Scattering of electromagnetic waves by helices and application to the modelling of chiral composites. I: simple effective-medium theories

Abstract

A boundary element code is used to study the electromagnetic field scattered by a helix at microwave frequencies. The far-field forward and backward scattering amplitudes are computed for an incident linearly polarized wave with various polarization directions, and a number of orientations of the helix. These computations allow us to study the magnitude of the field scattered in the forward and backward directions as a function of frequency and orientation. They are also the starting point for computing the effective wavenumbers of left and right circularly polarized waves in a chiral composite made of a dispersion of helices in a host medium. Several methods to compute the effective impedance of chiral composites in order to obtain all three constitutive parameters of such media are proposed. Numerical results are given and compared with existing experimental and theoretical data.

Rayleigh scattering by an infinitely long tube with a helical permittivity dyadic

“…As the permittivity dyadic (ρ) has a helical structure, the absence of cross-polarized components in the scattered field may strike one as a bit odd at first glance. This is because scattering by simple helices, multifilar helices and cylinders made of chiral materials [11][12][13] displays TE ↔ TM polarization conversions.…”

Experimental Characterization of Chiral Uniaxial Bianisotropic Composites at Microwave Frequencies

“…This is because of the symmetry on plane, as the array is invariant with respect to 90 rotation around its axis . Plane-wave excitation of a helix parallel with the wave polarization [35] generates a scattered magnetic field component, which is parallel with the incidence polarization. This indicates the ability of the helix in generating coupled fields and rotating the polarization.…”

The simulation of effective parameters of composite media with embedded metal-dielectric thin fibers

“…There are several techniques, based on the theory of effective media, that allow to find effective permeability ( eff μ ) and permittivity ( eff ε ) of the media using the characteristics of EMW interaction with a standalone inclusion. Radar cross section or polarizability may be the interaction characteristics [4,5]. The research shows the techniques and results of modeling of effective electrodynamic properties of the media, representing dielectric matrix with embedded thin wire conducting inclusions covered with a thin dielectric layer.…”

“…To calculate the effective parameters Maxwell-Garnett model is applied [4]: (7) where tr is the sum operator of tensor's diagonal elements, m ε , m μ are relative permittivity and permeability of the composite media, respectively, n is the concentration of inclusions.…”