Identifying the Resonances in Terahertz Wave Scattering from a Two-Layer Graphene Strip Grating Embedded in a Dielectric Slab

We study, using a convergent in-house numerical algorithm, the scattering and absorption of the H-polarized plane wave by a two-layer grating of identical coplanar graphene strips embedded in a lossless dielectric slab. Our instrument is the method of analytical regularization, or, more precisely, the projection of the associated singular integral equation on the set of the weighted second-kind Chebyshev polynomials, which invert the static part of the problem. We compute the reflectance, transmittance, and absorbance of such a composite metasurface versus the frequency, in the range from 0.1 to 10 THz. We reveal multiple resonances and explain their nature with the aid of the in-resonance near field portraits. Ultra-high-Q resonances on the grating (lattice) mode are paid special attention.