Exact Matrix Representation of the Transverse Magnetic Multiple Scattering of Obliquely Incident Plane Waves by the Diffraction Grating of Penetrable Cylinders

“An exact matrix conformation model” associated with the equations describing the exact behavior of the Fourier-Bessel multiple scattering coefficients of the diffraction grating consisting of an infinite number of infinitely long parallel penetrable circular cylinders, corresponding to the obliquely incident transverse-magnetic plane waves in “Twersky-Wait-Kavaklıoğlu representation,” originally excogitated in (Kavaklıoğlu, 2000), is acquired, and the exact solution for “the Fourier-Bessel multiple scattering coefficients of the diffraction grating at oblique incidence” is obtained by a matrix inversion procedure

Modélisation et simulation de la diffraction électromagnétique par des laminés plans renforcés par des fibres cylindriques arrangées périodiquement

The contribution is about the electromagnetic modeling of fiber-reinforced periodically organized composite laminates. The final goal is to gain a good understanding of their electromagnetic behavior as well as to acquire images that should exhibit the location of possibly damaged zones, and provide some quantification of these zones. The thesis focuses on the scattering of well-organized periodic structures and building up an efficient full-wave computational model for multilayered composites, wherein each layer is reinforced by periodically arranged fibers, which is the first step for further investigation of the disorganized one.The work firstly considered the scattering problem of a slab in which infinite circular fibers, with the same radius, are periodically embedded with the same orientation of their axes and the same center-to-center distance. A 2-dimensional problem with normally and obliquely incident E- and H-polarized plane waves as well as Gaussian beams is firstly considered for understanding the principles and philosophies of the used mode-matching method and multipole expansion. Then the work is extended to the investigation if the scattering of the slab under illumination of a conically incident 3-dimensional electromagnetic wave, which shows the potential of the work for obtaining the response of the structure to a point source.A more practical but complicated multilayered composite, constructed by stacking up the slabs one over the other, is further investigated. Two different composites are taken into account. To study the first composite, with fibers in different layers having the same orientations, T-matrix- and S-matrix-based methods are introduced into the work for solving the linear system produced by mode-matching at the boundaries between two adjacent layers. Then, further investigation of the second kind of composite, wherein the fibers within different layers are orientated into different directions, is carried out by extending the approach properly.Some attention is also given to homogenization issues, so as to link small-scale approaches as developed in the thesis with large-scale ones as often considered in non-destructive testing of composite laminates.Extensive numerical simulations are proposed, validated whenever possible by reference results taken from the literature (notably in the case of photonic crystals) and the use of brute-force solvers. Emphasis is also on special cases of composites (glass-fiber- and graphite-fiber-based ones) as most often faced in practical applications, with appropriate frequency bands in harmony with the dielectric or conductive aspect of the fibers.La thèse porte sur la modélisation électromagnétique et la simulation de composites stratifiés plans (laminés), renforcés par des fibres organisées périodiquement. L'objectif est d'acquérir une bonne compréhension du comportement électromagnétique de telles structures, en première et étape de ce que pourrait ultérieurement être la production d’images mettant en évidence la localisation de zones éventuellement endommagées, et fournissant une certaine quantification de celles-ci. La thèse proprement dite se concentre donc sur la construction et l’évaluation de modèles de la diffraction électromagnétique par des composites multicouches tels que chaque couche est renforcée par des fibres disposées périodiquement.Est d’abord investiguée la diffraction par une plaque diélectrique (mono-couche) au sein de laquelle des fibres cylindriques de section circulaire de même rayon sont incorporées périodiquement, ces fibres ayant la même orientation de leurs axes et la même distance de centre à centre. Un cas bidimensionnel impliquant des ondes planes E ou H-polarisées, ainsi que des faisceaux gaussiens, normalement ou obliquement incidents, est d'abord pris en considération afin de mieux comprendre principes et philosophies des méthodes de choix, le couplage de mode et l'expansion multipolaire. Puis le travail est étendu, la diffraction de la plaque sous un éclairement tridimensionnel (conique) étant alors traitée en détail, ce qui montre aussi le potentiel de la méthodologie mise en œuvre si l’on souhaite obtenir la réponse électromagnétique de la structure à une source ponctuelle.Un composite multicouche, plus courant, mais plus complexe, qui est fait d’un empilement de plaques l'une sur l'autre, est alors étudié. Deux différentes espèces de composites sont ici prises en compte. Pour étudier la première, dont les fibres dans les différentes couches possèdent les mêmes orientations, des méthodes à base de matrices dites S ou dites T sont introduites, impliquant entre autre de s’intéresser à une résolution convenable du système linéaire produit selon le couplage de mode à la transition entre deux couches adjacentes. Une investigation de la deuxième espèce de composites suit alors, pour lequel les fibres au sein des différentes couches sont orientées dans des directions différentes quelconques, ce que permet une extension précautionneuse des approches précédentes. Une certaine attention est également portée au problème de l'homogénéisation des composites, de manière à lier les démarches à petite échelle telles que développées dans la thèse à celles à grande échelle souvent les seules prises en compte dans le contrôle non destructif et l’imagerie des composites stratifiés.De nombreux résultats de simulations numériques sont proposés et validés autant que possible par des résultats de référence de la littérature (notamment dans le cas de cristaux photoniques) et l'utilisation de solveurs « brute-force ». L'accent est aussi mis sur des cas particuliers de matériaux composites (ceux à base de fibres de verre et ceux à base de fibres de carbone) qui sont le plus souvent rencontrés dans les applications pratiques, avec des bandes de fréquences appropriées choisies en accord avec le comportement des fibres, principalement diélectrique ou principalement conducteur

Computational studies of linear and non-linear optical properties of nano-Structured metamaterials

In this thesis, a comprehensive analytical and numerical study of optical non-linear effects in plasmonic metamaterials is presented. The new results reported and described in this work can potentially have a significant impact on our understanding of electromagnetic phenomena in artificial optical materials, and facilitate the design and fabrication of new active optical devices with new or enhanced functionality. Equally important, these results could lead to deeper physical insights into the fundamental properties of these metamaterials. To this end, a new analytical formalism based on the multiple scattering theory has been developed, a theoretical framework that allows one to fully characterise the linear and non-linear electromagnetic properties of arbitrary distributions of metallic nanowires. This formalism is unique in allowing readily retrieval of the spatial distribution of the electromagnetic field both at the fundamental frequency (linear analysis) and the second harmonic (non-linear optical response). The formalism also allows for both frequency- and time-domain investigations. Based on this work, a new software tool with unique features has been implemented and used to achieve a better understanding of the intricate electromagnetic phenomena occurring in nano-structured plasmonic systems. In particular, this tool has been used to design and investigate numerically several new non-linear plasmonic structures and nanodevices with remarkable properties. Amongst them were non-linear plasmonic cavities with high quality factors, plasmonic cavities that support non-linear whispering gallery modes and sub-wavelength non-linear plasmonic sensors with enhanced sensitivity and reduced device volume. Several other plasmonic systems that show tremendous potential for the development of advanced metamaterials-based devices have also been explored. Specifically, it was demonstrated that nano-patterned metasurfaces can be employed to achieve polarisation controlled electromagnetic response in arrays of cruciform apertures and magnetisation induced second harmonic generation in chiralmetallic structures. The numerical investigation of photonic superlattices exhibiting zero effective index of refraction has also been discussed

A Mortar Element Method for the Analysis of Electromagnetic Passive Devices

The thesis consists of two blocks. The first and main block concerns the application of multi-domain spectral methods to the analysis of electromagnetic guiding structures. A general scattering formulation for vector differential problems is developed. The boundary-value problems are discretized using basis functions synthesized according to the mortar-element method. An analysis technique of the scattering generated by skew-incident plane waves on 2-D dielectric periodic structures based on this idea is proposed; the boundary-value problem describing these devices is given by the system of two coupled Helmholtz equations, therefore it exhibits a vector nature. Then, a technique aimed at analyzing axisymmetric structures using the same concept has been developed; in this case, the boundary-value problem arises from the transversalization of Maxwell’s equations written in cylindrical coordinates with respect to the angular coordinate. Half of the second block concerns the design of a low-frequency Vivaldi antenna in the framework of the Sardinia Array Demonstrator project. This antenna has been realized and preliminarily characterized with a prototypical measurement system developed by CNR-IEIIT. The second half of this block is focused on the development of a boundary-integral equation method aimed at analyzing dielectric lens antennas. A preliminary version of this code has been implemented and compared with commercial simulators. This activity has been performed in the THz Sensing Group of TU-Delft, Delft, Netherlands

Diffraction and scattering of high frequency waves

This thesis examines certain aspects of diffraction and scattering of high frequency waves, utilising and extending upon the Geometrical Theory of Diffraction (GTD). The first problem considered is that of scattering of electromagnetic plane waves by a perfectly conducting thin body, of aspect ratio O(k^1/2), where k is the dimensionless wavenumber. The edges of such a body have a radius of curvature which is comparable to the wavelength of the incident field, which lies inbetween the sharp and blunt cases traditionally treated by the GTD. The local problem of scattering by such an edge is that of a parabolic cylinder with the appropriate radius of curvature at the edge. The far field of the integral solution to this problem is examined using the method of steepest descents, extending the recent work of Tew [44]; in particular the behaviour of the field in the vicinity of the shadow boundaries is determined. These are fatter than those in the sharp or blunt cases, with a novel transition function. The second problem considered is that of scattering by thin shells of dielectric material. Under the assumption that the refractive index of the dielectric is large, approximate transition conditions for a layer of half a wavelength in thickness are formulated which account for the effects of curvature of the layer. Using these transition conditions the directivity of the fields scattered by a tightly curved tip region is determined, provided certain conditions are met by the tip curvature. In addition, creeping ray and whispering gallery modes outside such a curved layer are examined in the context of the GTD, and their initiation at a point of tangential incidence upon the layer is studied. The final problem considered concerns the scattering matrix of a closed convex body. A straightforward and explicit discussion of scattering theory is presented. Then the approximations of the GTD are used to find the first two terms in the asymptotic behaviour of the scattering phase, and the connection between the external scattering problem and the internal eigenvalue problem is discussed

13th Annual Review of Progress in Applied Computational Electromagnetics at the Naval Postgraduate School, Monterey, CA, March 17-21, 1997, Conference Proceedings Volumes I & II

Includes Volumes 1 &

Electromagnetic Scattering from a Structured Slab Comprised of Periodically Placed Resistive Cards

Coordinated Science Laboratory was formerly known as Control Systems LaboratoryJoint Services Electronics Program / N00014-84-C-014

Annual Review of Progress in Applied Computational Electromagnetics

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