Enhanced electromagnetic characteristics of carbon nanotubes/carbonyl iron powders complex absorbers in 2–18 GHz ranges

The electromagnetic (EM) characteristics of the carbon nanotubes/carbonyl iron powders (CNTs/CIPs) complex absorbers synthesized by mixing CNTs with CIPs were studied at 2–18 GHz, for the aim of the absorbing coating with thinness, lightness, width, and strength. Compared with CIPs, the CNTs/CIPs composites had higher electrical conductivity, permittivity, and dielectric loss, which gradually increased with the increasing CNTs content (WCNTs). Among them, with WCNTs = 2.2 %, a reflection loss (RL) exceeding −20 dB was obtained in the frequency range of 6.4–14.8 GHz for a coating thickness of 1.2–2.5 mm. Particularly, a minimum RL of −33.3 dB was found at 11.2 GHz corresponding to a matching thickness of 1.5 mm. The excellent EM-wave absorption properties are a consequence of a proper EM matching and enhanced absorption abilities resulting from the addition of a small quantity of CNTs with high electrical conductivity, permittivity, and dielectric loss. Thus, CNTs/CIPs complex absorbers may be promising candidates for EM-wave-absorption materials with strong-absorption, thin-thickness, light-weight, and low-cost.

Research highlightsThis study suggests that with the permeability unchanged, the absorbing coating with thinness, lightness, width, and strength can be achieved by raising the dielectric constant and dielectric loss within a certain range. Therefore, the carbon nanotubes/carbonyl iron powders (CNTs/CIPs) complex absorbers were synthesized by mixing a small quantity of the CNTs of lightweight, high permittivity, and high conductivity with the CIPs of high magnetic loss and large density. The investigation of the electromagnetic characteristics showed that conductivity, permittivity, and dielectric loss corresponding to the CNTs/CIPs complex absorbers regularly augmented with the increase of the CNTs mass fraction (WCNTs). Thereinto, the wax-composites containing 35 vol% CNTs/CIPs with WCNTs = 2.2 % exhibited excellent electromagnetic-wave absorption properties, with a minimum RL value of −33.3 dB at 11.4 GHz on a coating with a matching thickness of 1.5 mm and <−20 dB (99 % attenuation of the incidence wave) with thickness of 1.2–2.5 mm in the 6.4–14.8 GHz. The enhanced electromagnetic-wave absorption properties are a consequence of a proper EM matching and high absorption abilities originating from the addition of a small quantity of CNTs with high permittivity and dielectric loss. Compared to the reported literatures, obviously, the method reported here is more concise and efficient and the absorbing bandwidth (RL ≤ −20 dB) gained in the 6.4–14.8 GHz are broader. Thus CNTs/CIPs complex absorbers may be promising candidates for electromagnetic-wave absorption materials with strong-absorption, thin-thickness, light-weight, and low-cost.