ELECTROMAGNETIC WAVE SCATTERING AND RADIATION IN MULTILAYERED CHIRAL MEDIA

Abstract

Chiral media, which were discovered in the last century, have been of much scientific interest, and many practical applications to scientists and engineers in many different fields (e.g., physics, chemistry, and biology). As a result of numerous applications in the fields of electromagnetic scattering, antenna radiation, and radio propagation, much attention has been paid to the interaction of electromagnetic fields with such chiral media during the past for decades. In this thesis, electromagnetic wave scattering and radiation in multilayered chiral structures are analyzed and the principle of scattering-to-radiation transform is developed, This theory is subsequently applied to Halve the problem of plane wave scattering by a multilayered achiral sphere in an infinitely extended chiral host medium. Scattering by a conducting sphere with an achiral coated layer in such a chiral host medium is also included. Firstly, an analytic analysis of electromagnetic scattering by an inhomogenous and multilayered chiral sphere is presented. Fields in each region of the multi-layered chiral sphere are obtained and expanded in terms of spherical vector wave functions. Their scattering coefficients are derived by applying boundary conditions at all the spherical interfaces and expressed in recursive coefficients matrices. After the correctness of the algorithm developed is examined, an inhomogeneous chiral sphere whose permittivity varies against its radial distance is then considered. The chiral sphere is discretized into ten layers, each of which is assumed to have approximately constant permittivity. The technique developed for a multilayered chiral sphere is then applied in the analysis. The algorithm developed is applicable to a chiral sphere of other dimensions and material characteristics for both parallel and perpendicular polarizations of the incident waves. Secondly, based on the scattering by multilayered structures of chiral media, the scattering-to-radiation transform is developed. In the analysis, the electromagnetic plane waves of parallel and perpendicular polarizations are equivalent to radiated waves due to two differently polarized electric sources located at infinity. The volumetric current distributions of the two sources at infinity are thus obtained. Instead of considering the electromagnetic plane wave scattering, we analyze the electromagnetic radiation due to the electric sources at infinity for the field distribution elsewhere outside of the scattering objects. To verify the transform, the method of vector wave eigenfunction expansion is utilized to derive electromagnetic scattered fields by such structures. Also, the electromagnetic fields are formulated in terms of integrals, consisting a volumetric current distribution and the dyadic Green's functions. The same expressions of the electromagnetic scattered fields are obtained by using the two methods in the cases of planar, cylindrical, and spherical scattering objects. It is thus concluded that scattering problems can be transformed into specific radiation problems where the radiated source of known distribution is located at infinity. Finally, the work is also extended to analyze the electromagnetic wave scattering by a multilayered achiral sphere in an infinitely extended chiral host media. Based on the scattering-to-radiation transform, the dyadic Green's function for unbounded chiral media and the sources located at infinity are utilized to obtain the incident waves, which are either circularly polarized or linearly polarized. Furthermore, the dyadic Green's function for multilayered spherically chiral media and the assumed sources are employed to calculate the scattered field in multilayered achiral media superimposed in chiral host media. Two cases are considered. The first one is a two-layered dielectric (lossless or lossy) sphere and the other is a concluding sphere with a dielectric coated layer. The dyadic Green's function for the latter case is modified in this thesis. Certain measurable polarization quantities, i.e., circular polarization and linear polarization degrees, are presented together with their interpretations.