Abstract In this study, the microwave, i.e. 0.5 to 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 (S21-magnitude) was significantly lower and its phase (S21-phase) was shifted toward the low-frequency region. Based on the obtained S21-parameter (S21-magnitude and S21-phase), the electric permittivity (e) of CNF was extracted and showed clear differences depending on the thickness, i.e., ethin = 1.20 (0.28), emiddle = 1.84 (0.60), ethick = 6.30 (1.15) at 0.5 GHz (7.8 GHz). From the analysis of electromagnetic fields, the microwave conductivity (σmw) of CNF linearly increased with the increasing thickness, i.e., σmw/thin = 0.35 (S/m), σmw/middle = 0.58 (S/m), σmw/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.

中文翻译：

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不同微米级厚度碳纳米纤维薄膜的微波传输特性

摘要 在这项研究中，使用共面波导传输线对三种不同微米级厚度的碳纳米纤维(CNF) 的微波传输特性进行了实验研究，即0.5 至10 GHz。在实验结果中，当CNF的薄膜较厚时，信号传输水平（S21-幅度）显着降低，其相位（S21-相位）向低频区域移动。根据获得的 S21 参数（S21 幅度和 S21 相），提取 CNF 的介电常数 (e) 并根据厚度显示出明显的差异，即 ethin = 1.20 (0.28)，emiddle = 1.84 (0.60) )，ethick = 6.30 (1.15) 在 0.5 GHz (7.8 GHz)。从电磁场分析，CNF的微波电导率（σmw）随着厚度的增加而线性增加，即，σmw/thin = 0.35 (S/m)，σmw/middle = 0.58 (S/m)，σmw/thick = 0.75 (S/m)，这是由于 CNF 薄膜和 CPW 线之间增强的电磁场耦合。结果，我们证明了 CNF 薄膜对微波范围内的信号传输具有显着的衰减作用，这取决于薄膜厚度的微米级变化。