Digital Commons Network^™

Establishment Of A Fabrication And Measurement Capability For Aperture-Fed Stacked Patch Microstrip Antennas At The Air Force Institute Of Technology, Christopher I. Terry

Theses and Dissertations

Much time and effort has been applied to accurately model aperture- fed stacked patch microstrip antennas at the Air Force Institute of Technology (AFIT). The results of this study provide AFIT with the capability to fabricate and measure these antennas for comparison of measured radiation characteristics to the predicted characteristics. Basic microstrip patch antenna theory is reviewed, as well as the motivation leading to the development of aperture-fed stacked patch microstrip antennas. The fabrication process used to produce the two antennas manufactured for this study is described in detail. The construction of a small anechoic chamber for pattern measurements is …

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 …

Te Scattering From A Dielectric Coated Conducting Strip, William D. Wood Jr.

Theses and Dissertations

Consider a plane wave incident on a conducting strip of infinite length coated on one side with a thin, uniform coating of lossless dielectric, and let the incident magnetic field vector be parallel to the edges of the strip. From first principles we develop the integral equations relating the total, incident, and scattered fields in the dielectric. We expand the fields in the dielectric slab as the sum of three plane waves (the 'forced' wave and two oppositely-directed surface waves). The phase constants in the x and y directions are known and the wave amplitudes are found using least-squared- error-point-matching. …

An Evaluation Of An Ada Implementation Of The Rete Algorithm For Embedded Flight Processors, F. Jesse Fanning

Theses and Dissertations

The purpose of this thesis was to design and develop an expert system shell in Ada, and to evaluate the shell's execution and size performance to determine its suitability for real-time operation on the MIL-STD-1750A embedded flight processor. The expert system shell uses the CLIPS/Ada inference engine, a forward-chaining Ada implementation of Rete. The expert system shell design is presented along with an overview of the target environment--the MIL-STD-1750A VHSIC Avionic Modular Processor (VAMP) running under the Ada Avionics Real-Time Software (AARTS) Operating System. Theoretical and empirical complexity analyses of the inference engine are presented and discussed in view of …

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 …

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 …

A 512 X 512 Random Addressable Variable Resolution Image Sensor, Chakravarthy Yarlagadda

Theses

This thesis presents the design and layout of a 512 x 512-element with 20μm x 20μm pixels image sensor that emulates the properties of the human eye and is useful in high speed processing of visual data for machine vision applications. The imager will be able to operate with random-address selection in variable resolution or with multiple regions of interest to reduce the number of pixels readout. The selection of the pixels is done by x-y addressing the MOS switches which connect the photodiode pixel to the output through the sense lines. The design of column decoder and row decoder …

Photo-Induced Electrochemical Etching Of Inp Semiconductor In A Thin Film Cell, Bungsu Iskandar

Theses

The Photo-Induced Electrochemical Etching of n-InP wafer in aqueous solution is investigated for both reservoir and capillary systems. A sinusoidal spatial variation of light intensity pattern is directly illuminated and promoting etching on an InP semiconductor wafer. The etching process is time-efficient, and produces highly isotropical and a promising high resolution pattern. It gives a good reproducibility and has less contaminating features. Its features may be explained by a non-linear relationship between the electrolyte concentration and the photo-generated holes density at the interaction surface. An optimal reaction rate is determined by the ratio of the reactivity to ionic diffusion, either …

Integrated Control Of Thermally Distorted Large Space Antennas, Robert H. Tolson

Mechanical & Aerospace Engineering Theses & Dissertations

Studies on controlling the thermal distortion of large space antennae have generally investigated a single orbital position and have optimized actuator locations based on minimizing the RMS surface deviation from the original parabolic shape. One study showed the benefits of directly using far zone electric field characteristics as the performance measure; but, this approach resulted in a nonlinear programming problem. The objective of the current study is to develop an approach to designing a control system that (1) recognizes the time dependence of the distortion and (2) controls variables that are directly related to far field performance in a quadratic …

The Modeling Of The Interactions Of Pellets With Magnetic Fusion Plasmas For Alpha Particle Diagnostics, Abdel-Ghafar Mahmood El-Cashlan

Electrical & Computer Engineering Theses & Dissertations

A model for the interactions of hydrogen and carbon pellets with thermonuclear fusion plasmas has been developed and solved to determine the charge-state spatial distributions in the ablation cloud surrounding the pellet. The ionization is treated in a self-consistent manner in the energy balance and the collisional radiative (CR) model is used to calculate the ionization levels. External plasma electron effects on ionization are included. The electron heat flux is modeled as a multigroup distribution. The channelling of the flow along the field line is treated phenomenologically by restricting the cross-sectional area of the flow. The predictions of the model …

Deep Level Characterization Studies In Gaas, Gordhan R. Barevadia

Electrical & Computer Engineering Theses & Dissertations

The goal of this research was to investigate deep levels in different types of GaAs, a material for high power optically controlled bulk semiconductor switches. For low resistivity semiconductors, such as silicon doped GaAs material (p =0.054 Ω cm), deep level transient spectroscopy (DLTS) was used to characterize deep levels. Three deep levels (EL6, EL3, and EL2) have been detected in this material. For high resistivity semiconductors (p > 10⁴ Ω cm), difficulty of electrical carrier injection and of making a junction does not permit the use of DLTS technique. Therefore, an experimental set-up of the photo-induced current transient spectroscopy …

Measurement Of Thermal Noise In Condenser Microphones In A Vacuum-Isolation Vessel, Kim Chi Thi Ngo

Electrical & Computer Engineering Theses & Dissertations

The electrical noise generated by thermal agitation of the air molecules impinging upon the membrane of a condenser microphone and from its associated preamplifier has been studied analytically and experimentally over a wide bandwidth. These background noise levels constitute one of the most important specifications of a microphone for they determine the lowest sound pressure that can be detected. Therefore, a new method for measuring the thermal agitation noise within a bandwidth of 1-25600 Hz has been developed. The theoretical and experimental measurements of thermal agitation noise in a condenser microphone by enclosing the microphone in a vessel which is …

Optimization Of Bandwidth Allocation In Atm Nets Through Simulated Annealing, Chien-Long Hou

Theses

Optimization of Bandwidth Allocation in ATM network is considered in this thesis. We address the problem of determining optimal bandwidth allocation in such BISDN's that adopt ATM as their basic switching. technique by using Simulated Annealing. Computer simulation shows that this optimal policy leads to the configuration which yields the minimum average packet delay.

Design Of A Cmos Temperature Sensor With Eeprom Error Correction Scheme, Jin-Ku Kang

Theses

This thesis describes the design and operation of a CMOS temperature sensor operating at very low power with an EEPROM error correction scheme including the physical layout. This device is designed for applications requiring very low power including biomedical and optically powered device applications. The sensor output is an analog voltage. The temperature sensing cell is implemented with two BJTs having different emitter areas. An op amp dissipating about 300 micro-watts power is designed and is used to amplify the sensor output voltage with a gain of 85dB. A novel EEPROM is used to correct nonlinearity error of the temperature …

A Transputer Based Distributed Graphics Display, Ramana V. Kattula

Theses

The design of a transputer based graphics display is discussed. The problems associated with the single processor graphics systems are described. A solution based on multiple transputers is proposed. The transputer based graphics display described is a general purpose graphics system which can achieve any required compute performance and drawing performance without using special hardware. The display resolution and color depth can be enhanced as per the user requirements with little or no change in hardware.

Landmark-Based Shape Recognition By A Modified Hopfield Neural Network, Kuowei Li

Theses

In this thesis, we introduce a new thethod to achieve partial shape recognition by means of a modified Hopfield neural network. To recognize partially visible object, we represent each object by a set of "landmarks." The landmarks of an object are points of interest relative to the object that have important shape attributes. Given a scene consisting of partially occluded objects, a model object in the scene is hypothesized by matching the landmarks of the model with those in the scene. A measure of similarity between two landmarks, one from a model and the other from the scene, is needed …

Landmark-Based Partial Shape Recognition By A Two-Stage Bam Neural Network, Xianjun Liu

Theses

In this thesis, we develop a Bitfirectional Associative Memory (BAM) based neural network to achieve partial shape recognition. To recognize objects which are partially occluded, we represent each object by a set of landmarks. The landmarks of an object are points of interest relative to the object that have important shape attributes. To achieve recognition, feature values (landmark values) of each model object are trained and stored in the network. Each memory cell is trained to store landmark values of a model object for all possible positions. Given a scene which may consist of several objects, landmarks in the scene …

Simulation And Analysis Of Priority Classes In Extended Token Based Local Area Networks, Bhavinkumar R. Pathak

Theses

Recently, Local Area Networks carrying multiple priority classes of messages have received considerable attention. The IEEE 802.5 token ring standard defines an optional priority scheme to handle different priority classes of messages. A simulation model of symmetric priority based networks, consisting of token ring networks interconnected by a bridge is considered. Messages are divided into two priority classes, namely, high priority traffic and low priority traffic. High priority traffic is guaranteed access on the channel, whereas low priority messages are served when the system determines that no high priority messages are currently waiting. The simulation results are used to evaluate …

A Self Testing Strategy For The Wafer Scale Hierarchical Memory Architecture, Maremanda V. R. Rao

Theses

Since the early 1960's, semiconductor chips have matured from single transistor devices to one million transistors per chip. The integration has been achieved by reducing transistor dimensions, and by increasing chip sizes. However, physical limits are being reached as submicrometre dimensions are approached. Fault tolerance has to be used to maintain the increase in the chip complexity. Yield improvement is only one of the many possible gains of fault tolerance. The dense integration of logic on a single chip also creates a huge test problem. in recent years a great deal of effort has gone into the development of yield …

A Novel Schottky Barrier Mosfet For Vlsi Applications, Venkata S. Simhadri

Theses

Schottky barrier MOSFETs are expected to offer certain fabrication advantages, low series resistance and the feasibility to go into sub-micron technology without having short-channel effects. A p-channel MOSFET using Schottky contacts as source and drain is reviewed theoritically. The limitations of the device arising from the oxide offset between source/channel is studied with the help of one dimensional simulation SEDAN. The process sequence leads to an offset between source and channel. The performance of the SBMOSFETs with and without offset is estimated using two dimensional device simulation program PISCES-II for PtSi and IrSi as source and drain material. A novel …

Reflection And Transmission Through Achiral-Chiral Interface, Jia-Feng Wang

Theses

Electromagnetic wave propagation through an achiral-chiral interface is analyzed via Maxwell's equations using the appropriate boundary conditions. Experimental data for reflected power from achiral-chiral interface was found to be in qualitative agreement with the analytical results. In addition, coupled mode equations for chiral cladding waveguides were derived and solved for weak coupling. The experimental results of chiral cladding waveguides show that an average of about 0.2° per cm in polarization rotation occurred. These waveguides were fabricated by using spin-coating deposition. The sense of the rotation was found to be independent of the handness of the cladding chirality, which was predicted …

Modeling And Analysis Of Electrical Properties Of Polycrystalline Silicon Films, Yunsheng Wang

Theses

In recent years, investigations on polysilicon grain structures have shown that all polysilicon films by LPCVD which are most used in today's integrated circuits are columnar in structure. In this work, a square columnar grain structure has been considered to model electrical properties of polycrystalline silicon films instead of all previous one-dimensional grain structure models. By solving Poisson's equation with certain boundary conditions, we find that the barrier height at the corners of the grain is lower than that in the one-dimensional case. Assuming the trapping state energy level as constant, we also find that this level has a value …

Microengineered Silicon Beam Switch For Fiber Optics, Hsu-Nien Yang

Theses

A novel microelectromechanical actuator has been designed for moving an optical input fiber into alignment with one of three stationary output fibers. This switching device thus can connect an input optical port to one of 3 selected optical ports. The actuation force is created by a vertical-drive armature measuring 0.5x2.7 mm² mechanically tethered to the input optical fiber. A force of 2.33 mN is obtained from the linear acturator when the vertical stator armature gap is one micron and the applied three phase voltage is 140 Volts. The required force is a function of the input fiber length, e.g. …

Neural Net Classification Of States In Finite State Vector Quantization, Zhigang Zhang

Theses

In this thesis, a new image coding technique based on Neural Network Finite State Vector Quantization(NNFSVQ) is presented. The new design takes advantage of the high interblock spatial correlation of pixels in typical grey-level images, in addition to intrablock correlation already exploited by vector quantization (VQ). Although many FSVQ require large memory space for the storage of the numerous state codebooks, the memory space requirement of NNFSVQ can be reduced by a very large factor (about 10²-10³) to manageable size without impairing image quality. Simulation experiments have shown that by using NNFSVQ the bit rate can …

Implementation Of Parallel Sorting Algorithms On A Transputer Network, Venkatraman U. Calidas

Theses

Many sorting algorithms, such as the bubble sort and the binary tree selection sort, are n-squared algorithms and take O (n2) time to sort n values. These can be easily parallelized; the resulting sorts are called the odd-even transposition sort and the parallel tree selection sort, respectively. These have O(nlogn) time complexity. The quicksort is an O(nlogn) algorithm and it can parallelized to make it an O(logn) algorithm.

A transputer is a microprocessor which has serial links to transmit and receive data from other transputers. The above algorithms are implemented on a network of transputers and the link connections for …

The Interconnection Network Analysis Package, Nadeem Sabbar

Theses

This thesis focuses on the development of the Interconnection Network Analysis Package (INAP), and the use of INAP to analyze minimal permutation networks. The INAP code is written in C language using Turbo C compiler. Although the INAP has been used to analyze the subject networks it is not a dedicated system. It gives the user the freedom to create the permutation network from scratch (1-8 inputs and 1-7 stages), and then to process it for any number of stages.

The INAP made the analysis of five input networks easy and efficient. The networks have been analyzed stage by stage. …

A Quantization Noise Feedback Technique In Pyramid Image Coding, Zhili Lin

Theses

In communication, we frequently encounter the problem about the trans-mission rate and quantization noise. That is, small quantization noise or high fidelity definitely increases transmission rate, or large quantization noise or low fidelity might require low transmission rate. In our research, we developed a quantization noise feedback technique, with which quantization noise can be reduced greatly at a given transmission rate. We applied this technique in pyramid image coding environment. An error analysis in frequency domain was carried out. Error estimation for pyramid image coding with and without quantization noise feedback was made. Finally, plenty of computer simulation confirms our …

Measurement Of Cluster Size By Retarding Potential And Time-Of- Flight Methods In An Ionized Cluster Beam Deposition System, Yung-Kuan Wang

Theses

The goal of this research was to study the mass distribution of ions generated in the Ionized Cluster Beam (ICB) deposition system. The ICB deposition method has been used to form high quality films of metals and other materials. It was postulated that the clusters consisting of hundreds and thousands of atoms produced by vapor expansion in the ICB source are responsible for the superior film properties. However, consistent experimental evidence concerning the cluster mass distribution, or even the existence of such clusters in the ICB apparatus, was lacking.

Two methods of cluster ion mass spectroscopy were used in this …

Optical Processors For Smart Structures, Barry G. Grossman, Howard Hou, Ramzi H. Nassar

Electrical Engineering and Computer Science Faculty Publications

For underwater fiber-optic sensor arrays containing hundreds of sensors as well as smart aerospace structures and skins using fiber-optic strain sensor arrays, the output of the sensors are optical signals that are a function of the measurand. We are also employing optical signals to energize smart-structure actuators (shape-memory alloys). An all-optical processor would thus seem to be logical choice for the processor since we must simultaneously process, in real time, multiple optical input (sensor) signals and generate multiple output (actuator) signals. In addition, with an all-optical processor, there would be no reduction in processor performance due to converting between optical …

Comparative Analysis Of Single And Double Dwell Acquisition Schemes, Gurinder Singh Ahluwalia

Theses

Single and double dwell pseudonoise (PN) acquisition systems are described, explained and analyzed. These systems are designed to synchronize a locally generated PN signal with a received PN signal of unknown phase in the presence of noise. The mean, variance and an approximate probability distribution function (PDF) of the acquisition time for the single and double dwell PN acquisition schemes is developed. Intuitively, the double dwell acquisition system should be superior to the single dwell system because of the ability to quickly dismiss incorrect cells and further verify probable hits. It is shown analytically that this is in fact true …