Metallic Coil-Polymer Braid Composites: II. Material Processing and Characterization

Thin metallic straight wires or thicker wire coils may be incorporated into composite materials to tune their overall electromagnetic (EM) properties, e.g., to render their index of refraction equal to 1, over a range of frequencies. These wire arrays act as scattering elements, providing controlled response to EM radiation such as RF communication signals, radar, or other signals in the infrared range. Integrated into composites, the arrays further contribute to their structural integrity. Braided composites function as ideal hosts for coiled wire arrays due to the helical nature of the braiding process and the periodicity of laminated composites. The coil's pitch and diameter, as primary EM tuning parameters, can be closely controlled in the braiding process to optimize EM properties. Structural fibers are braided with copper wire to form individual elements of the array. Additionally, thermoplastic matrix fibers are commingled into the core and outer portions of the braid to facilitate complete fiber wetting of the composite and ensure structural integrity. These elements are woven, or oriented otherwise, into layers to form arrays with periodic spacing in three dimensions. The composite is then laminated, together with additional thermoplastic matrix material, to yield a fully integrated system with tunable multifunctional properties. Chiral EM properties in the composite, resulting from the helical configuration and periodic arrangement of the wires, can be controlled or completely eliminated by design in the braiding and weaving processes. This paper deals with the processing and characterization of the metallic coil polymer braids and serves as a companion paper to a detailed study of EM properties and chirality effects, entitled "Metallic Coil-Polymer Braid Composites: I. Numerical Modeling and Chirality".