Carbon nanofiber mats for electromagnetic interference shielding

This paper reports the electromagnetic interference shielding effectiveness of carbon nanofiber (CNF, originally called carbon filament) mats made from 0.16-μm-diameter catalytically grown CNFs by the paper-making process (1.7–13.1 MPa compaction pressure). These low-cost lightweight binderless mats (2.9–5.4 mm thick, 0.13–0.22 g/cm3 bulk density, 6.1–10 vol% solid) provide high shielding effectiveness (SE, 52–81 dB, 1.5 GHz) and high SE/density (370–470 dB cm3/g), though SE/thickness is low (14–18 dB/mm). Compared to the spun CNF mats of prior work, they exhibit higher SE, but lower SE/thickness. With consideration of SE, SE/thickness, and SE/density, the CNF mats are superior to graphene aerogel, reduced-graphene-oxide polyurethane foam and reduced-graphene-oxide aerogel of prior work, but are inferior to carbon nanotube mats, graphene film, carbon foam and flexible graphite of prior work. Absorption is the dominant shielding mechanism of CNF mats, so both SE and absorption loss tend to decrease with decreasing thickness. The absorption-loss/thickness tends to decrease with increasing thickness. The reflection loss is independent of the thickness, density or mass, indicating saturated reflection. The reflection-loss/density increases with decreasing density, suggesting that a higher degree of three-dimensional electrical connectivity, as provided by a lower density, enables the reflection to occur at a greater depth into the mat surface.