Digital Commons Network^™

Slotted Aloha Protocol For Packet Transmission Via Satellite Link : Throughput Performance Of Continuous Transmission Packet, Solon Karashialis

Theses

The throughput performance of multi-access schemes for data traffic through a satellite channel is analyzed in this paper. Three general schemes are described: channel reservation schemes, random access schemes, and padket reservation schemes. This thesis considers only the random access schemes. Analysis and comparison between ALOHA and Slotted ALOHA are made, but the main emphasis is on satellite channel throughput. A continuous transmission protocol for Slotted ALOHA is suggested in which each ground earth station repeats the transmission of each packet in a number of random repetition slots. The channel is idle when no ground station (GS) is transmitting on …

An Integrated Circuit X-Ray Sensing Array Based On A Cmos Flip-Flop Cell, Huan-Chung Lee

Theses

A novel X-ray sensor IC has beeli designed which counts individual photons at rates up to 5,000,000 counts per second. A two-dimensional X-ray flip-flop sensor array, consisting of an 30 x 30 matrix of CMOS flip-flop sensors integrated in one chip together with an internal clock generator and access selection circuitry is described. A flip-flop sensing cell contains cross-coupled CMOS devices, one of which is connected to a large-area reverse-biased diode. A large area diode exposed to X-ray flux triggers the flip-flop. By reading out the final stable state of the flip-flop, the absence or presence of an X-ray photon …

Holographic Photo-Induced Electrochemical Etching Of Diffraction Grating In N-Inp, Pei-Chen Pien

Theses

Maskless laser-induced etching and plating is a novel technology for etching a three dimensional profile on semiconductor wafers. Using this technique, we may avoid the contaminating mask stage and achieve in-situ monitoring of the on-going process. In this thesis, we have presented findings on light diffraction from an etched pattern in a thin-film cell configuration. We suggest that the etched pattern develops mostly linearly in time with this arrangement, although indirect monitoring of the reaction process such as by light diffraction, should be carefully interpreted. In-situ light diffraction monitoring appear as if light was scattered from an etched pattern developed …

Electromagnetic Transients Program Interfacing, Enhancement And Comparison With Spice, Siswa Trihadi

Theses

The Electromagnetic Transients Program (EMTP) is a computer program used to simulate high speed power system transients. The EMTP input data structures and the rules in setting up the input data file are described in this thesis by means of two sample cases i.e an RLC series circuit and a sin le line to ground fault in power system.

The EMTP input data are very detailed an highly-structured column-dependent. To improve the user-friendliness of EMTP by ignoring the difficulty of arranging the column structures, this thesis presents the EM P User Interactive Program. Sample cases using this interactive program are …

Electrical Measurements Of Mos Structures Fabricated On Etched Silicon Surfaces, Venkata Ramana Vankayalapati

Theses

This thesis details the electrical characterization of thermally grown thin SiO₂ films on virgin and plasma etched silicon surfaces. The electrical characterization techniques employed for the present study are high frequency Capacitance Voltage(C-V) and Current-Voltage(I-V) measurements. The structures used in this study are Al/Polysilicon/SiO₂/Si/A1 capacitors fabricated on n-Si and p-Si substrates. These capacitors with areas in the range of 0.001-0.05 cm₂, were made using various plasma process conditions and etch reactors.

Based on the experimental results of the C-V anlaysis, in comparison of the controls samples with the plasma treated samples, we could not see …

Electron Field Emission Through A Very Thin Oxide Layer, Guang Yang

Theses

Field Emission of an emitter covered with a very thin oxide layer is modeled and calculated numerically. The additional barrier due to the oxide layer is included in the tunnelling problem by using the standard WKB method and tunnelling transmission matrix method. The following physical parameters are considered: the oxide barrier height, the oxide conduction band edge electron effective mass, and the oxide dielectric constant. Compared with the Fowler-Nordheim equation, which was derived for a clean metallic emitter, the calculation of this work shows a reduction of the emission current density from an emitter covered with an oxide layer a …

Simulation Study Of Monolithic 8-12 Micron Gaas/Algaas Multiple Quantum Well Infrared Image Sensor, Ye Zhu

Theses

The design of a monolithic 8-12 micron GaAs/AlGaAs multiple quantum well infrared image sensor has been tested by computer simulation using PISCES-IIB and SPICE3B.1 software packages. The device structure is in the form of a monolithic GaAs/AlGaAs multiple quantum well (MQW) photoconductor integrated with a GaAs MESFET readout circuit. The readout MESFET's are located in the top layer of the MQW so that a relatively standard GaAs MESFET design and processing technology can be used. The theoretical feasibility of such a vertically integrated structure and the processing compatibility of GaAs/AlGaAs MQW and GaAs MESFET's were investigated in this work.

Our …

A Petri Net Simulation Tool, Ashish H. Shukla

Theses

A user friendly and highly interactive graphical tool for drawing, editing and simulating translated Petri Net models is developed. This SunView based tool allows simulation to be carried out in the 'step' and 'run' modes. In the 'run' mode it produces a log file of the simulation run which consists of: a) total number of tokens in the net; b) names of the transitions that fired; and c) the system state reached after each step's execution. The tool offers a new solution to the problem of modeling concurrent and interlocked systems, such as computer systems, modular software, flexible manufacturing systems …

Characterization Of Multilayer Perceptrons And Their Application To Multisensor Automatic Target Detection, Dennis W. Ruck

Theses and Dissertations

The multilayer perceptron was extensively analyzed. A technique for analyzing the multilayer perceptron, the saliency measure, was developed which provides a measure of the importance of inputs. The method was compared to the conventional statistical technique of best features and shown to provide similar rankings of the input. Using the saliency measure, it is shown that the multilayer perceptron effectively ignores useless inputs and that whether it is trained using backpropagation or extended Kalman filtering, the weighting of the inputs is the same. The backpropagation training algorithm is shown to be a degenerate version of the extended Kalman filter. The …

Digital Signal Processing Schemes For Fiber Optic Rotation Rate Sensor Scale Factor Linearization, David T. Dembinski

Masters Theses

This study examined and evaluated several scale factor linearization techniques for a fiber optic rotation rate sensor (FORS). The process of scale factor linearization retrieves rotation rate from an FORS signal. Open and closed loop digital signal processing schemes are evaluated on dynamic range, accuracy, and cost.

The results of these experiments show that open loop schemes require few components but have an inherently low dynamic range of operation. Extending the dynamic range of an open loop system is expensive in additional components. Closed loop systems require more initial components, but have a considerably superior dynamic range. It was concluded …

Feasibility Analysis Of Developing A Formal Performance Model Of Ada Tasking, Kathryn J. Edwards

Theses and Dissertations

As software system requirements become more complex, software engineers must carefully design the systems to ensure the systems to ensure the systems adequately meet all requirements, both functional and non-functional. Because real-time systems have timing constraints, in addition to the more traditional behavioral constraints, a comprehensive software design analysis model is required which incorporate performance, timing, and behavioral constraints. Although the Ada language tasking constructs are compiler independent, Ada tasking is dependent on its runtime environment; therefore, a formal model of Ada tasking and its associated runtime environment is important in order for system designers to make realistic decisions when …

Digital Control Of The Utah/Mit Dexterous Hand: Initial Evaluation And Analysis, Lloyd W. Rainey Iii

Theses and Dissertations

An experimental digital platform is developed as an environment on which to evaluate digital control strategies for dexterous manipulation with a pneumatically actuated tendon-driven manipulator. This environment is used to begin the study of advanced control methods that are suitable for providing the tracking accuracy required for grasping and dexterous manipulation with a pneumatically actuated tendon-driven end-effector. The digital platform consists of a PC/AT-386 and a single board MC68020 microcomputer in a VME chassis with shared RAM between the two processors to control the Utah/MIT Dexterous Hand (UMDH). The MC68020 controls the A/D and D/A access for the UMDH, while …

Oscillation Frequency In High-Gain Lasers, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

The calculation of the oscillation frequency of a single-mode laser oscillator is examined systematically. Mode-pulling formulas are developed for a variety of laser systems, and the limitations of a standard approximation are explored.

Implementation Of The Modified Monte Carlo Technique Using Importance Sampling On The Block Oriented System Simulator, John B. Bennett

Theses and Dissertations

The purpose of this thesis was to implement the Modified Monte Carlo technique using Importance Sampling on the Block Oriented System Simulator (BOSS). Computer simulation techniques of communications systems were reviewed. Next, conventional Monte Carlo techniques and Modified Monte Carlo techniques using Importance Sampling were reviewed. Models of Binary Phase Shift Keying (BPSK) systems using both Monte Carlo techniques were implemented and simulated. Reasons for the model using Importance Sampling not working correctly are postulated. The Monte Carlo technique is a method of ensuring the an inherently infinite procedure, such as determining system bit error rate (BER), can be determined …

Microwave Nondestructive Detection And Evaluation Of Disbonding And Delamination In Layered-Dielectric Slabs, R. Zoughi, Sasan Bakhtiari

Electrical and Computer Engineering Faculty Research & Creative Works

A microwave nondestructive technique for detection and evaluation of disbonding and delamination in layered-dielectric-slabs backed by a conducting plate is discussed. The theoretical development begins by considering an incident wave illuminating such a medium and then formulating the characteristics of the wave reflected by the metal plate. An effective reflection coefficient is determined in this way whose phase characteristics are used in the detection and evaluation of delaminations in the media. The characteristics of this phase as a function of several parameters such as delamination dielectric constant and thickness, slab dielectric constant, and thickness and the frequency of operation are …

Estimation Of Evoked Fields Using A Time-Sequenced Adaptive Filter With The Modified P-Vector Algorithm, Jeffery A. Kepley

Theses and Dissertations

This thesis describes a time sequenced adaptive filter developed to estimate visually evoked fields (EF) using visually evoked potentials (EP). These non-stationary signals are buried in strong background noise. The two types of noise are magnetoencephalogram (MEG) and electronencephalogram (EEG). The filter implementation is based on the Ferrara Time Sequenced Adaptive (TSAF) using the Least-Mean-Square (LMS) algorithm and the Williams modified P-vector algorithm (mPa). This essentially results in two filters. A two stage filter structure is used in which the first stage removes the time-varying mean of the input signals. This allows the second stage to process zero-mean signals which …

Fractal Geometry Segmentation Of High Resolution Polarimetric Synthetic Aperture Radar Data, Joseph L. Brickey

Theses and Dissertations

This thesis investigated the potential of fractal dimension estimation for segmenting high resolution polarimetric synthetic aperture radar. The data used during this research were collected with the Advanced Detection Technology Sensor (ADTS) developed by Massachusetts Institute of Technology Lincoln Laboratory with Defense Advanced Research Projects Agency funding. ADTS is a fully polarimetric calibrated 35 GHz SAR with one foot impulse response. A method of applying the correlation dimension algorithm developed by Grassberger and Procaccia for estimating the dimension of time series data was implemented to estimate the correlation dimension of polarimetric SAR data. A threshold sensitivity study was performed to …

Predicting The Performance Of Airborne Antennas In The Microwave Regime, David P. Carroll

Theses and Dissertations

This study investigated the application of a high-frequency model (Uniform Geometrical Theory of Diffraction) of electromagnetic sources mounted on a curved surface of a complex structure. In particular, the purpose of the study was to determine if the model could be used to predict the radiation patterns of cavity-backed spiral antennas mounted on aircraft fuselages so that the optimum locations for the antennas could be chosen during the aircraft design phase. A review of literature revealed a good deal of work in modeling communications, navigation, identification antennas (blade monopoles and aperture slots) mounted on a wide variety of aircraft fuselages …

Classification Of Correlation Signatures Of Spread Spectrum Signals Using Neural Networks, Richard A. Chapman

Theses and Dissertations

The major goals of this thesis were to determine if Artificial Neural Networks (ANNs) could be trained to classify the correlation signatures of two classes of spread spectrum signals and four classes of spread spectrum signals. Also, the possibility of training an ANN to classify features of the signatures other than signal class was investigated. Radial Basis Function Networks and Back-Propagation Networks were used for the classification problems. Correlation signatures of four types or classes were obtained from United States Army Harry Diamond Laboratories. The four types are as follows: direct sequence (DS), linearly-stepped frequency hopped (LSFH), randomly-driven frequency hopped …

Numerical Approximations Of The Green's Functions For A Theoretical Model Of An Aperture Fed Stacked-Patch Microstrip Antenna, Ronald E. Erwert

Theses and Dissertations

The numerical approximations of the Green's functions for a theoretical model of an aperture fed stacked patch microstrip antenna are presented. The Green's functions approximated are those developed by Nazar (AFIT Thesis GE-89D-37), Green's Functions for a Theoretical Model of an Aperture Fed Stacked-Patch Microstrip Antenna. Each complex valued Green's function was written as a function of the source-observer separation. The behavior of each Green's function was analyzed, and it was found that they could all be approximated by three separate functions. The approximating functions were either polynomials or rational functions composed of polynomials. One component could be approximated by …

Kalman Filter Tracking Of A Reflective Target Using Forward Looking Infrared Measurements And Laser Illumination, Roger J. Evans

Theses and Dissertations

This thesis investigates Kalman filter tracking of a missile hardbody, at a range of 2,000 kilometers, using forward looking infrared (FLIR) measurements and low-energy laser illumination of the missile hardbody. A missile reflectivity model provides realism in the simulation. The tracking scenario uses one filter, provided with FLIR measurements, to estimate the intensity centroid location of the missile's plume. A second, independent, filter estimates the center-of-mass of the missile hardbody. The center-of-mass measurements provided to this filter are computed from information gathered by scanning a low-energy laser along the first filter's estimate of the missile velocity vector. Single scans of …

Network Reduction Using Error Prediction, Michael V. Gilsdorf

Theses and Dissertations

This thesis investigates gradient descent learning algorithms for multi-layer feed forward neural networks. A technique is developed which uses error prediction to reduce the number of weights/nodes in a network. The research begins by studying the first and second order back-prop training algorithms along with their convergence properties. A network is reduced by making an estimate of the amount of error which would occur when a weight(s) is removed. This error estimate is then used to determine if a particular weight is essential to the operation of the network. If not, it is removed and the network retrained. The process …

Electromagnetic Scattering From Impedance Strips And Impedance-Loaded Conducting Strips, Mark C. Heaton

Theses and Dissertations

This paper investigates the scattering from impedance strips and impedance-loaded conducting strips. The UTd diffraction coefficient for an edge in a conductor is heuristically modified for impedance edges and junctions. Essentially, this is done by scaling the UTD diffraction coefficients according to changes in the geometrical optics field. The new diffraction coefficients are then used to investigate the scattering from impedance strips and impedance- loaded conducting strips. Both uniform and tapered impedances are considered. Results are compared to moment method and physical optics predictions and to measured data. The scattering pattern of a uniform impedance strip was seen to behave …

Gabor Filters And Neural Networks For Segmentation Of Synthetic Aperture Radar Imagery, Albert P. L'Homme

Theses and Dissertations

This research investigates Gabor filters and artificial networks for autonomous segmentation of 1 foot by 1 foot) high resolution polarimetric synthetic aperture radar (SAR). Processing involved frequency correlation between the SAR imagery and biologically motivated Gabor functions. Methods for selecting the Gabor tuning parameters from the endless choices of frequency, rotation, standard deviation and bandwidth are discussed. Using these parameters, resulting Gabor correlation images were reduced in speckle, and more detailed. This research used cosine Gabor functions and operated on single polarization HH magnitude data. Following selection of the appropriate Gabor features, multiple Gabor representations were generated and converted for …

Design And Fabrication Of An Implantable Cortical Semiconductor Integrated Circuit Electrode Array, Pierre K. Lefevre

Theses and Dissertations

This research furthered the processing steps of the AFIT 16 by 16 implantable cortical semiconductor integrated circuit electrode array, or brain chip. The areas of interest include the brain chip electron ics, metallization, ionic permeation, and implantation. The electronics and metallization are heavily covered. A high speed, single clock divide-by-two circuit was modified with a reset transistor and cascaded to form a ripple counter. This device had stable operation at specific source voltage and clock voltage and frequency. A 7-stage inverter with 10 unmodified divide-by-two circuits cascaded operated between 1.7 and 8 volts, and between 39 Khz and 1 Mhz, …

Analysis And Testing Of A Bistatic Radar Cross Section Measurement Capability For The Afit Anechoic Chamber, Timothy D. Mccool

Theses and Dissertations

This research effort examined the feasibility of performing bistatic radar cross section (RCS) measurements in the AFIT anechoic chamber. The capability was established to measure the bistatic RCS of a target versus frequency and versus target azimuth angle. In either case, one of three bistatic angles (angle between transmit and receive antennas) is available: 45 degrees, 90 degrees, and 135 degrees. Accurate bistatic RCS measurements were obtained using a CW radar and utilizing background subtraction, bistatic calibration, and software range gating. Simple targets were selected for validation purposes since their bistatic RCS could be predicted. These consisted of spheres and …

Moving-Bank Multiple Model Adaptive Estimation And Control Applied To A Large Flexible Space Structure, Robert B. Moyle

Theses and Dissertations

The performance of moving-bank multiple model adaptive estimation (MMAE) and control (MMAC) algorithms for large space structure control is analyzed in this thesis. The performance of a six-state filter model and associated controller are evaluated on the basis of estimation/control performance against a 24-estate truth model. A model developed using finite element analysis is used to approximate a large flexible space structure. The space structure is configured as a two-bay truss which is attached to a large central hub, where the mass of the hub is considered to be much more larger than the mass of the flexible structure. The …

Analysis Of Visual Illusions Using Gabor Filters, Richard A. Oberndorf

Theses and Dissertations

This thesis has demonstrated the correctness of using spatial filters in the analysis of various visual illusions; the specific form of filter has been derived from a Gabor equation model of simple cell response on the visual cortex. The Gabor Low Pass Filter (GLPF) applied to these anomalies was derived from proposals made that simple cell response on the visual cortex may be modeled by a set of equations originally proposed by Gabor in the 1940's. Based upon the extension of these equations into two dimensions, a GLPF process was applied to computer-generated black and white illusions (the Kanizsa Triangle, …

Pulsed Compression For Aerosol Ranging With Coherent Pulse-Doppler Lidar Systems, Jerry L. Rogers

Theses and Dissertations

This thesis provides a thorough review of conventional matched filter radar theory as it applies to aerosol sensing lidar. Basic matched-filter radar theory and the complex, dense aerosol target model eventually lead to a general derivation of the matched-filter radar receiver response to a dense aerosol target environment. The matched-filter response is obtained in terms of a two dimensional convolution of the target scattering function and the radar ambiguity function. The range and radial velocity resolution of various radar signals were compared using the matched-filter radar receiver and scattering function models. Pulse compression radar signals were compared to the simple …

Radar Image Processing For The Afit Anechoic Chamber, Brian K. Sanders

Theses and Dissertations

The purpose of this study was to begin development of an Inverse Synthetic Aperture Radar imaging capability for the AFIT anechoic chamber. This began with an evaluation of the capabilities and limitations of the existing radar system and the chamber itself for this application. Then, after deciding on the image processing approach, software had to be written to collect the data necessary for image processing. This constituted the majority of this study, and resulted in a versatile, user-friendly program that automates the process of collecting data for high-resolution radar images. The program checks that the data to be collected will …