Several theoretical papers, and some experimental papers, have suggested that the well-known phenomenon of optical rotation and dichroism that results from the handedness of certain molecules or polymers may also be observed at micro- and millimeter-wave frequencies by introducing a chiral microstructure in an ordinary dielectric material. In this paper, we describe the preparation of chiral dielectric composite slabs that contain a random distribution of miniature helices. Samples containing 1) right-handed only, 2) left-handed only, and 3) an equal mixture of left- and right-handed springs of various concentrations were prepared. The reflection properties of the metal-backed samples were measured with a free-space system using a pair of spot focusing antennas and a vector network analyzer. The results were then compared with an ordinary composite containing a random distribution of metal spheres, each of which has the same volume as the helices and are dispersed at the same concentration as the samples containing helices. In this way, we could isolate the effects of chirality (as well as other geometrical factors pertaining to the microstructure) and study the effects of such factors on the reflection properties of the composite slabs. It is concluded that chirality can be used as a sensitive parameter to control EM wave propagation characteristics in dielectric composites. © 1990 IEEE
