Superfície seletiva em frequência inspirada na espiral de Fibonacci com resposta multibanda proximamente espaçada.

Abstract

In this thesis work, a cascade bioinspired frequency selective surface (FSS) is presented, with a tri-band frequency response, with closely spaced resonances, angular stability and polarization independence. The element geometry of the proposed FSS is a segmented Fibonacci spiral. The ratios between the resonance frequencies are very close, 1.5 from the first to the second resonance and 1.4 from the third to the second resonance. FSS simulation is performed using the HFSS software. Simulations of the proposed structures were carried out, for a better understanding of the frequency response behavior of the FSSs. The initial parametric analysis allowed obtaining the physical dimensions, which allowed the application of the proposed structure in modern communication systems. In simulations varying the parameter w, width of the spiral strip, it was observed that as the metallic area in the unit cell increases, a displacement to higher resonant frequencies is caused and, simultaneously, an increase in the width of band. This increase in the width of the spiral strip can be used as a parameter for adjusting the resonant frequencies or even the bandwidths. Initially, a simulation of the bioinspired FSS with one layer was performed. One resonance was observed for horizontal polarization and two resonances for vertical polarization. Structures with only one layer did not show polarization independence or angular stability. Thus, it was proposed to cascade the two structures, one FSS with the normal spiral and another FSS with the spiral rotated to the right by 90°, with an air gap of 18mm between them. This gap influences the electromagnetic behavior of the FSS and can be used to improve polarization independence, for example. A multiband frequency response was obtained with three resonant frequencies, operating in commercial bands such as ISM and 5G.