A perspective on the electromagnetic interference shielding behavior of nickel-coated filamentary carbons

This perspective provides a critical review of the electromagnetic interference (EMI) shielding behavior of nickel-coated filamentary carbons, including carbon fiber (CF), carbon nanofiber (CNF) and carbon nanotube (CNT). The nickel coating decreases the resistivity and provides magnetic character, which enhances shielding through absorption. The absorption loss SE_A dominates over the reflection loss SE_R. The CF can be continuous or discontinuous, whereas CNF and CNT are discontinuous. The continuous CF gives higher shielding effectiveness than discontinuous CF. Even without the nickel coating, continuous CF composites exhibit shielding effectiveness as high as 125 dB (1–2 GHz), which approaches the measurement limit and is higher than that of any discontinuous form of nickel-coated filamentary carbon. Preferred orientation of the discontinuous CF can be achieved by magnetic field application. Continuous CF is amenable to precise orientation control, including planar coil and linear configurations. The planar coil configuration accentuates the positive effect of the nickel coating on the shielding. The CNF and CNT are attractive for their high specific surface area, which enhances shielding because of the skin effect. Among the discontinuous filamentary carbons, nickel-coated CNF gives the highest shielding effectiveness of 87 dB (1–2 GHz). This material contains 94.4 vol% Ni, with diameter 0.4 μm and CNF core diameter 0.1 μm. The highest shielding effectiveness provided by nickel-coated CNT is 69 dB (8 GHz), compared to 50 dB without the coating. The highest shielding effectiveness provided by nickel-coated discontinuous CF is 80 dB (0.03–1.2 GHz).