Μερικές διαφορικές εξισώσεις και προβλήματα της επιστήμης των υλικών

Abstract

The main objective of this thesis is the homogenization of partial dierentialequations (mainly Maxwell'As equations) describing electromagneticphenomena in complex media. In particular, we study the homogenization ofMaxwell'As equations focusing on the periodic unfolding method in complexmedia under Drude-Born-Fedorov type, local in time, constitutive relations.Firstly, we formulate Maxwell'A s problem as an evolution initial value(Cauchy) problem in a Hilbert space supplemented with the constitutiverelations of a bianisotropic medium (the most general linear medium in electromagnetics).Further, we analyze the notion of homogenization and weapply it as examples to equations of elliptic type in divergence form and toMaxwell'As system in bianisotropic media.We present also the method of periodic unfolding in the case of an ellipticpartial dierential equation and in the main part of this work we considerthe problem of the well-posedness of the time-dependent Maxwell'As equationsin a Drude-Born-Fedorov type environment considering the elds to beelements of an appropriate Hilbert space. In order to prove the existence anduniqueness we apply the Faedo-Galerkin method and for the continuous dependencefrom the initial data we use semigroup theory for operators. Therest of the main part of the thesis deals with the homogenization of theconsidered problem, using the periodic unfolding method.In the last chapter, we examine the time-harmonic Maxwell problem ina bianisotropic cavity, which we study by transforming it to an eigenvalueproblem.