Wide angle terahertz sensing with a cross-dipole frequency selective surface

Abstract

In this work, a terahertz sensor based on a cross dipole frequency selective surface is analyzed and experimentally tested. The sensing structure is optimized for operation at the fundamental bandstop resonance near 0.7 THz and characterized under normal and oblique incidence. The sensing performance as a function of the incidence angle and the wave polarization is evaluated with good agreement between simulations and measurements. It is shown that a figure of merit for the proposed sensor can be enhanced from 0.2 up to 0.6 due to switching from normal to oblique excitation, which yields the maximum performance for TM polarization at the incidence angle of 70. The presented results demonstrate a wide angle operation regime in THz sensing that opens up an alternative approach in improving capabilities of sensing devices. V

Terahertz Sensing Based on Metasurfaces

“…[50] and corresponding amplitude reflection spectra (bottom) of the bare sample (black) and the coated sample with an 11 µm thick photoresist (red). [53] with relevant dimensions: d = 200 µm; cross length, L = 175 µm; strip width, w = 57 µm; polypropylene substrate height, h pp = 41 µm; analyte thickness h a (µm) (left). [50] Copyright 2015, AIP Publishing.…”

“…Reproduced with permission. [53] Copyright 2016, AIP Publishing. c) Different types of asymmetric square SRRs used for exciting Fano resonances: SRR used in ref.…”

“…[53] using a symmetric aluminum cross-dipole array on a low-loss flexible polypropylene substrate with a thickness of 41 µm, permittivity of 2.25, and loss tangent of only 0.0005 in the considered band (see the schematic as well as a microphotograph of the manufactured prototype in the left and center panels of Figure 2d). Rather, a narrowband response (and hence high quality factor) can be found in simple www.advopticalmat.de symmetric structures but introducing the asymmetry in the excitation by impinging, for instance, at oblique incidence.…”

“…Different solutions have been presented in the last years in which it is possible to use both the patterned and unpatterned surfaces of the structures, leading to a dual surface-sensing. [45][46][47][48]51,53] Furthermore, focusing on the use of the unpatterned side of the structure to perform an effective sensing, the substrate thickness was reduced so that the electric field could penetrate it and reach the analyte. [55], Srivastava et al presented a dual surface flexible metasurface based on an ultrathin low-refractive-index polyimide substrate.…”

“…d) Schematic of the unit cell reported in ref. [53] with relevant dimensions: d = 200 µm; cross length, L = 175 µm; strip width, w = 57 µm; polypropylene substrate height, h pp = 41 µm; analyte thickness h a (µm) (left). Photograph of the fabricated prototype (center).…”