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The European Corn Borer (ECB), Ostrinia nubilalis, is an agricultural pest which bores small holes in the rind of maize stalks and then proceeds to consume the pith. Because most of the damage to the stalk is internal, it is difficult to quantify the damage to an individual stalk without time-consuming, manual examination. This work explored the hypothesis that internal damage could be detected and quantified using non-destructive, electromagnetic measurements. Laboratory experiments and numerical simulation studies predicted changes in capacitance of stalks due to hollow core ECB damage. A guarded probe device to measure electrical impedance from 500 Hz to 100 kHz was designed and constructed for data collection. A field test with the measurement device was conducted and frequency-swept impedance measurements were taken on field-grown plants with and without ECB damage. Field measurements demonstrated that statistically significant capacitance changes associated with ECB damage could be detected in agreement with numerical simulations of stalk damage. Numerical, laboratory, and field test results all supported the hypothesis that electromagnetic impedance measurements, in particular, capacitance, provide a promising new avenue for ECB damage evaluation. While further research will be needed to further refine this concept, this measurement approach is non-destructive, thus allowing measurements to be performed without sacrificing the infested plants.

<p> The microstrip transmission line has been theoretically analysed using conformal transformation and variational techniques. The variational method has been used to compute the line capacitance, characteristic impedance and guide wavelength of the following microstrip structures: (i) Microstrip transmission lines having negligible and finite strip conductor thickness. (ii) Microstrip transmission lines on two layer dielectric substrates having negligible and finite strip conductor thickness.</p><p> The total losses incurred in microstrip lines on semiconductor substrates have been included. An experimental technique (based on the Deschamps method) for measuring the characteristic impedance of microstrip lines through a lossy junction using a high precision microwave reflection bridge has been described. Measurements of the characteristic impedance of microstrip lines on intrinsic germanium substrates have been carried out at 9.38 GHz, and good agreement between the theoretical and experimental results have been obtained.</p> / Thesis / Master of Engineering (MEngr)

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An adapted capacitance manometer is a sensor composed of one fixed plate and one movable plate that is able to make accurate pressure measurements in a low pressure environment. Using detection circuitry, a change in capacitance between the two plates can be measured and correlated to a differential pressure. First, a high sensitivity manometer is produced that exhibits a measurable change in capacitance when experiencing a pressure differential in a low pressure space environment. Second, an accurate and precise detection circuit is identified to measure the change in capacitance. Both, the manometer and the detection circuitry, are tested separately and together to confirm accurate measurements when experiencing small pressure differentials. The manometer shows low sensitivity at the desired differential pressure range but reacts predictably when compared to simulations. The manometer also shows an unexpected correlation in capacitance change to temperature change. / Master of Science

La stabilité est un facteur très important dans tous les modes de fonctionnement pour un Système à Puissance Distribué (SPD). En SPD, les charges sont connectées au bus DC à travers d’un filtre entré LC. La plupart des charges de SPD d'avions présents une caractéristique de charge à puissance constante dans un domaine de fonctionnement dans laquelle ils sont étroitement contrôlés. Ainsi, elles peuvent être modélisées comme une résistance négative. Changement de la charge dans un sous-système peut conduire un système stable dans l'instabilité.Une solution pratique pour diminuer le risque d'instabilité est présentée dans cette thèse qui consiste à modifier le contrôle des convertisseurs ou système onduleur-moteur connecté au bus DC. Cette solution permet de stabiliser le système, même avec un condensateur plus petit. Dans la première partie de la thèse, une méthode linéaire est présentée qui permet étudier la stabilité locale d'un système onduleur-moteur connecté au réseau par un filtre LC et un redresseur. Une technique de compensation d’oscillation est utilisée pour améliorer la marge de stabilité du système et la taille de la capacité dc-link sans modifier la structure des boucles de courant ou de couple. Cette technique consiste à superposer une puissance stabilisant sur la puissance absorbée par le drive. Bien que les modèles linéaires puissent être employées avec succès pour décrire le comportement d'un système physique au niveau local, ils échouent souvent de fournir une caractérisation satisfaisante de large-signal. Dans la deuxième partie, deux méthodes pour la stabilisation large-signal du système électrique sont présentées. Dans la dernière partie, une nouvelle méthode, basée sur les spécifications dynamiques est proposée pour étudier la stabilité d'un système électrique en cascade / Stability is the first and very important factor in all modes of operation for a Distributed Power System (DPS). In DPS, loads are connected to the DC-bus through an input LC filter. Most of the loads in DPS of aircraft present a constant power load characteristic within a domain of operation in which they are tightly controlled. So they can be modeled as negative resistance. Change of the load in one subsystem may lead a stable system into instability. A practical solution to decrease the risk of instability presented in this thesis which consists in modifying the control of the converters or inverter-motor drive system connected to the DC-bus. This solution permits to stabilize the system even with a smaller size of capacitor. In the first part of the thesis, a linear method is presented which allows investigating local stability of an inverter-motor-drive system connected to the grid through an LC filter and a rectifier. An oscillation compensation technique is used to improve the stability margin of the system and the size of the dc-link capacitance without modifying structure of the torque or current loops. This technique consists in superposing a stabilizing power on the absorbed power by the drive. Although linear models can be successfully employed to locally describe the behavior of a physical system, they often fail to provide a satisfactory large signal characterization. In the second part, two methods for the large signal stabilization of the electrical system are presented. In the last part, a new method, based on dynamic specifications, is proposed to study the stability of a cascaded electric system

Les mémoires résistives ReRAM (ou memristors) sont destinées à remplacer les mémoires non volatiles Flash. Les ReRAM utilisent le changement de résistance d’une structure MIM (Métal-Isolant-Métal) soumise à un stress en tension. Jusqu’à présent, l’attention était focalisée sur les mécanismes qui régissent la commutation de résistance dans les dispositifs ReRAM. Moins d’attention a été accordée à la variation de capacitance, c'est-à-dire à la variation de capacité des structures MIM lorsque ces dernières sont soumises à un stress en tension. C’est sur ce dernier point que notre travail porte. Nous étudions la variation d’impédance (conductance et capacitance dans le domaine RF) dans des structures MIM à base de HfO2. Au-delà d’une tension seuil (Set) une diminution de la capacitance est observée, conjointement à une augmentation de conductance. Des cycles mémoires capacité-tension (C-V) et conductance-tension (G-V) sont obtenus de manière reproductible. Des caractérisations en fréquence (C-f et G-f), sous différentes polarisations continues, sont effectuées pour mieux comprendre les mécanismes de commutation de l’impédance. La diminution de capacitance dans l’état conducteur (ON) est attribuée au caractère inductif des filaments conducteurs formés pendant l’étape de Set. Les mécanismes de transport conduisant à l’apparition de ce caractère inductif sont discutés. Nous montrons également l’influence du procédé de dépôt (ALD) de HfO2 sur les caractéristiques C-V et G-V, ainsi que les modifications apportées par l’emploi d’une structure bicouche. Ce travail ouvre la voie à la réalisation de dispositifs à mémoire de capacitance (mem-capacitors), et plus généralement de composants à mémoire d’impédance (ZRAM). Le potentiel de ces dispositifs pour réaliser un filtre reconfigurable (programmable en tension) est démontré d’une manière pratique. / Resistive random access memories (ReRAM) hold great potential for replacing Flash memories. A ReRAM memory (or MEMRISTOR) uses a resistive switching phenomenon found in Metal-Insulator-Metal (MIM) structures under a voltage stress. Most researches were focused on the mechanisms governing the resistance switching in ReRAM devices and less attention has been paid to capacitance variation of MIM structures under a voltage stress. Our work is focused on that latter phenomenon. We study impedance variation (conductance and capacitance in the RF domain) in HfO2-based MIM structures. Above a threshold voltage (Set), concurrently to conductance increase, a decrease in the capacitance value is observed. Reproducible capacitance-voltage (C-V) and conductance-voltage (G-V) memory cycles are obtained. Frequency dependent characterizations (C-f and G-f), under different DC bias voltages, are performed with the aim of understanding the mechanisms of impedance switching. The capacitance decrease observed in the conducting (ON) state is attributed to the inductance of the filament created during the Set stage. Transport phenomena responsible for the filament inductive behavior are discussed. Impact of HfO2 deposition process (ALD), as well as the use of bi-layer structures, on C-V and G-V characteristics are shown. This work paves the way for the realization of new capacitance memory devices (mem-capacitors) and most generally for impedance memories (ZRAM). Potential of these devices to design reconfigurable filters (controlled by voltage bias) is demonstrated in a practical way.

In this thesis the design, control, stability, input power quality, and motor drive performance of ac motor drives with front end three phase diode rectifiers utilizing low capacitance dc bus capacitor are investigated. Detailed computer simulations of conventional motor drives with diode rectifier front end utilizing high capacitance dc bus capacitor and the drives with low capacitance dc bus capacitor are conducted and the performances are compared. Performance evaluation of various active control methods found in previous studies aiming to provide the dc bus stability of drives with low capacitance dc bus capacitor are done at various load levels and types. Design recommendations are provided for the drives utilizing low capacitance dc bus capacitor.