Electrical and Computer Engineering Commons^™

Pulsed Optoacoustics In Solids, Zibiao Wei

Electrical & Computer Engineering Theses & Dissertations

Optoacoustic techniques are widely used to probe and characterize target materials including solids, liquids and gases. Included in such applications are diagnoses of thin films and semiconductor materials. The need to obtain greater spatial resolution requires the generation of shorter optoacoustic pulses. For such pulses, non-thermal effects may be quite important. On the other hand, even when an optoacoustic pulse is generated by an initially non-thermal technique, the thermal aspects become important in its evolution and propagation. The research undertaken in this Ph.D. dissertation included the generation and detection of optoacoustic signals through the thermal elastic mechanism. Several applications in …

Theory Of Sic Schottky Barrier Conduction And Model Analysis For Diode Breakdown With And Without Screw Dislocations, Lifeng Zheng

Electrical & Computer Engineering Theses & Dissertations

Silicon Carbide is a very promising candidate for applications in high-power, high-temperature, and high-radiation conditions under which conventional semiconductors cannot perform adequately. However, the SiC processing technology has not yet reached maturity. There is also limited knowledge of its physical and chemical characteristics, and its device behavior is not well understood. The aim of this thesis is to analyze two specific problems in the SiC area. The first issue involves the large discrepancy between experimental I - V characteristics of SiC Schottky diodes and their theoretical values. The observed data, especially at low voltages, is found to be orders of …

Evaluation Of The Transport Properties Of Gasb For Bipolar Applications Through Monte Carlo Simulations, Damayanthi Palaniappan

Electrical & Computer Engineering Theses & Dissertations

GaAs is currently the semiconductor material of choice for high speed, low power applications. Its electronic transport properties are superior to almost all other semiconductors. It is also used in a variety of bipolar applications such as photodetectors and photo-mixers. However, as is well known, the hole mobility and related transport parameters of GaAs are not very good. This is a serious drawback, and poses a potential problem for all applications involving bipolar conductivity. In order to increase the high :frequency limits and high-speed capability of bipolar devices, the choice of an alternative material, therefore, becomes necessary. An important first …

A Pressure Transducer Using Field Emitter Arrays, Mark David Richmond

Electrical & Computer Engineering Theses & Dissertations

A new pressure sensing device using field emission from diamond coated silicon tips has been developed. A high electric field applied between a nano-tip array and a diaphragm configured as electrodes produces electron emission governed by the Fowler - Nordheim equation. The electron emission is very sensitive to the separation between the diaphragm and the tips, which is fixed at an initial spacing and bonded such that a cavity is created between them. Pressure applied to the diaphragm decreases the spacing between the electrodes, thereby increasing the number of electrons emitted.

Silicon has been used as a substrate on which …

Newton Parameter Update Algorithm For Recurrent Neural Networks Applied To Adaptive System Identification And Control, Donald Allen Gates

Electrical & Computer Engineering Theses & Dissertations

This paper shows that the combination of a second-order neural network parameter update algorithm and internal network feedback can be effectively used for adaptive, nonlinear, dynamical system identification and control. Adaptive neural identification and control algorithms are typically utilized for real-time applications where the rate of adaptation is often critical. A fast, adaptive network parameter update algorithm is presented.

Simulation results show that this algorithm is capable of quickly identifying and adapting to changes in system parameters, making it feasible to use for real-time control and fault accommodation applications.

Field Enhancement In Silicon Nanotip Field Emitter Arrays, Ajith Varghese

Electrical & Computer Engineering Theses & Dissertations

No abstract.

Development And Testing Of An Ac Micro Hollow Cathode Simulator, Thomas E. Caldwell

Electrical & Computer Engineering Theses & Dissertations

The use of AC source plasma discharge devices in applications such as material processing and film deposition has increased in recent years due to improvements in discharge efficiency made possible by devices such as the micro hollow cathode. Designing hollow cathodes for specific applications requires an understanding of the processes that govern the discharge. Simulation is an inexpensive tool for understanding hollow cathode operation and optimizing the device for specific applications. This thesis describes the development of an AC micro hollow cathode simulator. It details the theoretical models used in the simulation and presents the results of test cases intended …

Stability Analysis And Augmentation Of A Closed-Loop Computer Control System Subject To Electromagnetic Disturbances, Mustafa Doğan

Electrical & Computer Engineering Theses & Dissertations

Most electronic and electrical equipment is not only a potential source of electromagnetic interference (EMI) but can also malfunction when exposed to certain levels of ambient EMI. This phenomena becomes more significant for digital control-computers automating the command and control performances in complex plants. Such EM disturbances can introduce transient signals on analog sensor and actuator lines, change data values on digital buses and in memory, or even produce logic changes in the CPU. The result of these so called computer upsets is the introduction of some degree of degradation in the quality of the control signal ranging from a …

Preparation And Surface Studies Of Negative Electron Affinity Semiconductors Photocathodes, Khaled A. Elamrawi

Electrical & Computer Engineering Theses & Dissertations

Fabrication of high quantum efficiency, long lifetime negative electron affinity photocathodes is important for applications such as photomultipliers, image intensifiers, electron beam lithography, electron microscopy, and polarized electron sources. The surface cleanliness of the III-V semiconductor photocathode is crucial in obtaining high photosensitivity.

GaAs(100) and InP(100) photocathodes are prepared by atomic hydrogen cleaning. The cleaning effect on the photocathode performance is discussed. The surface degradation mechanisms which reduce the photocathode lifetime are presented. The photocathode surface cleanliness, structure, and morphology are studied using reflection high-energy electron diffraction (RHEED).

Quantum efficiencies of ∼14% and 8% are obtained for GaAs and InP, …

Two Dimensional, Time Dependent Modeling And Simulation Of Semi-Insulating Gaas High-Power Photoconductive Switches, Prakasit Kayasit

Electrical & Computer Engineering Theses & Dissertations

The current-voltage (I-V) characteristics and photoconductive behavior of semi-insulating GaAs (SI GaAs) high-power switches have been investigated by using a two-dimensional, time dependent, drift diffusion transport model. The dc current-voltage behavior as predicted by the results of this model was compared with available experimental data to evaluate the accuracy and validity of the model. The results show very good agreement, Next, research was carried out to investigate the behavior of the switches under high-field operation.

Simulations at high voltages emphasize on the two following processes: (a) The mechanism of impact ionization and the effect of this mechanism on device stability …

Computer Simulations Of Electromigration Based On A Molecular Dynamics Approach, John Stephen Peake

Electrical & Computer Engineering Theses & Dissertations

Most research on electromigration has centered around macroscopic simulations of electromigration where a value for the diffusion coefficient was assumed to be spatially uniform throughout the material. The research in this thesis goes a step further and, through microscopic molecular dynamics computer simulations, calculates and updates the atomic drift velocity and atomic position as a function of time to analyze how various defects within the conductor affect these quantities. The simulations are carried out with defects in the form of dislocation half-planes placed in different locations within the simulation space. The atomic drift velocity and position changes derived from these …

Modeling And Simulation Of High-Field, High-Temperature Sic Devices, Sanjay Pathak

Electrical & Computer Engineering Theses & Dissertations

With superior properties such as a large band gap, high thermal conductivity, and large electron drift velocity, SiC is expected to give a new dimension to high power, high temperature electronic devices used in power applications, microwave circuits, and for the space and automobile industries. SiC possesses an inherent advantage over its other large bandgap competitors in terms of inherited processing and device technology from Si. However, there is inadequate understanding of SiC device and its parameters. Simple extrapolations from Si are known to be inadequate. The aim of this dissertation, therefore. is to produce better understanding of SiC devices …

Reactions Of Oxygen And Nitric Oxide In A Microhollow Electrode Discharge, Joseph L. Desormeaux Jr.

Electrical & Computer Engineering Theses & Dissertations

Microhollow electrode discharges have been developed and researched in the Physical Electronics Research Institute Laboratories. This discharge typically operates in direct current mode. Microhollow electrode discharges are non-thermal discharges that produce electrons with energies greater than 10 electron volts. Passing gas mixtures through non-equilibrium discharges invokes excitation or dissociation of gas molecules.

The scope of my research was to study the effect of the discharge on the chemistry of two gases, oxygen and nitric oxide in nitrogen mixture. Initial experiments were performed in an effort to produce ozone near atmospheric pressure. This seemed possible since the discharge has a high-energy …

Coupled Electrodynamic-Monte Carlo Simulations Of Nanoscale Gaas Terahertz Optical Mixers, Jiang Li

Electrical & Computer Engineering Theses & Dissertations

The concept of mixing or heterodyning has traditionally been used for microwaves and for radio frequency communications. However, the concept can easily be extended into the optical frequency regime. By doing so, the photomixing process can serve as a very versatile tool for both the generation of ultrahigh frequency (terahertz) and the detection of weak optical signals.

The aim of this thesis is to perform a theoretical study of the photomixing process inside GaAs devices as the non-linear elements. A coupled approach which combines the Monte Carlo simulation scheme for the carrier transport, with Maxwell's equation for the electrodynamics, has …

Effect Of Pulsed Electric Fields On Aquatic Nuisance Species, Amr Abou-Ghazala

Electrical & Computer Engineering Theses & Dissertations

Clinical and theoretical evidence indicate that electric fields have biological effects ranging from recoverable disturbance to mortality induction depending on the field parameters and time of exposure. In this thesis, the effect of electrical field in pulsed form on aquatic nuisance species is investigated. Pulse parameters in terms of amplitude, width, shape, and repetition rate that stimulate the species to desirable levels are to be defined. Applying the electrical pulses with appropriate parameters to stun aquatic nuisance species entering marine cooling systems will prevent it from attaching to pipe walls. The use of electrical fields to seek efficient, environmentally friendly, …

Microhollow Cathode Discharge Excimer Lamps, Ahmed El-Habachi

Electrical & Computer Engineering Theses & Dissertations

Microhollow cathode discharges are non-thermal discharges of such small sizes that thermalization of the electrons is prevented. By reducing the diameter of the cathode opening in these discharge geometries to values on the order of 100 $\mu$m we were able to operate discharges in argon and xenon in a direct current mode up to atmospheric pressure. The large concentration of high electrons, in combination with high pressures favors three body processes such as excimer formation. This was confirmed by experiments in xenon and argon where emission of excimer radiation at 172 nm and 130 nm, respectively, was observed when the …

An Injection Modelocked Titanium-Sapphire Laser, James C. Hovater

Electrical & Computer Engineering Theses & Dissertations

I have investigated the possibility of using an injection modelocked Ti-sapphire laser as a illumination source for GaAs photocathodes. A commercial Ti-sapphire laser was modified to accept a seed pulse from a gain-switched diode laser. Modelocked operation was obtained through gain modulation within the Ti-sapphire crystal as a result of injection seeding with a modelocked pulse train from a gain-switched diode laser. The Ti-sapphire laser essentially becomes a pulse amplifier for the diode laser. Unlike conventional modelocked lasers, the pulse repetition rate of this laser can be discretely varied by setting the seed laser repetition rate equal to multiples of …

Electrical Characteristics And Parallel Operation Of Microhollow Cathode Discharges, Wenhui Shi

Electrical & Computer Engineering Theses & Dissertations

This thesis describes the electrical properties of microhollow cathode discharges with argon as filling gas. The appearance and current-voltage characteristics of microhollow cathode discharges have been recorded. Three kinds of discharge modes (predischarge, hollow cathode discharge and abnormal discharge) have been observed. The range of operation of the hollow cathode discharge has been found to be 0.5 < pD & 5 Torr cm in argon. By reducing the hole diameter to 100 pm, we were able to operate the discharge to atmospheric pressure in a dc mode. The possibility of dc parallel operation of microhollow cathode discharges was explored. Parallel operation could be obtained without individual ballast for discharges with a positive I-V slope greater than 10 V/mA over a voltage range of more than 5 % of the sustaining voltage. For parallel operation outside the range the ballasting is required. This model was explored by using a segmented anode model. The result of the simple calculation coincides well with the experiment result, where a semi-insulator silicon was used as distributed ballast.

High Pressure Radio-Frequency Microhollow Cathode Discharges, Anja Annett Muller

Electrical & Computer Engineering Theses & Dissertations

A new field of microhollow cathode discharges is represented by the RF microhollow cathode discharge. So far, the behavior and related physical processes of the RF microhollow cathode discharge are not well investigated.

RF microhollow discharges in air at high pressures were investigated under different experimental conditions. The geometry was changed by reducing the cathode hole diameter and the dielectric spacer thickness. By adding a noble gas to air, the influence of additive gases was explored. Additionally, the parallel operation of RF microhollow discharges was investigated.

It was shown that stable RF microhollow cathode discharges could only be sustained up …

The Cluster Multipole Algorithm For Far-Field Computations, Rakesh R. Patel

Electrical & Computer Engineering Theses & Dissertations

Computer simulations of N-body systems are beneficial to study the overall behavior of a number of physical systems in fields such as astrophysics, molecular dynamics, and computational fluid dynamics. A new approach for computer simulations of N-body systems is proposed in this research. The new algorithm is called the Cluster Multipole Algorithm (CMA). The goals of the new algorithm are to improve the applicability to non-point sources and to provide more control on the accuracy over current algorithms. The algorithm is targeted to applications that do not require rebuilding the data structure about the system every time step due to …

Building Lms Adaptive Filters With Register-Based Fpgas, Li Ding

Electrical & Computer Engineering Theses & Dissertations

In this thesis, an 8-bit least mean squares (LMS) adaptive digital filter with 16 coefficients is implemented on a single FPGA, using the MaxPlus+2 design environment. The system is constructed as a hierarchical structure, using four different levels of design hierarchy. Subdesigns at each level of the hierarchy project are complied, fitted and simulated to test and verify their functional correctness. The complete system is tested and verified by checking the MaxPlus+2 simulator results against fixed-point integer arithmetic simulations written in Matlab. The resulting adaptive filter is subsequently mapped to the Alters FLEX I OK20TC144-3 device, resulting in a 14,500 …

Field Emission And Breakdown Processes In Vacuum Gaps With Sio(X)-Coated Cathodes, Raymond Jack Allen Iii

Electrical & Computer Engineering Theses & Dissertations

Field emission of electrons is the major cause of electrical breakdown in high voltage systems in vacuum. The highest hold-off electric field of the carefully polished and cleaned stainless steel cathodes was increased to 70MV/m. Thin silicon monoxide, SiO_x, cathode coatings reduced field emission and increased the hold-off field further. Coating the stainless steel cathodes with 2μ SiO_x reduced the field emission current by at least two orders of magnitude at field of 50MV/m and increased the breakdown field to 140MV/m, doubling the breakdown voltage.

The increase in hold-off voltage with SiO_x coatings is discussed in …

Material Evaluation By Pulsed Diode Laser Optoacoustics, Xiaodong Xu

Electrical & Computer Engineering Theses & Dissertations

Pulsed diode laser optoacoustic diagnostics were carried out to characterize solid sample materials. The apparatus developed is compact, portable, cost-effective and therefore very promising for both industrial as well as laboratory applications. To our knowledge, this is the first time that optoacoustic characterization and measurement have been performed with a diode laser. The method was successfully applied to measure the thickness of a multilayer structure non-intrusively. Internal cracks of the material were detected by this technique.

A theory for optoacoustic signal generation, propagation and detection is given. A numerical analysis technique is developed to solve for the expected signal. In …

Selective Cvd Growth Of Diamond Crystals On Tungsten, Charles Randal Cole

Electrical & Computer Engineering Theses & Dissertations

Typical field emitters consist of sharp metal tips which usually have a short life due to erosion and contamination. To improve the performance of regular field emitters, diamond can be placed on the emitter tip. This is done by selectively growing diamond on tungsten tips using chemical vapor deposition (CVD) processing. Diamond exhibits negative electron affinity, so that electrons will be emitted by properly biasing the tip.

To obtain single crystal growth right at the tip, a cantilever controlled nucleation method was developed which worked better than other methods. Surface preparation was also important to the growth process. An oxide …

Development Of A Photon Counting System For Ozone Differential Absorption Lidar Signal Detection, Bradley Allen Eccles

Electrical & Computer Engineering Theses & Dissertations

A photon counting system was assembled and integrated into an existing ozone differential absorption lidar signal detection system to improve the range of ozone measurement. Results of data extraction from decaying ozone return signals are presented. Photomultiplier tube detector models EMI 9214Q and EMI 9B17Q are evaluated and characterized. Detector operating performance was based on tube quantum efficiency, gain, dark current, and linearity. The influence of photomultiplier tube characteristics on photon counting performance are discussed along with the recommended optimum photon counting operating conditions. Two photomultiplier gating schemes, focus grid and four dynode gating, are described for use in photon …

A Piezoresistive Metal Thin Film Tilt Sensor, Todd Allan Lindley

Electrical & Computer Engineering Theses & Dissertations

Thin film strain gauges have many applications as transducers for monitoring pressure, vibration, and acceleration. In this thesis, a simple system, consisting of a Nichrome thin film strain gauge deposited on a glass substrate, is investigated in detail. Finite element analysis is used to model the expected sensor behavior. The substrate is shaped to exhibit a constant strain distribution, and is set up in a cantilever beam configuration. R. F. sputtering is used to deposit the Nichrome film, and the resistor pattern is transferred via photolithography. The gravitational force on a mass attached to the free end of the sensor …

Electromyography (Emg) Signal Classification By Artificial Neural Networks, Behnam Dashtipour

Electrical & Computer Engineering Theses & Dissertations

EMG signal processing is one of the active fields of biomedical signal processing. One unanswered question is how to determine whether a muscle is fatigued by analyzing the EMG signal. Fatigue detection could be useful in several different practical situations. There are several studies which show there are differences between EMG signal features before fatigue and after fatigue. Generally studies are based on an analytical analysis of the EMG signal instead of a quantitative analysis. In all previous studies in EMG signal processing for fatigue/nonfatigue detection, the result is that there exist some differences between the EMG signal before muscle …

High Resolution Wavelength Modulation Spectroscopy For Precise Gaseous Characterization, Audra Michiele Bullock

Electrical & Computer Engineering Theses & Dissertations

Wavelength modulation spectroscopy is a highly sensitive, non-intrusive technique for probing gaseous species. Parameters such as velocity, density, and temperature can be measured and monitored with a high degree of precision. In addition, with the use of this technique multiple molecular species may be identified with a single laser probe. This measurement technique utilizes the well-known principles of modulation absorption spectroscopy in a novel way.

The research focuses on harmonic detection and the advantages gained by performing detection at higher harmonics, those greater than the commonly used second harmonic. We show that there is an increase in the sensitivity to …

Diamond For Fiber-Optic Raman Spectroscopy, Jianli Zheng

Electrical & Computer Engineering Theses & Dissertations

Raman spectroscopy is a powerful technique for molecular structural studies and concentration measurement. Being a single beam technique, the Raman intensity depends on the optical power of the excitation source, optical alignment of the system, detector response as well as species concentration. To eliminate the unwanted variations in the system and get the concentration information of the species, intensity referencing is necessary. The existing referencing methods either use a constant Raman band of the sample, or add a chemically inert material with known concentration into the sample. Unfortunately, the former method is not always applicable and the latter is not …

Kramers-Kronig Anomalous Dispersion On Single-Mode Fiber-Optic Couplers And Tapers, Arnel C. Lavarias

Electrical & Computer Engineering Theses & Dissertations

The Kramers-Kronig relations couple the real and imaginary part of the dielectric constant of a medium, namely the refractive index n(ω) and the extinction coefficient κ(ω). Changes in n(ω) due to normal and anomalous dispersion (Kramers-Kronig effect) are investigated for the first time using fiber optic couplers and tapers. Kramers-Kronig effect is induced by evanescent wave absorption in these devices. Couplers and tapers have oscillatory spectral outputs that are highly sensitive to the refractive index of the surrounding medium. Theoretical modeling of the Kramers-Kronig effect on couplers and tapers shows two distinct effects. First, the spectral outputs of these devices …