Carbon nanotube (CNT)/cellulose composite materials were fabricated in a paper making process optimized for a CNT network to form on the cellulose fibers. The measured electric conductivity was from 0.05-671 S/m for 0.5-16.7-wt% CNT content, higher than that for other polymer composites. The real permittivities were the highest in the microwave region. The unique CNT network structure is thought to be the reason for these high conductivity and permittivity values. Compared to other carbon materials, our carbon CNT/cellulose composite material had improved parameters without decreased mechanical strength. The near-field electromagnetic shielding effectiveness (EMI SE) measured by a microstrip line method depended on the sheet conductivity and qualitatively matched the results of electromagnetic field simulations using a finite-difference time-domain simulator. A high near-field EMI SE of 50-dB was achieved in the 5-10 GHz frequency region with 4.8-wt% composite paper. The far-field EMI SE was measured by a free space method. Fairly good agreement was obtained between the measured and calculated results. Approximately 10-wt% CNT is required to achieve composite paper with 20-dB far-field EMI SE.

We fabricated multiwalled carbon-nanotube/cellulose composite papers and measured their temperature dependences of electrical conductivity. The dependences were described with the Sheng's fluctuation-induced tunneling ͑FIT͒ model. A possible mechanism of the electrical conduction in the composite paper was discussed in the context of the FIT model.

Low-frequency noise characteristics for carbon-nanotube (CNT)/cellulose composite paper were experimentally investigated. The measured low-frequency noise exhibited 1/f characteristics and can be explained by Hooge's empirical law. Large noise coefficients suggested that CNT–CNT junctions, not the CNTs themselves, are the dominant source of 1/f noise in the composite paper.