Fig. 1. Schematic diagram of the tube waveguide

Fig. 2. Raman spectroscopy of experimentally prepared carbon black, SWCNTs and graphene

Fig. 3. Schematic diagram of a THz-TDS system

Fig. 4. Measured time-domain signals for tube with SWCNTs and without SWCNTs

Fig. 5. Measured frequency domain signal for tube with SWCNTs and without SWCNTs

Fig. 6. Simulated transmission spectra of tube with SWCNTs and without SWCNTs

Fig. 7. Simulated cross-sectional electric field distributions of the SWCNTs coated tube and the bare tube

Fig. 8. Measured frequency domain signal for a pure tube and tube with graphene or carbon black