Dissertations / Theses on the topic 'Electrical resistance'
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1
Dhu, Tania. "Environmental monitoring using electrical resistance tomography (ERT) /." Title page, contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09SB/09sbd534.pdf.
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Georgakopoulos, Dimitrios. "Spectroscopic electrical capacitance and resistance tomography systems." Thesis, University of Manchester, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488162.
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Akram, Shakeel. "High temperature and high electrical resistance multilayer polyimide nanodielectrics for electric motors insulation." Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTS028.
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Dans cette thèse, les films multicouches PI / nanocomposites ont été préparés selon un processus de synthèse optimisé. Les échantillons synthétisés ont été caractérisés expérimentalement et par simulations. Tout d'abord, le mécanisme de dégradation des échantillons a été exploré à l'aide d’un générateur d’impulsions. La constante diélectrique, les pertes diélectriques, la rigidité diélectrique, le courant de conduction, la charge d'espace et le courant thermo-stimulé (CTS), ont été étudiées. Ensuite, les niveaux de piège ont été calculés à l'aide des données de déclin de la charge totale et de CTS. Enfin, des modèles 3D de multicouches PI / nanocomposites basés sur les conditions aux limites obtenues à partir d'images SEM / TEM ont été construits dans COMSOL Multiphysics. Ces modèles décrivent l'impact de la dispersion des nanoparticules sur l'amplification du champ électrique. Nos résultats démontrent moins d’agglomération de nanoparticules dans les multicouches et une diminution des charges d’espace et du champ électrique interne. Ainsi, l’utilisation d’isolations multicouches devraient permettre une meilleure fiabilité des moteurs électriquesIn this thesis, the multilayer PI/nanocomposite films were prepared using an optimized synthesis process. The synthesized samples are characterized by experiments and simulations. First, the samples degradation mechanism was explored using pulse power source. Second, dielectric constant, dielectric loss, insulation lifetime, dielectric strength, conduction current, space charge and thermal stimulated current (TSC) were investigated. Third, trap levels were calculated using total charge decay data and TSC data. In the end, multilayer PI/nanocomposite 3D models based on actual boundary conditions obtained from SEM/TEM images of synthesized samples were constructed in COMSOL Multiphysics software. The impact of nanoparticle dispersion on the electric field enhancement is explicitly described in this model. Our results demonstrate that the chances of nanoparticles agglomeration are reduced by using multilayer structure. In consequence, less space charge and low electrical fields are observed in multilayer films. Using multilayer insulations would ensure reliable operation for electric motors and increase its lifetime
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Cookson, Edward James. "Development of the Metal Foam Electrical Resistance Heater." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-04112003-105028/.
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This thesis presents a novel concept using a radial heating element made from porous Fe-Cr-Al metal foam in an air heater. Electrical resistance heating has been used extensively to convert the electrical energy into thermal energy. An analytic heat transfer model is first developed to estimate dimensions of the heating element. Four prototype Fe-Cr-Al metal foam electrical heaters with different levels of porosity and density are built. A more detailed computational fluid dynamics modeling of prototype heaters to include the temperature loss to the surroundings is developed. Experiments were conducted to evaluate effects of airflow rates and electrical current and measure the change of air inlet and outlet temperatures. The temperature rise in the airflow is directly proportional to electric current, and inversely proportional to the weight density of the foam. The temperature appears directly proportional to airflow rate in low density foams, while it is inversely proportional in foams of higher relative density. Experimental temperature measurements show reasonable agreement with modeling predictions. Finally, possible improvements to the initial concept are discussed.
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Ricard, Francois-Xavier. "Application of electrical resistance tomography to pharmaceutical processes." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417797.
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Covington, Brett A. "Activated carbon cloth regeneration with electrical resistance heating." Thesis, Monterey, California. Naval Postgraduate School, 1995. http://hdl.handle.net/10945/25649.
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Ricketts, David. "Diagnosis of occlusal caries by electrical resistance measurement." Thesis, King's College London (University of London), 1995. https://kclpure.kcl.ac.uk/portal/en/theses/diagnosis-of-occlusal-caries-by-electrical-resistance-measurement(1bbd1235-84ef-427f-ae04-65591cc71d66).html.
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Naidoo, Thoneshan. "Signal and image processing for electrical resistance tomography." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/5140.
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Bibliography: leaves 139-150.Electrical Resistance Tomography (ERT) is in essence an imaging technique.In ERT current is injected into and removed from a vessel via paired electrodes. The resulting voltage measurements are captured between the remaining electrode pairs. The principle behind ERT is to map these boundary voltages into a conductivity distribution that represents the domain of the vessel. The author has coded a versatile reconstruction algorithm based on the Newton-Raphson algorithm. The knowledge gained by implementing the algorithm is documented in this thesis. The literature covers the basic aspects of two-dimensional and three-dimensional ERT. It is hoped that this thesis will create a greater interest in ERT at the University of Cape Town (UCT) and also act as a building block for further developments. The thesis starts by presenting the basic concepts of ERT such as the underlying equations, the various boundary measurement strategies and a global perspective of ERT. The nature of this thesis is on software reconstruction and in so doing information on the incorporation of the Finite Element Method in ERT is provided. The thesis goes on to provide information about the reconstruction algorithms, which incorporate regularization. A novel aspect of this thesis involves the calibration and pre-processing of boundary voltages. These concepts were conceptualised and developed during formal communications with Dr. Wilkinson (2002) and Randal (2002). The calibration schemes try to eliminate the potential errors that can arise inthe captured data thus allowing for a clearer image to be reconstructed, Electrical Resistance Tomography. This thesis further develops the idea of parallelizing the Newton-Raphson algorithm to increase the speed of the algorithm. Various schemes on how this parallelization is achievable are put forward.
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Martin, Eric John. "Laboratory study evaluating electrical resistance heating of pooled trichloroethylene." Thesis, Kingston, Ont. : [s.n.], 2009. http://hdl.handle.net/1974/1723.
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Pereira, Paulo J. S. "An approximation method for electrical impedance tomography." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/1536.
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Electrical impedance tomography is an imaging method with applications
to geophysics and medical imaging. A new approximation is presented based on Nachman's 2-dimensional construction for closed domains. It
improves upon existing approximations by extending the range of application from resolving 2 times the surface conductivity to imaging perfect conductors and insulators. With perfect knowledge of boundary data, this approximation exactly resolves a single conductive disc embedded in a homogenous domain. The problem, however, is ill-posed, and imaging performance degrades quickly as the distance from the boundary increases.
The key to the approximation lies in (a) approximating Fadeev's Green's function (b) pre-processing measured voltages based on a boundary-integral equation (c) solving a linearized inverse problem (d) solving a d-bar equation, and (e) scaling the resulting image based on analytical results for a disc. In the development of the approximation, a new formula for Fadeev's Green's function is presented in terms of the Exponential Integral function. Also, new comparisons are made between reconstructions with and without solving the d-bar equation, showing that the added computational expense of solving the d-bar equation is not justified for radial problems. There is no discernible improvement in image quality. As a result, the approximation converts the inverse conductivity problem into a novel one-step linear problem with pre-conditioning of boundary data and scaling of the resulting image.
Several extensions to this work are possible. The approximation is implemented for a circular domain with unit conductivity near the boundary, and extensions to other domains, bounded and unbounded should be possible, with non-constant conductivity near the boundary requiring further approximation. Ultimately, further research is required to ascertain whether it is possible to extend these techniques to imaging problems in three dimensions.
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Elliott, Jeremy. "Monitoring an air core by means of electrical resistance tomography." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/5279.
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Gregory, Peter. "Analysis of sedimenting Kaolin suspensions by miniaturised Electrical Resistance Tomography." Thesis, University of Exeter, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302456.
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Russo, Analisa. "Variation of electrical resistance in superelastic NiTi for sensor applications." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/57875.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 32).
Nickel-Titanium (NiTi) is a most commonly known as a heat-activated shape memory alloy. However, the material sometimes displays a constant-temperature property called "superelasticity." A superelastic material is one which can undergo very high reversible strains due to stress-induced change in crystal structure. In the case of Superelastic NiTi, Martensitic transformation occurs. The two crystal structures differ to the extent that the gradual phase transformation is coupled to a gradual change in resistivity. In fact, resistive sensing is a common characterization technique for shape memory alloys. The unique material properties of superelastic NiTi could also be the basis for creating a resistive sensor that is sensitive enough to measure small displacements, and robust enough to measures large displacements. This study focuses on NiTi which displays superelastic behavior above room temperature. To assess the material's potential as a strain sensing medium, the NiTi wire is shape-set into coil springs which amplify the sensor's net deformation. The relationship between strain and resistance is measured. The study shows that various aspects of the strain-resistance response, including non-linear hysteretic behavior and temperature dependence of electrical resistivity, pose challenges to sensor design. Though the accuracy of the spring sensors is still under development, several recommendations are made with regard to effective device design. In addition, the design of a one-axis strain rate sensor, which differentiates between only two modes of behavior, is explored.
by Analisa Russo.
S.B.
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Wisung, Grete. "Method evaluation : Electrical surface resistance measurements on coated conductive textiles." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-14769.
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This thesis has evaluated how electrical surface resistance can be measured on conductive coated textiles using two different probes. The electrical surface resistance is a measurement for how difficult it is for current to flow through a material. For textiles, the surface resistance can be measured using four metallic plates, that measure the difference between current supply and voltage drop, this method is called a linear four-point probe. There is no standard method for measuring the electrical surface resistance on conductive textiles. Therefore, it is not possible to compare textiles made by different producers. It is also not possible to decide what the true resistance is and as conductive textiles are becoming more popular to use, this has started to become a problem in the industry. Two probes with electrodes of different dimensions were used to evaluate how different electrodes would affect the measured resistance. Measurements were conducted on conductive coated textiles with varying parameters, like coating thickness, sample size and textile construction, to show how the electrical resistance properties differ depending on what probe was used. It was found that in contrast to other research on conductive textiles and collinear four-point probes, the probes used in this study could detect electrical anisotropic properties. The resistance was different depending on what angle it was measured in. This was found for both a thicker coating and a thinner one. It was also found that the probes could detect a correlation between the angular resistance and the textile construction used. By measuring the resistance on small samples with the same dimension as the probes electrodes, the resistance was increased compared to when measurements were conducted on samples with dimensions significantly larger than the probes. Furthermore, the results showed that increasing the distance between the inner electrodes of the probe decreased the measured resistance for both large and small samples. Additionally, it was found that by increasing the width of the outer electrodes the resistance was decreased, an increase in outer electrode width also made it easier to detect electrical anisotropic properties.
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Faraj, Yousef. "Measurement and visualisation of slurry flow using electrical resistance tomography." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/4604/.
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Slurry transport has been a progressive technology for transporting a huge amount of solid materials across the world in both, long distance and short commodity pipelines. The occurrence of separation and slippage of the constituent phases within the pipeline make these flows unpredictable and time dependent. Therefore, it is paramount for the operator of slurry pipelines to monitor and measure the flow continuously, particularly from the local point of view. Undoubtedly, the measurement of local parameters governing the flow, requires an instrument that provides high temporal resolution. Besides, since each phase has different behaviour and flow characteristics within the pipe, it is enormously difficult to measure the flow parameters of each phase using only one conventional flow meter. Thus, a second auxiliary sensor is required to develop a compact and multiphase flow meter. This project proposes a new automated online slurry measurement, visualisation and characterization technique, in which a high performance dual-plane Electrical Resistance Tomography (ERT) system is employed with a capability of acquiring data at a rate of 1000 dual-frames per second. It also proposes an ERT based technique, which combines the ERT and an Electromagnetic Flow meter (EMF), to measure volumetric flow rate of each phase, and thus the total slurry volumetric flow rate. The ERT is further combined with the cross-correlation technique to estimate and image the axial solid’s velocity distribution, through which the transient phenomena of horizontal flow regimes can be visualised. The ERT is used for estimation of several parameters of stratified flow. The development of a novel automated technique for recognition of horizontal slurry flow regimes is also described. A series of experiments were carried out on horizontal and upward vertical sand-water flow through a pilot scale flow system with 50 mm ID pipeline. Two sands, medium and coarse, were employed in two throughput concentrations (2% and 10%) within the range of transport velocities 1.2-5.0 m/s. The solids volumetric concentration and velocity, along with slurry volumetric flow rate are compared with the corresponding results obtained from a sampling vessel.
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Xiao, Lianzhen. "Interpretation of hydration process of concrete based on electrical resistivity measurement /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20XIAO.
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Smith, Stewart. "Sheet resistance and electrical linewidth test structures for semiconductor process characterisation." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/11416.
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The thesis first examines the use of the cross-bridge electrical linewidth structure to measure the sheet resistance and critical dimensions of copper damascene interconnect. This was achieved through computer simulation of current flow in the structures and served to highlight the effects of the damascene process on the measurement. As a result layout design rules have been defined which minimise the errors introduced by diffusion barrier layers and dishing. Mono-crystalline silicon linewidth structures are being developed to meet the requirements for traceable metrology standards. The proposed test structures are fabricated using a wet etch process and have unusual geometries which affect their operation. Computer simulation has shown that the effects of surface interface charge and substrate biasing are the key issues that need to be addressed for accurate extraction of sheet resistance. This work has identified that increased doping of the silicon starting material reduces these effects. The use of on-mask electrical linewidth structures for alternating aperture phase shifting mask metrology has been investigated. The results compare very favourably, in terms of repeatability, with those obtained using the more common CD-SEM technique. Photolithographic simulation of submicron test structure layouts has been used to investigate the effects of applying optical proximity correction to cross-bridge linewidth structures. The effects of severe asymmetries on the Greek cross sheet resistance structure have also been examined. Finally the thesis presents examples of process characterisation using resistive test structures. In the first of these examples cross-bridge linewidth structures are used to quantify the effects of a bulk silicon, wet etch solution, which was designed to passivate metal interconnect, on the dimensions of aluminium tracks. This is followed by an investigation of the use of novel sheet resistance test structures to characterise the deposition of platinum in a focused ion beam system. The platinum sheet resistance has been characterised in terms of the main process parameters which facilitates the fabrication of resistive elements of a known value.
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Sunesson, Fredric. "Real-time stator resistance estimation for electrical drives : a control perspective." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-286793.
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The automotive industry is in the middle of a rapid transition towards electrical machines. This transition leads to a higher interest in electrical machine management. In this thesis a stator resistance estimation scheme for field oriented controlled motors is proposed and tested in both simulations and experiments. The proposed scheme uses a DC-current injection in the stationary reference frame with injection in one of the axes. Ohm’s law is used to estimate the stator resistance. The DC-component of the current is found by a zero-crossover detection scheme which calculates the average current over one electric period. The DC-current values is then eliminated from the feedback currents to the field oriented control to minimise disturbances in these controls. The injection is controlled by simple PI-regulators in both axes of the stationary frame to compensate for the cross-coupling between the α and β axis currents. Simulations shows that the accuracy of the estimated resistance improves and the speed of resistance estimation increases when the injection control is applied in both axis. However a continuous implementation of Ohm’s law is highly oscillatory. To prevent this an accumulator is introduced which averages the estimated resistance over several electrical periods. The trade off using this accumulator is that the speed of detection decreases to achieve higher accuracy. Torque oscillations are inevitable when a DC-current component is injected in the motor. But torque oscillations are solely dependent on the injected DC-current level. The experiments show promising initial results in both DC-current estimation and injection control. However future test are required to further improve the accuracy of the resistance estimation.Fordonsindustrin är mitt i en omsträllning mot elektriska motorer. Detta leder till ett ökat intresse i kontroll av elektriska motorer. I detta arbete föreslås en statorresistans estimering för elektriska motorer med fältorienterings reglering (FOC). Estimeringen testas både i simuleringar och experiment. Den föreslagna estimeringen utgår från att likström (DC) injiceras i en stationär referensram. Med hjälp av Ohms lag estimeras statorresistansen. Estimeringen av likströmmen kommer från en nollövergångs detekterings algoritm som räknar ut medelvärdet över en elektrisk period. Likströmmen elimineras därefter från feedbacken till övriga regulatorer för att minimera störningar i övriga regulatorer. Injektionen kontrolleras av enklar PI-regulatorer i både α och β för att kompensera för tvärkopplingen mellan dessa. Simuleringarna visar att noggrannheten ökar och estimerings tiden minskar när likströmmen kontrolleras i både α och β. Att kontinuerligt implementera Ohms lag är ostabilt. För att stabilisera estimeringen inför en ackumulator som räknar ut medelvärdet för estimering över flera elektriska perioder. Avvägning står dock mellan högre noggrannhet i estimeringen och längre tid för estimeringen. Vridmomentssvägnignar är oundvikliga när likström injiceras i motorn. Dock är vridmomentssvägnignarna endast beroende på hur stör likström som injiceras. Experimenten visar lovande initiala resultat i både likströms estimeringen och injicerings regleringen. Fler tester är dock nödvändiga för att ytterligare förbättra estimeringen.
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Herholdt, Siegfried. "Image reconstruction on electrical resistance tomography measurements in a settling process." Thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/6768.
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Includes bibliographical references (leaves 60-62).This thesis uses Electrical Resistance Tomography (ERT) to measure a settling process. The measurement hardware for this system was developed during previous work carried out by the author. This research is the continuation of this work by focusing on image reconstruction from the measured data. The reconstruction algorithm attempts to find the conductivity distribution of the interior of a rig from measurements made on its boundary. The method used in this thesis is the Newton-Raphson (NR) Algorithm, which employs iterative solutions of the Finite Element Method (FEM) in order to converge to a solution for conductivity. FEM is a numerical simulation method that discretises a region into elements and performs a global optimisation or minimisation in order to arrive at a solution. The NR-method is similar in principle to Newton's method, but is designed to operate on complex data and matrix equations in multiple dimensions. This thesis discusses the methods in reasonable detail and highlights several issues, including ill-conditioning, and regularisation as a method to improve the conditioning of the data. The results contain images of successful reconstruction of a settling process.
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Loh, Weng Wah. "Real-time monitoring of drilling cuttings transport using electrical resistance tomography." Thesis, University of Manchester, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501704.
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Weemees, Ilmar Andrew. "Development of an electrical resistivity cone for groundwater contamination studies." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28730.
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The evaluation of groundwater quality has become increasingly important as more industrial waste and solid domestic refuse comes into contact with groundwater. Often the quantity and extent of contamination is determined by direct sampling of the groundwater and soil. An alternative method of detecting contaminated groundwater is by noting the electrical resistivity of the contaminated soil. The feasibility of logging resistivity while conducting cone penetrometer testing has been investigated in this research. To this end a two stage program was devised, consisting of lab testing and then field tests of a working tool.
Lab testing was carried out using a prototype probe designed to evaluate the feasibility of the project. The lab testing consisted of determining the resistivity of a number of different soil, electrolyte, and organic contaminant mixtures while varying the configuration of the probe. On the basis of lab testing the necessary requirements for the module dimensions and electronics were chosen and were fine tuned by field tests. The module itself consists of an insulated four electrode array and is mounted behind a standard 15 sq cm piezo-cone (CPTU). Upon completion of the development phase the instrument was tested at four different sites. From field testing it was determined that the resistivity cone (RCPTU) was able to accurately map changes in groundwater chemistry on the basis of resistivity measurements. The results of the resistivity testing were verified by groundwater sampling. It was also found that changes in lithological properties, as determined by the cone penetration test (CPT), could influence the resistivity. Basic guidelines for the use of the RCPTU in contaminant investigations are presented.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Jia, Joey Zong-yi. "Voltage controlled resistance model for MOS transistors." PDXScholar, 1988. https://pdxscholar.library.pdx.edu/open_access_etds/3802.
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The voltage controlled resistance model is developed for a reliable MOS transistor resistance mapping. The model includes both system and local parameters, and incorporates the effect of rise and fall time variations on the gate delay. MOS transistor resistance mapping is applied in logic simulation and timing verification. Also, it can be used in automatic transistor sizing and critical path analysis.
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Tsappi, Philip. "Resistance heating of steel conductors of circular cross-section." Thesis, Aston University, 1987. http://publications.aston.ac.uk/8047/.
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The object of this thesis is to develop a method for calculating the losses developed in steel conductors of circular cross-section and at temperatures below 100oC, by the direct passage of a sinusoidally alternating current. Three cases are considered. 1. Isolated solid or tubular conductor. 2. Concentric arrangement of tube and solid return conductor. 3. Concentric arrangement of two tubes. These cases find applications in process temperature maintenance of pipelines, resistance heating of bars and design of bus-bars. The problems associated with the non-linearity of steel are examined. Resistance heating of bars and methods of surface heating of pipelines are briefly described. Magnetic-linear solutions based on Maxwell's equations are critically examined and conditions under which various formulae apply investigated. The conditions under which a tube is electrically equivalent to a solid conductor and to a semi-infinite plate are derived. Existing solutions for the calculation of losses in isolated steel conductors of circular cross-section are reviewed, evaluated and compared. Two methods of solution are developed for the three cases considered. The first is based on the magnetic-linear solutions and offers an alternative to the available methods which are not universal. The second solution extends the existing B/H step-function approximation method to small diameter conductors and to tubes in isolation or in a concentric arrangement. A comprehensive experimental investigation is presented for cases 1 and 2 above which confirms the validity of the proposed methods of solution. These are further supported by experimental results reported in the literature. Good agreement is obtained between measured and calculated loss values for surface field strengths beyond the linear part of the d.c. magnetisation characteristic. It is also shown that there is a difference in the electrical behaviour of a small diameter conductor or thin tube under resistance or induction heating conditions.
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Henry-Poulter, Siobhan. "An investigation of transport properties in natural soils using electrical resistance tomography." Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389933.
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Tan, Jin Chong. "Thermo-electrical properties of metallic sandwich sheets and their resistance welding characteristics." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615008.
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Shirhatti, Vijay Shamrao. "Characterisation and visualisation of particulate solid-liquid mixing using electrical resistance tomography." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441347.
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Clements, Randy Allen. "Development of an ohmic thawing apparatus for accurate measurement of electrical resistance." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013034.
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Chen, Zhangjing. "Measurement of wood moisture content above fiber saturation point by electrical resistance." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-11102009-020203/.
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Forrest, Andrew E. "Gas-liquid mixing in stirred vessels imaged using electrical resistance tomography (ERT)." Thesis, University of Manchester, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488332.
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A considerable effort has been invested over the past forty or so years in attempting to thoroughly understand the basic mechanisms which govern the dispersion of gas inside mechanically stirred mixing vessels. Previous research has concentrated on visual flow studies of gas-liquid flow structures and on measurement of overall properties such as agitator power consumption and gas hold-up. Any local measurements have usually been obtained intrusively and are point-wise giving limited information about the internal flow regime. The evolution of tomographic techniques for non-medical applications now offers a powerful method of obtaining a measurement based knowledge of the mixing processes which occur inside stirred tank reactors. This thesis addresses the use of Electrical Resistance Tomography(ERT) to quantify the mixing behaviour of a gas-liquid (air-water) system inside a plant scale stirred tank reactor. The technology from previous ERT applications was used to develop an 8-plane, 16- electrode measurement system which was installed inside a 2.3 m3 polypropylene tank. The existing Mk lb data acquisition system (DAS) was extended to allow almost instantaneous collection of data from all 8 electrode planes. The tank had a standard geometry with four full length baffles and a six-blade Rushton turbine. Qualitative and quantitative images of the internal, cross-sectional conductivity distribution were reconstructed from the ERT system measurements. 3-D solid body images which illustrate the effects of increasing stirrer speed on the internal gas-liquid. flow regime were constructed from the conductivity distributions obtained in all 8 planes. An existing network-of-zones (NWZ) model of gas-liquid mixing in stirred tank reactors was modified to allow direct comparison with the ERT images. The model was also used to quantify the inherent errors present in the quantitative, modified Newton-Raphson (MNR), reconstruction algorithm. From work carried out in conjunction with BNFL Fluorochemicals further reactor models are presented for the absorption and reaction of fluorine gas which incorporate the concept of interconnecting back-mixed elements/zones without making prior assumptions on the role of film wise and bulk wise reaction. In general the ERT images and the corresponding NWZ model's predicted gas distributions compare well with gas-liquid flow patterns obtained from visual flow studies. In particular, the solid body images describe the flow structure well and confirm that the spatial gas dispersion for a Rushton turbine is far from homogeneous. The similarities between the ERT images and the NWZ model are discussed at two different operating conditions. This illustrates the utility of ERT to verify and develop computational-based fluid dynamics( CFD) predictions. The sensitivity and spatial resolution of the ERT system were assessed using a specially constructed gas-liquid phantom. A full analysis was made of some experiments on the absorption of fluorine from a gas stream chain bubbled through a column of fomric/sulphuric acid. This analysis was used as a basis in developing two further reactor models for simplified co- and counter-current flow using interconnecting back-mixed elements. These models can predict not only the depletion of the reagents from the appropriate phases, but also how the relative amounts of film and bulk reaction change through the reactor. This approach needs further development for application to stirred vessels. It is an important element in properly understanding the chemical selectivity of a stirred gas-liquid reactor. The work demonstrates the ability of ERT to fully describe gas-liquid mixing processes inside a plant scale vessel. The potential use of ERT in the design, monitoring and control of industrial mixing vessels has been realistically assessed. The major areas where ERT needs improvement for ultimate use in industry are given in the recommendations. The necessity to extend the absorption and reaction models developed in this work to include complex reaction schemes is also discussed.
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Smith, Craig Edward. "Monitoring Damage Accumulation In SiC/SiC Ceramic Matrix Composites Using Electrical Resistance." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1249917100.
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Deshpande, Pranav K. "Wear Resistance and Electrical Property of Infrared Processed Copper/Tungsten Carbide Composites." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1147536455.
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Chung, Hye Won. "An energy efficient AES engine with DPA-resistance." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55146.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 73-75).
The advent of portable electronics which transmit and receive sensitive data via wireless communication have led to interest in the design of energy-efficient security engines. The hardware implementation of cryptographic algorithms, however, leaks side-channel information about the operations they process. Differential Power Analysis (DPA) is one of the most powerful attacks to disclose secret key of the engine. This thesis proposes an energy efficient AES-128 engine which is resilient to DPA attacks. A proposed design adopts extensive parallelism and voltage scaling to simultaneously achieve energy efficiency and throughput requirement. Optimized 128-bit architecture and 16 S-boxes placed in the encryption datapath allow the parallel operation of 16 bytes of encryption data at supply voltages in the subthreshold region while maintaining more than tens of Mbps throughput rate. The energy efficient AES core, which does not incorporate techniques to mitigate DPA attack, can operate at 0.35V with 54.12pJ/encrypt. and 64.6Mbps. Before developing countermeasures against DPA, a previously suggested DPA attack methodology in [1] is studied and modified to disclose secret key of our system. The transition power of register is estimated by using the byte-oriented reverse algorithm of AES with the knowledge of a ciphertext and a guess of a secret key. Correlation between the power estimate and the power measurement discloses 12 key bytes (among 16) within 20K encryption runs. A newly proposed AES architecture which balances the Hamming weight of register input can protect the system from DPA attacks.
(cont.) The secured core has been subjected to 100K encryptions, 33x more than the number of runs at which attack can disclose a secret key of the unprotected core, but none of its secret key have yet been disclosed. When running the encryption core at 0.4V and 10IMHz, power increases by 2x compared to the unprotected core. Maximum throughput at 1.OV is reduced by 2/3 for protected core compared with the unprotected core. This IC performance overhead comes at the cost of the increased security.
by Hye Won Chung.
S.M.
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Homer, Hannah S. "Stability Analysis of Negative Resistance-Based Source Combining Power Amplifiers." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1466.
Full textAbstract:
An investigation into the stability of negative resistance-based source combining power amplifiers is conducted in this thesis. Two different negative resistance-based source combining topologies, a series and parallel version, are considered. Stability is analyzed using a simple and intuitive broadband approach that leverages linear circuit stability criterion and two different linearization methods: linearization around the operating point and in the frequency domain. Using this strategy, it is shown that conditions for self-sustained oscillation exist for both topologies. For the series combining topology, self-sustained oscillation is prevented by means of injection locking.
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Deba, Charlie Nindjou. "Evaluation and verification of five different image reconstruction algorithms for electrical resistance tomography applications." Thesis, Cape Peninsula University of Technology, 2016. http://hdl.handle.net/20.500.11838/2465.
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Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016.Tomography is the ability to internally visualise an opaque medium or a body, using different imaging techniques. Electrical Resistance Tomography (ERT) technique is a method commonly used in process tomography. It uses a non-intrusive resistance measurement between a set of electrodes attached on the circumference of a fixed cross-section with a given conductivity and permittivity distribution. ERT appears to be simple, low cost, safe and non-invasive. Despite the advantages of ERT, the reconstruction of the internal conductivity of the pipe still face a crucial challenges such as noise, a relatively low spatial resolution, as well as ill-posedness of the inverse problem when doing the image reconstruction using reconstruction algorithms. Although previous work showed the potential of various algorithms for the reconstruction of ERT tomograms, no full characterisation and comparison of different algorithms could be found for real flow situations. The ERT system was tested in the identification of different objects and fluid beds in a real time situation. The data collected from the measurements were then used for the image reconstruction using an algorithm developed by Time Long (One-step algorithm) and four EIDORS-based algorithms namely: Gauss-Newton algorithm with Laplace Prior (LP) and Gaussian prior (Automatic Hyper Parameter Selection (AHSP)), the Total Variation (TV) algorithm and the Conjugate Gradient (CG) algorithm. The performance of each algorithm was tested in different scenarios. The results obtained were then compared based on the quality and the accuracy of the images as well as the computational time of each algorithm. Firstly, reconstructed images were obtained using objects placed inside the ERT pipe test. Secondly, the algorithm performances were put to test in a level bed setup experiment and finally, the algorithm reconstructions were applied to the real flow situation, where different flow rates were applied. The results obtained were then analysed and compared.
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Scholtz, J. P. "Improved transient earth fault clearing on solid and resistance earthed MV netwworks." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11151.
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Includes bibliographical references.The aim of this thesis is to endeavour to develop, through a literature study, a method or methods whereby transient earth faults on neutral earthed MV networks may be cleared without customer supply interruptions, without compromising public safety and without compromising network integrity. In order to propose such a method, or methods, it is important to understand the various earthing practices employed in MV networks in terms of network behaviour under earth fault conditions, as this may influence network component insulation rating requirements, as well as the way in which such a system may function.
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Martin, Elizabeth E. M. Eng Massachusetts Institute of Technology. "Determining patterns of cancer drug resistance from autopsy patients." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129922.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, February, 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 97-102).
Determining patterns of drug resistance is fundamentally required for improving clinical outcome of cancer treatment. The ability to study multiple samples from different metastatic sites of the same patient is a clinically and analytically challenging task, which has become possible with the advent of "rapid" autopsy procedures (<10 hours from death) conducted on cancer patients through the Massachusetts General Hospital (MGH) Rapid Autopsy Program. The dataset of whole-exome, whole genome and transcriptome sequencing data from advanced cancer samples uniquely captures genomic and transcriptomic information from multiple lesions of the same patient for advanced study of how resistance develops on the systemic level. Additionally, previously collected cell-free DNA samples enable the establishment of both a spatial and temporal picture of cancer drug resistance and progression.
Using RNA expression and pathway analysis, we can also identify unique transcriptional programs and differentially expressed genes between distinct clones within one patient as well as compare genetically similar clones across patents. This thesis integrates genomic and transcriptomic data through advanced clonal reconstruction methods, as well as clinical information such as cancer type, treatment history, and lesion location and response to investigate how the patient developed resistance to anti-cancer therapy. This thesis concentrates on findings in two cohorts of rapid autopsy patients: ER+ metastatic breast cancer, with a focus on patients treated with a CDK4/6 inhibitor, and cholangiocarcinoma, with a focus on patients with FGFR2-fusions treated with an FGFR-inhibitor.
In the ER+ breast cancer cohort, we identified multiple known and potentially novel resistance mechanisms in separate branches of the phylogenetic tree, often converging on distinct mutations in the same resistance genes. In cholangiocarcinoma, we found high levels of inter- and intra-tumoral heterogeneity in several patients, with a convergence on FGFR2 activating mutations as a form of resistance to FGFR-inhibitor therapy. The richness of the rapid autopsy dataset allows us to develop a fuller picture of convergent resistance mechanisms to therapy in cancer.
by Elizabeth E. Martin.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Hart, Robert James. "Electrical resistance based damage modeling of multifunctional carbon fiber reinforced polymer matrix composites." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5493.
Full textAbstract:
In the current thesis, the 4-probe electrical resistance of carbon fiber-reinforced polymer (CFRP) composites is utilized as a metric for sensing low-velocity impact damage. A robust method has been developed for recovering the directionally dependent electrical resistivities using an experimental line-type 4-probe resistance method. Next, the concept of effective conducting thickness was uniquely applied in the development of a brand new point-type 4-probe method for applications with electrically anisotropic materials. An extensive experimental study was completed to characterize the 4-probe electrical resistance of CFRP specimens using both the traditional line-type and new point-type methods. Leveraging the concept of effective conducting thickness, a novel method was developed for building 4-probe electrical finite element (FE) models in COMSOL. The electrical models were validated against experimental resistance measurements and the FE models demonstrated predictive capabilities when applied to CFRP specimens with varying thickness and layup. These new models demonstrated a significant improvement in accuracy compared to previous literature and could provide a framework for future advancements in FE modeling of electrically anisotropic materials. FE models were then developed in ABAQUS for evaluating the influence of prescribed localized damage on the 4-probe resistance. Experimental data was compiled on the impact response of various CFRP laminates, and was used in the development of quasi- static FE models for predicting presence of impact-induced delamination.
The simulation-based delamination predictions were then integrated into the electrical FE models for the purpose of studying the influence of realistic damage patterns on electrical resistance. When the size of the delamination damage was moderate compared to the electrode spacing, the electrical resistance increased by less than 1% due to the delamination damage. However, for a specimen with large delamination extending beyond the electrode locations, the oblique resistance increased by 30%. This result suggests that for damage sensing applications, the spacing of electrodes relative to the size of the delamination is important. Finally CT image data was used to model 3-D void distributions and the electrical response of such specimens were compared to models with no voids. As the void content increased, the electrical resistance increased non-linearly. The relationship between void content and electrical resistance was attributed to a combination of three factors: (i) size and shape, (ii) orientation, and (iii) distribution of voids. As a whole, the current thesis provides a comprehensive framework for developing predictive, resistance-based damage sensing models for CFRP laminates of various layup and thickness.
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Butler, Ivan Charles. "AN ANALYSIS OF RESISTANCE SPOT WELD QUALITY BASED ON ACOUSTIC AND ELECTRICAL SIGNATURES." UKnowledge, 2019. https://uknowledge.uky.edu/ms_etds/8.
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The union of a set of materials by way of Resistance Spot Welding is designed so that once fused together, a substantial amount of intentional, external force must be applied to separate the contents. Therefore, Resistance Spot Welding is often the preferred fusion method in high-volume manufacturing processes. The result of Resistance Spot Welding however is the formation of a weld nugget which is not visible to the naked eye. Destructive and/or ultrasonic methods applied off-line must be used to determine the quality of each weld; both inefficient and expensive processes. The following research analyzes the data fed back during resistance spot weld sequences in-line and establishes a correlation between emitted characteristics and the final quality of a spot weld.
The two characteristics researched to segregate weld quality are: the electrical sin wave signature and the acoustic sin wave signature produced during the welding sequence. Both features were discovered to have a direct correlation to the final quality of a weld once cured. By measuring and comparing these characteristics at the source, an opportunity is presented to decrease time and potential defects by confirming the quality of each weld in-process and at the source.
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Vithayathil, Anne M. (Anne Marie) 1978. "Substrate resistance extraction using a multi-domain surface integral formulation." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28543.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 65-66).
In recent years, mixed-signal designs have become more pervasive, due to their efficient use of area and power. Unfortunately, with sensitive analog and fast digital circuits sharing a common, non-ideal substrate, such designs carry the additional design burden of electromagnetic coupling between contacts. This thesis presents a method that quickly extracts the electroquasistatic coupling resistances between contacts on a planar, rectangular, two-layer lossy substrate, using an FFT-accelerated multi-domain surface integral formulation. The multi-domain surface integral formulation allows for multi-layered substrates, without meshing the volume. This method has the advantages of easy meshing, simple implementation, and FFT-accelerated iterative methods. Also, a three-dimensional variant of this method allows for more complex substrate geometries than some other surface integral techniques, such as multilayered Green's functions; this three-dimensional problem and its solution are presented in parallel with the planar substrate problem and solution. Results from a C++ implementation are presented for the planar problem.
by Anne M. Vithayathil.
S.M.
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Jin, Donghyun. "Dynamic ON-resistance in high voltage GaN field-effect-transistors." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91108.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Recently, the development of energy efficient electrical power management systems has received considerable interest due to its potential to realize significant energy savings for the world. With current Si-based power electronics system being matured, GaN Field-Effect-Transistors have emerged as a disruptive technology with great potential that arises from the outstanding material properties of GaN. However, in spite of great progress in GaN device fabrication, electrical reliability and a number of unique anomalies of GaN remain key challenges that prevent the wide deployment of this technology. In particular, the dynamic ON-resistance (RON), in which the RON of the transistor remains high for a certain period of time after a high-voltage OFF-ON switching event, is a critical concern. This phenomenon greatly affects the efficiency of electrical power management circuits based on GaN power transistors. This thesis investigates in depth this important issue. Firstly, we have developed a new dynamic RON measurement methodology which can observe dynamic RON transients after OFF-to-ON switching events over many decades in time. We have experimentally demonstrated this technique on GaN-on-SiC high-voltage HEMTs (High-Electron- Mobility-Transistors). The possible origin of the mechanisms responsible for dynamic RON in these devices has been postulated. Through our new technique, the impact of high-power stress on dynamic RON has been investigated as well. The results emphasize the importance of studying dynamic RON characteristics over very short time scale when conducting reliability studies of GaN transistors. Secondly, high-voltage GaN-on-Si MIS (Metal-Insulator-Semiconductor) HEMTs designed for > 600 V switching operation have been investigated. Excessive electron trapping leading to total current collapse has been observed. We have carried out an extensive characterization of this phenomenon and we have proposed "Zener trapping" as the responsible mechanism. In this view, electron trapping takes place inside the AlGaN/GaN heterostructure through a tunneling process under high-electric-field. The understanding derived here suggests that this effect can be mitigated through attention to defect control during epitaxial growth and appropriate design of the field plate structure of the device. Our findings in this thesis provide a path to achieve high performance GaN power transistors with minimum dynamic RON effects.
by Donghyun Jin.
Ph. D.
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Yenjaichon, Wisarn. "Characterization of in-line mixing of pulp fibre suspensions based on electrical resistance tomography." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43718.
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In pulp bleaching processes, pre-distribution of chemicals in suspensions ahead of tower reactors is essential to ensure efficient lignin removal and optimal use of the chemicals. In-line mixers, combined with chemical injectors, are commonly used to achieve this goal. In spite of its importance, in-line mixing of pulp suspensions is not well understood. In this thesis, liquid distribution and gas dispersion were investigated downstream of in-line mixers, including jet and mechanical mixers, to provide better understanding and guidance for mixer design and process optimization. In the present work, non-intrusive electrical resistance tomography (ERT) was used to quantify mixing based on two novel mixing indices, derived from the standard deviation of image pixel values. This technique was also implemented as a real-time mixing assessment tool in industrial pulp bleaching, with success in monitoring mixing quality as a function of process operating conditions. Liquid jet mixing was found to depend strongly on the flow regime and jet penetration. For turbulent flow, the criteria for in-line jet mixing in water apply also to suspensions. When a suspension flows as a plug, mixing differs greatly from that in water, depending on the fibre network strength in the core of the pipe. With an impeller present, mixing improved substantially, primarily in the high-shear zone around the impeller, with rapid reflocculation downstream. Gas mixing depended on the flow regime and buoyancy in a complex manner. When buoyancy was not significant, impeller operation enhanced mixing since bubbles dispersed throughout the pipe cross-section, whereas without the impeller, the bubbles congregated near the wall due to robust fibre networks in the core of the pipe. For buoyancy-dominated flow, the impeller worsened mixing since it disrupted the fibre networks and delivered gas to the top of the pipe, whereas the networks caused liquid/pulp slugs to flow at the top for a tee alone.
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Chandler, James Henry. "Direct current electrical resistance measurement techniques for assessment of colorectal cancer during laparoscopic surgery." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/12434/.
Full textAbstract:
The next generation of surgical tools will employ intraoperative sensing technologies to provide real-time information to the surgeon. Sensing in this way may facilitate personalised tissue resections during cancer surgery, thereby reducing radicality and improving outcomes for the patient. This thesis details the development and testing of electrochemical based sensing techniques aimed at integration into the next generation of laparoscopic surgical tools. Literature reviewed as part of the work highlights the broad nature of surgically appropriate sensing technologies. Based on the features of simplicity and scalability, the biogalvanic tissue characterisation technique was explored as the most practically suitable candidate. Development and systematic testing of a biogalvanic measurement system with porcine tissues showed variation that is not explained using the current system model. Correlation with electrochemical measurements verified this unaccounted system complexity. Electrode polarisation and diffusion controlled reduction at the cathode limit the tissue specificity of the output metrics. An improved analytic model fitting technique was developed to reduce the influence of the electrodes. Through collaborative development of a numerical model of the system, the practical limitations of the biogalvanic techniques as a surgical sensor were realised. To mitigate these limitations, a novel galvanostatic technique for improved resistance characterisation was developed. Testing was conducted on ex vivo tissues, showing stability for relevant parametric variation. Surgical applicability was found from a practical perspective, with results showing low sensitivity to switching rate, current range and tissue contact conditions. Testing was also conducted on a number of freshly excised cancerous human colon samples. Measurements were centralised on each tumour and compared to a corresponding healthy region. Every case showed a highly significant difference between tissue types with cancerous tissues having a consistently lower resistance. These findings suggest that the proposed technique of multi-reference galvanostatic resistance characterisation may be a suitable candidate for integration into surgical tools for colorectal cancer surgery.
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Chuang, Eugene (Eugene Yu) 1975. "Cyclic load resistance of reinforced concrete beams retrofitted with composite laminates." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/47496.
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Brand, Vitali. "Contamination- induced Interfacial Resistance in Ohmic Microswitch Contacts." Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/448.
Full textAbstract:
Ohmic nanoswitches have been recently regarded to complement transistors in applications where electrical current leakage is becoming a problem. Although the solid state metal oxide silicon field effect transistor (MOSFET) has fueled a global technology revolution, it is now reaching its performance limits because of device leakage. To avoid electric field-induced damage in MOSFETs, operating voltage and hence threshold voltage must be reduced as linewidth is reduced. However, below a limit, the current cannot be turned off. The ohmic switch approach solves this problem because an air gap that separates the electrical contacts provides excellent electrical isolation when the relay is open. Some applications require these relays to perform billions to trillions of cycles, yet typical devices that are exposed to ambient environment degrade electrically after just a few thousand cycles. A critical challenge here is that trace amounts of volatile hydrocarbons in air adsorb on the electrical contact surfaces for a large variety of coating materials, causing an insulating deposit to form that prevents signal transmission during switch closure. We address this challenge by exploring the interactions of hydrocarbon contaminants with contact materials and operating environment on device lifetime. Our materials of choice are Pt, a common contact material in switch applications due to its resistance to wear, and RuO2, which is believed to be somewhat resistant to hydrocarbon adsorption. We test our devices in N2 and O2 background environments with controlled hydrocarbon contaminant concentrations. We illustrate that the insulating hydrocarbon deposit can be electrically broken down and its resistance lowered. We show how electrical contacts that have degraded electrically due to contamination can have their performance restored to the original level by actuating them in clean N2-O2 environment. It is then shown how this process creates a highly conductive carbonaceous deposit that protects the contact from wear. It is also v demonstrated that RuO2 does not exhibit contaminant-induced degradation even at very high hydrocarbon presence, as long as O2 is also present. These results show that even though the contaminant is ubiquitous in the environment, there are many ways to reduce its effect on ohmic switches.
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Grönström, Niclas. "Optimal Demagnetization of Transformer After Winding Resistance Measurements." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291560.
Full textAbstract:
In this thesis, transformer demagnetization in connection to winding resistance tests is investigated. In transformer testing, winding resistance measurement (WRM) is an important test used to detect winding or connection faults. It is common practice to measure the resistance by injecting a DC current into the windings of a transformer. The method magnetizes the core, which leads to the transformer core remaining magnetized even after the test. A magnetized core can cause various problems, such as inrush currents that are several times higher than the rated current. Furthermore, residual magnetism may influence other AC diagnostic tests, such as the SFRA (Sweep Frequency Response Analysis) test and the excitation current test. Therefore, it is recommended to demagnetize transformers after WRM. The core-type and winding configuration may impact the demagnetization process. This makes the different demagnetization approaches of interest, so that the most efficient method can be used. This thesis presents demagnetization experiments on several power transformers with different core-types and winding configurations. The transformers were magnetized with WRM and then a TRAX (transformer and substation test system) was used to demagnetize the transformers with different approaches. Numerous measurements were performed on a three-limb and a five-limb power transformer. The effectiveness of the demagnetization methods was measured by using the excitation current in magnetized and demagnetized state as a comparative tool. It is shown that the demagnetization approach for the three-limb core had little impact on the magnetization result. The excitation currents at demagnetized state for the different combinations was roughly equal. The five-limb transformer was demagnetized on the middle limb, and then demagnetized on the outer limbs to see if the demagnetization gave better results. For the five-limb transformer, the measurements showed that the demagnetization approach impacted the results. Different Yy configurations were tested, and the result showed that the remanence was removed after one demagnetization with a phase to phase approach. However, if a Yy configuration was demagnetized with phase to neutral, then the transformer had to be demagnetized twice to remove the remanence. The result for the Yd configuration showed that it was not improved by a phase to phase approach. The phase that was magnetized did in general have a slightly larger excitation current than the other phases, even after demagnetization.I detta examensarbete undersöks avmagnetisering av transformatorer i samband med lindningsresistansprovning. Vid transformatorprovning är mätning av lindningsresistans ett viktigt test som används för att upptäcka lindningseller kopplingsfel. Vanligtvis mäts resistansen genom att en likström injiceras i transformatorns lindningar. Processen magnetiserar kärnan, vilket leder till att transformatorn förblir magnetiserad även efter testet. En magnetiserad transformator kan orsaka olika problem med diagnostiska tester och leda till inkopplingsströmmar som är flera gånger högre än märkströmmen. Vidare kan restmagnetism påverka AC-tester, såsom SFRA-testet (Sweep Frequency Response Analysis) och exciteringsströmstestet. Därför rekommenderas det att transformatorer avmagnetiseras efter lindningsresistanstest. Kärntyp och lindningskonfiguration kan ha påverkan på avmagnetiseringsprocessen. Det gör det intressant att undersöka olika avmagnetiseringsmetoder, så att den mest effektiva metoden kan användas. Detta arbete demonstrerar avmagnetiseringsexperiment på flera krafttransformatorer med olika kärntyper och lindningskonfigurationer. Transformatorerna magnetiserades genom lindningsresistansmätning och sedan användes en TRAX (transformer and substation test system) för att avmagnetisera transformatorerna med olika tillvägagångssätt. Flera mätningar utfördes på trebenta och fembenta krafttransformatorer. Avmagnetiseringsmetodernas effektivitet mättes genom att jämföra exciteringsströmmen i magnetiserat och avmagnetiserat tillstånd. Det visas att avmagnetiseringsmetoden för den trebenta kärnan hade liten inverkan på magnetiseringsresultatet. Exciteringsströmmarna vid avmagnetiserat tillstånd för de olika kombinationerna var ungefär lika. Den fembenta transformatorn avmagnetiserades först på mittbenet och sedan på de yttre benen för att se om resultaten förbättrades. För den fembenta transformatorn visade mätningarna att avmagnetiseringsmetoden påverkade resultaten. Olika Yy-konfigurationer testades och resultatet visade att remanensen avlägsnades efter den första avmagnetiseringen med fas till fas tillvägagångssättet. Men om Yy-konfigurationen avmagnetiserades med fas till neutral, då krävdes det att transformatorn avmagnetiseras två gånger för att få bort remanensen. Resultatet för Yd-konfigurationen visade ingen förbättring genom fas till fas tillvägagångssättet. Den fas som magnetiserades hade i allmänhet en något större exciteringsström än övriga faser, även efter avmagnetisering.
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Nygren, Kristian. "Magnetron Sputtering of Nanocomposite Carbide Coatings for Electrical Contacts." Doctoral thesis, Uppsala universitet, Oorganisk kemi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302063.
Full textAbstract:
Today’s electronic society relies on the functionality of electrical contacts. To achieve good contact properties, surface coatings are normally applied. Such coatings should ideally fulfill a combination of different properties, like high electrical conductivity, high corrosion resistance, high wear resistance and low cost. A common coating strategy is to use noble metals since these do not form insulating surface oxides. However, such coatings are expensive, have poor wear resistance and they are often applied by electroplating, which poses environmental and human health hazards. In this thesis, nanocomposite carbide-based coatings were studied and the aim was to evaluate if they could exhibit properties that were suitable for electrical contacts. Coatings in the Cr-C, Cr-C-Ag and Nb-C systems were deposited by magnetron sputtering using research-based equipment as well as industrial-based equipment designed for high-volume production. To achieve the aim, the microstructure and composition of the coatings were characterized, whereas mechanical, tribological, electrical, electrochemical and optical properties were evaluated. A method to optically measure the amount of carbon was developed. In the Cr-C system, a variety of deposition conditions were explored and amorphous carbide/amorphous carbon (a-C) nanocomposite coatings could be obtained at substrate temperatures up to 500 °C. The amount of a-C was highly dependent on the total carbon content. By co-sputtering with Ag, coatings comprising an amorphous carbide/carbon matrix, with embedded Ag nanoclusters, were obtained. Large numbers of Ag nanoparticles were also found on the surfaces. In the Nb-C system, nanocrystalline carbide/a-C coatings could be deposited. It was found that the nanocomposite coatings formed very thin passive films, consisting of both oxide and a-C. The Cr-C coatings exhibited low hardness and low-friction properties. In electrochemical experiments, the Cr-C coatings exhibited high oxidation resistance. For the Cr-C-Ag coatings, the Ag nanoparticles oxidized at much lower potentials than bulk Ag. Overall, electrical contact resistances for optimized samples were close to noble metal references at low contact load. Thus, the studied coatings were found to have properties that make them suitable for electrical contact applications.
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Smith, Jacob A. "Electrical Performance of Copper-Graphene Nano-Alloys." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1550675878730599.
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Imashuku, Susumu. "Electrical Conductivity of Grain Boundary in Accepter Doped Barium Zirconate." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/78014.
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Noman, Mohammad N. "Investigation of electroforming characteristics of TiO2 based resistance switching devices." Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/213.
Full textAbstract:
Resistance switching devices based on transition metal oxides have generated significant research interest over the last decade due to the promise they hold for non-volatile memory applications. Currently they are one of the leading candidates for replacing Flash memory technology as it nears its scaling limits. Despite many years of work and many encouraging demonstrations, the physical mechanism that drives the resistance switching phenomenon remains very poorly understood. A model based on migration of oxygen vacancies is often invoked, however direct proof of this model still remains illusive.
In this thesis, we developed a kinetic model of oxygen vacancy migration. Using this model, simulations were carried out on a 1-D device to examine the resistance switching and retention dynamics. It is found that in order to achieve fast switching (100 ns) and long retention (10 years), the vacancy migration based model requires unrealistic electric field (>10 MV/cm) and temperature (>1500 K) combinations. This situation does not change even when non-linear dependence of vacancy velocity on electric field is taken into account.
A significant portion of this thesis is focused on detailed examination of the electroforming characteristics of TiO2 based resistance switching devices. Electroforming is a step where a device is electrically stressed in order to trigger permanent changes to the oxide layer. During this process, the resistance of the device is usually lowered by 5-6 orders of magnitude. Stable resistance switching can only be obtained after performing electroforming. Most studies for this work were performed on 5 μm × 5 μm sized devices with Pt/TiO2/Pt structure. Transient pulsed method developed as part of this work allowed for precise determination of the voltage, time, and temperature combination that led to the onset of electroforming. Analysis of the transient data revealed that activation energy associated with electroforming decreases non-linearly with electric field. A vacancy migration based model cannot adequately explain this dependence. The experimental observations are better explained using a hole-injection model which asserts that onset of localized conduction is an electronic process rather than an ion migration based process.
Electroforming often produces pronounced morphological changes to the devices. These morphological changes are a strong function of the voltage pulse amplitude and width used to trigger electroforming. Electro-thermal simulations were used to correlate these changes with transient power dissipation during the electroforming process. The simulations indicate that electroforming did not produce extremely small conductive filaments (10-100 nm diameter) with very small resistance values (100-200 Ω), as it is sometimes reported in literature. Rather, the changes in the resistivity of the TiO2 layer spanned over an area as large as 8-9 μm2. Over this region, the resistivity changed gradually over 2-3 orders of magnitude. The filament(s) responsible for resistance switching can be located anywhere within this region.
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Fromknecht, Conner(Conner M. ). "LOKI : a lease-oriented key infrastructure with instant updates and seizure-resistance." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112914.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017Cataloged from PDF version of thesis.
Includes bibliographical references (pages 69-70).
Most of the secure communication protocols that power the Internet of today rely on a robust and frictionless mechanism for digital identity attestation. Authentication is typically achieved using a Public Key Infrastructure (PKI) that enables users to verify a counterparty's public key binding. Unfortunately, the structure of many existing PKIs present vulnerabilities and usability issues that stem from a lack of consistency, inefficient updates, or a dependence on centralized entities. In this work we present a decentralized marketplace for digital identities that autonomously leases the verification state of a globally-consistent PKI. Users express ownership of an identity through a sequence of leases, which incrementally defines the conditions under which ownership can be renewed and the identity's bindings can be updated. A careful structuring of the lease semantics, economic incentives and architectural design enables a fast update protocol, which permits clients to verify and accept a fresher binding without needing to wait for confirmation from the underlying consensus layer. The task of registration accuracy is extended naturally through the structure of the DNS namespace, after which the state of the system at any particular time acts as the root of trust during authentication. We discuss a novel seizure-resistance mechamism called dormancy, which in turn gives the existing owner of an identity substantial preference during the renewal process. Finally, we show how the system could be used to efficiently and unobtrusively secure today's communication protocols.
by Conner Fromknecht.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science