Analysis of slow‐wave propagation in coplanar transmission lines with inkjet printed multiwalled carbon nanotubes network

Abstract

This article investigates the propagation along coplanar waveguide (CPW) structures, where multiwalled carbon nanotubes (MWCNTs) network layers are deposited using inkjet printing. Electrical parameters are extracted from measured S-parameters data over the frequency range from 10 MHz to 26.5 GHz. The results clearly demonstrate two distinct propagation modes. At low-frequencies, a slow-wave factor up to 7 is achieved. With increasing frequency, attenuation becomes significant, while the propagation constant tends to a linear TEM regime. An equivalent lumped element circuit for CPW structure with MWCNTs network is developed and describes well the measured behavior up to 26.5 GHz. Thanks to the extracted equivalent circuit, the origin of the observed slow-wave phenomenon is confirmed: it is ascribed to a larger capacitance per unit length of the CPW line induced by the presence of the CNTs network that prevents/limits the expansion of fields into air.