Anisotropic Microwave Conductivity Dispersion of Horizontally Aligned Multi-Walled Carbon-Nanotube Thin Film on Flexible Substrate

In this paper, the anisotropic conductivity dispersion of horizontally aligned multi-walled carbon-nanotube (HA-MWCNT) thin films on a kapton substrate are characterized at microwave range. It is well known that a single carbon nanotube (CNT) presents highly 1-D conduction. For a thin film composed of numerous aligned CNTs, the anisotropic conduction may be preserved to some extent, as this is useful for various applications. In this paper, the anisotropic conduction of HA-MWCNT thin films is investigated in a rectangular waveguide measurement setup. The anisotropic surface conductivities of the films along the nanotube axial and radial directions are extracted from the measured S-parameters. The results reveal an anisotropic conductivity ratio of about 2 for the HA-MWCNTs thin film. Furthermore, it is observed that the real part of the extracted conductivity remains constant over the frequency band while the imaginary part increases almost linearly with frequency.