Terahertz metasurfaces based on bound states in the continuum (BIC) for high-sensitivity refractive index sensing

Terahertz metasurface has attracted much attention in the field of label-free refractive index sensing due to its special fingerprint spectrum. Combining the special electromagnetic response of the metasurface and the ultra-high Q property of the quasi-BIC, a novel high-sensitivity THz sensor is proposed based on symmetry-protected BIC. The breaking of the mirror symmetry means that the resulting dipole displacement excites the surface resonance, and the BIC state is verified by satisfying the quality factor of the inverse square law. It is verified that the oblique incident wave vector can excite the BIC to the quasi-BIC. And the two different asymmetric parameters (displacement S and incident angle θ) of generating quasi-BIC can influence or even counteract each other. In order to increase the accuracy of the detection results, two different sensing parameters are used to detect the same analyte at the same time. The sensitivity of frequency shift difference and amplitude difference is as high as 11.17 GHz/RIU and 0.1766 /RIU, respectively. This work not only provides new ideas for the design of high-sensitivity sensors, but also has potential applications in the field of low-concentration sensing.