Caracterização das propriedades dielétricas de grafeno e materiais derivados de biomassa pelo método da cavidade ressonante

Abstract

The dielectric properties of materials are particularly interesting in telecommunications, mainly in the areas of transmission line, wave propagation and antenna theory. Among these ones, the relative electrical permittivity (εr) and the dielectric loss tangent (tanδ) are considered as the most relevant properties. Allying the investigation of new alternative dielectric materials with the regional questions about the generation of agricultural residues by rice cultivation (rice husk) and the advance of the grass species Annoni grass as an invader in native countrysides, and also with the study of carbonaceous materials, the main goal of this work is to characterize the dielectric properties of samples produced from graphene and graphite; ashes from rice husk (RHA) and from Annoni grass (AGA); and glass produced from RHA using the resonant cavity method. These ashes were obtained through two different burning processes: 400 °C - 30 min and 800 °C - 5 h. The analyzed graphene and graphite were benefited by industrial processes. And, the characterized glass were produced with RHA, obtained from burning process at 800 °C - 5 h, as silica source. The resonant cavity was projected with cylindrical geometry and frequency of resonance (f0) equal to 3:5 GHz. The εr constant of each sample was calculated from the experimental data measured with this device (frequency of resonance for each sample, fa) using specific empirical equations for each sample geometry and the respective tanδ were estimated with parametric simulations in the ANSYS HFSS® software. In this analysis, it was verified that the carbonaceous materials (graphene and graphite) and the ashes derived from the biomass exhibit high dielectric loss tangent values, mainly graphene and ashes of Annoni grass obtained from the burning process at 800 °C - 5 h (AGA8005h), in which tanδ = 0:7000 and tanδ = 1:4900, respectively. And, its also has high dielectric constants, such that εr = 9:3203 (graphene), εr = 17:1508 (graphite) and εr = 15:1443 (AGA8005h). These results, in terms of high tanδ constants, allow to classify these materials as excellent electromagnetic energy absorbers. On the other hand, the glass samples were characterized as materials with acceptably low loss tangent values, tanδ = 0:0080, εr constantsvarying between 6:5673 and 6:9945, and isotropic deportment. Thereby, these materials can be used as potential alternatives for the design of dielectric resonator antennas.