Enhanced electromagnetic properties of carbon nanotubes and SiO2-coated carbonyl iron microwave absorber

The carbon nanotubes/SiO2-coated carbonyl iron (CNTs/CI@SiO2) composites were fabricated as microwave absorption materials (MAMs) by a simple mechanical mixing method for the purpose of the MAMs with lightweight, thin thickness, broad bandwidth and high oxidation resistance. The effects of different concentration of CNTs on the electromagnetic properties of the CNTs/CI@SiO2 composites were investigated. The results indicate that the complex permeability does not change obviously with the increasing concentration of CNTs because of the constant concentration of CI@SiO2 in the composites. While the complex permittivity and attenuation constant increase with the increasing concentration of CNTs, and the impedance matching ratio decreases with the increasing concentration of CNTs. The reflection loss (RL) calculation results show that 2 wt% CNTs mixed with 65 wt% CI@SiO2 has the optimum microwave absorption properties. The minimum RL is −51.54 dB at 15.44 GHz with a matching thickness of 1.41 mm. The bandwidth corresponding to the RL below −10 dB is more than 6.08 GHz with a thickness of 1.5 mm. The enhanced microwave attenuation ability, improved impedance matching in air-absorber interface and the quarter-wavelength cancellation are believed to contribute the excellent microwave absorption properties of the CNTs/CI@SiO2 composites.