Novas configurações de sensores planares para a caracterização não-destrutiva de materiais magneto-dielétricos em micro-ondas

Abstract

This work presents the design and fabrication of two new configurations of planar microstrip devices for sensing applications and to characterize non-destructively the complex permittivity of magneto-dielectric materials. Planar microwave sensors have demonstrated important functionalities in several applications, such as in the food, industrial and biomedical sectors. Microwave sensors have the advantages of low cost and ease of fabrication, in addition to the possibility of integration with other devices. The first proposed sensor is based on a two-port planar microstrip device with the insertion of a Complementary Split Ring Resonator (CSRR) in its patch, this element is responsible for determining the electrical properties of the materials under test (MUT). Two samples of materials widely known in the literature were investigated. With the first proposed sensor, it was possible to obtain the complex permittivity of two solid materials. The second proposed sensor is based on a bioinspired microstrip planar antenna with a change in the ground plane structure (Defected Ground Structure – DGS), in order to obtain, also in a non-destructive way, the magneto-dielectric characteristics, i.e., the electrical permittivity and magnetic permeability, of nine solid materials also known in the literature, using the same resonator for both characterizations. The proposed sensor has a patch bioinspired by the Spondias Tuberosa leaf, and a CSRR was inserted in the center of the ground plane, responsible for the permittivity characterization. The permeability was obtained by means of slits positioned close to the CSRR. In this work, the sensitivities of the two proposed sensors were also analyzed, presenting excellent results. The sensors were analyzed by means of simulations in the commercial software Ansys HFSS. The prototypes were manufactured using the FR-4 dielectric, which has a relative electrical permittivity of 4.4, a loss constant of 0.02 and a thickness of 1.57 mm, and the measurements were performed using the E5071C vector network analyzer (VNA) on nine different samples (MUT) of dielectric and magnetic materials. The simulated and measured results were discussed and compared with values found in the literature, showing good agreement.