Enhancement of Electromagnetic Wave Shielding Effectiveness of Carbon Fiber-based Fabrics via Carbon Fiber-Carbon Microcoil Hybrid Formation or H2 Plasma Treatment

Carbon fiber-carbon microcoil (CF-CMC) hybrids were formed on carbon fiber (CF)-based fabrics using thermal chemical vapor deposition system. For the CF-based nonwoven fabrics (c-NFs), the shielding effectiveness (SE) values were improved by the CF-CMC hybridization reaction, although the electrical conductivities of the nonwoven fabric were reduced by the CF-CMC hybrid formation. For the CF-based woven fabrics (c-WFs), the SE values were improved by more than twofold throughout the entire range of frequencies, owing to the CF-CMC hybrid formation. This dramatic improvement was partly ascribed to the enhanced electrical conductivity, particularly in the transverse direction to the individual CFs. Because the c-NFs consist of randomly oriented carbon fibers, the SE values of the samples based on c-NFs are higher than those of the samples based on c-WFs. For c-NFs, H2 plasma treatment was performed on c-NFs to improve the SE values. Consequently, the SE values of the c-NFs was significantly enhanced across the operating frequency range of 0.04 to 20.0 GHz. We compared the SE values of the H2 plasma-treated c-NFs samples with those of the c-NFs samples coated with nano-sized Ag particles. Despite having a lower surface electrical conductivity, H2 plasma-treated c-NFs samples exhibited a considerably higher SE than the Ag-coated c-NFs samples did, across the relatively high operating frequency range of 7.0 to 20.0 GHz. The carbon component of H2 plasma-treated c-NFs samples increased significantly compared with the oxygen component. The H2 plasma treatment transformed the alcohol-type (C-O-H) compounds formed by carbon-oxygen bonds on the surface of the native c-NFs samples into ether-type (C-O-C) compounds. Based on these results, we proposed a mechanism to explain the SE enhancement observed in H2 plasma-treated c-NFs.