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Articles 31 - 45 of 45
Full-Text Articles in Engineering
Effects Of Polarization And Coherence On The Propagation And The Detection Of Stochastic Electromagnetic Beams, Mohamed Fouad Salem
Effects Of Polarization And Coherence On The Propagation And The Detection Of Stochastic Electromagnetic Beams, Mohamed Fouad Salem
Electronic Theses and Dissertations
Most of the physically realizable optical sources are radiating in a random manner given the random nature of the radiation of a large number of atoms that constitute the source. Besides, a lot of natural and synthetic materials are fluctuating randomly. Hence, the optical fields that one encounters, in most of the applications are fluctuating and must be treated using random or stochastic functions. Within the framework of the scalar-coherence theory, one can describe changes of the properties of any stochastic field such as the spectral density and the spectral degree of coherence on propagation in any linear medium, deterministic …
Probing Random Media With Singular Waves, Chaim Schwartz
Probing Random Media With Singular Waves, Chaim Schwartz
Electronic Theses and Dissertations
In recent years a resurgence of interest in wave singularities (of which optical vortices are a prominent example), light angular momentum and the relations between them has occurred. Many applications in various areas of linear and non-linear optics have been based on studying effects related to angular momentum and optical vortices. This dissertation examines the use of such wave singularities for studying the light propagation in highly inhomogeneous media and the relationship to angular momentum transfer. Angular momentum carried by light can be, in many cases, divided in two terms. The first one relates to the polarization of light and …
A Study On The Nature Of Anomalous Current Conduction In Gallium Nitride, Joshua K. Spradlin
A Study On The Nature Of Anomalous Current Conduction In Gallium Nitride, Joshua K. Spradlin
Theses and Dissertations
Current leakage in GaN thin films limits reliable device fabrication. A variety of Ga and N rich MBE GaN thin films grown by Rf, NH3, and Rf+ NH3, are examined with electrical measurements on NiIAu Schottky diodes and CAFM. Current-voltage (IV) mechanisms will identify conduction mechanisms on diodes, and CAFM measurements will investigate the microstructure of conduction in GaN thin films. With CAFM, enhanced conduction has been shown to decorate some extended defects and surface features, while CAFM spectroscopy on a MODFET structure indicates a correlation between extended defects and field conduction behavior at room temperature. A remedy for poor …
Automatic Detection And Validity Of The Sea-Ice Edge: An Application Of Enhanced-Resolution Quikscat/Seawinds Data, David G. Long, Jorg Haarpaintner, Rasmus T. Tonboe, Michael L. Van Woert
Automatic Detection And Validity Of The Sea-Ice Edge: An Application Of Enhanced-Resolution Quikscat/Seawinds Data, David G. Long, Jorg Haarpaintner, Rasmus T. Tonboe, Michael L. Van Woert
Faculty Publications
Sea-ice edge detection is an essential task at the different national ice services to secure navigation in ice-covered seas. Comparison between the Remund and Long ice mask image from enhanced-resolution QuikScat/SeaWinds (QS) products and the analyzed ice edge from high-resolution RADARSAT synthetic aperture radar has shown that the automatically determined QS ice mask underestimates the Arctic ice extent. QS data was statistically analyzed by colocating the data with ice charts around Greenland and with the National Aeronautics and Space Administration Team's Special Sensor Microwave/Imager (SSM/I) ice concentration algorithm over the whole Arctic region. All variables, i.e., the backscatter in vertical …
Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala
Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala
Electrical & Computer Engineering Faculty Publications
The effect of the direction of the detected beam on the intensity of ECE is studied. It is found that the combined effects of the strong dependence of the conversion efficiencey of O mode at the plasma resonance on the direction of the incident wave and the partial screening of the beam waist by the MAST vessel wall, can be responsible for the weakening of ECE emission for some frequencies. The theoretical model for ECE data interpretation on MAST has been significantly improved. New features of the model are as follows: the quasioptical treatment of the receiving antenna, interference, polarization …
Polarization Effects In Photoluminescence Of C- And M-Plane Gan/Algan Multiple Quantum Wells, E. Kuokstis, C. Q. Chen, M. E. Gaevski, W. H. Sun, J. W. Yang, Grigory Simin, M. Asif Khan, H. P. Maruska, D. W. Hill, M. C. Chou, J. J. Gallagher, B. Chai
Polarization Effects In Photoluminescence Of C- And M-Plane Gan/Algan Multiple Quantum Wells, E. Kuokstis, C. Q. Chen, M. E. Gaevski, W. H. Sun, J. W. Yang, Grigory Simin, M. Asif Khan, H. P. Maruska, D. W. Hill, M. C. Chou, J. J. Gallagher, B. Chai
Faculty Publications
Polarizationeffects have been studied in GaN/AlGaN multiple quantum wells(MQWs) with different c-axis orientation by means of excitation-dependent photoluminescence(PL) analysis. Quantum structures were grown on [0001]-oriented sapphire substrates (C plane) and single-crystalline [11̄00]-oriented freestanding GaN (M plane) using the metalorganic chemical vapor deposition technique. Strong PL spectrum line blueshifts (up to 140 meV) which are correlated with the excitation intensity have been obtained for C-plane MQWs, whereas no shift has been observed for M-plane MQWs.Theoretical calculations and comparison with the PL data confirm that the built-in electric field for C-plane structures is much stronger than the field present for M-plane MQWs. …
Differential Signalling In Pcbs: Modeling And Validation Of Dielectric Losses And Effects Of Discontinuities, R. Araneo, Chen Wang, Xiaoxiong Gu, S. Celozzi, James L. Drewniak
Differential Signalling In Pcbs: Modeling And Validation Of Dielectric Losses And Effects Of Discontinuities, R. Araneo, Chen Wang, Xiaoxiong Gu, S. Celozzi, James L. Drewniak
Electrical and Computer Engineering Faculty Research & Creative Works
This paper focuses on differential signal transmission above ground planes with gaps, taking into account the dielectric and conductive losses of the substrate. An equivalent lumped-circuit is proposed and its suitability is investigated by comparing the obtained numerical results with the measured data. Furthermore the differential to common mode conversion of the waves, while crossing the gap, is theoretically analyzed and experimentally verified.
Finite-Aperture Wire Grid Polarizers, Michael A. Jensen, Gregory P. Nordin
Finite-Aperture Wire Grid Polarizers, Michael A. Jensen, Gregory P. Nordin
Faculty Publications
The transmission characteristics of wire grid polarizers fabricated in finite apertures are investigated by using a three-dimensional finite-difference time-domain formulation. Specifically, the optical transmissivity and extinction ratio are characterized for a wide variety of geometrical parameters including aperture size in both dimensions, conducting wire fill factor, and polarizer thickness. A dispersive material model is used to investigate the performance of polarizers fabricated by using realistic metals at infrared wavelengths. The results indicate that the aperture dimension significantly impacts the polarizer transmission behavior and that the extinction of the unwanted polarization is often limited by depolarizing scattering that is due to …
Studies On Methods Of Fuel Cells Electrodes Preparation, Jun Gu, Sheng Sui, Guangqiang Li, Zhitong Sui
Studies On Methods Of Fuel Cells Electrodes Preparation, Jun Gu, Sheng Sui, Guangqiang Li, Zhitong Sui
Journal of Electrochemistry
In fuel cells,the structure of electrodes is an important factor which effect the cell performance.To improve the structure and the performance of electrodes,a new method of providing fuel cell electrodes is proposed in this paper.PTFE(polytetrafluoroethylene) and ethyne black was ground for about half an hour in a high_speed grinder,then the catalyst was added into the grinder and milled for an hour.This milled catalyst was transferred into a mixer followed by the addition of surface_active agent. After a suspension was formed,it was filtered under vacuum condition.Then a thin uniform filter_cake of the catalyst was formed,which was rolled together with a current_collecting …
Application Of A Hybrid Fem/Mom Method To A Canonical Pcb Problem, Yun Ji, J. Chen, Todd H. Hubing, James L. Drewniak
Application Of A Hybrid Fem/Mom Method To A Canonical Pcb Problem, Yun Ji, J. Chen, Todd H. Hubing, James L. Drewniak
Electrical and Computer Engineering Faculty Research & Creative Works
A hybrid FEM/MOM method was used to solve a canonical printed circuit board (PCB) problem. The PCB is populated with three traces. One is a signal line and the other two are I/O lines that extend beyond the boundary of the board. The finite element method (FEM) was used to model the fields in the volume around the on-board trace. The method of moments (MOM) was employed to model the equivalent surface currents on the board and the current on the off-board traces. The FEM and MOM equations were coupled by forcing the continuity of tangential fields on the dielectric …
Terrain Backscattering Coefficient Generator, Ricardo Mediavilla
Terrain Backscattering Coefficient Generator, Ricardo Mediavilla
Theses and Dissertations
Using already available data, a backscattering coefficient generator (BCG) for several types of terrain and measurement conditions is developed. The types of terrain are: (1) soils and rocks, (2) trees, (3) grasses, (4) shrubs, (5) short vegetation, (6) roads, (7) urban areas, (8) dry snow, and (9) wet snow. These data sets typically cover incidence angles ranging between 0 and 80 degrees where 0 is normal to the terrain. Measurement conditions are defined by: (1) incidence angle, (2) wave polarizations configuration (HH, HV, or VV), and (3) radar band (L, C, S, X, Ku, Ka, or W). The BCG output …
Effects Of Clutter Height Distribution On Adaptive Clutter Erasure Performance, Kelce Steven Wilson
Effects Of Clutter Height Distribution On Adaptive Clutter Erasure Performance, Kelce Steven Wilson
Theses and Dissertations
A new real beam interferometric processing technique, called Adaptive Clutter Erasure (ACE), is investigated for applicability to ground clutter suppression in airborne radar systems. By analysis and simulation, the viability of the ACE concept as a next generation clutter suppression technique is demonstrated to achieve performance enhancements commensurate with currently implemented techniques. Research results indicate the ACE concept provides a reliably consistent 10dB Signal-to-Clutter Ratio (SCR) advantage over the APG-63, an operational radar system used for baseline comparison. ACE system concept development and performance predictions are conducted in conformity with the physical and operational design parameters of the APG-63, namely …
The Synthesis Of Patterns Using A Series-Fed Array Of Annular Sector Radiating Line (Anserlin) Elements: Low-Profile, Circularly Polarized Radiators, James L. Drewniak, P. E. Mayes
The Synthesis Of Patterns Using A Series-Fed Array Of Annular Sector Radiating Line (Anserlin) Elements: Low-Profile, Circularly Polarized Radiators, James L. Drewniak, P. E. Mayes
Electrical and Computer Engineering Faculty Research & Creative Works
A series-fed, circularly polarized array of annular sector radiating-line elements that operates over a ground plane and has a low profile is presented. Pattern shaping can be achieved through control of the fraction of the incident power that is radiated by each element. This can be accomplished over a wide range by a simple adjustment in the geometry of each element. A synthesis technique is given, and experimental results are presented. The array is demonstrated to have a high return loss (good impedance match) and a low axial ratio
Anserlin. A Broad-Band, Low-Profile, Circularly Polarized Antenna, James L. Drewniak, P. E. Mayes
Anserlin. A Broad-Band, Low-Profile, Circularly Polarized Antenna, James L. Drewniak, P. E. Mayes
Electrical and Computer Engineering Faculty Research & Creative Works
A technique is presented for improving the performance of low-profile, circularly polarized (CP) radiating-line antennas. The essential elements of the technique pertain to establishing a single traveling wave on an annular sector of conducting strip that is positioned parallel and close to a large conducting surface. The antenna is named the annular sector, radiating-line (ANSERLIN) antenna. Using this technique, the impedance bandwidth becomes so large that it no longer has any bearing on the operating bandwidth. Instead, the pattern shape and axial ratio become the factors that limit the bandwidth. Both senses of circular polarization can be transmitted or received …
A Log-Spiral, Radiating-Line Antenna, James L. Drewniak, P. E. Mayes, D. Tanner, R. Waller
A Log-Spiral, Radiating-Line Antenna, James L. Drewniak, P. E. Mayes, D. Tanner, R. Waller
Electrical and Computer Engineering Faculty Research & Creative Works
No abstract provided.