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Articles 34831 - 34860 of 36789

Full-Text Articles in Engineering

Characterization Of An Air-To-Air Optical Heterodyne Communication System, Rebecca N. Seeger Dec 1990

Characterization Of An Air-To-Air Optical Heterodyne Communication System, Rebecca N. Seeger

Theses and Dissertations

The primary goal of this research was to determine the feasibility of air-to-air optical communications systems using coherent detection in a turbulent environment. Secondary goals were to determine (1) the signal-to-noise ratio (SNR) degradation due to turbulence and (2) the effect of varying the wavelength (1.5, 830, 904 nm), altitude (5000-12500 m), path length (40-160 km) and aperture side length (1-15 cm) on the turbulence affected SNR. The research was conducted under the following assumptions: (1) ideal transmitter and receiver, (2) equally sized, uniformly weighted, square transmitter and receiver apertures, (3) ideal tracking by the receiver, and (4) zero losses …

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Kalman Filter Tracking Of A Reflective Target Using Forward Looking Infrared Measurements And Laser Illumination, Roger J. Evans Dec 1990

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 …

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Rule-Based Frequency Domain Speech Coding, Vance M. Mcmillan Dec 1990

Rule-Based Frequency Domain Speech Coding, Vance M. Mcmillan

Theses and Dissertations

A speech processing system is designed to simulate the transmission of speech signals using a speech coding scheme. The transmitter portion of the simulation extracts a minimized set of frequencies in Fourier space which represents the essence of each of the speech timeslices. These parameters are then adaptively quantized and transmitted to a receiver portion of the coding scheme. The receiver then generates an estimate of the original timeslice from the transmitted parameters using a sinusoidal speech model. After initial design, the thesis investigates how each of the design parameters affect the human perceived quality of speech. This is done …

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Characterization Of Radar Signals Using Neural Networks, Daniel R. Zahirniak Dec 1990

Characterization Of Radar Signals Using Neural Networks, Daniel R. Zahirniak

Theses and Dissertations

Recent work concerning artificial neural networks has focused on decreasing network training times. Kernel Classifier networks, using radial basis functions (RBFs) as the kernel function, can be trained quickly with little performance degradation. Short training times are critical for systems which must adapt to changing environments. The function of Kernel Classifier networks is based on the principle that multivariate functions can be approximated via linear combinations of RBFs. RBFs can also perform probability density estimations, making classifications approximating a Baye's optimal descriminant. Methods used to set the RBF centers included matching the training data, Kohonen Training, K-Means Clustering and placement …

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Model-Based Reasoning In The Detection Of Satellite Anomalies, Ralph W. Dries Dec 1990

Model-Based Reasoning In The Detection Of Satellite Anomalies, Ralph W. Dries

Theses and Dissertations

Automatic fault detection and recovery would be a mandatory requirement for a satellite where some degree of autonomy is required. This thesis reviews some AI techniques used for the detection of satellite anomalies, and concludes that the model-based reasoning paradigm is best suited for automated on-board fault detection because it can cope with situations not necessarily programmed into the knowledge base. Using the Scheme language and its SCOOPS object oriented extension, development of software is described that models the pitch control channel in the attitude and velocity control subsystem of a typical geo-stationary communications satellite. This model is used by …

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Model-Based Reasoning In Electronic Repair, Kenneth B. Cohen Dec 1990

Model-Based Reasoning In Electronic Repair, Kenneth B. Cohen

Theses and Dissertations

Diagnosis is the process of identifying the cause for an observed behavior of a system. Model-based reasoning uses knowledge of the behavior of the component and the interconnection of the components to diagnose a system. This thesis investigates the application of model-based reasoning to the problem of isolating faulty components of an analog electronic circuit. More specifically, this thesis describes an architecture for a model-based diagnostic system for electronic modules, implements an assumption-based truth maintenance system (one of the component parts of a model-based diagnostic system), and creates the interface between the truth maintenance system and the diagnostic system.

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Implementation Of The Modified Monte Carlo Technique Using Importance Sampling On The Block Oriented System Simulator, John B. Bennett Dec 1990

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 …

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Network Reduction Using Error Prediction, Michael V. Gilsdorf Dec 1990

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 …

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Silicon Hybrid Wafer Scale Integration (Wsi) Used To Fabricate A Hilbert Transform Integrated Circuit Module, Daniel J. Gaughan Dec 1990

Silicon Hybrid Wafer Scale Integration (Wsi) Used To Fabricate A Hilbert Transform Integrated Circuit Module, Daniel J. Gaughan

Theses and Dissertations

This research was performed in order to develop a superior processing schedule for fabricating Wafer-Scale Integration (WSI) circuit modules. This technology allows the design of circuitry that spans the entire surface of a silicon substrate wafer. The circuit element employed in this research was the Hilbert transform, a digital phase-shifting circuit. The transform was incorporated into a three Integrated Circuit (IC) die package that consisted of a mechanically supportive silicon wafer, three IC die, and a planarizing silicon wafer. The die were epoxied into this wafer using a Teflon block as a flat, and the combination was epoxied onto the …

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A Study Of The Effects Of Noise Jamming On Radar Receivers, Paul E. Bishop Dec 1990

A Study Of The Effects Of Noise Jamming On Radar Receivers, Paul E. Bishop

Theses and Dissertations

A comprehensive study of the effects of noise jamming on various pulsed radar receiver types is proposed. First, a literature review on the sources of electrical noise and various jamming waveforms is presented. The power spectra for three noise jamming waveforms are rigorously derived. These cases are shot noise in a parallel-plate diode, a series of pulses with random amplitudes and intervals, and for a series of pulses with random amplitudes, spacing and phases. Next, the probability density functions for the output of linear and quadratic detectors are developed. For each detector type, the probability density functions for the cases …

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Comparison Of Digital Controllers Used In Magnetic Suspension And Balance Systems, William A. Kilgore Dec 1990

Comparison Of Digital Controllers Used In Magnetic Suspension And Balance Systems, William A. Kilgore

Mechanical & Aerospace Engineering Faculty Publications

Dynamic systems that were once controlled by analog circuits are now controlled by digital computers. Presented is a comparison of the digital controllers presently used with magnetic suspension and balance systems. The overall responses of the systems are compared using a computer simulation of the magnetic suspension and balance system and the digital controllers. The comparisons include responses to both simulated force and position inputs. A preferred digital controller is determined from the simulated responses.

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Microwave Nondestructive Detection And Evaluation Of Disbonding And Delamination In Layered-Dielectric Slabs, R. Zoughi, Sasan Bakhtiari Dec 1990

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 …

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The Waveform Relaxation Method For Systems Of Differential/Algebraic Equations, Marija D. Ilić, Mariesa Crow Dec 1990

The Waveform Relaxation Method For Systems Of Differential/Algebraic Equations, Marija D. Ilić, Mariesa Crow

Electrical and Computer Engineering Faculty Research & Creative Works

An extension of the waveform relaxation (WR) algorithm to systems of differential/algebraic equations (DAE) is presented. Although this type of application has been explored earlier in relation to VLSI circuits, the algorithm has not been generalized to include the vast array of DAE system structures. The solvability and convergence requirements of the WR algorithm for higher-index systems are established. Many systems in robotics and control applications are modeled with DAE systems having an index greater than two. Computer simulation of these systems has been hampered by numerical integration methods which perform poorly and must be explicitly tailored to the system. …

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Characterization Of Multilayer Perceptrons And Their Application To Multisensor Automatic Target Detection, Dennis W. Ruck Dec 1990

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 …

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Brightness Invariant Port Recognition For Robotic Aircraft Refueling, Richard A. Bennett Dec 1990

Brightness Invariant Port Recognition For Robotic Aircraft Refueling, Richard A. Bennett

Theses and Dissertations

The purpose of this thesis effort was to develop and test a brightness invariant recognition algorithm that would locate and identify the half-scale mock up of a Universal Aerial Refueling Receptacle Slipway Installation (UARRSI) aerial refueling port in different lightening conditions. This was accomplished by developing a brightness invariant port recognition of identifiable attributes of the refueling port to locate and identify the UARRSI port. Based on this approach, a brightness invariant port recognition system (BIPRS) was demonstrated which identified the refueling receptacle in different lightening conditions. The BIPRS was also invariant to orientation and size of the UARRSI port. …

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Interference Cancellation In Rf Signals Using Adaptive Array Techniques, Mark E. Brown Dec 1990

Interference Cancellation In Rf Signals Using Adaptive Array Techniques, Mark E. Brown

Theses and Dissertations

This study investigated the effectiveness of the Least Means Squared (LMS) algorithm against various types of common jammers. The LMS algorithm was implemented using the Block Oriented Systems Simulator (BOSS). The LMS algorithm was inserted at the output of a two element antenna array. The array was configured so as to have one-half wavelength spacing. A quadrature hybrid signal structure was used. The array was then tested against a barrage and sweep jammer. The barrage jammer testing consisted of varying each of the three available jammer parameters; power, frequency and angle of arrival individually. The sweep jammer testing consisted of …

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Evaluation Of An Interdigitated Gate Electrode Field-Effect Transistor For Detecting Organophosphorus Compounds, Charles P. Brothers Jr. Dec 1990

Evaluation Of An Interdigitated Gate Electrode Field-Effect Transistor For Detecting Organophosphorus Compounds, Charles P. Brothers Jr.

Theses and Dissertations

This study used integrated circuit microsensors to detect organophosphorus compounds. Chemically-sensitive thin films, copper phthalocyanine, DFPase, succinyl chloride, succinylcholine chloride, 2- naphthol(B), and L-histidine dihydrochloride,were deposited on interdigitated gate electrode (IGE) structures, with an average thickness of 2000A. Thin film electrical performance characteristics were measured for several parameters, including: DC resistance, AC impedance, time-domain, and spectral responses from 10 Hz to 1 MHz. Each microsensor contained nine IGEs; each IGE possessed an in situ field-effect transistor amplifier. After purging each sensor with filtered air, it was exposed to one or two of the following gases: diisopropyl fluorophosphate (DFP), diisopropyl methylphosphonate, …

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Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas Dec 1990

Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas

Theses and Dissertations

The optical sensors of United States Air Force reconnaissance vehicles, such as satellites, are subject to temporary or permanent blinding from hostile (or threat) laser radiation. By detecting and determining the angle of arrival (AOA) of the hostile radiation, the reconnaissance vehicle may be able to protect its optical sensors by taking evasive maneuvers or by shutting down the optical sensor (such as closing a shutter) until the threat has passed. In addition, the vehicle can relay information to its ground terminal allowing the intelligence community to determine the source of the hostile laser radiation. This thesis demonstrated that an …

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Predicting The Performance Of Airborne Antennas In The Microwave Regime, David P. Carroll Dec 1990

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 …

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Classification Of Correlation Signatures Of Spread Spectrum Signals Using Neural Networks, Richard A. Chapman Dec 1990

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 …

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Feasibility Analysis Of Developing A Formal Performance Model Of Ada Tasking, Kathryn J. Edwards Dec 1990

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 …

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Numerical Approximations Of The Green's Functions For A Theoretical Model Of An Aperture Fed Stacked-Patch Microstrip Antenna, Ronald E. Erwert Dec 1990

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 …

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Fractal Geometry Segmentation Of High Resolution Polarimetric Synthetic Aperture Radar Data, Joseph L. Brickey Dec 1990

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 …

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Electromagnetic Scattering From Impedance Strips And Impedance-Loaded Conducting Strips, Mark C. Heaton Dec 1990

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 …

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A Method Of Moments Solution For The Electric Currents On An Aperture-Fed, Stacked Patch Microstrip Antenna, William L. Irvin Dec 1990

A Method Of Moments Solution For The Electric Currents On An Aperture-Fed, Stacked Patch Microstrip Antenna, William L. Irvin

Theses and Dissertations

This study presents a method of moments solution for the surface currents and charge distributions on an aperture-fed, stacked patch antenna. To make the solution independent of the antenna excitation technique, an aperture magnetic current distribution is assumed, and the spatial Green's functions of the antenna are used to calculate the tangential fields on the antenna patches and coefficients for a finite series expression of the surface currents and charge densities. The Green's functions of the antenna are modeled with polynomials that are a function of the radial distance separating observer and source locations. The method of moments solution is …

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Design And Fabrication Of An Implantable Cortical Semiconductor Integrated Circuit Electrode Array, Pierre K. Lefevre Dec 1990

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, …

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Gabor Filters And Neural Networks For Segmentation Of Synthetic Aperture Radar Imagery, Albert P. L'Homme Dec 1990

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 …

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A Robotic Tactile Sensor Incorporating Silicon Planar Technology: A Piezoelectric Polyvinylidene Fluoride Film, And On-Chip Signal Processing, Robert C. Fitch Jr. Dec 1990

A Robotic Tactile Sensor Incorporating Silicon Planar Technology: A Piezoelectric Polyvinylidene Fluoride Film, And On-Chip Signal Processing, Robert C. Fitch Jr.

Theses and Dissertations

This research effort pursued the design, fabrication, and test of a robotic tactile sensor. The VLSI integrated circuit (IC) portion of the sensor included a 7 x 7 array of metal electrodes which were individually connected to identical MOSFET amplifiers. A 25 micrometers thick patch (6 mm x 6 mm) of piezoelectric polyvinylidene fluoride (PVDF) film was attached to the array with a non-conductive adhesive, thereby creating an array of taxels. Charge, generated by the PVDF film, was detected by the amplifiers. The outputs of these amplifiers were connected to onchip signal circuitry designed to produce a single stream of …

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Analysis And Testing Of A Bistatic Radar Cross Section Measurement Capability For The Afit Anechoic Chamber, Timothy D. Mccool Dec 1990

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 …

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Analysis Of Visual Illusions Using Gabor Filters, Richard A. Oberndorf Dec 1990

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, …

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