Metallic Coil-Polymer Braid Composites: I. The Numerical Modeling and Chirality

Incorporation of metallic inductive elements into composites introduces a new opportunity to tune the overall electromagnetic (EM) properties of such materials over certain frequency ranges. The design can incorporate arrays of straight wire or coiled wire conductors. The straight wires must be very thin in order to tune the composite to operate within microwave regimes. Coil arrays, on the other hand, can use relatively thick wires. The coiled wires are integrated into the composite within reinforcing braids, where one or more metallic wires are woven with necessary polymer fiber bundles. The coils however introduce chirality in the EM response of the material. In this study we consider two approaches to cancel this chirality effect. One is to use a 1- or 2-D grid of left- and right-handed coils. This does not alter the frequency characteristics of the material, but requires more effort in the arrangement of the two types of coils during manufacturing. Another approach is to use a double coil, with the outer and the inner coils having opposite handedness. This method does not require the extra effort for the arrangement however needs more complex braids. It also shows interesting effects in the dispersion behavior of the material. Both methods will be discussed and some of the simulation results will be presented.