Caracterização eletromagnética de filmes poliméricos e de nanocompósitos poliméricos na faixa de micro-ondas

Abstract

Carbon nanotubes have become promising for the manufacture of electro-electronic devices. Since their discovery, a wide range of applications have been developed mainly in the civil, industrial, military and aerospace sectors, which leveraged research in the areas of sensors, especially for gases and liquids, antennas and materials for the mitigation of electromagnetic compatibility problems.

The development of new devices using nanomaterials requires their characterization, be it microscopic and/or macroscopic. The electromagnetic characterization is necessary when you want to know the interaction of an electromagnetic field with a material, and often requires the use of expensive equipment and also a complex preparation of samples.

In this work the parallel plate method, a common method for dielectric material characterization, is used to perform an electromagnetic characterization of thin films in the microwave range. Generally this technique is used for low frequency applications. This limitation is due to the fact that above the resonant regions, the expressions used in the model to characterize the electrical permittivity are no longer valid. For the present study, this problem is circumvented by using a computational tool based on the Finite Element Method (FEM). The procedure allowed comparing the simulated and experimental results, recovering the parameters through an optimization process, which made it possible to extract the electrical permittivity and also, the magnetic permeability and the electrical conductivity of the films.

The method was applied to characterize Polyurethane with Carbon Nanotubes (PU+NTCs), Polyurethane (PU) and Polytetrafluoroethylene (PTFE) in the 9 kHz to 3 GHz range using a Vector Network Analyzer (VNA). The results showed that the use of a computational tool expanded the frequency applicability of the parallel plate method. To obtain more accurate results and minimize errors, the measurements and simulations were subjected to two calibration methods.