Dual resonance based on quasi-bound states in continuum in the all-dielectric terahertz metasurface and its application in sensing

In recent years, the concept of bound states in continuum (BIC) in metasurfaces has become a topic of interest. BIC involves the physical mechanics of wave optics, metamaterial sensors and other high-quality factor (Q-factor) applications. In this paper, the basic concept of BIC is introduced, followed by a brief description of the progression of the research regarding the application of BIC in terahertz (THz) metasurfaces. Subsequently, an all-dielectric metasurface consisting of tetramer clusters with dual terahertz resonances is proposed. The materials used for the substrate and the tetramer cluster are quartz and silicon, respectively. Quasi-BIC works by varying the cylinder radius on the metasurface structure. The transmission spectra are analyzed under different structural and material parameters with control variables. When the metasurface is applied as a refractive-index sensor, the Q-factor is 2303.77 and the figure of merit (FOM) is 7022.90, which are calculated using the asymmetric parameter k = 0.8 μm. Additionally, when the incident wave is x- or y-polarized, resonance peaks with the same frequencies can be obtained, and the overall trend of the transmission spectrum remains the same.