Chiral Slab Research Articles

Microwave absorption characteristics of chiral materials with Fe3O4-polyaniline composite matrix

Fe3O4-polyaniline composites have been prepared in which the concentrations of Fe3O4 are 10%, 15%, 20%, 30% and 40% by weight. Microwave chiral composites are then prepared employing copper helices as chiral inclusions and the Fe3O4-polyaniline composites as the matrix. The electromagnetic parameters of the chiral Fe3O4-polyaniline composites are measured using a circular waveguide method at 9.5 GHz, and the normal reflectance from a perfect conductor-backed chiral slab is calculated. The microwave absorption characteristics of the chiral Fe3O4- polyaniline composites are studied and compared with those of a non-chiral Fe3O4-polyaniline composite matrix. The results show that the addition of the chiral inclusions to the non-chiral matrix improves both the dielectric and the magnetic losses. As well as this improvement in losses, the chiral materials have higher microwave absorption. The optimal concentration of Fe3O4 in the matrix is about 15% to obtain the lowest reflectance of chiral Fe3O4-polyaniline composites.

The radiation of a semi-infinite chiral slab waveguide

The reflection and transmission coefficients of electromagnetic waves, whose transverse electric and magnetic field components possess a given symmetric distribution, have been determined by the rigorous analysis of these components at the aperture plane of a semi-infinite chiral slab, either embedded between two semi-infinite dielectric media and placed in front of an air half space, or totally immersed in a uniform dielectric medium. The discrete spectrum of incident and reflected surface modes as well as the continuous spectrum of reflected and transmitted modes have been taken into consideration in this analysis. The ensuing integral equations have been transformed, by using an appropriate complete set of basis functions, into a system of algebraic equations which have been solved numerically. The tangential components of the electromagnetic field at the aperture plane, the radiation field in the far region, as well as the transmission and reflection coefficients variation as a function of chirality have been obtained, and different excitation schemes have been analyzed. ©2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 335–340, 2000.

The radiation of a semi-infinite chiral slab waveguide

The radiation of a semi-infinite chiral slab waveguide

Electromagnetic Fields of a Thin Circula Loop Antenna Above a (Un)Grounded Multi-Layered Chiral Slabs: the Non-Uniform Current Excitation - Abstract

The technique of dyadic Green's function (DGF) expressed in terms of the normalised cylindrical vector wave functions is adopted in this study for examining the electromagnetic fields excited by one thin circular loop antenna above a (un)grounded multi-layered chiral slabs. The current carried on such a circular loop antenna is expressed in a generalized Fourier series so as to incorporate practical situations. Thereby, exact representations of the radiated fields in both near and far zones are obtained in closed form, in a superposition of the right-and left-handed circularly polarized waves. Furthermore, numerical results are presented to show the radiation characteristics of the loop antenna in different layered chiral slab structures. The contributions of the lower- as well as higher-order current excitations to the far-zone field are examined in detail.

BI-FDTD: A new technique for modeling electromagnetic wave interaction with bi-isotropic media

A novel FDTD scheme that can be used to effectively model the interaction of electromagnetic waves with bi-isotropic (BI) media is developed. This new technique exploits the fact that the electromagnetic fields in a BI medium may be decomposed into a set of two uncoupled waves, each of which may be viewed as propagating in an associated isotropic medium. The main advantages of this approach are the inherent simplicity of the resulting BI–FDTD scheme, and the ability to easily extend it to include dispersive bi-isotropic as well as bi-anisotropic materials. For purposes of illustration, the new BI–FDTD formulation will be validated for a one-dimensional chiral slab bounded by free space. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 239–242, 2000.

Scattering characteristics of the chiral slab for normally incident longitudinal elastic waves

Acoustically active materials (chiral materials) that lack centrosymmetry due to chirality in their microstructures can be characterized by the constitutive relations and governing equations for noncentrosymmetric, isotropic micropolar materials. Accordingly, two longitudinally, two right circularly and two left circularly polarized transversal elastic waves can propagate in chiral medium. Using appropriate field representations along with prescribed boundary conditions, scattering characteristics at chiral interfaces can be realized. In this paper, reflection and transmission characteristics of chiral slabs bounded by achiral media for longitudinally elastic waves with normal incidence are thoroughly discussed. Through the above investigations we are in a position to design the chiral slab by tailoring the material parameters and determine the number and the locations of approximately vanishing reflection of the chiral slab over frequency ranges of interest. Results obtained can be applied for the design of broadband acoustic impedance transformer and acoustic absorbers.

Mechanical Activity of a Chiral Slab Sandwiched between Achiral Half-Spaces

A plane wave propagating in effectively chiral composites (ECC) has been asymptotically investigated. In general, the ECC can be fabricated by embedding a helical arrangement of microstructures in the soft matrix. Such a material is mirror asymmetric or chiral; therefore, six independent wave numbers can be found. They are associated with two sets of nondispersive longitudinal fields and four sets of dispersive circularity polarized transverse fields. In this work, we study the reflected and transmitted fields of a normally incident plane wave propagating at achiral-chiral-achiral interfaces. The numerical study indicates that the longitudinal wave is unaffected by the sandwiched chiral layer, while the polarization of the transverse transmitted wave is significantly influenced by it. Furthermore, when a normally incident SV-wave (vertical shear wave) propagates in the upper half-space, the coupled SV- and SH-waves (horizontal shear wave) can be found in the lower half-space. The polarization of the transmitted field is affected by the handedness of the intermediate chiral layer.

Waveguide characterization of chiral material: experiments

This paper is devoted to waveguide experiments on chiral materials: the constitutive parameters are extracted from the measured response of two chiral slabs of different length. Practical aspects of the implementation are discussed. This includes the injection molding technique used to manufacture the chiral material. Preliminary investigations are performed to qualitatively assess the material properties. These are quantitatively confirmed by the extracted constitutive parameters. The measurements are validated by experiments on a reference material.

Elastic activity of the chiral medium

Chiral materials are noncentrosymmetric due to handedness in their microstructures. The elastic field behavior in a chiral medium is readily described herein using the governing equations and constitutive relations for noncentrosymmetric, isotropic micropolar materials. Accordingly, linearly polarized longitudinal waves and left and right circularly polarized transverse waves are eigenstates for elastic waves in the chiral medium. Consequently, by using appropriate field representations along with prescribed boundary conditions, scattering characteristics at chiral interfaces can be readily determined. In this paper, transmission characteristics, i.e., magnitudes and rotation angles, of the chiral slab bounded by achiral media for normally incident transverse waves are the focus of this investigation. Simulation results show the Cotton effect in the magnitude and rotation angle curves, verifying theoretically the elastic activity of a chiral medium.

Waveguide characterization of chiral material: theory

A new procedure to extract all three constitutive parameters of chiral material from waveguide measurements is presented. Two chiral slabs of different length must be measured. Their scattering parameters are inverted in a largely analytical way, complemented by a simple and fast convergent numerical algorithm. Tests with synthetic scattering data show the method to be very accurate and stable.

Reflection of obliquely incident plane wave from chiral slab backed by soft and hard surface

The general case of a plane wave reflection from a chiral slab backed by a soft and hard surface is considered. Fields in the chiral slab are represented in right-hand and left-hand circularly polarised basis. The same basis is used to derive the reflection dyadic. Expanding fields in circularly polarised vectors are advantageous, because circularly polarised waves are the eigenwaves of the chiral medium; moreover they are not coupled by the boundary condition of the soft and hard surface. However, there is some coupling at the interface of the chiral medium and free space, which complicates the analysis.

Reflection and transmission by a uniaxially bi-anisotropic slab under normal incidence of plane waves

In this paper plane-wave reflection and transmission phenomena in slabs of uniaxial bi-anisotropic media are theoretically considered. The axis direction is in the interface plane and normal incidence of the plane wave is assumed. Chiral reciprocal slabs and a special class of non-reciprocal media are covered. The study is relevant to recent experimental studies of arrays of parallel spirals. The present theory gives an analytical model of such artificial bi-anisotropic media.

Scattering Characteristics of the Chiral Slab for Normally Incident Transverse Waves

The elastic field behavior in a chiral medium is readily described using governing equations and constitutive relations for noncentrosymmetric, isotropic micropolar materials. Accordingly, two longitudinally, two left circularly and two right circularly polarized elastic waves can propagate in a chiral medium. Using appropriate field representations along with prescribed boundary conditions, scattering characteristics at chiral interfaces can be readily determined. In this paper, reflection and transmission characteristics of the chiral slab bounded by achiral media for normally incident transverse waves are thoroughly discussed. The method for approximately determining the vanishing reflection of the chiral slab over related frequency ranges is elucidated. Simulation results show that the scattering characteristics of the chiral slab can be designed by tailoring the material properties. These results can be used to design acoustic impedance transformers and acoustic absorbers.

Plane wave propagation through a uniaxial chiral slab and transmission coefficient

Plane wave propagation through a uniaxial chiral slab and transmission coefficient

Plane wave propagation through a uniaxial chiral slab and transmission coefficient

Plane wave propagation through a uniaxial chiral slab and transmission coefficient

Inverse scattering problem for a stratified bi-isotropic medium at oblique incidence

Propagation of a transversely polarized time-harmonic electromagnetic plane wave in a stratified nonreciprocal chiral (bi-isotropic) slab under oblique incidence is considered. The inverse problem of reconstruction of material characteristics of a medium is studied. A reconstruction procedure is given and a uniqueness theorem is proven.

Plane wave reflection from a chiral slab backed by soft and hard surfaces with application to polarisation transformers

Plane wave reflection from soft and hard surfaces coated with chiral material is analysed for normal incidence. The fields inside the chiral slab are presented with circularly polarised eigenwaves. The eigenwaves are not coupled at the soft and hard surfaces: the coupling occurs at the interface between free space and chiral medium. Reflection coefficients are calculated and the polarisation properties of the reflected field are studied. The soft and hard surfaces coated with chiral medium can be used for applications such as polarisation transformers and twist reflectors.

Transition boundary conditions for simulation of thin chiral slab

Approximate two-side boundary conditions are deduced for the simulation of a thin chiral slab. It is also shown that, even in the leading approximation, when the thickness of a slab tends to zero, the transition conditions depend on chirality parameters, which leads to the possibility of studying the influence of a chiral slab on the external field in many diffraction problems.

Chiral slab polarization transformer for aperture antennas

The cross polarization of large aperture antennas can be eliminated by a chiral slab transformer in front of the aperture to obtain a more efficient field pattern. The inhomogeneous chirality distribution required can easily be achieved by using a mixture of right- and left-hand helices so that the total density of the helices is constant inside the slab. Reflection from the slab can be eliminated by a proper design.

Properties of a chiral slab waveguide

The symmetrized constitutive relations of Condon are used to find possible solutions in a waveguide formed from an isotropic chiral slab. Two eigenstates are found, related to positive and negative helicity plane-wave modes in an unbounded chiral medium. These eigenstates propagate along the slab, but are standing waves across the slab. Combinations of these eigenstates satisfy the boundary conditions when the slab is bounded by parallel conducting plates. The combinations are not transverse electric or transverse magnetic, but near cut-off these combinations correspond closely to TE or TM modes in achiral parallel-plate waveguides. Equations defining the dispersion relations are derived, and analytic solutions are obtained near cut-off and at high frequencies. At high frequencies one of the helicity eigenstates dominates, for all modes. Chirality of the slab medium splits the TE - TM degeneracy, but crossings of the dispersion curves are possible (and are demonstrated for a particular case).