Ultrasensitive Flexible Terahertz Plasmonic Metasurface Sensor Based on Bound States in the Continuum

In recent years, bound states in the continuum (BICs) have attracted attention of researchers because they are located above the light cone without leakage and have infinite lifetimes. In this study, we propose and examine a plasmonic metasurface based on BICs, design and fabricate a unit cell with an open ring, breaking the symmetry to excite Fano resonance by changing the position of an open gap. The surface current and electromagnetic field distribution were further analyzed, the internal physical mechanism was studied, and a significant near-field enhancement effect of the electromagnetic field was obtained. The simulation results show that when the analyte thickness reaches 30 $\mu \text{m}$ , the refractive index sensitivity of the proposed metasurface can reach 265.06 GHz/RIU. The designed terahertz metasurface is easy and inexpensive to fabricate, and is widely applicable as a nonlinear metamaterial in the fields of biosensing or imaging.