Rayleigh anomalies in the E-polarized wave scattering by finite flat gratings of silver nanostrips or nanowires

We study numerically the optical properties of the finite periodic flat gratings made of multiple silver nanowires or silver nanostrips suspended in free space, in the context of periodicity-induced resonance effects. Our analysis is based on the use of two techniques: the angular field expansions in local coordinates and addition theorems for cylindrical functions for the nanowire gratings, and the generalized (effective) boundary conditions (GBCs) imposed on the strip median lines and the Nystrom-type discretization of the relevant singular and hyper-singular integral equations (IEs) for the strip gratings. In the E-polarization case, in contrast to the H-case, there are no localized surface plasmons and sharp periodicity-induced grating resonances are not visible in the scattering and absorption cross-sections. Instead, the suppression of the scattering near to the emerging Rayleigh anomalies is seen if the strip number gets larger.