Electromagnetic wave propagation in an almost circular bundle of closely packed metallic carbon nanotubes

An equivalent-multishell approach for the approximate calculation of the characteristics of electromagnetic waves propagating in almost circular (azimuthally symmetric), closely packed bundles of parallel, identical, and metallic carbon nanotubes (CNTs) yields results in reasonably good agreement with a many-body technique, for infinitely long bundles when the number of CNTs is moderately high. The slow-wave coefficients for azimuthally symmetric guided waves increase with the number of metallic CNTs in the bundle, tending for thick bundles to unity, which is characteristic of macroscopic metallic wires. The existence of an azimuthally nonsymmetric guided wave at low frequencies in a bundle of a large number of finite-length CNTs stands in contrast to the characteristics of guided-wave propagation in a single CNT. The equivalent-multishell approach yields the polarizability scalar and the antenna efficiency of a bundle of finite-length CNTs in the long-wavelength regime over a wide frequency range spanning the terahertz and the near-infrared regimes. Edge effects give rise to geometric resonances in such bundles. The antenna efficiency of a CNT bundle at the first resonance can exceed that of a single CNT by 4 orders of magnitude, which is promising for the design and development of CNT-bundle antennas and composite materials containing CNT bundles as inclusions.