All-dielectric metasurface terahertz biosensor with built-in notches and eccentric cylindrical depressions

The terahertz metasurface with bound states in the continuum (BICs) has the characteristics of infinite Q factor resonance and elimination of radiation loss, which bind the electromagnetic beam near the structure to achieve localization and enhancement effects of the optical field, and has been widely studied in recent years. The absence of ohmic losses on all-dielectric metasurfaces can further enhance the Q factor and is highly favored by researchers in biosensors. In this paper, we propose a rectangular metasurface with built-in notches and eccentric cylindrical depressions. By changing the eccentricity of the concave cylinder, a quasi-continuous domain bound state (QBIC) mode with observable sharp resonance peaks is formed during the leakage of BIC to the far field, achieving high-quality factor, refractive index sensing sensitivity, and figure of merit (FoM). We use the scattering power and electromagnetic field distribution of multipoles to study the resonance mechanism and analyze the influence of different size parameters on the sensing performance of all-dielectric metasurfaces with built-in notches and eccentric cylindrical depressions. The Q factor of the sensor is 7211, and the FoM is 951.32. It has broad application prospects in gas and liquid medium biosensing.