Negative permittivity behavior of aligned carbon nanotube films

Abstract

This paper reports a negative permittivity of aligned carbon nanotube (CNT) film materials by mechanical stretching. A CNT laminate with five layers of aligned CNT film exhibited unique negative permittivity, which was measured with waveguide method. Based on the microscopic morphology of aligned CNTs, a structure model from classical periodic array was introduced to describe the CNT arrangement and investigate the negative permittivity behavior of aligned CNT film. The influences of film's electrical conductivity, radius of CNT bundle, and lattice constant of aligned CNT assembly on real part of permittivity were discussed. Both experimental and simulation results indicate that the negative permittivity of aligned CNT film is closely related to its stretching ratio. The real part of permittivity drops below zero when stretching ratio reaches a certain level, which is about 15% stretching ratio in our experiment, and then it keeps decreasing with increasing stretching ratio.