Microwave transmission characteristics of carbon nanofiber films with different micrometer-scale thickness

In this study, the microwave, i.e. 0.5-10 GHz, transmission characteristics of carbon nanofiber (CNF) with three different micrometer-scale thicknesses were experimentally investigated using a coplanar waveguide transmission line. In the experimental results, when the film of CNF was thick, the signal transmission level (S-21-magnitude) was significantly lower and its phase (S-21-phase) was shifted toward the low-frequency region. Based on the obtained S-21-parameter (S-21-magnitude and S-21-phase), the electric permittivity (epsilon) of CNF was extracted and showed clear differences depending on the thickness, i.e., epsilon(thin) = 1.20 (0.28), epsilon(middle) = 1.84 (0.60), epsilon(thick) = 6.30 (1.15) at 0.5 GHz (7.8 GHz). From the analysis of electromagnetic fields, the microwave conductivity (sigma(mw)) of CNF linearly increased with the increasing thickness, i.e., sigma(mw/thin) = 0.35 (S/m), sigma(mw/middle) = 0.58 (S/m), sigma(mw/thick) = 0.75 (S/m), due to enhanced electromagnetic field coupling between the film of CNF and the CPW line. As a result, we demonstrated that the film of CNF has a significant attenuation effect on signal transmission in the microwave regime, depending on micrometer-scale changes in film thickness. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study experimentally investigated the microwave transmission characteristics of carbon nanofiber (CNF) with different micrometer-scale thicknesses. The results showed that the thickness of CNF film significantly affected signal transmission level and electromagnetic properties in the microwave regime, with changes in electrical permittivity and microwave conductivity observed as thickness increased.