Electromagnetic wave absorption properties of carbon nanotubes-epoxy composites at microwave frequencies

This paper focuses on the absorption properties of electromagnetic waves, both electric and magnetic, from multiwalled carbon nanotubes (MWCNTs)-epoxy composites. A microwave resonant cavity was utilized as a probe. Six groups of MWCNT-epoxy composite samples with different MWCNT outside diameters (ODs) were fabricated and tested. The weight percentages of MWCNTs in each sample group were in the range of 1%-10%. The line widths at half-power-maxima, the shifts in resonant frequency under load, and the amplitudes of the absorption profiles for the six groups of composite samples were compared. In general, the MWCNTs with smaller ODs had higher microwave absorption efficiency at 9.968 GHz than the large diameter ones. However, the sample group M5 (OD <8 nm) showed unusual results, a lower microwave absorption than other sample groups, even though the OD of the MWCNTs in the sample group M5 was smaller than those of other groups. The scanning electron microscope analysis and microwave absorption measurements showed that the microwave absorption efficiency of the CNTs was strongly affected by the morphologies of MWCNTs in individual bundles. It was found that a higher density of MWCNTs in the CNT bundles results in relatively lower efficiency in absorbing the microwave fields at the central frequency of 9.968 GHz. (C) 2010 American Institute of Physics. [doi:10.1063/1.3477195]