Super cavity mode in volumetric resonators: a comparative analysis of a dielectric resonator and an array of split-ring resonators

Quasi-bound states in the continuum (quasi-BIC) or supercavity mode are fascinating phenomena due to the interaction of the resonant modes, which allows for a high-quality factor (Qfactor). In particular, it was demonstrated that the dielectric resonators of cylindrical shapes support this high-Q mode. However, dielectric resonators have several limitations, including expensive cost, fragility, and difficulty in frequency fine-tuning. Here, we propose a volumetric resonator comprising an array of split-ring resonators (SRRs) that are spatially oriented to achieve a similar Q-factor to its dielectric counterpart. The resonator design replicates Fabry-Perot and Mie-like modes, in which interference produces the quasi-BIC-related mode. The advantages of the proposed structure include an open space design, ease of manufacturing, and the possibility of frequency adjustment in the microwave range.