Effects of gradual deformation of identical and nonidentical, rotated and nonrotated U-shaped subwavelength resonators in few-layer metasurfaces.

Raising of negative-index medium has been going hand-by-hand with the exploration of quasiplanar subwavelength resonators. Now they are widely used in modern microwave, terahertz, and infrared devices, as well as in advanced physics research. Effects of stacking of the arrays of subwavelength resonators in one few-layer metasurface is connected with the key problems of modern electrical engineering, applied physics, and beyond. Recently, the interest to subwavelength resonators has been growing due to the progress in topological photonics and non-Hermitian photonics. In this paper, the selected effects of arrays coupling in a few-layer metasurface are revisited with yet uncommon focus, i.e., survival and (dis)appearance of subwavelength resonances at the gradual deformation of the resonators at a given lattice period. Microwave frequency range has been chosen to illustrate the concept. The case when the metasurfaces comprise two periodically placed U-shaped resonator arrays is considered. The sizes of the resonators are either varied simultaneously for both front-side and back-side arrays or for the back-side array only. The main purpose of this study is to explore the basic scenarios of resonance evolution in the space of geometrical parameters. It is shown that different resonances may be sensitive to the variations in geometrical parameters and to the dissimilarity between the front-side and back-side arrays to a different extent. The obtained results point to the existence of the bands, resonances, polarization-conversion and related asymmetric transmission regimes that are robust to the deformations. They can serve as the starting point in understanding the functional capability of the physical features while adjusting the size for a much wider variety of the types of subwavelength resonators. Their unveiling promises a wide avenue towards the realization of new frequency-domain and angle-domain filters, ultrathin polarization-plane convertors, asymmetric transmission devices and advanced microwave antennas.