ISSN:0920-5071    

DOI:10.1163/156939392X01291

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The main goal of this paper is to establish general constitutive relations for the electromagnetic fields E, D, B, and H in a time domain setting. The four basic assumptions of the medium are linearity, invariance to time translations, causality, and continuity. These four assumptions imply that the constitutive relations are convolutions of the Riemann-Stieltjes type. A review of the classification of media in bianisotropic, biisotropic, anisotropic, and isotropic media, respectively, is made. Dissipation and reciprocity are defined and the constraints these concepts make on the constitutive relations are analyzed. Furthermore, an appropriate form of time reversal and functions of positive type are introduced and some consequences of these concepts are showed.

ISSN:0920-5071    

DOI:10.1163/156939392X01309

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper discusses the macroscopic properties of heterogeneous media containing chiral components. Starting with the derivation of the polarizability matrix of a chiral sphere, the components of this matrix are used in calculating the effective constitutive parameters of a mixture consisting of a nonchiral background material in which chiral spherical scatterers are immersed. The analysis is quasistatic, i.e., the spatial variation of the fields is neglected in the scale of the particle dimensions, and the scattering effects are neglected, limiting the applicability of the results to low frequencies. Generalized Lorenz-Lorentz formulae and Maxwell-Garnett formulae are given, and all three effective material parameters of the mixture are seen to be dependent on all the material parameters of the components and their volume fractions. Still, there is symmetry in the mixing relations, and through perturbation analysis, it is shown that the chirality effect on the permittivity and permeability is of the second order. In later sections, ellipsoidal chiral inclusions and multiphase chiral mixtures are discussed, and finally the derived expressions are illustrated with graphs.

ISSN:0920-5071    

DOI:10.1163/156939392X01318

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The experimental results of optical activity investigations have been analyzed for three classes of wide band gap semiconductors: cubic crystals of the sillenite-type (point group 23) and tetragonal crystals of II - IV - V2(I - III - VI2) (42 m) and II - V2(422) types. The sign and magnitude of optical rotation in these semiconductors have been discussed on the basis of structural models of optical activity in terms of the coupled linear oscillators.

ISSN:0920-5071    

DOI:10.1163/156939392X01327

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Multiple reflection of light at the interface of an isotropic chiral medium (either transparent or absorbing) and a transparent achiral dielectric is studied as a function of angle of incidence and number of reflections to ascertain whether there is an enhancement (with respect to single-pass reflection) of (i) the difference in reflected left and right circularly polarized waves, and (ii) the ellipticity of reflected linearly polarized waves. It is shown that for ordinary reflection, where the mean refractive index n of the chiral medium is greate than the refractive index no of the incident medium, multiple reflection does not lead to a significant enhancement. However, in the vicinity of total reflection (no> n) the chiral asymmetries resulting from N reflections are significantly greater than those for one reflection; at critical angle the enhancement is approximately by a factor N.

ISSN:0920-5071    

DOI:10.1163/156939392X01336

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper describes the phenomena that occur when a Gaussian beam is reflected from a dielectric-chiral interface. These phenomena include an angular shift of the peak of the reflected fields in the far field and, near the critical angle or angles, a lateral shift of the fields in the plane of the interface, known as the Goos- Hänchen shift. The waist size of the reflected fields is also found to differ from that of the incident beam, and an apparent propagation distance known as the "focal shift" also arises. The spectral domain solution of the problem is described, and approximate formulas for determining the parameters for the reflected fields are derived. The problem is also solved numerically for three specific cases of interest and the results are compared to those predicted by the approximate formulas. Lateral, angular, and focal shifts are observed for both components of the reflected field near the critical angles for the interface. It is shown that both positive and negative lateral shifts occur when beams are reflected at the dielectric-chiral interface, whereas only negative shifts are observed for the dielectric-dielectric interface. These shifts are found to occur even when the dielectric constant of the chiral region is larger than that of the pure dielectric region, if a sufficient amount of chirality exists. In all cases well known results for the dielectric-dielectric interface are recovered by setting the chirality of the second medium to zero.

ISSN:0920-5071    

DOI:10.1163/156939392X01345

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Modal propagation of electromagnetic waves in waveguides filled with chiral media, known as chirowaveguides, is studied. The waveguide walls are assumed to behave as constant impedance surfaces. This can model corrugated surfaces, dielectric coated metallic surfaces, as well as perfectly or imperfectly conducting walls. Conditions leading to modes with pure circular polarization are derived. Under these conditions, a chirowaveguide can act as a low crosspolar feed for reflector antennas.

ISSN:0920-5071    

DOI:10.1163/156939392X01354

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Propagation of the electromagnetic wave in a symmetrical structure of two identical parallel guides coupled via a chiral medium is investigated using the coupled mode method. It is found that the chirality causes periodic transfer of energy between guides. Possible applications of the effects observed in the structure to the construction of depolarizers, polarimeters, diplexers, frequency meters, frequency/amplitude converters, sensors, switches, and modulators is discussed.

ISSN:0920-5071    

DOI:10.1163/156939392X01363

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Here the reflection from chiral coated planar surfaces is investigated. This canonical problem is formulated in terms of the Riccati equation for local reflection to provide an understanding of the fundamental physical processes involved with reflection and absorption by chiral layers. The link between chiral and achiral formulations is noted. We also derive jump conditions for thin chiral layers, introduce appropriate transmission-line models, and indicate methods for treating an arbitrary number of layers and surface impedances. A number of examples involving chiral coatings are examined and compared to their achiral counterparts for electric and magnetic screens. Through front surface matching and increased absorption, specified chiral coatings can offer enhanced broadband reduction of backscatter over their conventional achiral counterparts.

ISSN:0920-5071    

DOI:10.1163/156939392X01372

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Backscatter from curved metallic surfaces coated with chiral layers is investigated. Here we examine canonical cylindrical and spherical geometries to understand basic scattering and absorption mechanisms, and to find the efficacy of chiral coatings in reducing radar cross-section. Of special interest is the combined effect of the degree of chirality and structure curvature on backscatter cross-section for lossy screens. The physical principles underlying the reduction of scattering are discussed, fundamental formulations are given, and relevant comparisons to the planar geometry case are noted. The backscatter cross-section for coated curved surfaces can be intelpreted as a modulation of chiral planar results by achiral structural resonances.

ISSN:0920-5071    

DOI:10.1163/156939392X01381

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor