Uniaxial Chiral Medium Research Articles

Scattering due to uniaxial anisotropic chiral medium-coated PEC cylinder with conducting helix loading

ABSTRACT A perfect electrically conducting (PEC) cylinder (having a circular cross-section) encapsulated with uniaxial anisotropic chiral medium was studied emphasizing the features of scattering. A conducting sheath helix structure having a varying orientation with respect to the optical axis (or pitch angle) was assumed to be at the outermost surface. This allows alterations in scattering patterns. The echo width of the structure was evaluated under the assumption of parallel polarized oblique incidence of waves. The effect on scattering was evaluated under varying chirality and permittivity of the coating medium along with the variations in the helix pitch angle. The obtained results are compared with those achieved by replacing the chiral coating with a simple anisotropic kind of medium (without chirality).

Scattering response of featured uniaxial anisotropic chiral medium-coated twisted PEC cylinder

Scattering of electromagnetic waves from a perfectly electrical conducting (PEC) cylinder of circular cross-section, coated with uniaxial non-magnetic chiral anisotropic medium, was discussed. A conducting sheath helix structure with adjustable pitch angle exists over the outer surface of coated cylinder, which is interfaced with the free-space. Under the uniform parallel polarized plane wave with fixed oblique incidence angle, the echo widths were determined emphasizing the other relevant scattering-related parameters (e.g. scattering/extinction efficiency etc.), taking into account different pitch angle values (of the sheath helix) and the kinds of coating mediums. The results revealed that the coating of negative uniaxial chiral medium causes enhancement in scattering efficiency (of the scatterer). Also, the scattering efficiency was found to be the same as the extinction efficiency, thereby yielding vanishing absorption of the medium. The obtained results were also compared with the situation of vanishing chirality of coating medium over the PEC cylinder; the echo width and scattering efficiency both decrease in this case.

Electromagnetic waves in parallel plate uniaxial anisotropic chiral waveguides

Theoretical analysis of electromagnetic wave propagation in planar waveguides filled with uniaxial chiral anisotropic media is presented. The guide parallel plates are assumed to be perfect electric conductors. The material filling the waveguide is a generalized medium that incorporates chiral and metamaterials. The behavior of the field intensities, the dispersion curves, and the energy flux for three varieties of uniaxial chiral media are examined numerically. The results demonstrate the phenomena of backward waves in uniaxial anisotropic chiral media. The comparisons of the computed results of the presented general formulations with published results for some material cases confirm the accuracy of the presented analysis.

Radiation properties of a uniaxial chiral quadratic inhomogeneous slab under oblique incidence

In this paper, the focussing of the transmitted electromagnetic field through a quadric inhomogeneous slab of lossless uniaxial chiral medium is derived using transmission coefficient under oblique incidence. The inhomogeneity in the uniaxial chiral slab has been incorporated through permittivity parameter. Asymptotic ray theory provides valid field everywhere except at focal point where it gives infinite value. Singularity of the field at focal point is addressed using Maslov's method. The derived analytical field expressions at caustic or focal point of uniaxial quadratic inhomogeneous slab have been solved numerically using MATHEMATICA. The effects of chirality parameter, axial permittivity, transvers permittivity, angle of incidence on the refracted field are discussed and the effects of Brewster angle on the focussed field are also discussed. The results obtained using Maslov's method are compared with Huygens–Kirchhoff's integral which are in good agreement.

Electromagnetic Characterization of Uniaxial Chiral Composites Using State Transition Matrix Method

An analytic frequency domain technique is presented for reconstructing constitutive parameters of uniaxial chiral media. First, forward analysis of the problem is discussed using 4 × 4 transition matrix method. Based on this analysis, a procedure is illustrated for retrieving all the constitutive tensor parameters of uniaxial chiral slab. In the proposed retrieval method, scattering parameters (reflection and transmission coefficients) are employed for plane wave incident normally on a uniaxial chiral slab. This characterization algorithm is based on the state transition matrix and its properties, discussed as two proven theorems. Unlike conventional methods, in this method it is not necessary to directly consider complicated eigenpolarizations of the uniaxial chiral medium resulting in complexity. To validate the proposed method, constitutive tensor parameters of two dispersive uniaxial chiral composites are retrieved at microwave frequencies. The results showed that when the scattering parameters combined with the properties of state transition matrix, they could provide a powerful technique for characterizing uniaxial chiral composites.

Propagation through uniaxial anisotropic chiral waveguide under DB-boundary conditions

The paper describes the propagation of electromagnetic waves through a cylindrical waveguide composed of uniaxial anisotropic chiral medium that is treated under the DB-boundary. The emphasis is given on the energy flux density in the guide considering varieties of chiral mediums and the waveguide dimensions. For this purpose, the eigenvalue equation is obtained using the appropriate boundary conditions, and the modal propagation constants of the guide are deduced. It has been investigated that the flux density mostly remains confined in the central regions of guide which, however, strongly depends on the type of waveguide medium as well as the dimensional measures. Both forward and backward wave propagations are observed in such guides – the feature essentially governed by the characteristics of the guiding medium.

Guided modes in the circular waveguide filled with uniaxial chiral medium

Guided modes in the circular waveguide filled with uniaxial chiral medium

Analysis Of Electromagnetic Field Transmitted By A Uniaxial Chiral Lens

—In this paper, the transmission of the electromagnetic waves through a plano convex lens of lossless uniaxial chiral medium is derived using dyadic transmission coefficient. Derived geometrical optics field is valid everywhere except at focal point where it gives infinite value.Singularity of the field at focal point is addressed using Maslov’s method. The effects of different constitutive parameters on the refracted field are also discussed.

Experimental Characterization of Chiral Uniaxial Bianisotropic Composites at Microwave Frequencies

This paper presents an experimental procedure for retrieving the effective constitutive parameters of chiral materials. Unlike past research that primarily deals with isotropic materials, this study considers a lossy uniaxial bianisotropic slab with a nonzero chirality along its axial direction. First, plane-wave scattering off the uniaxial slab in a free-space environment is studied analytically. This forward analysis gives insight into the problem and the choice of proper independent measurements required for the inverse process, i.e., retrieving the slab constitutive parameters from its S-parameters. Based on this analysis, three sets of co-polarized and cross-polarized S-parameters are required, including both the transmission and reflection coefficients of the slab. Given the measured scattering data, the complex permittivity, permeability, and chirality tensors are determined numerically using the results of the analytic study. To test the performance of the new retrieval method, an array of 2 × 56 long, metallic helices is designed and fabricated for operation at C-band. Having the same handedness, the helices are closely spaced and held in parallel to each other in a wooden frame in order to create an effective uni-axial chiral medium. A conventional transmission/reflection setup measures the array scattering parameters, which are fed into the retrieval process to obtain the effective parameters. The measured parameters well model the array scattering response, exhibiting a significant averaged chirality of ~0.4 over 5.5-8.7 GHz and a plasmonic behavior at ~7.1GHz.

CHARACTERISTICS OF GUIDED MODES IN UNIAXIAL CHIRAL CIRCULAR WAVEGUIDES

The characteristics of guided modes in the circular waveguide consist of uniaxial chiral medium have been investigated. The characteristic equation of guided modes is derived. The dispersion curves and energy ∞ux of guided modes for three kinds of uniaxial chiral media are presented. Unusual dispersion characteristics and negative energy ∞ux are found, i.e., backward wave is supported in the uniaxial chiral waveguide.

Light Propagation in Chiral Media with Large Pitch

The peculiarities of light propagation in uniaxial chiral media with large pitch are studied. In this case there are the forbidden zones for extraordinary beams. The existence of the forbidden zones leads to the effective reflection on zones boundaries and to damping of the wave inside the forbidden zone. We analyze the vicinities of the turning points and the transition of an extraordinary wave through the forbidden zone. It is shown that the optical effects for beams propagating near the turning points are equivalent to the tunnelling and reflection above the barrier for the parabolic potential barrier in quantum mechanics.

Light propagation in chiral media with large pitch

Light propagation in uniaxial chiral media with large pitch is studied. In these systems there are forbidden zones for extraordinary beams, which lead to effective reflection on zone boundaries and to wave damping inside the forbidden zone. We analyze the vicinities of the turning points and the transition of an extraordinary wave through the forbidden zone. Narrow forbidden zones with merging turning points are studied in detail. The transition through the forbidden zone is studied experimentally in nematic liquid crystal doped with a chiral addition. There is a good agreement between experimental results and theoretical calculations.

Analysis of diffraction from a uniaxial chiral slab with a two‐dimensional array of patches

AbstractDiffraction from a uniaxial chiral slab with a two‐dimensional periodic array of conducting patches is analyzed by the matrix‐based approach. Equatorial anisotropy is assumed for the chirality and permittivity whose optical axis is parallel to the plane of incidence. In the analysis, the total fields are given by the superposition of the current‐dependent scattering fields, which are expanded in terms of the two‐dimensional space harmonics and the incidence fields. The coupled mode equations for the equatorial uniaxial chiral media give the general solutions of fields as superpositions of elliptically polarized eigenmodes. The unknown currents on the patches are determined by applying the method of moments to the boundary conditions of the conducting array. In the numerical computations, the polarization characteristics of diffracted waves are investigated considering the design parameters. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(3): 1–8, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10293

MODES IN A HARD SURFACE WAVEGUIDE WITH UNIAXIALLY ANISOTROPIC CHIRAL MATERIAL FILLING - Abstract

Propagation of waves in circular waveguide with the boundary condition of hard surface is considered. The waveguide is filled with uniaxial chiral material. This study is a generalization of previously studied cases with isotropic chiral or anisotropic material filling. The eigenvalue equation is formed and the corresponding eigenmodes are presented. It is seen that the hard surface boundary condition simplifies the field analysis remarkable. While the eigenwaves in anisotropic waveguide were TE and TM fields in this more general case the eigenwaves are elliptically polarized hybrid fields. Since the eigenwaves are certain combinations of TE and TM fields and propagate with different propagation factors, uniaxial chiral medium can be used for polarization transformation. Reflection and transmission from a uniaxial chiral section of a waveguide is analyzed with numerical examples.

ELECTROMAGNETIC SCATTERING BY A MULTILAYER GYROTROPIC BIANISOTROPIC CIRCULAR CYLINDER - Abstract

In this paper, we investigate the electromagnetic scattering by a multilayer gyrotropic bianisotropic circular cylinder in free space. The coupled wave equations of longitudinal field components in the gyrotropic bianisotropic medium are derived. The eigenfunction expansion method is used to solve the scattering problem after uncoupling the coupled wave equations. A 12 × 12 or 16 × 16 linear algebraic equation is solved for two cases: one with the center being a perfect electric conducting (PEC) cylinder; and one without the PEC center, respectively. The gyrotropic bianisotropic media can be degenerated into gyrotropic medium, uniaxial bianisotropic medium, biisotropic medium and chiral medium etc. Numerical results presented for the last case was shown to agree exactly with published results. Numerical results of electromagnetic scattering by gyrotropic bianisotropic circular cylinders are presented also.

Analysis of Diffraction from a Uniaxial Chiral Slab with a Two-Dimensional Array of Patches.

Diffraction from a uniaxial chiral slab with a two-dimensional periodic array of conducting patches is analyzed by the 4 × 4 matrix-based approach. Equitorial anisotropy is assumed for the chirality whose optical axis is parallel to the plane of incidence. In the analysis, the total fields are given by the superposition of the current-dependent scattered fields which are expanded in terms of the two-dimensional space harmonics and the primary fields. The coupled mode equations for the equitorial uniaxial chiral media give the general solutions of fields as the superposition of elliptically-polarized eigen modes. The unknown currents on the patches are determined by applying Moment method to the boundary condition of the conducting array. In the numerical computations, the polarization characteristics of diffracted waves are investigated considering the design parameters.

Analysis of diffracted waves from a grounded uniaxial chiral medium with a plane metallic grating

Analysis of diffracted waves from a grounded uniaxial chiral medium with a plane metallic grating

Electromagnetic scattering by a conducting cylinder coatedwith a uniaxial chiral layer of varying thickness: generalized mode-matching method

Based on the concept of characteristic waves and the method of angular spectral expansion, cylindrical vector wave functions are developed to represent the electromagnetic waves in a uniaxial chiral medium. To illustrate how to use the present cylindrical vector wave functions in a practical way, a generalized mode-matching method is proposed to study the electromagnetic scattering of a conducting circular cylinder coated with a uniaxial chiral layer of varying thickness. The excellent convergence property of the bistatic echo width is numerically verified, which establishes the reliability and applicability of the present cylindrical vector wave functions and generalized mode-matching method for a two-dimensional problem with a curved surface coating of a uniaxial chiral medium.

Vector Wave Functions in Gyromagnetic Uniaxial Chiral Medium and Applications - Abstract

The gyromagnetic uniaxial chiral medium, which is a generalization of the well-studied reciprocal chiral material, can be created by mixing three sets of small metal helices in a host gyromagnetic medium (e.g., magnetically biased ferrite), with the axes of two sets perpendicular and parallel to a fixed direction, respectively, and the other set distributed in random orientations and locations. Based on the concept of characteristic waves and the method of angular spectral expansion, vector wave functions are rigorously developed to represent the electromagnetic fields in a source-free gyromagnetic uniaxial chiral medium. The analysis reveals that the solutions of the source-free vector wave equation for the gyromagnetic uniaxial chiral medium, which are composed of two transverse waves and a longitudinal wave, can be represented in sum-integral forms of the cylindrical vector wave functions. Addition theorem of the vector wave functions for gyromagnetic uniaxial chiral medium can be directly obtained from its counterpart for isotropic medium. To apply the present formulations for practical applications, an extended mode-matching method is proposed to study the two-dimensional electromagnetic scattering of a gyromagnetic uniaxial chiral cylinder with arbitrary cross section and a conducting circular cylinder with an inhomogeneous coating thickness. To check the convergence of the present cylindrical vector wave functions for multiple-body problem, electromagnetic scattering of two circular cylinders of gyromagnetic uniaxial chiral media is also investigated. Excellent convergence properties of the cylindrical vector wave functions in these application examples are numerically verified, which

Radiation from an open‐end circular waveguide filled with a uniaxial chiral medium

Radiation from an open‐end circular waveguide filled with a uniaxial chiral medium