Browsing by Subject "Electrical engineering"
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Item Bispectral analysis of nonlinear acoustic propagation(2011-05) Gagnon, David Edward; Hamilton, Mark F.; Wochner, Mark S.Higher-order spectral analysis of acoustical waveforms can provide phase information that is not retained in calculations of power spectral density. In the propagation of high intensity sound, nonlinearity can cause substantial changes in the waveform as frequency components interact with one another. The bispectrum, which is one order higher than power spectral density, may provide a useful measure of nonlinearity in propagation by highlighting spectral regions of interaction. This thesis provides a review of the bispectrum, places it in the context of nonlinear acoustic propagation, and presents spectra calculated as a function of distance for numerically propagated acoustic waveforms. The calculated spectra include power spectral density, quad-spectral density, bispectrum, spatial derivative of the bispectrum, bicoherence, and skewness function.Item Development of an advanced electrical system for a solar powered racing vehicle with an emphasis on the battery protection and management system(2011-05) Engelkemeir, Frederick Donald; Hallock, G. A.; Grady, MackThis thesis describes the development of an electrical system for a solar powered racing vehicle with en emphasis on the Battery Protection System (BPS). This battery protection system was designed for the UTSVT’s (University of Texas Solar Vehicles Team) solar powered vehicle, the Samsung Solorean. The system is required due to the dangers of the lithium-ion cobalt battery chemistry. The system monitors the voltage, temperature, and current of each battery module in the 22 module battery pack and will physically isolate the pack from the rest of the vehicle with a high-current electromechanical contactor if any parameter is outside of the safe range. The system can be expanded to monitor any number of series battery cells. The system uses a master-slave microcontroller architecture with a single master microcontroller that interrogates several slave microcontroller boards for readings over a common serial bus. The system uses a new voltage sensing ASIC to monitor cell voltages, along with an analog current output device to measure temperature and a hall-effect device to measure current. The system was a complete success and has allowed the UT solar car to finish the American Solar Challenge cross-country “Rayce.”Item Light transport simulation in reflective displays(2012-05) Feng, Zhanpeng; Nutter, Brian; Mitra, Sunanda; Karp, Tanja; Gale, Richard O.; Westfall, Peter H.In the last several years, reflective displays have gained substantial popularity in mobile devices such as e-readers, because of their significant advantages in power consumption and sunlight readability. A typical reflective display consists of a stack of optical layers. Accurate and efficient simulation of light transport in these layers provides valuable information for optical design and analysis. Physically based ray tracing algorithms are able to produce simulation results that mirror the real world display performance in a wide range of illumination conditions, viewing angles, and distances. These simulation outcomes help system architects make far reaching decisions as early as possible in the design process. In this dissertation, a reflective display is modeled as a layered material, with a FOS (front of screen) layer on the top, a diffusive layer (diffuser) underneath the FOS, a transparent layer (glass) in the middle, and a wavelength-dependent reflective layer (pixel array) at the bottom. A set of simple and efficient spectral functions is developed to model the reflectance and absorption of FOS. A novel hybrid approach combining both spectro-radiometer based and imaging based measurement methods is developed to acquire high resolution reflectance data in both angular and spectral domains. A BTDF (bidirectional transmittance distribution function) is generated from the measured data to model the diffuser. A wavelength dependent BRDF (bidirectional reflectance distribution function) is used to model the pixels. Realistic light transport simulation requires interplay of three factors: surface geometry, lighting, and material reflectance. Monte Carlo ray tracing methods are used to link these factors together. Path tracing is employed to provide unbiased results. Stratified sampling and importance sampling are used for effective variance reduction. Stratified sampling produces well distributed random samples, and importance sampling helps Monte Carlo simulation converge more quickly. Different importance sampling methods are compared and analyzed. Simulation results of display performance, including reflectance, color gamut, contrast ratio, and daylight readability, are presented. The impact of different lighting conditions, diffusers, and FOS designs are studied. Measurement data and physically based analyses are used to confirm the validity of the simulation tool. The simulation tool provides the desired accuracy and predictability for display design in a wide range of lighting conditions, which makes it a valuable mechanism for display designers to find the optimal solution for real world applications.Item MegaGauss : a portable 40T magnetic field generator(2011-05) Wisher, Matthew Louis; Hallock, G. A.; Bengtson, Roger D.Fusion neutrons from high energy density plasmas generated by pulsed laser irradiation of nanoscale atomic clusters have been explored in recent experiments at the University of Texas at Austin. A sufficiently strong (~200 T) magnetic field is expected to produce a magnetized, high temperature (10 keV) plasma with beta [approximately equal to] 1. Such a field along the laser axis may confine the plasma’s radial expansion, thus increasing fusion yield. As part of a multi-stage project to implement this experiment, a scaled (~40 T, ~500 KA) version of the final 200 T, 2.2 MA pulsed power device has been designed and built by Sandia National Laboratories and is now at UT-Austin. This apparatus, named MegaGauss, is meant to serve as a preparation tool for the 200 T system; as such, its current pulse was recorded for analysis, and is compared to a theoretical model to verify its response parameters (e.g. peak current, time to peak). Techniques and results of this comparison are discussed, followed by explanations of basic construction of the 40 T device and current sensing instrumentation. Discussion of MegaGauss is completed with a survey of notable failure modes, and a description of the often severe effects the miniature field-generating Helmholtz coil experiences due to the current pulse and magnetic field. Finally, a novel data archive scheme, structured around the familiar MDSplus archive system, is implemented in Labview and integrated into the main pulsed power control program. Specifically, methods for linking MDSplus’s robust functionality with Labview’s intuitive development environment are realized by means of a specialized software bridge between the two. These methods are used in software that allows MDSplus archives to be written and read exclusively through Labview.Item Modeling and simulation of distribution system components in anticipation of a smarter electric power grid(2011-05) Toliyat, Amir; Kwasinski, Alexis; Grady, WiliamSuccessful development of the electric power grid of the future, hereinafter referred to as a smart grid, implicitly demands the capability to model the behavior, performance, and cost of distribution-level smart grid components. The modeling and simulation of such individual components, together with their overall interaction, will provide a foundation for the design and configuration of a smart grid. It is the primary intent of this thesis, to provide a basic insight into the energy transfer of various distribution-level components by modeling and simulating their dynamic behavior. The principal operations of a smart grid must be considered, including variable renewable generation, energy storage, power electronic interfaces, variable load, and plug-in electric vehicles. The methodology involves deriving the mathematical equations of components, and, using the MATLAB/Simulink environment, creating modules for each component. Ultimately, these individual modules may be connected together via a voltage interface to perform various analyses, such as the treatment of harmonics, or to acquire an understanding of design parameters such as capacity, runtime, and optimal asset utilization.Item Test and characterization of engineering nanocoatings for mems and nanoenergetic materials(2012-05) Vijayasai, Ashwin; Dallas, Timothy E. J.; Gale, Richard O.; Pantoya, Michelle; Weeks, Brandon L.; Hase, William L.; Yeo, ChangdongThis dissertation presents the development, test and characterization of engineered nanocoatings for MEMS and nano-energetic reactive materials. Surface modification on MEMS and nano-energetic reactive materials are developed using a commercially available nanocoating tool. Surface modifications include Chemical Vapor Deposition of Fluorocarbon SAM and nanoparticles and Atomic Layer Deposition of thin oxides. Detailed descriptions of the nanocoating process and their chemical reactions are explained. An F-SAM coated MEMS tribogauge is characterized to estimate the adhesive and frictional forces. In-situ frictional measurements were made. Increasing adhesion force was observed for increasing number of load cycles. The tribogauge is later used as an ex-situ characterization tool to observe the performance of various nanocoating recipes for F-SAM coating. Characterization of the tribogauge is performed using an electronic sense tool. Contact angle goniometer was used to characterize the performance of various recipes. Various types of nanocoatings were deposited on witness samples and nano-energetic materials. A comparison study of underwater combustion tests were made on these thermite pellets. An aging study was performed on both nanocoated witness samples and pellets. The aging experiment is performed by submerging them in de-ionized water for 10 days. Contact angle goniometer and few optical microscopes were used to characterize the performance of various recipes. Apart from the nanocoating based projects, this dissertation briefly explains other projects that were part of the graduate program. A brief description and initial results of a few MEMS device designs are explained in this dissertation. As part of future work new MEMS devices were designed that will allow follow-up nanocoatings projects.Item Yield enhancement in microelectronic technologies: Reduction of variability in transistor threshold voltage(2012-05) Garcia-Sagredo, Michelle M.; Gale, Richard O.; Borhani, MarcusThe work behind this thesis exemplifies a methodology regularly followed in the semiconductor industry in order to identify a root cause to a low yield issue, determine actions to eradicate or ameliorate the problem, design the experiments meant to gather evidence from test wafer lots in support of the suggested improvement, as well as analyzing the experiment’s results and implementing the solution in production wafer lots. Yield Enhancement engineers deal daily with this kind of scenario. It is in their hands to ensure the company’s profitability not only by identifying and fixing the obvious manufacturing recurring problems, but by pointing out areas of opportunity for better process control, and therefore being able to provide higher yield for their customers. The particular issue covered on this paper is the fluctuation of process control parameters from Standard Low Voltage (SLV) P-channel Metal-Oxide-Semiconductor Field Effect Transistors at a certain semiconductor Fab. Historically, the devices processed with the SLV option at this fab have shown severe Threshold Voltage (Vt) variation lot to lot. This variation has lead to whole lots being out of spec, and therefore, scrapped. Due to the high amount of lots processed with this option that have gotten scrapped, finding the root cause for this issue and fixing it became one of the most important goals for the Fab’s Yield Enhancement Engineers in the past years. In order to find a starting point for the solution of the problem, several trends for the parameters of interest were analyzed. The trends indicated a possible correlation of the scrapped lots to the Anti-Punch-Through (APT) Implanter used for their processing. Given the close relationship between the APT and the Threshold Adjust (PVt) Implant, the last one also became an important line of investigation. The theoretical background on CMOS fabrication, the importance of metrics such as Cp and Cpk in the industry, and the approach followed to solve the Fab’s SLV Threshold Voltage fluctuation issue are a few of the topics one can read about on the present work.