Toroidal quasi-dark supermodes in microwave dielectric metasurfaces

We report a class of dielectric metasurfaces that support quasi-dark microwave resonances with tailored toroidal and antitoroidal field profiles. The metasurfaces are realized using quadrumers of high-permittivity and low-loss ceramic disk resonators as elementary building blocks, assembled on laser-processed dielectric foam substrates. The physical origin and symmetry properties of the supported modes are elucidated through group-theoretical analysis and validated by eigenfrequency and full-wave finite-element simulations. Experimental measurements confirm the existence of quasi-dark resonances with suppressed radiation losses. Owing to its generic and scalable design strategy, this approach can be readily extended to a broad range of dielectric metasurfaces composed of ceramic Mie resonators. The demonstrated metasurfaces provide a versatile platform for low-profile and strongly resonant devices, e.g., for sensing or narrowband filtering.