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Multi-walled carbon nanotube aerogels in quasi-optical terahertz beams

The paper presents the modeling of the reflectance in the terahertz range from the plane-parallel aerogel layers formed by multi-walled carbon nanotubes (MWCNTs), which were synthesized via the original one-step technique using a preformed Fe–Co/CaO catalyst at 650–700°C in C2H4/Ar feedstock. With an increase in frequency from 100 GHz to 1.5 THz, the reflectance decreases by more than a factor of two. Based on the experimental data and the well-known wire medium model formed by a three-dimensional lattice of intersecting conductors, a model of a regular wire medium is constructed using MWCNTs with effective electrophysical characteristics equivalent to those of an irregular aerogel medium. This model reveals that a significant drop in the reflectance in the terahertz frequency range occurs because the plasma frequency of the equivalent medium is located here. The model allows estimating the properties of the aerogel environment in the frequency range extending up to 5 THz and with variations in the packing density of MWCNTs in aerogel. Estimates of the reflection, transmission, and absorption are presented for the case of normal EMI incidence on thin (submillimeter) layers of such a medium.