Multi-walled carbon nanotubes (MWNT) are characterized at X-band (8-12 GHz) by waveguide measurements. The scattering parameters (S-parameters) of thin MWNT papers containing a large ensemble of randomly oriented nanotubes are measured by a vector network analyzer. An extraction algorithm has been developed to compute the effective complex permittivity (epsiv = epsiv' - j epsiv") and permeability (mu = mu' - j mu") of the MWNT papers from the measured S-parameters. The extracted effective medium parameters are verified by finite-element simulations using Ansoft HFSS. The uncertainties for this characterization method are analyzed. The extracted conductivity of the MWNT papers is on the order of 1500 S/m and the dielectric constant is on the order of -500. No significant magnetic responses are observed. To overcome the relatively large uncertainty associated with the reflection coefficient Sll, the extracted imaginary permittivity (epsiv") is fitted by the Drude model and the dielectric constant (epsiv') and permeability are recalculated.
"ARBON nano-tube (CNT) composites have potential electromagnetic and space applications due to their high conductivity and absorption mechanisms. Some of the complex permittivity and permeability extraction techniques for CNT composites are reported in –. The objective of this paper is to demonstrate the possibility of characterizing CNT composites in a waveguide of square cross section, which enables us to measure the complex permittivity and complex permeability with all four possible rotations of the sample. "
[Show abstract][Hide abstract] ABSTRACT: Multiwalled carbon nanotube (MWCNT) composites are characterized within 8-10 GHz using a waveguide of square cross section. The complex permittivity is extracted and empirical expressions are obtained as a function of frequency by minimizing the difference between the measured and theoretical values of the scattering parameters. Composites with CNT concentrations ranging from 0%-20% are investigated. The square cross section of the waveguide allows for different orientations of samples to test the anisotropy of MWCNT composites.
"The sample used in our experiment is a sheet form of MWNTs with a thickness of 88.9 m ( 3.5 mil), manufac- Fig. 1. MWNT paper photograph (left) and a 3.8 m 2 2.8 m SEM image (right) (From ). Fig. 2. Experimental setup. "
[Show abstract][Hide abstract] ABSTRACT: Multiwalled carbon nanotubes (MWNTs) are characterized at X-, Ku-, Ka-, and Q-bands by rectangular waveguide measurements. The scattering parameters (S-parameters) of thin MWNT papers containing a large ensemble of randomly oriented nanotubes are measured by a vector network analyzer from 8 to 50 GHz. A rigorous extraction algorithm has been developed to compute the effective complex permittivity ( epsiv = epsiv'- jepsiv") and permeability ( mu = mu' - jmu") of the nanotube papers from the measured -parameters. The extracted effective medium parameters are verified by finite-element simulations using Ansoft's High Frequency Structure Simulator (HFSS). The uncertainties for this characterization method are analyzed. The systematic uncertainties are found larger at lower frequencies than at higher frequencies. The extracted conductivity of the nanotube papers is in the range of 810-1500 S/m and the dielectric constant is from 250 to 700. The extracted complex permittivity can be fitted with the Drude-Lorentz model for the 8-50-GHz frequency range. The effective medium theory is then applied to remove the impact of air in the nanotube paper.
IEEE Transactions on Microwave Theory and Techniques 03/2008; 56(2-56):499 - 506. DOI:10.1109/TMTT.2007.914627 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Study on a novel polarized nano-material (PNM) textile for microwave application has been carried out in this paper. Based on the PNM textile fabricated by Tsinghua-Foxconn Nanotechnology Center, we set up a waveguide test bed to evaluate different kinds of polarized PNM samples. In this paper, Crossed polarized, horizontal polarized and vertical polarized samples (all in waveguide) have been measured in the proposed test bed respectively. Experimental results show the polarization of the nanotube has dominant effect on the performance. The vertical polarized sample has the best performance in shielding effectiveness, the isolation between the two ports of the transmission waveguide is better than 15 dB in average by using 20 layers of PNM yarns, and the horizontal polarized sample is almost invisible. This experiment gives a much deeper sight on the electromagnetic shielding principle of the nanotube materials, and will advance the application of PNM materials in many fields.
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