Análise e projeto de estruturas ultraminiaturizadas de FSS para aplicações em sistemas de sensoriamento de temperatura

Abstract

This paper presents the design and proposal of new configurations of ultra-miniaturized Frequency Selective Surfaces (FSS) for applications in temperature sensing systems. Two 2.5D FSS are proposed with elements inspired by convoluted metal lines with metal vias inserted and printed on a dielectric FR4 substrate. The vias contribute to the capacitive and inductive effects in the structure, providing ultraminiaturization of the unit cell dimensions. The size of the unit cells of the proposed FSS is equal to 4.42 % and 6.80 % of the wavelengths in free space for the frequencies of 2.21 GHz and 2.72 GHz (resonance frequencies), respectively, with one of the proposed structures exhibiting dual-band behavior. The principle of operation of the FSS is evaluated using the equivalent circuit models proposed in this work. A new application for ultra-miniaturized FSS based on convoluted geometries as non-contact temperature sensors is analyzed in this thesis. According to the literature, the electrical permittivity of the dielectric material used as the FSS substrate changes with the change in temperature of the environment in which the circuit is inserted, thus altering its frequency response. Numerical analyses were carried out and found that the FSS showed a linear relationship between resonance frequency and temperature. The numerical results simulated for the prototypes designed were obtained using the ANSYS HFSS software and the equivalent circuit model. The prototype sensors were built and the transmission coefficients, bandwidth and resonance frequency were experimentally characterized. The two proposed sensors were experimentally analyzed from room temperature up to 120 °C and both showed excellent sensitivity to temperature changes when compared to other sensors in the literature. The values obtained in the experiments were compared and discussed with the results of the simulations, which showed good agreement.