better performance in all investigated aspects.</p>