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University of Nebraska - Lincoln
Department of Electrical and Computer Engineering: Faculty Publications
- Discipline
- Keyword
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- Permutations; inversions; multiset permutations; data compaction; dynamic range reduction; sparse histogram (1)
- Plasma deposition; Thin film; Optical materials (1)
- Pointing accuracy and stability; gyros; star-trackers; Kalman filter. (1)
- Pointing and tracking system; attitude control; observer; feedback linearization (1)
Articles 1 - 11 of 11
Full-Text Articles in Engineering
Trade-Off Study And Computer Simulation For Assessing Spacecraft Pointing Accuracy And Stability Capabilities, Marcelo C. Algrain, Richard M. Powers
Trade-Off Study And Computer Simulation For Assessing Spacecraft Pointing Accuracy And Stability Capabilities, Marcelo C. Algrain, Richard M. Powers
Department of Electrical and Computer Engineering: Faculty Publications
A case study, written in a tutorial manner, is presented where a comprehensive computer simulation is developed to determine the driving factors contributing to spacecraft pointing accuracy and stability. Models for major system components are described. Among them are spacecraft bus, attitude controller, reaction wheel assembly, star-tracker unit, inertial reference unit, and gyro drift estimators (Kalman filter). The predicted spacecraft performance is analyzed for a variety of input commands and system disturbances. The primary deterministic inputs are the desired attitude angles and rate set points. The stochastic inputs include random torque disturbances acting on the spacecraft, random gyro bias noise, …
Ellipsometer/Polarmeterbased Process Monitor And Control System Suitable For Simultaneous Retrofit On Molecular Beam Epitaxy System Rheed/Leed Interface System, And Method Of Use, John A. Woollam, Blaine D. Johs, Peter P. Chow
Ellipsometer/Polarmeterbased Process Monitor And Control System Suitable For Simultaneous Retrofit On Molecular Beam Epitaxy System Rheed/Leed Interface System, And Method Of Use, John A. Woollam, Blaine D. Johs, Peter P. Chow
Department of Electrical and Computer Engineering: Faculty Publications
A method of, and system for applying light beam producing systems, such as ellipsometers, polarimeters, polarized light reflectance and functionally similar systems, such that a beam of light produced thereby is caused to be incident upon a process element at an angle in excess of an associated Brewster angle while enabling the production of a signal sufficiently sensitive to changes in process element parameters, for use in "real-time" process element process monitoring and control, is disclosed. In addition, a process element processing system and electron beam producing system and light beam producing system combination system is taught, wherein the electron …
Ellipsometer/Polarmeter Based Process Monitor And Control System Suitable For Simultaneous Retrofit On Molecular Beam Eptaxy System Rheed/Leed Interface System, And Method Of Use, John A. Woollam, Blaine D. Johs, Peter P. Chow
Ellipsometer/Polarmeter Based Process Monitor And Control System Suitable For Simultaneous Retrofit On Molecular Beam Eptaxy System Rheed/Leed Interface System, And Method Of Use, John A. Woollam, Blaine D. Johs, Peter P. Chow
Department of Electrical and Computer Engineering: Faculty Publications
A method of, and system for, applying light beam producing systems such as ellipsometers, polarimeters, polarized light reflectance and functionally similar systems, such that a beam of light produced thereby is caused to be incident upon a process element at an angle in excess of an associated Brewster angle while enabling the production of a signal sufficiently sensitive to changes in process element parameters, for use in "real-time' process element process monitoring and control, is disclosed. In addition a process element processing system and electron beam producing system and light beam producing system combination system is taught, wherein the electronbeam …
Growth Of Diamond By Rf Plasma-Assisted Chemical Vapor Deposition, Duane E. Meyer, Natale J. Ianno, John A. Woollam, A. B. Swartzlander, A. J. Nelson
Growth Of Diamond By Rf Plasma-Assisted Chemical Vapor Deposition, Duane E. Meyer, Natale J. Ianno, John A. Woollam, A. B. Swartzlander, A. J. Nelson
Department of Electrical and Computer Engineering: Faculty Publications
A system has been designed and constructed to produce diamond particles by inductively coupled radio-frequency, plasma-assisted chemical vapor deposition. This is a low-pressure, low-temperature process used in an attempt to deposit diamond on substrates of glass, quartz, silicon, nickel, and boron nitride. Several deposition parameters have been varied including substrate temperature, gas concentration, gas pressure, total gas flow rate, rf input power, and deposition time. Analytical methods employed to determine composition and structure of the deposits include scanning electron microscopy, absorption spectroscopy, scanning Auger microprobe spectroscopy, and Raman spectroscopy. Analysis indicates that particles having a thin graphite surface, as well …
Controlling Three-Axis Attitude Rates On A Pointing System Using Nonlinear Observer And Two Axis Measurements, Marcelo C. Algrain
Controlling Three-Axis Attitude Rates On A Pointing System Using Nonlinear Observer And Two Axis Measurements, Marcelo C. Algrain
Department of Electrical and Computer Engineering: Faculty Publications
A new observer design method that allows for estimating the angular rates along a vehicle’s three principal axes is described. The observer uses measurements from a single two-axis angular rate sensor (gyro) and determines the rates for the third axis using a nonlinear observer. Unlike conventional approaches where the equations governing vehicle motion (Euler’s equations) are linearized and then an observer is constructed based on the linear model, this method does not require linearization of the system. Instead, a pseudo-linear representation is used. The pseudo-linear model is obtained by systematically decomposing a nonlinear system into linear and nonlinear terms. The …
Application Of Inversions To Lossless Image Compression, Ziya Arnavut
Application Of Inversions To Lossless Image Compression, Ziya Arnavut
Department of Electrical and Computer Engineering: Faculty Publications
Linear prediction schemes, such as that of the Joint Photographic Experts Group (JPEG), are simple and normally produces a residual sequence with lower zero-order entropy. Occasionally the entropy of the prediction error becomes greater than that of the original image. Such situations frequently occur when the image data have discrete gray levels located within certain intervals. To alleviate this problem, various authors have suggested different preprocessing methods. However, the techniques reported require two passes. We extend the definition of Lehmer-type inversions (Lehmer 1960 and 1964) from permutations to multiset permutations and present a one-pass algorithm based on inversions of a …
Oxygen Plasma Asher Contamination: An Analysis Of Sources And Remedies, R. A. Synowicki, Jeffrey S. Hale, William A. Mcgahan, Natale J. Ianno, John A. Woollam
Oxygen Plasma Asher Contamination: An Analysis Of Sources And Remedies, R. A. Synowicki, Jeffrey S. Hale, William A. Mcgahan, Natale J. Ianno, John A. Woollam
Department of Electrical and Computer Engineering: Faculty Publications
The low Earth orbit (LEO) environment is commonly simulated using oxygen plasma ashers to determine the effects of LEO on spacecraft materials. However, plasma ashers can also contaminate samples during plasma exposure, making them less than ideal for space simulation. This study results from attempts to minimize or eliminate contamination. Optical methods of variable angle spectroscopic ellipsometry and reflectance spectrophotometry were used to quantify contaminant stoichiometry and deposition rate. Auger electron spectroscopy identified deposited contaminants and their surface coverage. Contamination results from etching of the rubber chamber seals by the plasma. The deposited contaminant was nearly indistinguishable from fully stoichiometric …
United States Patent: System And Method For Compensating Polarization-Dependent Sensitivity Of Dispersive Optics In A Rotating Analyzer Ellipsometer System, Steven E. Green, Shakil A. Pittal, Blaine D. Johs, John A. Woollam, David W. Doerr, Reed A. Christenson
United States Patent: System And Method For Compensating Polarization-Dependent Sensitivity Of Dispersive Optics In A Rotating Analyzer Ellipsometer System, Steven E. Green, Shakil A. Pittal, Blaine D. Johs, John A. Woollam, David W. Doerr, Reed A. Christenson
Department of Electrical and Computer Engineering: Faculty Publications
An ellipsometer system which includes a pivotal dispersive optics positioned to receive polychromatic light from an analyzer thereof, without further focusing after reflection from a substrate system, is presented. In addition, a rotating compensator, positioned between the analyzer and the dispersive optics, which serves to reduce detector element polarization dependent sensitivity to light entering thereto after it interacts with the dispersive optics, is disclosed. The method of the present invention can include application of mathematical correction factors to, for instance, substrate system characterizing PSI and DELTA values, or Fourier ALPHA and BETA coefficients.
In Situ And Ex Situ Optical Characterization Of Electro Deposited Magneto-Optic Materials, James N. Hilfiker, Darin W. Glenn, Scott W. Heckens, John A. Woollam, Kurt W. Weirman
In Situ And Ex Situ Optical Characterization Of Electro Deposited Magneto-Optic Materials, James N. Hilfiker, Darin W. Glenn, Scott W. Heckens, John A. Woollam, Kurt W. Weirman
Department of Electrical and Computer Engineering: Faculty Publications
Electrodeposition is being investigated as a novel and low-cost method to prepare magneto-optic thin film and nanostructured materials. This deposition method allows precise control over thin-film properties and permits deposition of novel magnetic geometries. Multilayers and alloys can be deposited and controlled by adjusting deposition potentials and ion concentrations in the bath. Nickel/cobalt alloys have been electrodeposited from sulfamate, sulfate, and chloride solutions onto Au substrates. The optical properties were monitored in situ with a real-time spectroscopic ellipsometer measuring simultaneously at 44 wavelengths in the 410–750 nm spectral range. In situ measurements have the advantage of determining the material microstructural …
United States Patent: System And Method For Compensating Polarization-Dependent Sensitivity Of Dispersive Optics In A Rotating Analyzer Ellipsometer System, Blaine D. Johs, Shakil A. Pittal, Steven E. Green, John A. Woollam, David W. Doerr, Reed A. Christenson
United States Patent: System And Method For Compensating Polarization-Dependent Sensitivity Of Dispersive Optics In A Rotating Analyzer Ellipsometer System, Blaine D. Johs, Shakil A. Pittal, Steven E. Green, John A. Woollam, David W. Doerr, Reed A. Christenson
Department of Electrical and Computer Engineering: Faculty Publications
An ellipsometer system which includes a pivotal dispersive optics positioned to receive polychromatic light from an analyzer thereof, without further focusing after reflection from a substrate system, is presented. In addition, a stationary compensator, positioned between an analyzer and the dispersive optics, which serves to reduce detector element polarization dependent sensitivity to light entering thereto after it interacts with the dispersive optics, is disclosed. The use of a light fiber to carry light from a source thereof, to a polarization state generator, is also disclosed. The method of the present invention can include application of mathematical correction factors to, for …
Studies Of Thin Strained Inas, Alas, And Alsb Layers By Spectroscopic Ellipsometry, C. M. Herzinger, Paul G. Snyder, F. G. Celii, Y.-C. Kao, D. Chow, B. Johs, John A. Woollam
Studies Of Thin Strained Inas, Alas, And Alsb Layers By Spectroscopic Ellipsometry, C. M. Herzinger, Paul G. Snyder, F. G. Celii, Y.-C. Kao, D. Chow, B. Johs, John A. Woollam
Department of Electrical and Computer Engineering: Faculty Publications
The optical constants for thin layers of strained InAs, AlAs, and AlSb have been investigated by spectroscopic ellipsometry and multi-sample analyses. These materials are important for high-speed resonant tunneling diodes in the AlAs/InAs/In0.53Ga0.47As and AlSb/InAs material systems. Understanding the optical properties for these thin layers is important for developing in situ growth control using spectroscopic ellipsometry. Ex situ room-temperature measurements were made on multiple samples. The resulting fitted optical constants are interpreted as apparent values because they are dependent on the fit model and sample structure. These apparent optical constants for very thin layers can be …