Engineering Commons^™

Comments On Hilbert Transform Based Signal Analysis, David G. Long

Faculty Publications

The use of the Hilbert transform for time/frequency analysis of signals is briefly considered. While the Hilbert transform is based on arbitrary continuous signals, most practical signals are digitially sampled and time-limited. To avoid aliasing in the sampling process the signals must also be bandlimited. It is argued that it is reasonable to consider such sampled signals as periodic (this is the basis of the Discrete Fourier Transform [DFT]) since any other interpretation is inconsistent. A simple derivation of the Hilbert transform for a sampled, periodic is then given. It is shown that the instantaneous frequency can be easily computed …

Evaluating The Effect Of Rain On Seawinds Scatterometer Measurements, David G. Long, David Draper

Faculty Publications

A simple wind/rain backscatter model is used with co-located precipitation radar (PR) data from the Tropical Rainfall Measuring Mission (TRMM) satellite to evaluate the effect of rain on SeaWinds on QuikSCAT σ° observations. The model incorporates wind-induced surface scattering, the surface rain perturbation, and atmospheric rain attenuation and scattering. The co-located PR measurements afford direct computation of SeaWinds-scale averaged rain rate and atmospheric rain attenuation and scattering. An estimate of the wind-induced surface backscatter is computed via numerical weather prediction (NWP) winds. By synergistically combining the SeaWinds, NWP, and PR data, estimates of surface rain perturbation and combined surface/atmospheric scattering …

Integrated Microbattery Charger For Autonomous Systems, Brian W. Lefevre

Theses and Dissertations

This thesis presents a microbattery recharging circuit suitable for autonomous microsystems. The battery charger chosen for this design is a constant current battery charger. Two methods of regulating the constant-current are discussed. A published shunt regulator design is analyzed and is presented with enhancements to the design. A series regulator that controls the current to the battery with a switch is designed and fabricated in a 1.5µm CMOS process. The fabricated prototype occupies less than 2.20x2.20mm and is expected to dissipate less than 25µW of power. A discrete model of the integrated circuit is constructed and tested to demonstrate that …

Laboratory Project In Wireless Fsk Receiver Design, Michael A. Jensen, Cynthia Fuse, Raymond Woodward

Faculty Publications

This paper describes a wireless local area network laboratory project that provides senior and first-year graduate students in microwave engineering courses the opportunity to design, build, and test several passive microstrip components and integrate them into a working system. Students design filters, couplers, amplifiers, diode detectors, quarter-wave transformers, antennas, and stub matching networks in weekly labs that parallel-lectures in a one-semester microwave engineering course. This paper also describes simple inexpensive prototyping and testing methods that have been used in this course. Laboratory materials and technical details of the design are provided on the web for students and educators.

Studies In Multiple-Antenna Wireless Communications, Christian Bruce Peel

Theses and Dissertations

Wireless communications systems are used today in a variety of milieux, with a recurring theme: users and applications regularly require higher throughput. Multiple antennas enable higher throughput and/or more robust performance than single-antenna communications, with no increase in power or frequency bandwidth. Systems are required which achieve the full potential of this "space-time" communication channel under the significant challenges of time-varying fading, multiple users, and the choice of appropriate coding schemes. This dissertation is focused on solutions to these problems. For the single-user case, there are many well-known coding techniques available; in the first part of this dissertation, the performance …

Modeling The Direct Solar Conversion Of Co2 To Co And O2, Thomas H. Fletcher

Faculty Publications

At high temperatures (greater than 2300 K), CO₂ is known to dissociate to CO and O. A prototype solar collector was previously demonstrated to achieve such high temperatures, achieving 4-6 mol % CO in the product stream from an inlet stream of pure CO₂. This paper describes the results of computer modeling performed to determine the flow, temperature, and reactions occurring in the prototype device. Of particular interest are the heat-transfer and reaction mechanisms involved and how much photolysis occurs in the prototype. Predictions were performed with two different computational fluid dynamic codes (Fluent and PCGC-3). The …

Microstructure Design Of A Two Phase Composite Using Two-Point Correlation Functions, Brent L. Adams, H. Garmestani, G. Saheli

Faculty Publications

This work has been funded under the AFOSR Grant no. F49620-03-1-0011 and Army Research Lab contract no. DAAD17-02-P-0398 and DAAD 19-01-1-0742. Two-point distribution functions are used here as to introduce "Microstructure Sensitive Design" in two-phase composites. Statistical distribution functions are commonly used for the representation of microstructures and also for homogenization of materials properties. The use of two-point statistics allows the composite designer to include the morphology and distribution in addition to the properties of the individual phases and components. Statistical continuum mechanics is used to make a direct link between the microstructure and properties (elastic and plastic) in terms …

Termination-Dependent Diversity Performance Of Coupled Antennas: Network Theory Analysis, Michael A. Jensen, Jon W. Wallace

Faculty Publications

A new analysis of mutually coupled diversity antenna systems is presented that includes the effects of coupling on the radiation pattern and received power. This analysis, based upon the network scattering parameters, makes use of the singular value decomposition to both specify the characteristics of and analyze terminated antenna networks. The approach facilitates a simplified proof of the multiport conjugate matching condition as well as development of expressions for diversity performance as a function of various impedance terminations. Application of the analysis to coupled dipole antennas characterized using full-wave electromagnetic analysis leads to a comprehensive examination of the diversity performance …

Ignition Behavior Of Live California Chaparral Leaves, Joshua D. Engstrom, Jared K. Butler, Steven G. Smith, Larry L. Baxter, Thomas H. Fletcher, David R. Weise

Faculty Publications

Current forest fire models are largely empirical correlations based on data from beds of dead vegetation. Improvement in model capabilities is sought by developing models of the combustion of live fuels. A facility was developed to determine the combustion behavior of small samples of live fuels, consisting of a flat-flame burner on a moveable platform. Qualitative and quantitative combustion data are presented for representative samples of California chaparral: manzanita (Arctostaphylos parryana); oak (Quercus berberidifolia); ceanothus (Ceanothus crassifolius), and chamise (Adenostoma fasciculatum). Times to ignition were significantly influenced by shape effects, whereas ignition temperature was more dependent on chemical composition

Microstructures By Design: Linear Problems In Elastic-Plastic Design, Brent L. Adams, B. Henrie, M. Lyon

Faculty Publications

Materials microstructure is considered to be a design variable in the methodology called microstructure sensitive design (MSD). Based upon existing homogenization relations, relating the first-order representation of microstructure (the local state distribution function) to elastic and yield properties, the paper describes the construction of properties closures. These establish the theoretically-possible combinations of properties achievable by the set of all possible microstructures, which is called the microstructure hull. Exemplary homogenization relations are shown to be, typically, hypersurfaces (often hyperplanes) in the Fourier space in which the microstructure hull resides. All points lying on (or to one side of) the hypersurface, that …

Wideband Channel Model For Aeronautical Telemetry, Christian Bettweiser, Adam Davis, Michael D. Rice

Faculty Publications

A multipath channel model for wideband aeronautical telemetry links is presented. Channel sounding data were collected at Edwards AFB, CA, at both L-band and lower S-band. Frequency domain analysis techniques were used to evaluate candidate channel models. The channel model is composed of three propagation paths: a line-of-sight direct path and two specular reflections. The first specular reflection is characterized by a relative amplitude of 70% to 96% of the line-of-sight amplitude and a delay of 10—80 ns. This path is the result of “ground bounces” off the dry lake bed at Edwards and is a typical terrain feature at …

Motivating Undergraduate Feedback Control Through Robot Soccer, Randal Beard

Faculty Publications

One of the challenges in control engineering education is to motivate students to invest the effort necessary to understand the theoretical foundations of feedback control. We have found that many students are inherently interested in robotics and are attracted to control engineering when they understand that it plays a central role in robotic systems. To capitalize on this appeal, we have established a one semester robot soccer senior design course that uses the undergraduate feedback control course to introduce the prerequisite material. As a consequence, the undergraduate feedback control course and its lab have been redesigned to focus on mobile …

A Survey Of Pattern Classifier Research, Donald Comer, Lisha Li

Faculty Publications

This paper is a survey of research on pattern classifier. In particular, it emphasizes on the different types of pattern classifiers and their performance factors. Pattern classifiers use the algorithms of pattern recognition to classify various input classes into their respective categories. Recently many algorithms for pattern classifiers have been proposed. However no study of the normalized performance of pattern classifier has been done. Based on the implementation methods, in general there are three types of pattern classifiers: I.C. based, optical based, and software based using general-purpose computers. Advantages, disadvantages, and performance factors of each classifiers is discussed in this …

Dynamic Spill Monitoring: A Coordinated Approach, Peter Jones, James K. Archibald, Randal Beard, Matthew Blake

Faculty Publications

Sponsorship: INEEL. This paper presents a coordinated control strategy for autonomous monitoring of a dynamically changing hazardous spill. The control strategy is a two level hierarchy that uses use coordination variables to communicate between the levels. The upper level is a resource allocator. The lower level consists of several "commanders" each with a possibly different objective. A physical description of the problem is given, as well as the methods of spill modeling and simulation. Tactics for locating, gravitating to and circling the spill are presented. Finally, both simulation and hardware results are given.

Uav Coordinate Frames And Rigid Body Dynamics, Randal Beard

Faculty Publications

This section describes the various coordinate systems that are used to describe the position of orientation of aircraft, and the transformation between these coordinate systems. It is necessary to use several different coordinate systems for the following reasons: Newton's equations of motion are given the coordinate frame attached to the UAV. Some of the on-board sensors take measurements in the body frame, e.g., rate gyros, while some of the sensors take measurements in the inertial frame, e.g., GPS. Aerodynamics forces and torques are exerted in the body frame. Most system requirements, e.g., flight trajectories, are specified in the inertial frame.

Coordinated Uav Target Assignment Using Distributed Tour Calculation, David H. Walker, Timothy W. Mclain, Jason K. Kowlett

Faculty Publications

In this chapter a method for assigning unmanned aerial vehicle agents to targets through the use of preplanned vehicle tours is presented. Assignments are based on multi-target tours that consider the spread of the targets and the sensor capabilities of the vehicles. In this way, the individual agents and the team as a whole make better use of team resources and improve team cooperation. Planning and assignments are accomplished in reasonable computational time through the use of heuristics to reduce the problem size.

Wind Scatterometry With Improved Ambiguity Selection And Rain Modeling, David W. Draper

Theses and Dissertations

Although generally accurate, the quality of SeaWinds on QuikSCAT scatterometer ocean vector winds is compromised by certain natural phenomena and retrieval algorithm limitations. This dissertation addresses three main contributers to scatterometer estimate error: poor ambiguity selection, estimate uncertainty at low wind speeds, and rain corruption. A quality assurance (QA) analysis performed on SeaWinds data suggests that about 5% of SeaWinds data contain ambiguity selection errors and that scatterometer estimation error is correlated with low wind speeds and rain events.

Ambiguity selection errors are partly due to the "nudging" step (initialization from outside data). A sophisticated new non-nudging ambiguity selection approach …

Establishing A Quantitative Foundation For Exactly Constrained Design, Alisha M. Hammond

Theses and Dissertations

Exactly constrained (EC) design is a robust design method which can be used for mechanical assemblies. It entails using the minimum number of constraints to eliminate all desired motion.

While found by some engineers in industry to have many benefits (including robust assembly, no binding or play, ease of assembly, and the ability to tolerate the wear of parts), EC designs remain somewhat unrecognized by academia. One reason for this minimal exposure may be the lack of a quantitative foundation for such designs. This thesis describes the history and current background for EC designs, and it also begins to develop …

Selecting Appropriate Product Concepts For Manufacture In Developing Countries, Danielle Johnson

Theses and Dissertations

There is a noticeable lack of production of indigenously engineered and manufactured products in Less Developed Countries (LDC's). Few products developed in these LDC's could be viable in competitive markets or even sold as components and supplies to other manufacturers of competitive goods. Assumintg that these less developed countries do not innovate and manufacture because they cannot, the next logical question to ask is why can they not?

This thesis looks at the problems of manufacture and design in LDC's from the standpoint of Product Development. It begins by looking at development theories, namely top down and bottom up and …

Rotational Molding Of Acrylonitrile-Butadiene-Styrene Polymers And Blends, Mark Grant Spencer

Theses and Dissertations

The development of acrylonitrile-butadiene-styrene (ABS) resins for use in rotational molding would provide a medium performance material, thus opening doors to new markets for the rotational molding industry. Unfortunately, ABS resins have shown serious problems during the rotational molding process, namely discoloration, bridging, and poor impact strength. It is believed that these effects are due to degradation of the carbon-carbon double bond in the butadiene, through attack by either oxygen or heat. Previous efforts have shown some success in addressing these issues. However, additional improvements are necessary to make ABS resins commercially viable to rotational molders. This study, fourth in …

Satellite Scatterometers: Calibration Using A Ground Station And Statistical Measurement Theory, Peter Kenneth Yoho

Theses and Dissertations

Satellite scatterometers have recently gained popularity due to their unique ability to measure global geophysical data on a daily basis. Increased interest in scatterometry mandates improved design and calibration of these instruments. This dissertation presents new techniques for scatterometer calibration and addresses issues related to the design of future instruments and applications. First, the use of a calibration ground station is considered. A new methodology is established for calibration of SeaWinds, NASA's current scatterometer, using a receive-only ground station. Principles of the methodology are implemented, new analysis techniques developed, and important results obtained for instrument timing, frequency, power, position, and …

Dynamic Modeling Of Compliant Constant-Force Compression Mechanisms, Cameron Boyle, Larry L. Howell, Spencer P. Magleby, Mark S. Evans

Faculty Publications

A mathematical dynamic model is derived for compliant, constant-force compression-mechanisms, based on the pseudo-rigid-body model simplification of the device. The compliant constant-force compression mechanism (CFCM) is a slider mechanism incorporating large-deflection beams, which outputs near-constant-force across the range of its designed deflection. The equation of motion is successfully calibrated with empirical data from five separate mechanisms, comprising two basic configurations of CFCMs. The dynamic equation is derived from a generalized pseudo-rigid-body model. This allows every configuration to be represented by the same model, so a separate treatment is not required for each configuration. An unexpected dynamic trait of the constant-force …

Multiple Uav Cooperative Search Under Collision Avoidance And Limited Range Communication Constraints, Randal W. Beard, Timothy W. Mclain

Faculty Publications

This paper focuses on the problem of cooperatively searching, using a team of unmanned air vehicles (UAVs), an area of interest that contains regions of opportunity and regions of potential hazard. The objective of the UAV team is to visit as many opportunities as possible, while avoiding as many hazards as possible. To enable cooperation, the UAVs are constrained to stay within communication range of one another. Collision avoidance is also required. Algorithms for team-optimal and individually-optimal/team-suboptimal solutions are developed and their computational complexity compared. Simulation results demonstrating the feasibility of the cooperative search algorithms are presented.

Parallel Microgenetic Algorithm Design For Photonic Crystal And Waveguide Structures, J. Cai, L. Li, Gregory P. Nordin, J. Jiang

Faculty Publications

We have developed a powerful parallel genetic algorithm design tool for photonic crystal and waveguide structures. The tool employs a small-population-size genetic algorithm (microgenetic algorithm) for global optimization and a two-dimensional finite-difference time-domain method to rigorously design and optimize the performance of photonic devices. We discuss the implementation and performance of this design tool. We demonstrate its application to two photonic devices, a defect taper coupler to connect conventional waveguides and photonic crystal waveguides, and a sharp 90˚ waveguide bend for low index contrast waveguides.

Ultracompact High-Efficiency Polarizing Beam Splitter With A Hybrid Photonic Crystal And Conventional Waveguide Structure, J. Cai, S. Kim, Gregory P. Nordin, J. Jiang

Faculty Publications

We propose an ultracompact high-efficiency polarizing beam splitter that operates over a wide wavelength range and is based on a hybrid photonic crystal and a conventional waveguide structure. Within a small area (15 mm 3 10 mm), this polarizing beam splitter separates TM- and TE-polarized modes into orthogonal output waveguides. Results of simulations with the two-dimensional finite-difference time-domain method show that 99.3% of TM-polarized light is def lected by the photonic crystal structure (with a 28.0-dB extinction ratio), whereas 99.0% of TE-polarized light propagates through the structure (with a 32.2-dB extinction ratio). Wave vector diagrams are employed to explain the …

The Distribution Of Internal Interfaces In Polycrystals, Brent L. Adams, Bassem S. El-Dasher, Gregory S. Rohrer, Anthony D. Rollett, David M. Saylor, Paul Wynblatt

Faculty Publications

This work was supported by the MRSEC program of the National Science Foundation under Award Number DMR-0079996. Recent advances both in experimental instrumentation and computing power have made it possible to interrogate the distribution of internal interfaces in polycrystals and the three dimensional structure of the grain boundary network with an unprecedented level of detail. The purpose of this paper is to review techniques that can be used to study the mesoscopic crystallographic structure of grain boundary networks and to summarize current findings. Recent studies have shown that grain surfaces within dense polycrystals favor the same low energy planes that …

Modeling The Transient Response Of A Thermosyphon, James Kirk Storey

Theses and Dissertations

Thermosyphon transient operation was numerically modeled. The numerical model presented in this work overcame the limitations of previous studies by including transient conduction in the vessel wall, shear stress between the rising vapor and the falling film in the thermosyphon, the influence of the mass in the liquid pool in the evaporator, and by using a more refined and accurate numerical grid. Unique to this model was the accounting for temporal changes in the effective length of the vapor space due to the expanding and contracting of non-condensable gases in the vapor space. The model assumed quasi-steady one-dimensional vapor flow, …

Thermodynamic Property Prediction For Solid Organic Compounds Based On Molecular Structure, Benjamin T. Goodman

Theses and Dissertations

A knowledge of thermophysical properties is necessary for the design of all process units. Reliable property prediction methods are essential because reliable experimental data are often not available due to concerns about measurement difficulty, cost, scarcity, safety, or environment. In particular, there is a lack of prediction methods for solid properties. Predicted property values can also be used to fill holes in property databases to understand more fully compound characteristics. This work is a comprehensive analysis of the prediction methods available for five commonly needed solid properties. Where satisfactory methods are available, recommendations are made; where methods are unsatisfactory in …

A Closed-Form Dynamic Model Of The Compliant Constant-Force Mechanism Using The Pseudo-Rigid-Body Model, Cameron Boyle

Theses and Dissertations

A mathematical dynamic model is derived for the compliant constant-force mechanism, based on the pseudo-rigid-body model simplification of the device. The compliant constant-force mechanism is a slider mechanism incorporating large-deflection beams, which outputs near-constant-force across the range of its designed deflection. The equation of motion is successfully validated with empirical data from five separate mechanisms, comprising two configurations of compliant constant-force mechanism. The dynamic model is cast in generalized form to represent all possible configurations of compliant constant-force mechanism. Deriving the dynamic equation from the pseudo-rigid-body model is useful because every configuration is represented by the same model, so a …

Predicting Drag Polars For Micro Air Vehicles, Mark Elden Luke

Theses and Dissertations

Drag polars for three Micro Air Vehicles (MAVs) were measured at Reynolds numbers of 70,000, 50,000, 30,000, and 10,000 and compared to predictions generated using the classical approach. The MAVs tested had different configurations and aspect ratios varying from 1.2 to 1.6 and ratios of wetted surface area to planform area from 2.6 to 3.9.

A force balance was used to measure the lift and drag on the MAVs at angles of attack ranging from -5 degrees (or -10 degrees) to 10 degrees. The force balance allowed the MAVs to rotate in the pitching axis. The MAV angle of attack …