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

摘要

Thin metallic straight wires or thicker wire coils may be incorporated into composite materials to tune theiroverall electromagnetic (EM) properties, e.g., to render their index of refraction equal to 1, over a range offrequencies. These wire arrays act as scattering elements, providing controlled response to EM radiationsuch 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 forcoiled wire arrays due to the helical nature of the braiding process and the periodicity of laminatedcomposites. The coil's pitch and diameter, as primary EM tuning parameters, can be closely controlled inthe braiding process to optimize EM properties. Structural fibers are braided with copper wire to formindividual elements of the array. Additionally, thermoplastic matrix fibers are commingled into the coreand outer portions of the braid to facilitate complete fiber wetting of the composite and ensure structuralintegrity. These elements are woven, or oriented otherwise, into layers to form arrays with periodic spacingin three dimensions. The composite is then laminated, together with additional thermoplastic matrixmaterial, to yield a fully integrated system with tunable multifunctional properties. Chiral EM properties inthe composite, resulting from the helical configuration and periodic arrangement of the wires, can becontrolled or completely eliminated by design in the braiding and weaving processes. This paper dealswith the processing and characterization of the metallic coil polymer braids and serves as a companionpaper to a detailed study of EM properties and chirality effects, entitled "Metallic Coil-Polymer BraidComposites: Ⅰ. Numerical Modeling and Chirality".