Engineering Commons^™

Trade-Off Study And Computer Simulation For Assessing Spacecraft Pointing Accuracy And Stability Capabilities, Marcelo C. Algrain, Richard M. Powers

Department of Electrical and Computer Engineering: Faculty Publications

A case study, written in a tutorial manner, is presented where a comprehensive computer simulation is developed to determine the driving factors contributing to spacecraft pointing accuracy and stability. Models for major system components are described. Among them are spacecraft bus, attitude controller, reaction wheel assembly, star-tracker unit, inertial reference unit, and gyro drift estimators (Kalman filter). The predicted spacecraft performance is analyzed for a variety of input commands and system disturbances. The primary deterministic inputs are the desired attitude angles and rate set points. The stochastic inputs include random torque disturbances acting on the spacecraft, random gyro bias noise, …

Ellipsometer/Polarmeterbased Process Monitor And Control System Suitable For Simultaneous Retrofit On Molecular Beam Epitaxy System Rheed/Leed Interface System, And Method Of Use, John A. Woollam, Blaine D. Johs, Peter P. Chow

Department of Electrical and Computer Engineering: Faculty Publications

A method of, and system for applying light beam producing systems, such as ellipsometers, polarimeters, polarized light reflectance and functionally similar systems, such that a beam of light produced thereby is caused to be incident upon a process element at an angle in excess of an associated Brewster angle while enabling the production of a signal sufficiently sensitive to changes in process element parameters, for use in "real-time" process element process monitoring and control, is disclosed. In addition, a process element processing system and electron beam producing system and light beam producing system combination system is taught, wherein the electron …

Ellipsometer/Polarmeter Based Process Monitor And Control System Suitable For Simultaneous Retrofit On Molecular Beam Eptaxy System Rheed/Leed Interface System, And Method Of Use, John A. Woollam, Blaine D. Johs, Peter P. Chow

Department of Electrical and Computer Engineering: Faculty Publications

A method of, and system for, applying light beam producing systems such as ellipsometers, polarimeters, polarized light reflectance and functionally similar systems, such that a beam of light produced thereby is caused to be incident upon a process element at an angle in excess of an associated Brewster angle while enabling the production of a signal sufficiently sensitive to changes in process element parameters, for use in "real-time' process element process monitoring and control, is disclosed. In addition a process element processing system and electron beam producing system and light beam producing system combination system is taught, wherein the electronbeam …

Equalization Of A Non-Linear Phase Of A Low-Pass Filter, Rabih Khodor

Dissertations and Theses

In practice, an IIR filter can distort the information content of the signal because of its inherent non-linear phase characteristics introduced through the design of the filter. If the the receiver of the signal is the human ear, e.g., when a speech or music signal is to be processed, phase distortion is quite tolerable. But, in other applications it can be rejected as phase characteristics is required to be fairly linear. Applications of this type include data transmission, where the signal is to be interpreted by digital hardware, and image processing, where the signal is used to reconstruct an image …

An Asic Power Analysis System For Digital Cmos Design, Du Van Nguyen

Dissertations and Theses

Consumers demand for products with ever-increasing functionality, performance, and longer battery life is making low power a critical factor in most system designs. Lower-power designs are less expensive to produce, more reliable, and cost less to operate - factors which create a real competitive advantage. As a result, ASIC designers are demanding better ways to analyze the power of their designs.

In this thesis, an ASIC Power Analysis System (APAS) is developed. APAS is an interactive simulation-based power analysis tool. Using a non-intrusive design technique, APAS can dynamically "snap on" to an existing simulation environment. APAS currently supports three ASIC …

Properties Of Schottky Contacts Of Aluminum On Strained Si1-X-YGeXCY Layers, Jian Mi, Ashawant Gupta, Cary Y. Yang

Electrical and Computer Engineering

Schottky contacts of Al/Si_1-x-yGe_xC_y were fabricated using conventional Si technology. Effects of thermal processing of the alloys on the electrical properties of the Al/Si_1-x-yGe_xC_y Schottky diodes were investigated. Current–voltage (I–V), capacitance–voltage (C–V), and x‐ray diffraction measurements were performed. These thick alloy films (100–150 nm) experienced strain relaxation upon annealing at 700 °C. Nearly ideal I–V and C–V behaviors were obtained for strain‐compensated samples. I–V and C–Vcharacteristics show evidence of dislocation‐related traps for strain‐relaxed samples. Carbon incorporation improves the I–V and C–V characteristics by lessening the extent of lattice relaxation due …

Growth Of Diamond By Rf Plasma-Assisted Chemical Vapor Deposition, Duane E. Meyer, Natale J. Ianno, John A. Woollam, A. B. Swartzlander, A. J. Nelson

Department of Electrical and Computer Engineering: Faculty Publications

A system has been designed and constructed to produce diamond particles by inductively coupled radio-frequency, plasma-assisted chemical vapor deposition. This is a low-pressure, low-temperature process used in an attempt to deposit diamond on substrates of glass, quartz, silicon, nickel, and boron nitride. Several deposition parameters have been varied including substrate temperature, gas concentration, gas pressure, total gas flow rate, rf input power, and deposition time. Analytical methods employed to determine composition and structure of the deposits include scanning electron microscopy, absorption spectroscopy, scanning Auger microprobe spectroscopy, and Raman spectroscopy. Analysis indicates that particles having a thin graphite surface, as well …

The Multiple Pool Migrating Worker Paradigm : A Distributed System Framework And Model, Cynthia Ann Stanley

Dissertations and Theses

A network of workstations (NOW) can provide an inexpensive and effective distributed processing platform. The purpose of this thesis is two-fold, providing a methodology for distributed computing on a NOW first, and providing a model to predict and monitor performance second. The Multiple Pool-Migrating Worker (MPMW) paradigm uses multiple job pools to divide up tasks and migrating workers to balance the work load. The MPMW paradigm is a quick and efficient way of implementing problems using distributed processing without extensive knowledge of parallel programming. A model describing the MPMW paradigm is developed using queuing theory and Mean Value Analysis techniques. …

Perceptual Fidelity For Digital Color Imagery, Curtis E. Martin

Theses and Dissertations

The problem of measuring the fidelity of digital color images in a manner that corresponds to human perceptual assessments is addressed. Experiments are performed to validate human visual system (HVS) models, which provide access to a 'perceptual space' in which visual distortions may be measured, and then a model is proposed for assessing the perceptual fidelity of digital color image. Color Mach bands are produced in the first experiment, demonstrating that, as in the brightness channel, low spatial frequency attenuation occurs in the chromatic channels of the HVS. In the second experiment, a correlation between the chromatic channels of the …

Application Of A Finite-Volume Time-Domain Maxwell Equation Solver To Three-Dimensional Objects, Frederick G. Harmon

Theses and Dissertations

Concurrent engineering approaches for the disciplines of computational fluid dynamics (CFD) and electromagnetics (CEM) are necessary for designing future high-performance, low-observable aircraft. A characteristic-based finite-volume time-domain (FVTD) computational algorithm, developed for CFD and now applied to CEM, is implemented to analyze the radar cross section (RCS) of two three-dimensional objects, the ogive and cone-sphere. The FVTD formulation implements a Monotone Upstream-Centered Scheme for Conservation Laws (MUSCL) algorithm for the flux evaluation and a Runge-Kutta multi-stage scheme for the time integration. Developmental FVTD work for the thesis focused on algorithm development to analyze scattering and obtain RCS data for closed-surface perfect …

Evaluation Of Design Tools For Rapid Prototyping Of Parallel Signal Processing Algorithms, James C. Savage

Theses and Dissertations

Digital signal processing (DSP) has become a popular method for handling not only signal processing, but communications, and control system applications. A DSP application of interest to the Air Force is high speed avionics processing. The real time computing requirements of avionics processing exceed the capabilities of current single chip DSP processors, and parallelization of multiple DSP processors is a solution to handle such requirements. Designing and implementing a parallel DSP algorithm has been a lengthy process often requiring different design tools and extensive programming experience. Through the use of integrated software development tools, rapid prototyping becomes possible by simulating …

A Stochastic Model For Crystal-Amorphous Transition In Low Temperature Molecular Beam Epitaxial Si(111), R. Venkatasubramanian, Suresh Gorantla, S. Muthuvenkatraman, Donald L. Dorsey

Electrical & Computer Engineering Faculty Research

Molecular beam epitaxial Si (111) grown below a certain temperature result in amorphous structure due to the limited surface mobility of atoms in finding correct epitaxial sites. In spite of many experimental and theoretical studies, the mechanism of crystal‐amorphous transition and its dynamics related to the growth conditions are not well understood. In this article, we present a theoretical model based on the formation of stacking fault like defects as a precursor to the amorphous transition of the layer. The model is simulated based on a stochastic model approach and the results are compared to that of experiments for temperatures …

A Multimedia Manual On The World Wide Web For Telecommunications Equipment, Andrew L. Sears, Steve E. Watkins

Electrical and Computer Engineering Faculty Research & Creative Works

An interactive multimedia educational manual on the Internet through the World Wide Web for commercial optical fiber telecommunications equipment is described. The Telecommunications Laboratory Manual is a vehicle for enhancing engineering education with realistic laboratory or virtual laboratory experience. The manual provides a brief system tutorial, operating instructions, on-line help, and multimedia experimental demonstrations. It incorporates block diagrams, photographic images, and hypertext links that are mouse clickable, allowing users to access documents or links describing components or processes in any order. An experimental section guides students through laboratory experiences, demonstrates selected equipment characteristics, and provides for direct instructor contact through …

Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo

Theses and Dissertations

This research expanded Low Probability of Intercept (LPI) communications analysis in two areas. First, multimode communication was included to account for ground to ground and air to ground links in addition to the standard air to air links traditionally used in LPI analysis. The propagation equations for the three modes of interest were derived and included in LPI analytic models in the form of a mode quality factor to account for multimode LPI scenarios. This new quality factor was used in studying several communication and interception link combinations. Variations due to differences between the communication and interception modes were presented …

Performance Analysis Of A Hartman Wavefront Sensor Used For Sensing Atmospheric Turbulence Statistics, Toby D. Reeves

Theses and Dissertations

Atmospheric turbulence parameters, such as Fried's coherence diameter, the outer scale of turbulence, and the turbulence power law, are related to the wavefront slope structure function (SSF). The SSF is defined as the second moment of the wavefront slope difference as a function of both time and position. Knowledge of the SSF allows turbulence parameters to be estimated. Hartmann wavefront sensor (H-WFS) slope measurements composed of both signal and noise, allow the SSF to be estimated by computing a mean square difference of H-WFS slope measurements. The quality of the SSF estimate is quantified by the signal-to-noise ratio (SNR) of …

Development Of Object-Based Teleoperator Control For Unstructured Applications, Hyunki Cho

Theses and Dissertations

For multi-fingered end effectors in unstructured applications, the main issues are control in the presence of uncertainties and providing grasp stability and object manipulability. The suggested concept in this thesis is object based teleoperator control which provides an intuitive way to control the robot in terms of the grasped object and reduces the operator's conceptual constraints. The general control law is developed using a hierarchical control structure, i.e., human interface I gross motion control level in teleoperation control and fine motion control/object grasp stability in autonomous control. The gross motion control is required to provide the position/orientation of the Super …

Adaptive Neural Network Controller For Atm Traffic, Jeffrey E. Larson

Theses and Dissertations

Broadband-Integrated Services Digital Networks (B-ISDN), along with Asynchronous Transfer Mode (ATM), were designed to meet the requirements of modern communication networks to handle multiple users and a wide variety of diverse traffic including voice, data and video. ATM responds to requests for admission to the network by analyzing whether or not the grade of service (GOS) requirement, specified in the admission request, can be guaranteed without violating the GOS guaranteed to traffic already accepted into the network. The GOS is typically a parameter such as cell loss rate (CLR), average delay, or some other measurement associated with network performance. In …

Optimization Of A Gps-Based Navigation Reference System, Jason B. Mckay

Theses and Dissertations

The development of increasingly accurate new aircraft navigation systems has caused the Air Force to develop a new Navigation Reference System to test them, called the Submeter Accuracy Reference System (SARS). The SARS is an inverted GPS system which consists of an array of GPS receivers on the ground and an airborne pseudolite mounted on the test aircraft. The SARS will provide a proof position estimate that is used to check the navigation system under test. Unfortunately, ground based inverted GPS systems tend to suffer from high geometric sensitivity to measurement errors. This research tackles the problem of optimizing the …

Countering The Effects Of Measurement Noise During The Identification Of Dynamical Systems, Odell R. Reynolds

Theses and Dissertations

Sensor noise is an unavoidable fact of life when it comes to measurements on physical systems, as is the case in feedback control. Therefore, it must be properly addressed during dynamic system identification. In this work, a novel approach is developed toward the treatment of measurement noise in dynamical systems. This approach hinges on proper stochastic modeling, and it can be adapted easily to many different scenarios, where it yields consistently good parameter estimates. The Generalized Minimum Variance algorithm developed and used in this work is based on the theory behind the minimum variance identification process, and the estimate produced …

A Two-Phase Damped-Exponential Model For Speech Synthesis, H. Allan Arb

Theses and Dissertations

It is well known that there is room for improvement in the resultant quality of speech synthesizers in use today. This research focuses on the improvement of speech synthesis by analyzing various models for speech signals. An improvement in synthesis quality will benefit any system incorporating speech synthesis. Many synthesizers in use today use linear predictive coding (LPC) techniques and only use one set of vocal tract parameters per analysis frame or pitch period for pitch-synchronous synthesizers. This work is motivated by the two-phase analysis-synthesis model proposed by Krishnamurthy. In lieu of electroglottograph data for vocal tract model transition point …

Investigation Of Various Shaping Methods For The Development Of A Fully-Monolithic Cmos Constant-Fraction Discriminator, Robert Gentry Jackson

Masters Theses

In this work the design of a constant-fraction discriminator (CFD) fabricated in the Orbit Semiconductor l.2-Jl n-well CMOS process is presented. This timing pick-off circuit is designed for use in the readout electronics of the Lead-Scintillator subsystem of the Pioneering High Eenergy Nuclear Ion eXperiment (PHENIX) Electromagnetic Calorimeter at the Relativistic Heavy Ion Collider (RHIC). The design was driven by stringent requirements including low power consumption, small area, arrayable, low cost and a fully integratable shaping network. Various integratable CFD shaping methods are investigated, and the candidate methods chosen for fabrication were the distributed R-C delay-line shaping, lumped-element R-C shaping …

Detection For A Statistically-Known, Time-Varying Dispersive Channel, David W. Matolak, S. G. Wilson

Faculty Publications

Detection for the statistically known channel (SKC) is aimed at obtaining good performance in situations where our statistical knowledge of a time-varying channel is good, and where other equalization/detection schemes are either too complex to implement, or their performance is limited due to the rapidity of channel fading, or where we are simply unable to perform channel estimation. By using a statistical characterization of the channel, we develop a new detector that performs maximum-likelihood sequence estimation (MLSE) (given the channel model) on blocks of N symbols. Both symbol-spaced and fractionally spaced samples are used, to obtain two different detectors, that …

Interference Suppression For Spread Spectrum Signals Using Adaptive Beamforming And Adaptive Temporal Filter, Wonjin Park

Theses and Dissertations

Interference and jamming signals are a serious concern in an operational military communication environment. This thesis examines the utility and performance of combining adaptive temporal filtering with adaptive spatial filtering (i.e. adaptive beamforming) to improve the signal-to-jammer ratio (SJR) in the presence of narrowband and wideband interference. Adaptive temporal filters are used for narrowband interference suppression while adaptive beamforming is used to suppress wideband interference signals. A procedure is presented for the design and implementation of a linear constraints minimum variance generalized sidelobe canceler (LCMV-GSC) beamformer. The adaptive beamformer processes the desired signal with unity gain while simultaneously and adaptively …

Experimental Investigation Of Radar Cross Section Spatial Correlation Properties For A Point Scattering Target, John D. Shannon

Theses and Dissertations

This research investigates the spatial correlation of RCS. In pulsed radar systems, probability of detection for partially correlated signals depends on the autocovariance of the target's RCS. The RCS changes pulse to pulse due to spatial and time fluctuations. Spatial fluctuation are due to the motion of all scatterers relative to the radar (i.e. changing aspect angle). Time fluctuations are due to relative motion of scatterers to each other (i.e. wings flexing, engines spinning). Theory developed at AFIT [9] can generate autocovariance estimates from a distribution of scatterers. Theory based autocovariance estimates are compared to static measurement based autocovariance estimates …

Mmae Detection Of Interference/Jamming And Spoofing In A Dpgs-Aided Inertial System, Nathan A. White

Theses and Dissertations

Previous research at AFIT has resulted in the development of a DGPS-aided INS-based precision landing system (PLS) capable of meeting the FAA precision requirements for instrument landings. The susceptibility of DGPS transmissions to interference/jamming and spoofing must be addressed before DGPS may be used in such a safety-of-flight critical role. This thesis applies multiple model adaptive estimation (MMAE) techniques to the problem of detecting and identifying interference/jamming and spoofing failures in the DGPS signal. Such an MMAE is composed of a bank of parallel filters, each hypothesizing a different failure status, along with an evaluation of the current probability of …

Three-Dimensional Display Utilizing A Diffractive Optical Element And An Active Matrix Liquid Crystal Display, Gregory P. Nordin, M. W. Jones, S. T. Kowel, J. H. Kulick, R. G. Lindquist

Faculty Publications

We describe the design, construction, and performance of the first real-time autostereoscopic three-dimensional (3-D) display based on the partial pixel 3-D display architecture. The primary optical components of the 3-D display are an active-matrix liquid crystal display and a diffractive optical element (DOE). The display operates at video frame rates and is driven with a conventional VGA signal. Three-dimensional animations with horizontal motion parallax are readily viewable as sets of stereo images. Formation of the virtual viewing slits by diffraction from the partial pixel apertures is experimentally verified. The measured contrast and perceived brightness of the display are excellent, but …

Controlling Three-Axis Attitude Rates On A Pointing System Using Nonlinear Observer And Two Axis Measurements, Marcelo C. Algrain

Department of Electrical and Computer Engineering: Faculty Publications

A new observer design method that allows for estimating the angular rates along a vehicle’s three principal axes is described. The observer uses measurements from a single two-axis angular rate sensor (gyro) and determines the rates for the third axis using a nonlinear observer. Unlike conventional approaches where the equations governing vehicle motion (Euler’s equations) are linearized and then an observer is constructed based on the linear model, this method does not require linearization of the system. Instead, a pseudo-linear representation is used. The pseudo-linear model is obtained by systematically decomposing a nonlinear system into linear and nonlinear terms. The …

Comparison Of The Charge/Discharge Charasteristics Between Ni Cd And Ni Mh Battery And Its Improvement Of Manufacture Technique, Yumimg Wang

Journal of Electrochemistry

Based on the difference of charge discharge charasteristies between Ni Cd and Ni MH battery, some appropriate manufacture technoque to improve the battery performances or to extend its service life are adopted

The Current Distribution On The Anode Surface Of The Seale Oval Tubular Lead Acid Battery, Renao Gu, Jianlin Yao, Zhengfa Deng, Ru Sun

Journal of Electrochemistry

The current distribution on anode surface of sealed lead acid batter under different discharge current and degree was studied by chemical analytical method for the first time. We can conclude that the current distribution is not even. The current density on the edge of the electrode surface and the electrode terminal are bigger than other areas, that is, there are edge effect and terminal effect, and these effect are more obvious when the discharge current is 100 A and degree is 100%.

Surface Modifications Of Carbon Materials Used As Anode Of Lithium Ion Battery Ⅰ.Influences Of Oxidation And Reduction Pretreatment On Anode Performance, Shuhua Ma, Hanju Guo, Ji Li, Hongze Liang, Xiabin Jing, Fosong Wang

Journal of Electrochemistry

The influences of the trace oxygen containing functional groups on surface of carbon material on cell performance of carbon anode for lithium ion batteries were studied by means of the pretreament in various oxidant/reductant systems.The results showed that the rich oxygen containing functional groups impaired the cell performance of carbon material anode,and the reduction of these groups in quantity and oxidation degree can increase charge/discharge capacity and improve first charge/discharge efficiency.The reason was also discussed in the light of effects of surface organic groups on decomposition reactivity of electrolyte and formation process of surface passivating film.