Investigation of Surface Plasmon Polaritons in THz Metagrids
Il giorno 10 luglio 2019, ore 14:30, aula 2G27
il dott. Gianpaolo Papari, Dip. Fisica,
terrà il seminario dal titolo:
"Investigation of Surface Plasmon Polaritons in THz Metagrids for Accurate Sensing"
Surface plasmon polaritons (SPPs) can be easily activated in the THz band by operating a periodic removal of patches from an homogeneous conducting film, reducing in such a way the plasma frequency . In this work we deal with metagrids (MGs), which show a plasma frequency dependent on the metal filling factor, and study the THz response of two different geometries realized by standard PCB processing over a FR4 layer 160 mm thick. The first MG is in shape of a typical grid realized intersecting horizontal and vertical wires 300 mm wide, whereas the second one consists of a chessboard arrangement of square metal patches 300 mm sized. With the aid of full-wave electromagnetic simulations we can trace out the dependence of the plasma frequency on the MG filling factor, showing that the system undergoes a transition from a fully homogeneous "metamaterial" (inductive) behavior to a diffractive "photonic crystal" (capacitive) regime . In the plot, measurements (black dots) and numerical results (blue and red symbol continuous curves for the two different geometries) are presented and compared with the analytical behavior (black dash-dotted line) expected using a simple lumped element model. The evanescent field of SPPs can then be employed to perform label free sensing of biological fluids. We present a preliminary investigation where MGs can be used as bio-sensors, measuring the changes in the SPP resonances induced by the presence of an analyte. Using a suitable algorithm to improve the figure of merit, one can theoretically reach sensitivities comparable with the best values available in literature.
 J. B. Pendry, L. Martin-Moreno, and F. J. Garcia-Vidal, "Mimicking Surface Plasmons with Structured Surfaces," Science 305, no. 5685, pp. 847–848, 2004.
 G. P. Papari, C. Koral, and A. Andreone, "Geometrical Dependence on the Onset of Surface Plasmon Polaritons in THz Grid Metasurfaces," Sci. Rep., vol. 9, no. 1, pp. 1–12, 2019.