Pulsed electro-acoustic (PEA) measurements of embedded charge distributions

Knowledge of the spatial distribution and evolution of embedded charge in thin dielectric materials has important applications in semiconductor, high-power electronic device, high-voltage DC power cable insulation, high-energy and plasma physics apparatus, and spacecraft industries. Knowing how, where, and how much charge accumulates and how it redistributes and dissipates can predict destructive charging effects. Pulsed Electro-acoustic (PEA) measurements— and two closely related methods, Pressure Wave Propagation (PWP) and Laser Intensity Modulation (LIMM)— nondestructively probe such internal charge distributions. We review the instrumentation, methods, theory and signal processing of simple PEA experiments, as well as the related PPW and LIMM methods. We emphasize system improvements required to achieve high spatial resolution for in vacuo measurements of thin dielectrics charged using electron beam injection

Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

Supercell electrostatics of charged defects in periodic density functional theory

Charged defects are often studied using density functional theory (DFT). However, the use of periodic boundary conditions (PBC) introduces a fictitious jellium background required to maintain charge neutrality, along with periodic images of the defect. As a consequence, the calculations are found to be sensitive to the size of the supercell used. Several competing correction methods have been developed for bulk materials, but do not provide a completely satisfactory solution to this problem. One source of error in these corrections is suggested to be the simple density models employed. I propose a new electrostatic correction based on calculating electronic charge density differences between reference DFT calculations, and then solving Poisson equation for these charge models. For bulk materials, I demonstrate that this new correction is in agreement with the existing Lany-Zunger (LZ) method. This demonstrates that using more realistic density models is not sufficient to improve the corrections, but the new method does allow an improved understanding of potential alignment. I found that alignment errors are introduced by adding or removing atoms from the supercell to form the defect, and that these errors are related to their atomic radius. Secondly, the charge models I constructed are found to be in good agreement with the predictions of classical electrostatics, corresponding to both bound and free charges. I derive a new analytic charge correction based on this model, but it produces smaller corrections than anticipated. Further calculations demonstrate that the remaining unexplained finite-size error is introduced by the finite-size dependence of the exchange-correlation energy of the screening bound charge, rather than on electrostatic grounds. Improved empirical corrections are constructed, which display differences between unrelaxed and relaxed defects. The developed arguments are extended to surface slab models, where the observed errors are found to be dependent on the shape of the supercell employed

Pulsed dynamics in silicon and diamond photonic nanostructures

The work carried out in this thesis has been motivated by the promising applicability of photonic nanostructures in optical communications, internet data centers (ICD) and biosensing, to name a few. In particular, the dispersion and nonlinear engineering that silicon photonic crystal waveguides (Si-PhCWGs) and diamond-fin waveguides allow, can be exploited in the design of important photonic components, such as frequency comb generators, Raman amplifiers or filters. Within such objectives, we present rigorous and comprehensive theoretical models where all relevant linear and nonlinear optical effects, including modal dispersion, waveguide loss, free-carrier (FC), Kerr and Raman effects are considered. In the case of the newly developed subwavelength diamond-fin waveg- uides, we complete a detailed characterization of their dispersion and nonlinear optical properties, along with an analysis of pulsed dynamics in these structures. As a relevant application, we demonstrate how these waveguides can be employed to efficiently gener- ate soliton frequency combs in the visible spectral domain. With regards to Si-PhCWGs, we firstly explore the effect of stimulated Raman scattering in the slow-light regime, and demonstrate that signal amplification without pulse distortion can be achieved. Secondly, we add photonic crystal cavities (PhCCs) alongside the Si-PhCWG, with the associated inter-cavity coupling and waveguide-cavity interactions. Therefore, we describe a novel mathematical model and its corresponding computational tool that solves the dynamics of the forwards and backwards propagating pulses, the energy in the cavities and the FCs at the waveguide and at the cavities. Finally, we show the potential practical use of the model by simulating a photonic drop-filter with back reflection nulling

Silicon carbide power devices

Abstract unavailable please refer to PD

Engineering Education and Research Using MATLAB

MATLAB is a software package used primarily in the field of engineering for signal processing, numerical data analysis, modeling, programming, simulation, and computer graphic visualization. In the last few years, it has become widely accepted as an efficient tool, and, therefore, its use has significantly increased in scientific communities and academic institutions. This book consists of 20 chapters presenting research works using MATLAB tools. Chapters include techniques for programming and developing Graphical User Interfaces (GUIs), dynamic systems, electric machines, signal and image processing, power electronics, mixed signal circuits, genetic programming, digital watermarking, control systems, time-series regression modeling, and artificial neural networks

Removal of Synthetic Organic Compounds and NOM by Single-Walled Carbon Nanotubes-Ultrafiltration and Forward Osmosis Membrane System

This overall theme of this dissertation is to investigate the potential engineered application of low pressure membranes incorporated with single-walled carbon nanotubes (SWNTs) and forward osmosis (FO) membrane systems for the removal of synthetic organic compounds (SOCs) and natural organic matter (NOM) from drinking water sources. The focus is on the use of SWNTs-ultrafiltration (UF) and FO membrane systems to facilitate the removal of these compounds and potential applications of these membrane system designs for reducing the energy demands and membrane fouling in environmental water filtration process and seawater desalination. The SWNTs-UF results indicate that SOCs transport is influenced by NOM, which fouls the membrane through pore blockage and cake/gel formation. A strong linear correlation between the retention and adsorption of SOCs was observed, indicating that retention by the SWNTs-UF membranes is mainly due to the adsorption of SOCs onto the membrane, the SWNTs, and/or NOM. The performance of SWNTs-UF was also evaluated on the basis of a resistance-in-series model, filtration laws, and NOM transportation mechanisms. The addition of SWNTs to the UF process did not significantly exacerbate the permeate flux decline and total membrane resistances. Further, it appeared that the effect of SWNTs on membrane fouling is a function of hydrodynamic and operational conditions. The results suggest that the NOM transportation in SWNTs-UF systems depends, to a significant extent, on the concentration polarization and cake/gel layer formation at the membrane boundary. In the application for artificial seawater in SWNTs-UF, the presence of SWNTs shows 20% increase in membrane flux and a strong linear correlation between retention and adsorption of SOCs was obtained. In FO membrane systems, the cellulose triacetate based FO membrane exhibited the better separation properties than that of polyamide based reverse osmosis (RO) membrane. And, in active layer (AL)-facing-feed solution (FS) configuration in FO mode, the RO membrane exhibited higher removal efficiency at the expense of severe internal concentration polarization (ICP) and flux reduction. Under higher cross-flow velocity operations in FO mode, both reduced external concentration polarization and retarded SOC diffusion from the reverse flux of sodium chloride contributed to the improved SOC removal performance. The FO membrane removal behavior was principally related to size exclusion, while the RO membrane removal behavior was related to interactions between hydrophobicity, size, and electrostatic repulsion. The results significantly confirmed the dominant role of ICP, and the trade-off between flux and removal efficiency depends on the porous supporting layer in AL-facing-FS configurations in the FO process

Axisymmetric simulation codes for hall effect thrusters and plasma plumes

Mención Internacional en el título de doctorThe development of reliable and versatile plasma discharges simulation codes is becoming of central importance, given the rapidly evolving electric propulsion landscape. These tools are essential for facilitating and complementing the design of new prototypes, signiffcantly reducing development time and costs. Moreover, they can provide a deeper insight on already proven technologies, revealing optimization opportunities so as to improve the thruster performance and lifetime, and predicting the operational parameters at different regimes of interest. This Thesis is devoted to the numerical study of different plasma discharges and, in particular, the Hall effect thruster (HET) discharge. With special focus on particle-based modeling, two simulation codes have been developed. The first one, named HYPHEN, is a new two-dimensional axisymmetric hybrid, particle-in-cell (PIC)/fluid multi-thruster simulation platform. Its versatile PIC-based module for heavy species supports the simulation of inner active surfaces, mixed specular-diffuse neutral-wall reflection, and chargeexchange (CEX) collisions, thus extending the code capabilities and enabling the simulation of axisymmetric plasma plumes. Moreover, it features a new population control which monitors independently every heavy species and limits the statistical noise at a low computational cost. Furthermore, an improved version of the HET electron fluid module for the isotropic electron pressure case is presented. Three major studies have been carried out with this code. First, the simulation of an ion thruster plasma plume has permitted to benchmark HYPHEN against the 3D plasma plume code EP2PLUS. Second, an investigation on the neutral-wall interaction effects on an unmagnetized plasma discharge in a surface-dominated cylindrical channel with isothermal electrons has been performed. The discharge ignition requires different propellant injection mass ows in the diffuse and specular neutral-wall reflection cases. Third, preliminary simulations of a SPT-100 HET have been carried out to demonstrate the code capabilities and reveal its limitations. Consistent results have been obtained for different cathode locations in the near plume region and various electron turbulent transport parameter profiles. The second code corresponds to a new version of the one-dimensional radial particle model of a HET discharge, originally developed by F. Taccogna. The major improvements are an ionization controlled discharge algorithm, which enables sustaining a steady-state discharge, and an extended volumetric weighting algorithm which provides a more accurate macroscopic description of the low populated species, such as the wall-emitted secondary electrons. The radial dynamics of both the primary and secondary electron populations have been analyzed in detail, assessing the temperature anisotropy ratio of their velocity distribution functions and the asymmetries introduced by cylindrical geometry effects in the macroscopic laws of interest, thus aiming at a future improvement of the plasma-wall interaction module implemented in HYPHEN.El desarrollo de códigos fiables y versátiles para la simulación de descargas de plasma es cada vez más importante dada la rápida evolución de la propulsión espacial eléctrica. Estas herramientas son esenciales para facilitar y complementar el diseño de nuevos prototipos, reduciendo significativamente los tiempos y costes de desarrollo. Además, pueden ampliar la comprensión de las tecnologías ya establecidas, revelar vías de optimización del propulsor que permitan mejorar su rendimiento y vida útil, y predecir los parámetros de operación del mismo en diferentes regímenes de interés. Esta Tesis está dedicada al estudio numérico de diferentes descargas de plasma y, en particular, de descargas HET. Se han desarrollado dos códigos de simulación, con especial énfasis en los modelos de partículas. El primero de ellos, llamado HYPHEN, es una nueva plataforma de simulación multi-propulsor, híbrida PIC/fluida y axisimétrica. Su módulo PIC para especies pesadas permite la simulación de superficies activas inmersas en el plasma, procesos de reflexión especular-difuso de neutros en pared y colisiones CEX, extendiendo por tanto las capacidades del código y permitiendo la simulación de plumas de plasma axisimétricas. Además, incluye un nuevo control de población que monitoriza a cada especie pesada por separado limitando el ruido estadístico y el coste computacional. Por otra parte, se presenta una versión mejorada del modelo fluido de electrones isótropos para HET. Tres estudios principales se han llevado a cabo con este código. En primer lugar, la simulación de la pluma de plasma de un motor iónico ha permitido validar HYPHEN con el código de plumas 3D EP2PLUS. Por otro lado, se ha investigado el efecto de la interacción del gas neutro con la pared en una descarga no magnetizada con electrones isotermos en un canal cilíndrico esbelto. La ignición de la descarga requiere inyectar diferentes gastos másicos de propulsante en los casos de reflexión difusa y especular. En tercer lugar, se han realizado simulaciones preliminares de un motor HET de tipo SPT- 100 con el objeto de demostrar las capacidades del código y revelar sus limitaciones, obteniendo resultados consistentes para diferentes posiciones del cátodo en la región de la pluma cercana, y perfies del parámetro de turbulencia de electrones. El segundo código representa una nueva versión del modelo radial de partículas de una descarga HET desarrollado originalmente por F. Taccogna. Las principales mejoras consisten en un algoritmo de control de la descarga a través de la ionización, que permite obtener una descarga estacionaria, y un algoritmo de pesado volumétrico extendido, que proporciona una descripción macroscópica más precisa de las especies poco pobladas, como los electrones secundarios emitidos desde las paredes del motor. Para posibilitar una futura mejora del módulo de HYPHEN de interacción plasma-pared, se han analizado en detalle la dinámica radial de los electrones primarios y secundarios, la anisotropía de temperatura de sus funciones de distribución de velocidad, y las asimetrías cilíndricas en las leyes macroscópicas de interés.Programa Oficial de Doctorado en Mecánica de Fluidos por la Universidad Carlos III de Madrid; la Universidad de Jaén; la Universidad de Zaragoza; la Universidad Nacional de Educación a Distancia; la Universidad Politécnica de Madrid y la Universidad Rovira i Virgili.Presidente: Iván Calvo Rubio.- Secretario: Gonzalo Sánchez Arriaga.- Vocal: Daniela Pedrin