Electrically Tunable Liquid-Crystal-Integrated Quasi-BIC Terahertz Metasurface for VOC Sensing

Conventional quasi-bound state in the continuum (quasi-BIC) terahertz (THz) metasurfaces usually operate at fixed resonance frequencies and lack electrically controlled dynamic tunability. To address this limitation, we propose two schemes for realizing liquid-crystal-integrated quasi-BIC THz metasurfaces by exploiting the electrically tunable refractive index of liquid crystals in the THz regime. A microfluidic multilayer architecture combining a liquid-crystal functional layer with a silicon (Si)-based metasurface is constructed, in which the transition from an ideal BIC to a quasi-BIC is realized through two distinct mechanisms: pixelated control of the liquid-crystal orientation and geometric symmetry breaking of the Si resonators. Cartesian multipole decomposition reveals that the resonances in both configurations are dominated by magnetic dipole modes. The effects of the liquid-crystal orientation angle and key geometric parameters on the resonance frequency, peak absorptance, and quality factor are systematically investigated. Numerical results demonstrate continuous tuning of the terahertz resonance through variation in the liquid-crystal orientation angle, corresponding to electrically driven liquid-crystal reorientation in practical devices. The sensing performance of the optimized Si-resonator-based configuration is further evaluated, achieving a refractive index sensitivity of 117 GHz RIU−1 and a figure of merit (FOM) of 146.25. This work overcomes the fixed-frequency limitation of conventional static quasi-BIC metasurfaces and provides a feasible route toward electrically reconfigurable terahertz microfluidic sensing devices with tunable operating frequencies.