Banca de DEFESA: MYCHAEL JALES DUARTE

Analysis and Design of Ultraminiaturized FSS Structures for Applications in Temperature Sensing Systems

Frequency Selective Surfaces; Ultraminiaturization, Equivalent Circuit; Temperature Sensing.

This paper presents a study on 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 printed on an FR-4 dielectric substrate. The inserted vias contribute to the capacitive and inductive effects in the structure, providing ultraminiaturization of the unit cell dimensions. The FSS have unit cell sizes equal to 4.68 % and 6.80 % of the wavelengths in free space for the frequencies of 2.34 GHz and 2.72 GHz (resonance frequencies), respectively, with the second structure exhibiting dual-band behavior. Two equivalent circuit models are proposed to better understand the operating principle of the FSS. The application of these structures for use in temperature sensing is studied. According to the literature, the electrical permittivity of the dielectric material used changes with the change in the material's temperature. With this in mind, simulations were carried out and the FSS showed a linear relationship between resonance frequency and temperature. The two proposed sensors were built and measured from room temperature up to 120 °C, and both showed excellent sensitivity to temperature changes. The numerical results simulated for the prototypes designed were obtained using the ANSYS HFSS software and the equivalent circuit model. The prototypes were built and the experimental characterization of the transmission coefficients, bandwidth and resonance frequency was carried out. The values obtained in the experiments were compared and discussed with the simulation results, which showed good agreement.