Thin Surface Coatings to Provide Low Cost EMI Shielding and Surface Conductivity in Compo-site Structures

摘要

Fiber reinforced polymer composites are finding increasing application in Army aviation and missile sys-tems due to their high specific strength and superior in-sensitive munitions performance. As traditional metals are replaced with polymer composites, the inherent elec-trical conductivity and electromagnetic interference (EMI) shielding effectiveness are reduced. Additional-ly, polymer composites are more susceptible to impact damage than metal structures. This work explores the use of various thin surface coatings to reduce the surface re-sistivity, provide EMI shielding, and add impact damage resistance for non-conductive fiber reinforced polymer composite structures. Multiwall carbon nanotubes (MWCNT) possess excellent electrical properties at a fraction of the weight of metals; therefore, providing an excellent solution for EMI shielding of composites with only a surface coating. Additionally, extremely thin coatings of metal can achieve similar resistivity and shielding effectiveness as fully metallic parts with great weight savings. The use of surface coatings is more cost effective and less time consuming than methods of EMI shielding that are currently used for composite missile applications. Test method ASTM D4935-99 was used to measure shielding effectiveness in decibels (dB) across a frequency range of 30MHz-600MHz; and four-point re-sistivity measurements were made using test method ASTM D257-99. Damage tolerance of both the MWCNT and metallic coatings was evaluated by mea-suring damage area caused by various impact energies using ultrasonic scanning. Surface coatings are com-pared based on conductivity, weight, cost, and damage tolerance.