High-Q Metasurface-Enabled Cavities with Effective Electric and Magnetic Surface Impedances

Planar and cylindrical metasurface cavities are investigated for bound states in the continuum. Resonant cavities formed by regular mirrors, such as perfect electric conductors, require specific cavity sizes. Instead, using metasurfaces with combined magnetic and electric responses enable resonant excitation for any cavity size. Presently, the metasurfaces are modelled using effective electric and magnetic surface impedances, and it is shown that the required surface characteristics can be achieved with simple arrays of dielectric spheres. Given the canonical structure, a fully analytical approach is developed, and expressions for the surface impedance values are presented. The analytical results are compared with full wave simulations showing great agreement. The proposed metasurface cavities may be of interest for the design of filters, antennas, sensors, and nonlinear systems.