Effects of Multi-walled Carbon Nanotubes on the Electromagnetic Absorbing Characteristics of Composites Filled with Carbonyl Iron Particles

The electromagnetic (EM) wave absorbing property of silicone rubber filled with carbonyl iron particles (CIPs) and multi-walled carbon nanotubes (MWCNTs) was examined. Absorbents including MWCNTs and spherical/flaky CIPs were added to silicone rubber using a two-roll mixer. The complex permittivity and complex permeability were measured over the frequency range of 1-18 GHz. The two EM parameters were verified and the uniform dispersion of MWCNTs and CIPs was confirmed by comparing the measured reflection loss (RL) with the calculated one. As the MWCNT weight percent increased, the RL of the spherical CIPs/silicone rubber composites changed insignificantly. It was attributed to the random distribution of spherical CIPs and less content of MWCNTs. On the contrary, for composites filled with flaky CIPs the absorption bandwidth increased at thickness 0.5 mm (RL value lower than 5 dB in 8-18 GHz) and the absorption ratio increased at lower frequency (minimum 35 dB at 3.5 GHz). This effect was attributed to the oriented distribution of flaky CIPs caused by interactions between the two absorbents. Therefore, mixing MWCNTs and flaky CIPs could achieve wider-band and higher-absorption ratio absorbing materials.