Engineering Commons^™

Growth And Characterization Of Zno For The Front Contact Of Cu(In,Ga)Se2, Rita Bhatt

USF Tampa Graduate Theses and Dissertations

ZnO window layers for CIGS solar cells are grown with a DC sputtering technique instead of a conventional RF sputtering technique. Transparent window layers and buffer layers are sputtered from the Zn target in the presence of Oxygen. The window layer is doped with Aluminum in order to achieve high electrical conductivity and thermal stability. The effect of different sputtering parameters on the electrical and optical properties of the films is elaborately studied. Sets of annealing experiments are also performed. Combinations of different deposition parameters are examined to design the optimum fabrication conditions. We are able to deposit 85% transparent, …

Pd/Ni Metal-Oxide-Semiconductor Hydrogen Sensor Utilizing A Segregated Pd-Ti Adhesion Layer, Mark Wayne Jenkins

Electrical and Computer Engineering ETDs

A novel technique has been developed that incorporates an adhesion layer into a hydrogen sensor that is based on a MOS structure. Previous structures containing no adhesion layer exhibited long-term drift and device failure due to delamination of the gate. While devices that did incorporate a normal adhesion layer lost all of their sensitivity. This is the first demonstration of combining virtues of an adhesion layer for a noble metal on insulator while retaining hydrogen sensitivity in a field effect sensor. The design issues related to utilizing Pd films for hydrogen sensors are presented. The recipes for fabricating the sensors …

Studies Related To The Design And Implementation Of A Magnetic Suspension And Balance System, Syed Adeel Akhtar Jafri

Electrical & Computer Engineering Theses & Dissertations

This thesis presents studies related to the magnetic suspension and balance system (MSBS) of the Princeton/ONR High Reynolds Number Testing Facility (HRTF). The main motivation for developing the MSBS is to provide interference free aero/hydrodynamic testing of submersible models, which will lead to more accurate measurements. From the controls point of view, the main specification of the MSBS is to robustly control the position of a submersible model in five degrees of freedom (DOF), including three translational as well as pitching and yawing positions. The MSBS should not only regulate the submersible model's position but should also allow for small …

Fabrication And Characterization Of Silicon Field Emitter Arrays, Aaron M. Brock

Electrical & Computer Engineering Theses & Dissertations

Field emission is a process through which the application of a large electric field to the surface of a material causes electron emission into vacuum. The electron emission current is a strong function of the geometry of the emitting material. The focus of this thesis is to investigate the effect of geometry on the emission current. Specifically, silicon field emitter arrays were fabricated using two separate fabrication processes termed the standard process and the new process. The uniformity of the arrays was measured experimentally. The arrays were used in field emission tests from which parameters controlling field emission were extracted. …

Phase Tunability In A Conductor Backed Coplanar Waveguide Patch Antenna, Idan Mandelbaum

Theses

Traditionally beam steering in phase array antenna systems is achieved using tunable phase shifters or switched feed networks. Here, a tunable patch antenna element is suggested as a novel alternative to a combination of a radiating element and a phase shifter. A conductor backed coplanar waveguide patch antenna is chosen due to its suitability to mounted external tuning elements, using varactor diodes. Limited types of lumped tuning circuits, using varactor diodes, have been tested, though a lumped as well as distributed tuning is feasible in the chosen antenna configuration. Approximate analytical models for coplanar waveguide patch antennas with finite ground …

Reduction Of Peak To Average Power Ratio In Ofdm And Ofdm-Cdma System, Jie Cheng

Theses

High Peak to Average Power Ratio is a main problem in Orthogonal Frequency Division Multiplexing(OFDM) system and Orthogonal Frequency Division Multiplexing -Code Division Multiple Access (OFDM-CDMA) system. Considering a compensated High Power Amplifier(HPA), in order to keep linearity for amplification, Input Back-Off(IBO) of the HP-A, has to be increased for handling a high PAPR. Higher 1130 will make HPA less efficient. Additionally, a signal with high PAPR will suffer clipping when PAPR is larger than 1130 of the HPA. Clipping can cause the distortion of the signal and deteriorate the performance of the system. Reduction of PAPR is a main …

Analysis Of The Anodic Bonding Process And The Packaging Effects In Mems Devices, Sonya G. Iyasere

Electronic Dissertations and Theses

This paper gives a brief overview of the process of completely sealing and permanently joining glass to a semi-conductor without the use of adhesives known as anodic or electrostatic bonding. It is well known that this process will introduce thermal strain due to different coefficients of thermal expansion between any metal or semiconductor and glass. This paper will also describe the effect of the MEMS packaging process on various devices that are bonded electrostatically.

Numerical Simulation Of Acoustic Wave In A Convergent-Divergent Nozzle Using A Characeristic Based Algorithm, Haitham Maher Mahmoud

Archived Theses and Dissertations

No abstract provided.

Advanced Atmospheric Water Vapor Dial Detection System, Tamer Refaat

Electrical & Computer Engineering Theses & Dissertations

Measurement of atmospheric water vapor is very important for understanding the Earth's climate and water cycle. The remote sensing Differential Absorption Lidar (DIAL) technique is a powerful method to perform such measurement from aircraft and space. This thesis describes a new advanced detection system, which incorporates major improvements regarding sensitivity and size. These improvements include a low noise advanced avalanche photodiode detector, a custom analog circuit, a 14-bit digitizer, a microcontroller for on board averaging and finally a fast computer interface.

This thesis describes the design and validation of this new water vapor DIAL detection system which was integrated onto …

Resolution Of Overlapping Spectra By Wavelength Modulation Spectroscopy, Audra Michiele Bullock

Electrical & Computer Engineering Theses & Dissertations

Wavelength modulation absorption spectroscopy is a highly sensitive, non-intrusive technique for probing gaseous species, which employs the well-known principles of modulation spectroscopy in a novel way. With this technique, parameters such as velocity, density, and temperature can be measured with a high degree of precision. The research presented here shows that wavelength modulation is a convenient means of increasing the sensitivity of an absorption spectroscopy measurement because it allows for harmonic detection. The focus of the dissertation is resolution of overlapping spectra by harmonic detection and the advantages gained by performing detection at the higher harmonics, e.g., sixth and eighth. …

The Fundamental Use And Extension Of Mode Stirred Chambers, Stephen A. Scearce

Electrical & Computer Engineering Theses & Dissertations

Mode stirred chambers are used to perform radiated susceptibility tests on equipment that is expected to operate normally when exposed to electromagnetic (EM) fields. These tests are useful in identifying failure events in airborne equipment and other electronic equipment that are exposed to EM fields. This thesis is focused on further defining the operating environment of mode stirred chambers and relating the electromagnetic environment in the chamber to the electromagnetic environment of an actual aircraft. The majority of mode stirred chamber tests are implemented by using mechanical mode stirring. Mechanical mode stirring is the process of varying boundary conditions in …

Simulation Studies Of Cellular Electroporation Due To Ultra-Fast Electric Pulses, Gayathri R. Barthaki

Electrical & Computer Engineering Theses & Dissertations

Biological systems, from cells to ecosystems, are intrinsically complex information-processing networks. It often becomes difficult to predict their behavior during an experimental investigation, as their behavior is fundamentally chaotic, Hence, building models that mimic the dynamics of such systems and performing computer simulations would help in understanding, predicting, controlling and optimizing these systems. This thesis is aimed at the development of a mathematical model for the process of electroporation in biological cells when they are subjected to ultra-fast electric pulses and at conducting simulations to understand its dynamic behavior with special emphasis on the physics of ultra-short time scales.

With …

Signal Modeling With Non-Uniform Time Sampling Of Features For Automatic Speech Recognition, Montri Karnjanadecha

Electrical & Computer Engineering Theses & Dissertations

This dissertation presents an investigation of non-uniform time sampling methods for spectral/temporal feature extraction in speech. Frame-based features were computed based on an encoding of the global spectral shape using a Discrete Cosine Transform. In most current “standard” methods, trajectory (dynamic) features are determined from frame-based parameters using a fixed time sampling, i.e., fixed block length and fixed block spacing. In this research, new methods are proposed and investigated in which block length and/or block spacing are variable. The idea was initially tested with HMM-based isolated word recognition, and a significant performance improvement resulted when a variable block length and …

Routing Optimization Through Computer-Aided Simulation, Madhusudhan Akundi

Electrical & Computer Engineering Theses & Dissertations

Routing has always been a challenging field, and the various techniques of mathematics and operations research have been developed. For commercial organizations, routing has begun to receive extensive attention because of the savings gained in terms of time, money, personnel, and the transportation fleet by developing optimized routing networks. Until recently, it was difficult to develop optimized networks due to the computational difficulties of the problem. However, with the advancement in computer technology and processing speeds, it has become possible to simulate a large number of routing scenarios and determine optimal solutions for a given set of constraints. Not only …

Video Traffic Modeling And Delivery, Hai Liu

Dissertations

Video is becoming a major component of the network traffic, and thus there has been a great interest to model video traffic. It is known that video traffic possesses short range dependence (SRD) and long range dependence (LRD) properties, which can drastically affect network performance. By decomposing a video sequence into three parts, according to its motion activity, Markov-modulated self-similar process model is first proposed to capture autocorrelation function (ACF) characteristics of MPEG video traffic. Furthermore, generalized Beta distribution is proposed to model the probability density functions (PDFs) of MPEG video traffic.

It is observed that the ACF of MPEG …

Investigation Of The Baroreflex Of The Rat : Steady State And Dynamic Features, Xiaorui Tang

Dissertations

The baroreflex is one of the most important feedback systems in the body to maintain blood pressure variation within the homeostatic range. In this dissertation, the important features of the carotid and aortic baroreflexes have been extensively investigated on ventilated, central nervous system intact, neuromuscular blocked (NMB) rats using different control system and signal processing tools. Studies have demonstrated that sinoaortic denervation (SAD) caused substantial increases in the blood pressure variability. Comparing the pre- and post-SAD blood pressure spectra, there was a significant increase of power in the very low frequency region (0.00195 -0.2 Hz), and a significant decrease of …

Design And Analysis Of A Scalable Terabit Multicast Packet Switch : Architecture And Scheduling Algorithms, Feihong Chen

Dissertations

Internet growth and success not only open a primary route of information exchange for millions of people around the world, but also create unprecedented demand for core network capacity. Existing switches/routers, due to the bottleneck from either switch architecture or arbitration complexity, can reach a capacity on the order of gigabits per second, but few of them are scalable to large capacity of terabits per second.

In this dissertation, we propose three novel switch architectures with cooperated scheduling algorithms to design a terabit backbone switch/router which is able to deliver large capacity, multicasting, and high performance along with Quality of …

Programmable Latching Probe Microstructures For Wafer Testing Applications, Salima Taifa Sadeq

Theses

The objective of this thesis is to design a programmable wafer testing array on a single chip based on micro electromechanical systems (MEMS) and VLSI. The wafer-scale integration in this thesis is a programmable array of test probes that are used for engineering test of VLSI and ULSI silicon integrated circuits at the wafer level. This consists of two subsystems (1) the VLSI address circuits used for addressing and controlling the MEMS on the chip and (2) the latching probe MEMS microstructure array that actuates into position for testing VLSI wafers. Each of the subsystems have been designed, analyzed and …

Bounded Beam Wave Pulse Propagation And Scattering In Random Media Based On The Radiative Transfer Theory Using 2-D Gauss Quadrature Formula, Sheng-Kai Hu

Theses

The scalar time-dependent equation of radiative transfer is used to develop a theory of bounded beam wave narrow band pulse propagation and scattering in a medium characterized by many random discrete scatters, which scatters energy strongly in the forward scattering direction. Applications include the scattering of highly collimated millimeter waves in vegetation and optical beams in the atmosphere. The specific problem analyzed is that of a periodic sequence of Gaussian shaped pulses normally incident from free space onto the planar boundary surface of a random medium half-space, such as a forest, that possesses a scatter (phase) function consisting of a …

Cramer-Rao Bound And Optimal Amplitude Estimator Of Superimposed Sinusoidal Signals With Unknown Frequencies, Shaohui Jia

Doctoral Dissertations

This dissertation addresses optimally estimating the amplitudes of superimposed sinusoidal signals with unknown frequencies. The Cramer-Rao Bound of estimating the amplitudes in white Gaussian noise is given, and the maximum likelihood estimator of the amplitudes in this case is shown to be asymptotically efficient at high signal to noise ratio but finite sample size. Applying the theoretical results to signal resolutions, it is shown that the optimal resolution of multiple signals using a finite sample is given by the maximum likelihood estimator of the amplitudes of signals.

Kinetics Of Laser Chemical Vapor Deposition Of Carbon And Refractory Metals, Feng Gao

Doctoral Dissertations

Three-dimensional laser chemical vapor deposition (3D-LCVD) has been used to grow rods of carbon, tungsten, titanium, and hafnium from a variety of hydrocarbons and metal halide-based precursors. A novel computerized 3D-LCVD system was designed and successfully used in the experiments. A focused Nd:Yag laser beam (λ = 1.06 μm) was utilized to locally heat up a substrate to deposition temperature. The rods, which grew along the axis of the laser beam, had a typical diameter of 30–80 μm and a length of about 1 mm. The precursors for carbon deposition were the alkynes: propyne, butyne, pentyne, hexyne, and octyne. Propyne …

Bulk Micromachining Of Silicon For Moems Prototype, Sung-Dong Suh

Doctoral Dissertations

In this dissertation, the optical application of silicon micromachining technology was investigated in order to create the three-dimensional microstructures that can be used as the components for the MOEMS prototype. These microstructures were designed and fabricated by utilizing corner compensation techniques and silicon bulk micromachining technologies. The fabricated microstructures are silicon mirror arrays that have a 1250 μm etch depth and through-holes across the OE-MCM substrate that has sixteen-fan-out OCDN on front side and a 1mm thickness.

Guided-wave OCDN on MCMs are designed and fabricated to meet the high-speed clocking requirements of next-generation digital systems through a realization of superior …

Efficient Algorithms And Implementations For Signal Processing, Changbai Xiao

Doctoral Dissertations

A scheme is presented to regain a finite number of lost samples from a Nyquist-rate-sampled band-limited signal f of finite energy by replenishing new sample values of the same number. The result can also be viewed as the solution to a special non-uniform sampling problem.

A scheme is also presented to recover a band-limited function f of finite energy from its sampling values on real sequences with an accumulation point. The result given here can also be viewed as an approach to the extrapolation problem of determination a band-limited function in terms of its given values on a finite interval. …

A Cmos Chaotic Oscillator, Boonsin Chansilp

Masters Theses

A chaotic oscillator may be used as the basic component of an associative memory (AM). An AM is capable of pattern separation and noise reduction. Chua's circuit is a widely used chaotic oscillator. This circuit consists of a nonlinear resistor, two capacitors, an inductor and a resistor. A discrete implementation of Chua's circuit may be built using operational amplifiers, resistors, diodes, or discrete bipolar transistors. CMOS integrated circuit technology provides the opportunity for a compact implementation which enables construction of systems requiring a large number of oscillators. This thesis develops an integrated circuit design based on previous work performed by …

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 A Method For Kinematic Gps Carrier-Phase Ambiguity Resolution Using A Network Of Reference Receivers, Brian L. Bracy

Theses and Dissertations

New applications for GPS have driven a demand for increased positioning accuracy. The emerging GPS technology particularly affects the test community. The testing equipment and method must provide a solution that is an order of magnitude more precise than the tested equipment to achieve the desired accuracy. Carrier-phase differential GPS methods using a network of reference receivers can provide the centimeter-level accuracy required over a large geographical area. This thesis evaluates the performance of a 5-receiver network over a 50 km x 120 km area of New Mexico, using a GPS network algorithm called NetAdjust. The percentage of time a …

Investigation Of Conformal High-Impedance Ground Planes, Michael A. Saville

Theses and Dissertations

Applique antennas are a long range vision for military vehicles because they are lighter, quicker to replace, less expensive, and can have better performance than conventional antennas. Two newly reported high-impedance ground planes have potential to begin the realization of the applique antenna vision and each is investigated for use with thin conformal antenna structures. Bistatic reflection measurements completely characterize the high-impedance region of planar, thumbtack high-impedance ground planes, and periodic moment method models validate the measurement results. Rigorous planar and conformal surface wave coupling measurements clarity the reported photonic band gap behavior of the thumbtack high-impedance ground plane, and …

Effects Of Jamming On Radars, Ahmet Okuyucu

Theses and Dissertations

Although jamming of radars has been in vogue for nearly 50 years there appears to be no comprehensive report on the subject matter. The purpose of this research is to fill this gap. The methodology consisted of analysis, simulation, and where feasible experimental demonstrations. Experimental equipment consisted of a digital noise generator whose output was used to modulate a high frequency carrier in various fashions. The modulated output was fed into a very sensitive super-heterodyne receiver whose Intermediate frequency (IF) bandwidth could be varied from tens of Hz to mega Hz range. The detected output was displayed on a sampling …

Comparative Analysis Of Mobility Management Schemes In A Low Earth Orbit Satellite Network, Stephen R. Conkling

Theses and Dissertations

In the 60's the United States and the Union of Soviet Socialist Republics engaged in a "space race" to be the first to put a man on the moon. Today, the space race is between large multinational telecommunication corporations with the winner receiving the financial rewards by providing communication services to the billions without even a simple telephone. Many entrants are using Low Earth Orbit (LEO) satellites to provide the communications infrastructure, but the number of customers a satellite can support is limited by bandwidth available. This resource must be used efficiently, and this involves reducing the management overhead. This …