Quasi-BIC Resonance in Terahertz Metasurface for Sensing Application

The terahertz (THz) metasurface based on the bound states in the continuum (BIC) provides a promising platform for various applications by overcoming the weak interaction between the THz waves and the trace analyte. In this work, a metasurface with a high Q-factor resonance based on split ring resonators (SRRs) metamolecules is proposed. Multiple quasi-BIC resonances in the range of $1\sim 1.5 \mathrm{THz}$ are excited on the metasurface, through different arrangements in the $2 \times 2$ array of SRRs with different angles. The temporal coupled mode theory (TCMT) and the multipole expansion of far-field scattering power are employed to explain the physical mechanism of quasi-BIC. The sensing of glucose solution in the concentration range of 1 ppm to 100 ppm is achieved experimentally by combining it with the microfluidic chip. Moreover, a permittivity retrieval method based on grating-assisted BIC metasurface is proposed. Our researches offer a possible strategy for achieving multiple quasi-BIC resonances on the metasurface and provide a potential candidate for sensing and spectral analysis of the biochemical in the THz frequency band.