SBIR Program Yields Lightweight, Highly Conductive Electromagnetic Shielding Coatings

  • Published
  • By Heyward Burnette
  • Materials and Manufacturing
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  The Air Force Research Laboratory Small Business Innovation Research partner Conductive Composites Company created nanostructured materials and coatings that--in their capacity to provide conductivity and shielding for a variety of applications--are collectively poised to become standard technology in the electromagnetic material designer's toolbox. Specifically, the company's lightweight, highly conductive carbon fiber composites can be used to tailor the electromagnetic properties of polymer materials (e.g., coatings, resins, adhesives, and elastomers) and are therefore especially relevant to the development of structures able to survive high-power microwave and directed energy attack. While the newfound ability to incorporate these conductive materials directly into a composite offers weight advantages, labor savings, and fabrication time reduction, it also overcomes several challenges associated with previous methods requiring foils and appliqués. Of the materials available in the newly developed suite, nickel (Ni) chemical vapor deposition-coated nonwoven materials are the first to have reached continuous manufacturability.  The most promising shielding material developed during this SBIR effort is a NiCVD-coated, nonwoven-carbon-fiber-based "broad good" (e.g., paper or cloth). In addition to being the thinnest, lightest, and most effective shielding material that is currently available commercially, the technology matches the per-gram shielding efficiency of carbon nanotube sheets. Creating this end product involves coating a continuous roll of the broad good with the coating material (via NiCVD reactor). This method enables the outer surfaces of the fibers and the binders to be coated with a thin, uniform film of pure, ductile Ni. The film may be as thin as 50 nm or as thick as 1-2 µ, but a film of about 200 nm provides the most effective return for shielding applications.

NiCVD-coated nonwoven material is available on a continuous roll basis. Rolls of a 28 in. width and several hundred feet in length are regularly produced on a pilot scale coater. The small pilot process is capable of producing 25 ft2/hr. These rates have precipitated product prices in the realm of dollars per square foot. The process is readily scalable to any width of reactor and any size of feed roll. Performed on a reel-to-reel basis, the manufacturing process has very high throughput capabilities and is also suitable for coating Kevlar, felts, foams, and woven cloths. Once manufactured via this technique, the NiCVD nonwoven material can be co-cured directly into laminate structures or applied as a secondary operation.

Base carbon nonwoven materials are typically 8 gsm, and the addition of the Ni coating can occur anywhere in the range from 2-100 gsm. At Ni's weight of 7 gsm (for 15 gsm total), the material affords approximately 55 dB of broadband shielding effectiveness. Further, stacking these sheets will provide an additional 20 dB of shielding per layer. For other applications, such as lightning strike protective material, NiCVD-coated materials present advantages over conventional materials.