MEASUREMENT OF THE ELECTROMAGNETIC PROPERTIES OF CHIRAL COMPOSITE-MATERIALS IN THE 8-40 GHZ RANGE

Materials described by the constitutive equations D = epsilonE + betae psilon del x E and B = muH + betamu del x H lack inversion symmetry du e to chirality or handedness in their microstructure. In this paper, w e describe the first direct measurements of the material properties ep silon, mu, and beta for microwave chiral composite materials prepared in our laboratory in the frequency range of 8-40 GHz. We have used bot h reflection and transmission measurements for normally incident , lin early polarized plane waves in a specially designed free-space facilit y using spot focusing antennas. Different concentrations of the chiral inclusions in the form of miniature metallic springs that are left-ha nded only, right-handed only or equally mixed (racemic) have been stud ied. It is shown that epsilon and mu are comparable for all three samp les at a given concentration, but beta has equal but opposite values f or the left- and right-handed samples, whereas it is nearly zero for t he equichiral sample. The values of beta thus obtained are compared to estimated values for suspensions of naturally occurring chiral molecu les. The accuracy of the measurements is assessed by using the experim ental procedure and inversion algorithm for standard materials like qu artz. A new technique involving time domain repines has been used to r emove the ambiguity that is usually encountered in the inversion of me asured S parameters.