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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 12 Apr 2024 15:47:52 +0000I. Relaxation Time of One-Dimensional, Laminar Deflagration for First Order Reactions. II. Reflection and Transmission of Electromagnetic Waves at Electron Density Gradients
https://resolver.caltech.edu/CaltechTHESIS:07262011-115318209
Authors: {'items': [{'id': 'Albini-Frank-Addison', 'name': {'family': 'Albini', 'given': 'Frank Addison'}, 'show_email': 'NO'}]}
Year: 1962
DOI: 10.7907/TYH3-ZQ11
<p>Part I</p>
<p>The one-dimensional, time-dependent equations describing laminar deflagration are solved by an integral method, under the assumption of a physical model for the flame structure and behavior, with restrictions on the type of deviation from steady-state behavior. By virtue of application of a hot-boundary approximation of the von Kármán type, certain sensitive integrals are expressed in a form independent of the temperature profile assumed. Two cases are considered: the "thermal theory" neglecting diffusion, and the case of unity Lewis number (temperature/concentration similarity). Only first order reactions are considered. Arguments supporting the generality of the results are included, along with a discussion of accuracy, and some comparison with experimental work. Graphical display of the results anticipates the utility of the theory for correlating and cross-checking experimental data.</p>
<p>It is concluded that the relaxation time is closely related to the time required for the gas undergoing rapid chemical reaction to pass through the flame.</p>
<p>Part II</p>
<p>The interaction of an electromagnetic wave with a mildly ionized gas is described by an ensemble average treatment of electron motion, and under this description, electromagnetic wave propagation parameters derived. Motivated by the fact that mildly ionized gases in general exhibit inhomogeneous boundary regions, exemplary transition zones are described in terms of varying electron density but constant collision frequency, in order to simplify the solution of wave problems. The half-space reflection problem with a linear transition zone is solved exactly and under two approximations. It is discovered that the reflection and transmission coefficients are strong functions of zone thickness for thin zones. A piecewise-linear transition zone solution exemplifies the procedure for constructing an approximate solution to an arbitrary profile and illustrates the relative insensitivity of reflection and transmission coefficients to detailed zone structure. The "slab" reflection problem with symmetrical, linear transition zones is solved exactly, and it is discovered that the basic periodicity of reflection and transmission coefficients with slab thickness is unchanged, although shifted to higher values of slab thickness/wavelength. The text is supported by fairly extensive graphical presentation of results.</p>https://thesis.library.caltech.edu/id/eprint/6547Electromagnetic Pulses at the Boundary of a Nonlinear Plasma
https://resolver.caltech.edu/CaltechTHESIS:09172021-215240263
Authors: {'items': [{'id': 'Satorius-Edgar-Harry', 'name': {'family': 'Satorius', 'given': 'Edgar Harry'}, 'show_email': 'NO'}]}
Year: 1975
DOI: 10.7907/d6ww-a643
<p>This paper describes an investigation of the behavior of strong electromagnetic pulses at the boundary of a nonlinear, cold, collision-less, and uniform plasma. The nonlinearity considered here is due to the nonlinear terms in the fluid equation which is used to describe the plasma.</p>
<p>Two cases are studied. First, we consider the case where there is a voltage pulse applied across the plane boundary of a semi-infinite, nonlinear plasma. Two different voltage pulses are considered: a delta function pulse and a suddenly turned-on sinusoidal pulse. The resulting electromagnetic fields propagating in the nonlinear plasma are found in this case. In the second case, we consider the reflection of incident E-polarized and H-polarized, electromagnetic pulses at various angles of incidence from a nonlinear, semi-infinite plasma. Again, two forms of incident pulses are considered: a delta function pulse and a suddenly turned-on sinusoidal pulse. In case two, the reflected electromagnetic fields are found.</p>
<p>In both cases, the method used for finding the fields is to first solve the fluid equation (which describes the plasma) for the nonlinear conduction current in terms of the electric field using a perturbation method (since the nonlinear effects are assumed to be small). Next, this current is substituted into Maxwell's equations, and finally the electromagnetic fields which satisfy the boundary conditions are found.</p>https://thesis.library.caltech.edu/id/eprint/14366Wave interactions in periodic structures and periodic dielectric waveguides
https://resolver.caltech.edu/CaltechTHESIS:07172014-155953992
Authors: {'items': [{'email': 'gover@eng.tau.ac.il', 'id': 'Gover-A', 'name': {'family': 'Gover', 'given': 'Avraham'}, 'show_email': 'YES'}]}
Year: 1976
DOI: 10.7907/V0RY-GY17
<p>This work is concerned with a general analysis of wave interactions
in periodic structures and particularly periodic thin film
dielectric waveguides.</p>
<p>The electromagnetic wave propagation in an asymmetric dielectric
waveguide with a periodically perturbed surface is analyzed in
terms of a Floquet mode solution. First order approximate analytical
expressions for the space harmonics are obtained. The solution is
used to analyze various applications: (1) phase matched second harmonic
generation in periodically perturbed optical waveguides;
(2) grating couplers and thin film filters; (3) Bragg reflection devices;
(4) the calculation of the traveling wave interaction impedance
for solid state and vacuum tube optical traveling wave amplifiers
which utilize periodic dielectric waveguides. Some of these applications
are of interest in the field of integrated optics.</p>
<p>A special emphasis is put on the analysis of traveling wave
interaction between electrons and electromagnetic waves in various
operation regimes. Interactions with a finite temperature electron
beam at the collision-dominated, collisionless, and quantum regimes
are analyzed in detail assuming a one-dimensional model and longitudinal
coupling.</p>
<p>The analysis is used to examine the possibility of solid state
traveling wave devices (amplifiers, modulators), and some monolithic
structures of these devices are suggested, designed to operate at the
submillimeter-far infrared frequency regime. The estimates of
attainable traveling wave interaction gain are quite low (on the order
of a few inverse centimeters). However, the possibility of attaining
net gain with different materials, structures and operation condition
is not ruled out.</p>
<p>The developed model is used to discuss the possibility and
the theoretical limitations of high frequency (optical) operation of
vacuum electron beam tube; and the relation to other electron-electromagnetic
wave interaction effects (Smith-Purcell and Cerenkov
radiation and the free electron laser) are pointed out. Finally, the
case where the periodic structure is the natural crystal lattice is
briefly discussed. The longitudinal component of optical space harmonics
in the crystal is calculated and found to be of the order of
magnitude of the macroscopic wave, and some comments are made on the
possibility of coherent bremsstrahlung and distributed feedback
lasers in single crystals.</p>https://thesis.library.caltech.edu/id/eprint/8556Electromagnetic wave propagation in almost periodic media
https://resolver.caltech.edu/CaltechTHESIS:03122012-112325331
Authors: {'items': [{'email': 'alan.mickelson@colorado.edu', 'id': 'Mickelson-Alan-Rolf', 'name': {'family': 'Mickelson', 'given': 'Alan Rolf'}, 'orcid': '0000-0003-2529-8301', 'show_email': 'YES'}]}
Year: 1978
DOI: 10.7907/SZMY-A964
The problem of electromagnetic wave propagation in almost periodic
media is investigated and a solution is obtained directly from Maxwell's
equations. Techniques to evaluate this solution are developed. These
techniques involve a generalization to almost periodic media of the
Brillouin diagram of periodic media. The method of invariant imbedding
is applied to the coupled mode equations which determine the Brillouin
diagram for the purpose of transforming them to coupled Riccati equations.
These coupled Riccati equations, when subjected to a single boundary condition,
determine the solutions to both the periodic and almost periodic
boundary value problems. These evaluation techniques are used to place
in evidence similarities and differences of wave propagation in periodic
and almost periodic media. It is shown that although the periodic and
almost periodic theories agree in many cases of interest, there exist
cases in which distinct differences appear. In cases of multi-tone perturbations,
the almost periodic theory yields both simpler and more reasonable
results than the periodic theory.https://thesis.library.caltech.edu/id/eprint/6849Stark-Induced Optical Nonlinearity in Gaseous NH₂D and Optical Waves in Layered Media
https://resolver.caltech.edu/CaltechTHESIS:12072017-095000115
Authors: {'items': [{'email': 'Pochi@ucsb.edu', 'id': 'Yeh-Pochi-Albert', 'name': {'family': 'Yeh', 'given': 'Pochi Albert'}, 'show_email': 'YES'}]}
Year: 1978
DOI: 10.7907/MBFM-X335
<p>The first part of this work describes theoretical and experimental
studies of Stark-induced three-wave mixing in gaseous NH<sub>2</sub>D. Application
of a dc electric field to a gaseous system destroys the basic inversion
symmetry and allows two-photon mixing processes to occur. A theoretical
derivation of this effect under conditions of resonantly enhanced
non-linearities is given for a three-level system. Calculations are presented
for mixing of a CO<sub>2</sub> laser with a 4 GHz microwaves in the molecule NH<sub>2</sub>D,
producing single lower sideband radiation.</p>
<p>Experimental observation of resonantly enhanced, dc-induced,
three-wave mixing in gaseous NH<sub>2</sub>D is presented. The dependence of this effect
on gas pressure, microwave frequency, applied dc field, and microwave
power are presented and compared with theoretical predictions. The
experiment was done at Hughes Research Laboratories by Abrams and his coworkers.</p>
<p>The second part of this work describes the propagation of electromagnetic
waves in periodic layered media. The propagation of electromagnetic
radiation in periodically stratified media is considered. Media
of finite, semi-finite and infinite extent are treated. A diagonalization
of the unit cell translation operator is used to obtain exact
solutions for the Bloch waves, the dispersion relations, and the band
structure of the medium.</p>
<p>The theory of electromagnetic Bloch waves in periodic stratified
media is then applied to the problems of birefringence, and group velocity
in these media. The relevance of periodic media to phase matching
in nonlinear mixing experiments-and to laser action in the x-ray region
is discussed.</p>
<p>New types of guided waves such as Bragg guided waves and optical
surface waves are theoretically predicted and experimentally observed.</p>https://thesis.library.caltech.edu/id/eprint/10595Investigations of Near-Zone Doppler Effects
https://resolver.caltech.edu/CaltechETD:etd-09142006-111227
Authors: {'items': [{'id': 'Prouty-Dale-Austen', 'name': {'family': 'Prouty', 'given': 'Dale Austen'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/vfzj-7d74
<p>Far away from an electromagnetic source the normal Doppler shifts in frequency occur – a red shift for receding and a blue shift for approaching. As indicated by previous work with an infinitesimal dipole, different frequency shifts occur when the source and observer move closer together, into the near-zone. These "near-zone Doppler effects" are investigated for general sources and subsequently two specific examples are presented.</p>
<p>The general results show that near-zone shifts are similar to far-zone shifts, but the local phase velocity must be used, i.e. ω' ≃ ω(1 ± (v/v<sub>ph</sub>)). In the far zone the phase velocity is the speed of light; in the near zone it differs. Fundamentally, the distance between surfaces of constant phase in the near zone is changed. The surfaces of constant phase for the waves are no longer spherical, but more ellipsoidal or spheroidal, so that a moving observer sees a different frequency shift.</p>
<p>Two specific examples are presented to indicate the actual magnitude of near-zone effects. The examples include a prolate spheroidal antenna and a circular aperture.</p>
<p>Once the magnitude of the effects is determined, the measurability of near-zone Doppler effects is discussed. The investigation concentrates on Fresnel zone effects due to the measurement problem.</p>
<p>Finally, it is shown that for an electrically large wire antenna (the spheroidal example) near-zone Doppler effects are measurable.</p>https://thesis.library.caltech.edu/id/eprint/3536On the Radiation Patterns of Interfacial Antennas
https://resolver.caltech.edu/CaltechETD:etd-09142006-080653
Authors: {'items': [{'id': 'Engheta-Nader', 'name': {'family': 'Engheta', 'given': 'Nader'}, 'orcid': '0000-0003-3219-9520', 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/y86x-2709
<p>The radiation pattern of an interfacial radiating source is obtained for the case where the source is an infinitely long line source lying along the plane interface of two dielectric half-spaces; for the case where the source is an infinitesimal electric dipole vertically located on the interface; and for the case where the dipole is lying horizontally along the interface. For all the three cases, it is found that the radiation pattern at the interface has a null (interface extinction). For the infinitely long line source, it is obtained that the pattern in the upper half-space, whose index of refraction is taken to be less than that of the lower half-space, has a single lobe with a maximum normal to the interface, and that the pattern in the lower half-space (subsurface region) has two maxima straddling symmetrically a minimum. Interpretation of these results in terms of ray optics, Oseen's extinction theorem, and the Cerenkov effect are given. For the vertical dipole, it is found that the radiation pattern along the dipole axis has a null. For the horizontal dipole, it is obtained that the pattern in the upper half-space has a single lobe whose maximum is normal to the interface; that in the lower half-space, in the plane normal to the interface and containing the dipole, the pattern has three lobes; whereas in the plane normal to the interface and normally bisecting the dipole, the pattern has two maxima located symmetrically about a minimum. Interpretation of these results in terms of the Cerenkov effect is also given.</p>https://thesis.library.caltech.edu/id/eprint/3533An Analytical Study of Electromagnetic Vector Field Propagation in a Nonlinear Electron Plasma
https://resolver.caltech.edu/CaltechETD:etd-10312005-133116
Authors: {'items': [{'id': 'Tatoian-James-Zareh', 'name': {'family': 'Tatoian', 'given': 'James Zareh'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/hzt3-s585
<p>From the equations of hydrodynamics and electrodynamics, a system of a coupled nonlinear equations governing the propagation of plane electromagnetic waves in a collisionless electron plasma is obtained. It is shown that solitary wave solutions exist for both the longitudinal and transverse components of the electromagnetic field. It is found that the velocity of the electromagnetic vector solitary wave depends on the amplitudes of all components of the field linearly. The relations among the longitudinal and transverse components that support the solitary waves are determined for different values of plasma temperature. It is shown that while transverse solitary waves cannot exist, except when they are supported by longitudinal waves, the latter can exist by themselves. The dynamics of the plasma electrons during the passage of a longitudinal wave is analyzed and the interaction of such waves with each other is studied. An upper bound on the amplitudes of these waves is obtained. The uniqueness and stability of the longitudinal waves are demonstrated. A Lagrangian density function and two conservation laws for the longitudinal wave equation are found. Frequency spectra of the solitary waves are calculated and their low frequency content is emphasized.</p>
https://thesis.library.caltech.edu/id/eprint/4338Scattering of Light from Large Cylinders
https://resolver.caltech.edu/CaltechETD:etd-11102005-102554
Authors: {'items': [{'id': 'Abushagur-Mustafa-A-G', 'name': {'family': 'Abushagur', 'given': 'Mustafa A. G.'}, 'show_email': 'NO'}]}
Year: 1984
DOI: 10.7907/akkw-r889
<p>Scattering of a plane electromagnetic wave from circular conducting and dielectric cylinders is analyzed. Both polarizations of the incident electric field, parallel and normal to the axis of the cylinder, are considered. The study of the rigorous solutions gives an insightful understanding of the scattered field and its dependence on the material of the cylinder, the polarizations of the incident field, and the three dimensionality of the object which usually are not considered in Fourier optics. It is shown that a combination of Fourier optics and ray theory can give good approximations for the scattered field from both conducting and dielectric cylinders. It is shown that the scattered pattern from a conducting cylinder consists of a main lobe and a number of side lobes. The spacing between the side lobes decreases as ka increases, where k is the wave number of the incident field and a the radius of the cylinder. It is found that for a certain conducting cylinder the side lobes terminate in a smaller scattering angle when the incident field is polarized parallel to the axis than when the incident field is polarized normal to the axis of the cylinder. The surface current density in the shadow region is found to be larger for the normal polarization case than for the parallel polarization case. The pattern of the scattered field from a dielectric cylinder has fringes all around the cylinder. The contrast of the fringes for the dielectric cylinder is much larger when the polarization of the incident field is parallel to the axis than that when the polarization is normal to the axis. The backscattered field of the dielectric cylinder has a peak which depends in its position on the refractive-index of the cylinder for the parallel polarization case. The fine structure of the scattering by a dielectric cylinder is studied. It is shown that the dielectric cylinder has resonant frequencies which depend on the radius and refractive-index of the cylinder. It is found that there are significant differences in the shape of the scattered pattern depending on whether the cylinder is at-resonance or at off-resonance. Experimental investigations are carried out to verify the theory derived in this study and it is found that both theory and experiments are in good agreement.</p>https://thesis.library.caltech.edu/id/eprint/4489Electromagnetic Radiation and Scattering in a Plasma with an Azimuthal Biasing Field
https://resolver.caltech.edu/CaltechETD:etd-01232007-143259
Authors: {'items': [{'id': 'Warne-Larry-Kevin', 'name': {'family': 'Warne', 'given': 'Larry Kevin'}, 'show_email': 'NO'}]}
Year: 1984
DOI: 10.7907/tja8-zp12
<p>The problem of radiation from an electric line source in a homogeneous, cold, incompressible electron plasma is considered when a large static current is superposed. The static axial current gives rise to a magnetostatic biasing field which is oriented in the azimuthal direction and varies with radial distance. When the driving frequency is greater than the plasma frequency, and the medium is assumed to be unbounded, the presence of the static current reduces the amount of radiation. On the other hand, if the driving frequency is less than the plasma frequency and the medium is assumed to be bounded, the amount of radiation is increased.</p>
<p>The problem of scattering from an axial current in a plasma is also considered. The medium in this problem is taken to be a bounded column of plasma containing a radially distributed axial current. At normal incidence the scattered wave contains a cross polarized field component due to the gyrotropic nature of the column. The scattered cross polarized component vanishes in the incident direction as well as in the backward direction. This null is explained by considering the effect of Faraday rotation on various rays traversing the column. Solutions to the scattering problem when the axial current density varies inversely with radial distance are considered in some detail. This case is labeled "homogeneous" since the dielectric tensor does not vary with radial distance and the resulting field equations are thus simplified. The field behavior in the vicinity of the origin is also considered in detail since phenomena similar to those encountered in wedge type media (unbounded fields) occur.</p>https://thesis.library.caltech.edu/id/eprint/297Non-Perturbative Analysis of Some Simple Field Theories on a Momentum Space Lattice
https://resolver.caltech.edu/CaltechETD:etd-04132005-100141
Authors: {'items': [{'email': 'brooks3@llnl.gov', 'id': 'Brooks-Eugene-David-III', 'name': {'family': 'Brooks', 'given': 'Eugene David, III'}, 'show_email': 'YES'}]}
Year: 1984
DOI: 10.7907/333S-XC47
<p>In this work, we develop a new technique for the numerical study of quantum field theory. The procedure, borrowed from non-relativistic quantum mechanics, is that of finding the eigenvalues of a finite Hamiltonian matrix. The matrix is created by evaluating the matrix elements of the Hamiltonian operator on a finite basis of states. The eigenvalues and eigenvectors of the finite dimensional matrix become an accurate approximation to those of the physical system as the finite basis of states is extended to become more complete.</p>
<p>We study a model of scalars coupled to fermions in 0+1 dimensions as a simple field theory to consider in the course of developing the technique. We find in the course of studying this model a change of basis which diagonalizes the Hamiltonian in the large coupling limit. The importance of this transformation is that it can be generalized to higher dimensional field theories involving a trilinear coupling between a Bose and a Fermi field.</p>
<p>Having developed the numerical and analytical techniques, we consider a Fermi field coupled to a Bose field in 1+1 dimensions with the Yukawa coupling λΨΨΨ. We extend the large coupling limit basis of the 0+1 dimensional model to this case using a Bogoliubov transformation on the fermions. Although we do not use this basis in the numerical work due to its complexity, it provides a handle on the behavior of the system in the large coupling limit. In this model we consider the effects of renormalization and the generation of bound states.</p>https://thesis.library.caltech.edu/id/eprint/1371Analysis of Resonant Converters
https://resolver.caltech.edu/CaltechETD:etd-04082005-150525
Authors: {'items': [{'email': 'vatche.vorperian@jpl.nasa.gov', 'id': 'Vorpérian-Vatché', 'name': {'family': 'Vorpérian', 'given': 'Vatché'}, 'show_email': 'NO'}]}
Year: 1984
DOI: 10.7907/NWMH-AP27
<p>The load parameter, Q, and the ratio of the switching frequency to the resonant frequency, F<sub>s</sub>/F<sub>o</sub>, characterize the operation of resonant converters. An accurate do analysis of the series and parallel resonant converters is given in terms of these parameters whereby the conversion ratio, peak stresses, and diode conduction time are determined. An exact and systematic method of small-signal analysis is given whereby the control-to-output transfer function, audio susceptibility, and input impedance are determined at a given operating point. In addition, simple and approximate transfer functions are obtained under high-Q assumption.</p>https://thesis.library.caltech.edu/id/eprint/1308Millimeter-Wave Integrated-Circuit Antenna Arrays
https://resolver.caltech.edu/CaltechETD:etd-08172005-102232
Authors: {'items': [{'id': 'Tong-Peter-Ping-Tak', 'name': {'family': 'Tong', 'given': 'Peter Ping Tak'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/ddxq-rj80
<p>This thesis presents three different types of millimeter-wave integrated-circuit antenna array. They are a linearly polarized antenna array that can form polarization and intensity line images, a circularly polarized spiral antenna and a two-dimensional tracking antenna array. They are all integrated-circuit antennas with detectors on quartz substrates using quasi-optical systems to collect and focus the waves.</p>
https://thesis.library.caltech.edu/id/eprint/3155On the Importance of Polarization in Radar Scattering Problems
https://resolver.caltech.edu/CaltechETD:etd-06262006-133025
Authors: {'items': [{'id': 'van-Zyl-Jakob-Johannes', 'name': {'family': 'van Zyl', 'given': 'Jakob Johannes'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/QRD0-YE09
<p>In this thesis, the importance of polarization in radar scattering problems is investigated. The different matrix characterizations of scatterers are discussed in detail. The problem of finding the polarizations which would yield an optimum amount of power received from the scatterer is solved for the most general case. This shows that for certain classes of scatterers six optimum polarizations exist. The concept of a polarization spectrum to characterize a scatterer is introduced. The usefulness of these spectrums is illustrated when results, using measured multipolarization synthetic aperture radar data, are discussed. Another useful parameter, the coefficient of variation, is introduced. Measured results show that this parameter may be used to form an idea of the scale over which the scattering properties of the scene being imaged vary. The problem of finding the effective scattering operator of a slab filled with different scatterers is formulated. Detailed expressions are given for the effective single scattering operators. This formulation is illustrated by calculating the effective single scattering operators for models of different types of vegetation.</p>https://thesis.library.caltech.edu/id/eprint/2734Optical Interactions in a Dielectric Material with Multiple Perturbations
https://resolver.caltech.edu/CaltechTHESIS:04152019-101001395
Authors: {'items': [{'id': 'Lee-Hyuk', 'name': {'family': 'Lee', 'given': 'Hyuk'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/ek2w-4557
<p>The interaction of light propagating through a dielectric material with multiple perturbations is investigated.</p>
<p>A general coupled mode theory of two gratings is presented. The acousto-electro-optic effect is introduced as an example of an indirect interaction due to the acousto-optic and electro-optic effects. The acousto-electro-optic effect is analyzed using the general theory and is demonstrated experimentally. The application of this effect to light modulation and deflection is discussed in detail. Also a correlator that is based on the photorefractive acousto-electrooptic effect is demonstrated and analyzed theoretically.</p>https://thesis.library.caltech.edu/id/eprint/11461Topics in Millimeter-Wave Imaging Arrays
https://resolver.caltech.edu/CaltechETD:etd-03012008-134009
Authors: {'items': [{'id': 'Kasilingam-Dayalan-P', 'name': {'family': 'Kasilingam', 'given': 'Dayalan P.'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/rt21-jt48
<p>In this thesis two different types of antenna arrays are investigated as possible configurations for <i>two-dimensional</i> diffraction limited imaging arrays. The first configuration is the "fly's-eye" array of microlenses. It is shown that this configuration may be utilized to achieve diffraction limited imaging with theoretical coupling efficiencies of around 50%. The other configuration is the two-dimensional horn array. It is shown that in this configuration, wide-angled horns etched into silicon achieve theoretical coupling efficiencies of 60%. A design for a <i>two-dimensional</i> imaging array, using horn elements of aperture size 1.5λ<sub>0</sub> was suggested. Also covered in this thesis are the radiation losses and the substrate-mode losses of coplanar transmission lines. It is shown that at millimeter-wave frequencies these losses are prohibitively high. Finally in the appendix a simulation of Schottky diode mixers is described as a possible design tool for analyzing millimeter-wave detector circuits.</p>https://thesis.library.caltech.edu/id/eprint/827Electromagnetic Wave Propagation and Radiation in Chiral Media
https://resolver.caltech.edu/CaltechETD:etd-02282008-090141
Authors: {'items': [{'id': 'Bassiri-Sassan', 'name': {'family': 'Bassiri', 'given': 'Sassan'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/RFST-5K65
<p>Propagation and radiation of electromagnetic waves in a lossless, reciprocal, chiral medium is studied in this thesis. Such a medium is described electromagnetically by the constitutive relations D = εE + iγB and H = iγE + (1/µ)B. The constants ε, µ, γ are real and have values that are fixed by the size, shape, and the spatial distribution of the elements that collectively compose the medium. The plane wave propagation in an unbounded chiral medium is considered. The propagation constants are obtained and the polarization properties of electromagnetic waves in such a medium are discussed in detail. The problem of reflection from, and transmission through a semi-infinite chiral medium is solved by obtaining the Fresnel equations. The conditions for the total internal reflection of the incident wave from the interface, and the existance of the Brewster angle are obtained. The effects of the chirality on the polarization and intensity of the reflected wave from the chiral half-space are discussed and illustrated by employing the Stokes parameters. The propagation of electromagnetic waves through an infinite slab of chiral medium is formulated for oblique incidence and solved analytically for the case of normal incidence. The radiation emitted by an oscillating dipole in an unbounded, lossless, chiral medium is calculated. From the constitutive relations and from the time-harmonic Maxwell equations ∇ x E = iωB and ∇ x H = J - iωD, it is seen that the wave equation for such a medium is given by ∇ x ∇ x E - ω<sup>2</sup>µεE - 2ωµγ∇ x E = iωµJ where the source term J is the current density of the oscillating dipole and where E is the electric vector of the radiated field. The desired solution of this wave equation is found by the dyadic Green's function method, that is, by first constructing the dyadic Green's function Γ and then evaluating the expression E = iωµ∫Γ(r,r')•J(r')dV'. The dyadic Green's function Γ and the components of the radiated electric field E are obtained in closed form. The components of the radiated B, D, and H fields can be derived from knowledge of E by using the Maxwell equation B = (1/iω)∇ x E and the constitutive relations. The wave impedance of the medium and the radiation resistance of the dipole are also obtained. The effects of the chiral medium on the polarization and intensity of the dipole radiation are discussed.</p>https://thesis.library.caltech.edu/id/eprint/808The Critical Points of Poynting Vector Fields
https://resolver.caltech.edu/CaltechETD:etd-11082007-131130
Authors: {'items': [{'id': 'Rizvi-Syed-Azhar-Abbas', 'name': {'family': 'Rizvi', 'given': 'Syed Azhar Abbas'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/gj18-eq28
<p>In a thought provoking paper Maxwell [The Scientific Papers of James Clerk Maxwell, ed. W. D. Niven, vol. 2, 233-240, Dover Publications, New York (1952)] studied the flow of water on the Earth's surface and how this flow is affected by the local geography. His results linking number of hills and lake bottoms to valleys are simple and the conclusions elegant. Critical points such as summits and lake bottoms play a key role in the overall organization and structuring of the flow lines. This is the spirit in which electromagnetic power flow represented by the Poynting vector field (S) is studied in this thesis. The specialized case of a planar S field which arises due to a single electromagnetic field component <i>E<sup>z</sup></i> or <i>H<sup>z</sup></i> is dealt with here in considerable detail.</p>
<p>In order to analyse the behaviour of the flow lines of a plane Poynting vector field in the neighbourhood of a critical point, the S field is expanded in a Taylor series. Critical points can be classified according to their order, degeneracy or structural stability. The order of a critical point refers to the degree of the leading non zero term in the Taylor series. A critical point is non degenerate if this leading term is sufficient to give a qualitative description of the flow lines in the neighbourhood. A critical point is structurally stable if the flow lines in the neighbourhood do not change drastically when there is a small perturbation of the electromagnetic field. It is found that lowest order critical points, i.e., elementary center point and elementary saddle point, are the only structurally stable critical points. These critical points are always non degenerate. All degenerate and non elementary critical points are found to be structurally unstable. A formula for the index of rotation of the S field at a critical point is derived. The behaviour of the electric or the magnetic field component which lies in the <i>x-y</i> plane is also studied. It is shown that structurally unstable configurations of flow lines change into structurally stable configurations under small perturbations in such a way that the index of rotation is conserved. The statements made above in connection with the behaviour of flow lines and structural stability are illustrated with the help of examples involving linearly polarized system of interfering plane and/or cylindrical waves.</p>
<p>The flow lines of the S field in the vicinity of a perfectly conducting surface are studied. It is found that in structurally stable situations these lines are either parallel to the surface or they form critical points of half saddle type on this surface. Two types of problems involving flow lines and conducting surfaces are identified. The interior problem deals with the situations where all the flow lines are inside a region bounded by a perfect conductor. In the exterior problems all the flow lines are outside a region bounded by a perfectly conducting surface. Conclusions regarding the existence of critical points and the behaviour of flow lines are drawn in the two above mentioned problems. These conclusions are verified by computation of flow lines in a few well known problems of scattering and diffraction.</p>
<p>Finally the critical points of three dimensional Poynting vector fields are considered. A complete classification of these critical points requires further study at this time. In this thesis only structurally stable critical points are classified for these S fields. An example demonstrating the existence of such critical points is given.</p>https://thesis.library.caltech.edu/id/eprint/4465