SCATTERING OF ELECTROMAGNETIC-WAVES BY HELICES AND APPLICATION TO THEMODELING OF CHIRAL COMPOSITES .1. SIMPLE EFFECTIVE-MEDIUM THEORIES

A boundary element code is used to study the electromagnetic field sca ttered by a helix at microwave frequencies. The far-field forward and backward scattering amplitudes are computed for an incident linearly p olarized wave with various polarization directions, and a number of or ientations of the helix. These computations allow us to study the magn itude of the field scattered in the forward and backward directions as a function of frequency and orientation. They are also the starting p oint for computing the effective wavenumbers of left and right circula rly polarized waves in a chiral composite made of a dispersion of heli ces in a host medium. Several methods to compute the effective impedan ce of chiral composites in order to obtain all three constitutive para meters of such media are proposed. Numerical results are given and com pared with existing experimental and theoretical data.