Metasuperfícies Dielétricas Baseadas em Quadrúmeros com Modo Dipolo Toroidal

Abstract

In this work, we propose and investigate a new planar metasurface based on dielectric disks. The unit cell of this metasurface is composed of a quadrumer of disks, that is, a grouping of four disks that enables the excitation of quasi-dark modes, characterized by very low radiation emission, associated with toroidal dipole resonances. These quadrumers are arranged into larger groupings, called supercells, designed with the highest possible geometrical symmetry, corresponding to the C4v symmetry group. To make the toroidal modes accessible in the metasurface, we employed group representation theory and the symmetry-adapted linear combination (SALC) method, demonstrating that it is necessary, first, to break the symmetry of the quadrumer and, subsequently, the symmetry of the supercell. We present and discuss in detail different mechanisms for symmetry reduction, a process by which the geometrical symmetry of the structure is modified to activate specific electromagnetic modes. When the supercell symmetry, originally of the C4v type, is reduced to the Cs group, the metasurface starts to exhibit both toroidal and antitoroidal resonances, the latter associated with field distributions of opposite topology to those of conventional toroidal dipoles. The theoretical predictions were validated through full-wave electromagnetic simulations, considering the incidence of plane waves on the structure, confirming the expected behavior. Finally, we discuss potential applications for the analyzed structures, highlighting their use in advanced optical devices and photonic systems.