Wideband (10–67 GHz) Dielectric Properties of Biosourced Cellulose Ester Flexible Films

Abstract

In this article, the dielectric properties of a biosourced polymer are investigated. To that end, coplanar transmission lines were fabricated on a 600- $\mu \text{m}$ thick cellulose palmitate substrate by using a photolithographic process and a transfer technique. The ${S}$ -parameters of the transmission lines were measured in a broad microwave frequency band spanning from 10 to 67 GHz in order to determine the propagation constant. From these data, the complex dielectric permittivity was extracted by using two analytical methods (RLCG method, based on resistance, inductance, capacitance and conductance of transmission lines and conformal mapping method) and a numerical one [finite element method (FEM)]. The three methods allow distinguishing the dielectric losses from the total measured losses of the transmission lines. Finally, the dielectric constant and the loss tangent of this biopolymer were compared to the data of common and commercially available substrates: polyimide and polyethylene naphthalate.