On the diffraction by biperiodic anisotropic structures

This paper studies the scattering of electromagnetic waves by a nonmagnetic biperiodic structure. The structure consists of anisotropic optical materials and separates two regions with constant dielectric coefficients. The time harmonic Maxwell equations are transformed to an equivalent strongly elliptic variational problem for the magnetic field in a bounded biperiodic cell with nonlocal boundary conditions. This guarantees the existence of quasiperiodic magnetic fields in 퐻1 and electric fields in 퐻(curl) solving Maxwell's equations. The uniqueness is proved for all frequencies excluding possibly a discrete set. The analytic dependence of these solutions on frequency and incident angles is studied

Mode conversion in periodically disturbed thin‐film waveguides

Mode conversion in a periodically perturbed thin‐film optical waveguide is studied in detail. Three different types of perturbations are considered: periodic index of refraction of the film, periodic index of refraction of the substrate, and periodic boundary. The applications in filters, mode converters, and distributed feedback lasers are discussed

Theoretical, Experimental, and Computational Evaluation of Several Vane-Type Slow-Wave Structures

Several types of periodic vane slow-wave structures were fabricated. The dispersion characteristics were found by theoretical analysis, experimental testing, and computer simulation using the MAFIA code. Computer-generated characteristics agreed to approximately within 2 percent of the experimental characteristics for all structures. The theoretical characteristics, however, deviated increasingly as the width to height ratio became smaller. Interaction impedances were also computed based on the experimental and computer-generated resonance frequency shifts due to the introduction of a perturbing dielectric rod

Conical diffraction by periodic structures: Variation of interfaces and gradient formulas

This paper studies the dependence of solutions to conical diffraction problems upon geometric parameters of non-smooth profiles and interfaces between different materials of diffractive gratings. This problem arises in the design of those optical devices to diffract time-harmonic oblique incident plane waves to a specified far-field pattern. We prove the stability of solutions and give analytic formulas for the derivatives of reflection and transmission coefficients with respect to Lipschitz perturbations of interfaces. These derivatives are expressible as contour integrals involving the direct and adjoint solutions of conical diffraction problems

Computational Investigation of Experimental Interaction Impedance Obtained by Perturbation for Helical Traveling-Wave Tube Structures

Conventional methods used to measure the cold-test interaction impedance of helical slow-wave structures involve perturbing a helical circuit with a cylindrical dielectric rod placed on the central axis of the circuit. It has been shown that the difference in resonant frequency or axial phase shift between the perturbed and unperturbed circuits can be related to the interaction impedance. However, because of the complex configuration of the helical circuit, deriving this relationship involves-several approximations. With the advent of accurate three- dimensional helical circuit models, these standard approximations can be fully investigated. This paper addresses the most prominent approximations made in the analysis for measured interaction impedance by Lagerstrom and investigates their accuracy using the three-dimensional simulation code MAFIA. It is shown that a more accurate value of interaction impedance can be obtained by using three-dimensional computational methods rather than performing costly and time consuming experimental cold-test measurements

A New Foundation for Modern Science

This research is a continuation of recent efforts to expand classical electrodynamics to embrace elastic finite-size elementary particles with internal structure in an effort to satisfy the logical criteria that undergird the scientific method and point scientific theories in the direction of truth. Earlier work reported the logical inconsistencies, false assumptions, and defects of the relativistic quantum electrodynamic theory of the atom, including relativity theory and quantum mechanics.[14] This was followed by derivations of Maxwell\u27s equations of electrodynamics showing where the point particle approximation is used and the field transformation information between moving frames is removed causing them to fail for relativistic phenomena.[15) Then the principal results of special relativity theory were derived from classical electrodynamics for finite size elementary particles using the Galilean transformation .[16] More recent research has shown from combinatorial geometry for arbitrary-shaped finite size electrons and protons obeying classical electrodynamics under the assumption of spherical packing symmetry that the details of the periodic table of the elements as well as the structure of the nucleus could be predicted more completely and accurately than previously possible with the relativistic quantum theories.[16,17,18) This work derives expressions for the blackbody radiation, the photoelectric effect, and the emission spectra of atoms from classical electrodynamics for finite size electrons in the shape of a toroidal ring. The results are logically superior to the relativistic quantum electrodynamic theory as developed by Planck, Einstein, and Dirac and describe experimental data previously unexplained by quantum electrodynamics

Plasma processes in pulsar environments

The aim of this thesis is to study coherent plasma effects and collective plasma processes in pulsar environments. Pulsars are one of the most enigmatic objects in the universe. Formed in supernova explosions, pulsars are rapidly rotating neutron stars identified by their periodically pulsed electromagnetic emission. The source of the radiation is believed to be associated with the electron-positron (pair) plasma populating the pulsar magnetosphere. The theory of pulsar radiation is still in its infancy and there is lack of understanding about the energetic processes involved. The initial aim of this thesis is to study a possible emission mechanism in which electrostatic oscillations are coupled to propagating electromagnetic waves by a magnetic field inhomogeneity, thus creating a source of radiation in the pulsar magnetosphere. The full nonlinear equations in cylindrical geometry for a streaming cold pair plasma are solved numerically, together with Maxwell's equations, using a Finite-Difference Time Domain method. Electrostatic oscillations are induced in a streaming plasma in the presence of a non-uniform magnetic field, and the resulting electromagnetic waves are modelled self-consistently. Also presented is the linear perturbation analysis of these model equations perturbed from a dynamical equilibrium in order to probe the fundamental modes present in the system. These simulations successfully exhibit the coupling mechanism and the nonlinear interaction between electromagnetic waves and independent plasma oscillations, confirming the importance of coherent plasma effects and collective plasma processes in the pulsar magnetosphere. The observed electromagnetic signature is characterised by the nature of the emission mechanism and possibly by the menagerie of dust it encounters as it propagates through the surrounding supernova remnant. Supernova remnants are composed of multi-species electron-ion dusty plasmas. Conventional modelling of dust growth in this environment is based upon coagulation and nucleation of gas phase material. The second aim of this thesis is to study a possible spheroidal dust growth mechanism via plasma deposition. Dust grains immersed in a plasma acquire a net negative charge forming a plasma sheath. Ions are accelerated from the bulk plasma into the sheath and are deposited on the surface of the grain altering its shape and size. Grains with an elliptical geometry have a non-radial electric field and further anisotropic growth occurs if the deposited ions are non-inertial. In reality the extent of such growth depends upon the initial kinetic energy of the ions and the magnitude of the electric field in the sheath. Laplace's equation for the electric field for a range grain eccentricities is numerically solved using a bespoke finite difference method, the dynamics of the ions in the sheath are solved, showing how elliptical growth is related to the initial eccentricity and size of the seed relative to the sheath length