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Electromagnetic scattering from a periodic array of open-ended rectangular waveguide apertures
Title
Electromagnetic scattering from a periodic array of open-ended rectangular waveguide apertures.
Creator
Bohning, Terry., Florida Atlantic University, Helmken, Henry, College of Engineering and Computer Science, Department of Computer and Electrical Engineering and Computer Science
Abstract/Description
In this dissertation, the Radar Cross Section (RCS) of a large periodic array of rectangular open-ended waveguide apertures is determined numerically using several methods. The aperture boundaries are presumed to be Perfect Electrical Conductors (PEC). Although the problems of radiation from such a waveguide array and of aperture array scattering have been treated in the literature, the problem of scattering from an array of waveguide apertures does not appear to have been solved before....
Show moreIn this dissertation, the Radar Cross Section (RCS) of a large periodic array of rectangular open-ended waveguide apertures is determined numerically using several methods. The aperture boundaries are presumed to be Perfect Electrical Conductors (PEC). Although the problems of radiation from such a waveguide array and of aperture array scattering have been treated in the literature, the problem of scattering from an array of waveguide apertures does not appear to have been solved before. Considering the case of an array with constituent guides of semi-infinite length, the RCS is computed by several numerical methods based on the Integral Equation (IE) method, a least-squared error minimization technique referred to as Squared Field Error (SFE) method, direct solution of a surface integral equation, the Spectral Domain Method, and by using waveguide modes computed via the Finite Element Method (FEM). The case of finite-length guides is also treated using the IE and SFE methods. The results of these methods are compared with experimental data obtained from an outdoor RCS range. In order to simulate the semi-infinite case, the finite-length waveguides were terminated with radar absorbing foam so that nearly all reflection occurred at the apertures impinged upon by the incident plane wave. For all the methods cited, the infinite array approximation (cell-to-cell field periodicity except for a linear progressive interelement phase shift) is assumed to hold. A derivation of Floquet modes which implement this "phase-periodic" boundary condition is provided in an appendix, where an incidental discussion concerning the scalar and vector Laplacian operators is also furnished. A description of the structure and user interface of the software which has been written to implement the various methods is also given. The purposes of major subroutines and data structures are also delineated and several control-flow diagrams are included. As a foundation to extend the present work to analysis of the electromagnetic fields within an absorber coated PEC waveguide, a brief survey and a discussion of related work is provided.
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Date Issued
1992
PURL
http://purl.flvc.org/fcla/dt/12308
Subject Headings
Wave guides, Electromagnetic fields
Format
Document (PDF)
Finite element analysis of inhomogeneous waveguides
Title
Finite element analysis of inhomogeneous waveguides.
Creator
Dervain, Suzanne Tai., Florida Atlantic University, Sadiku, Matthew
Abstract/Description
In this thesis, discretized finite element equations were derived and applied to the solution of electromagnetic fields in homogeneous and inhomogeneous waveguides. To improve the accuracy of the results several approaches were taken. Higher order elements were first introduced in the finite element formulation, then a penalty function was applied with explicit boundary conditions, which limit the appearance of nonphysical solutions. The results obtained from the finite element analysis were...
Show moreIn this thesis, discretized finite element equations were derived and applied to the solution of electromagnetic fields in homogeneous and inhomogeneous waveguides. To improve the accuracy of the results several approaches were taken. Higher order elements were first introduced in the finite element formulation, then a penalty function was applied with explicit boundary conditions, which limit the appearance of nonphysical solutions. The results obtained from the finite element analysis were compared to analytical results when available and found to be very accurate.
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Date Issued
1988
PURL
http://purl.flvc.org/fcla/dt/14448
Subject Headings
Finite element method, Wave guides
Format
Document (PDF)
PREDICTING FREQUENCIES AND POWER FOR A CYLINDRICAL CERENKOV SLOW WAVE STRUCTURE
Title
PREDICTING FREQUENCIES AND POWER FOR A CYLINDRICAL CERENKOV SLOW WAVE STRUCTURE.
Creator
HOLSTEIN, DANNY GUY, Florida Atlantic University, Lamborn, Bjorn, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description
The dispersion relation for a dielectrically loaded cylindrical waveguide, both with and without a beam of electrons, is found. It is shown that in the limit of Cerenkov threshold, the frequency goes to infinity. Also, using the fields derived, the Poynting vector is computed. It is shown that the Poynting vector increases and the operating frequency decreases with the thickness of the liner.
Date Issued
1982
PURL
http://purl.flvc.org/fcla/dt/14136
Subject Headings
Dielectric wave guides, Cherenkov radiation
Format
Document (PDF)
Free and random vibrations of shells of revolution with interior supports
Title
Free and random vibrations of shells of revolution with interior supports.
Creator
Xia, Zhiyong., Florida Atlantic University, Yong, Yan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A new analytical method based on the wave propagation scheme has been developed for the dynamic analysis of axially symmetric shells with arbitrary boundary conditions and interior supports. In this approach, a shell structure is considered as a waveguide and the response to external excitations is treated as a superposition of wave motions. To segregate the effect of the interior supports, the waveguide is first divided into several sub-waveguides. Upon analyzing these sub-waveguides...
Show moreA new analytical method based on the wave propagation scheme has been developed for the dynamic analysis of axially symmetric shells with arbitrary boundary conditions and interior supports. In this approach, a shell structure is considered as a waveguide and the response to external excitations is treated as a superposition of wave motions. To segregate the effect of the interior supports, the waveguide is first divided into several sub-waveguides. Upon analyzing these sub-waveguides separately, a composition scheme is adopted to relate them by connecting the wave components according to the continuity conditions for the state variables at each interior supports. Closed form solutions for free and random vibration are derived. The proposed method is presented in a general fashion and numerical examples are given to illustrate the application of the theory.
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Date Issued
1990
PURL
http://purl.flvc.org/fcla/dt/14659
Subject Headings
Shells (Engineering)--Vibration, Wave guides
Format
Document (PDF)
Compound compensation strategies for wireless data communications over the multimodal acoustic ocean waveguide
Title
Compound compensation strategies for wireless data communications over the multimodal acoustic ocean waveguide.
Creator
Bessios, Anthony G., Harbor Branch Oceanographic Institute
Date Issued
1996
PURL
http://purl.flvc.org/FCLA/DT/3351960
Subject Headings
Underwater acoustic telemetry, Underwater acoustics, Wireless communication systems, Wave guides
Format
Document (PDF)
Image improvement using dynamic optical low-pass filter
Title
Image improvement using dynamic optical low-pass filter.
Creator
Petljanski, Branko., College of Engineering and Computer Science, Department of Computer and Electrical Engineering and Computer Science
Abstract/Description
Professional imaging systems, particularly motion picture cameras, usually employ larger photosites and lower pixel counts than many amateur cameras. This results in the desirable characteristics of improved dynamic range, signal to noise and sensitivity. However, high performance optics often have frequency response characteristics that exceed the Nyquist limit of the sensor, which, if not properly addressed, results in aliasing artifacts in the captured image. Most contemporary still and...
Show moreProfessional imaging systems, particularly motion picture cameras, usually employ larger photosites and lower pixel counts than many amateur cameras. This results in the desirable characteristics of improved dynamic range, signal to noise and sensitivity. However, high performance optics often have frequency response characteristics that exceed the Nyquist limit of the sensor, which, if not properly addressed, results in aliasing artifacts in the captured image. Most contemporary still and video cameras employ various optically birefringent materials as optical low-pass filters (OLPF) in order to minimize aliasing artifacts in the image. Most OLPFs are designed as optical elements with a frequency response that does not change even if the frequency responses of the other elements of the capturing systems are altered. An extended evaluation of currently used birefringent-based OLPFs is provided. In this work, the author proposed and demonstrated the use of a parallel optical window p ositioned between a lens and a sensor as an OLPF. Controlled X- and Y-axes rotations of the optical window during the image exposure results in a manipulation of the system's point-spread function (PSF). Consequently, changing the PSF affects some portions of the frequency components contained in the image formed on the sensor. The system frequency response is evaluated when various window functions are used to shape the lens' PSF, such as rectangle, triangle, Tukey, Gaussian, Blackman-Harris etc. In addition to the ability to change the PSF, this work demonstrated that the PSF can be manipulated dynamically, which allowed us to modify the PSF to counteract any alteration of other optical elements of the capturing system. There are several instances presented in the dissertation in which it is desirable to change the characteristics of an OLPF in a controlled way., In these instances, an OLPF whose characteristics can be altered dynamically results in an improvement of the image quality.
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Date Issued
2010
PURL
http://purl.flvc.org/FAU/1927613
Subject Headings
Image processing, Digital techniques, Signal processing, Digital techniques, Frequency response (Dynamics), Polymers and polymerization, Optical wave guides
Format
Document (PDF)