Frequency and density dependencies of the electromagnetic parameters of carbon nanotube and graphene nanoplatelet based composites in the microwave and terahertz ranges

Frequency and density dependencies of the effective conductivity and permittivity of carbon nanotube (CNT) and graphene nanoplatelet (GNP) based polymer composites are studied in the microwave (0.1-20, 26-36 GHz) and terahertz (0.2-1.0 THz) ranges. Strong frequency dependencies of the effective conductivity are associated with the screening effect occurred in individual nanoparticles and their agglomerates. Density dependencies are fitted with power-law formulas with frequency dependent exponents. Thin films comprising the CNTs or GNPs were proposed to consider as 'perfect' composites with the maximal possible electromagnetic interaction of the inclusions. Comparison between films and polymer composites has been done. The ratio of the microwave to terahertz conductivities of the composite is proposed to estimate the efficacy of GNP interaction with the electromagnetic field. Synergy effect in the enhancement of the effective microwave conductivity is demonstrated for the composite comprising a mixture of CNTs and GNPs.