An All-Dielectric Metasurface Sensor Based on Bound States In the Continuum

The terahertz (THz) band harbors a wealth of information, given that the rotational or vibrational energy levels of numerous biological macromolecules and chemical substances reside within THz spectral range. However, the sensing performance in the THz band is often hampered by the weak interaction between THz waves and trace analytes. In this study, we introduce an all-dielectric metasurface sensor driven by symmetry-protected bound states in the continuum (BICs). Symmetry-protected BIC resonances, characterized by zero line-width, are converted into observable quasi-BIC resonances by introducing asymmetry to the $\mathrm{C}_{4 \mathrm{v}}$ structure. By expanding the far-field scattering power using a multipole expansion, we elucidate the underlying physical mechanism of the quasi-BIC resonance. Leveraging the high local field enhancement effect generated by quasi-BICs, the interaction between THz waves and the analyte is substantially amplified. Owing to the distinctive structure of the designed metasurface, the analyte is efficiently localized within the high-field enhancement region, further boosting the sensor’s sensitivity. The proposed all-dielectric metasurface sensor, driven by quasi-BICs, exhibits high Q-factor and pronounced localized field enhancement, significantly enhancing both the sensitivity and Figure of Merit (FOM) of the sensor. This design presents a promising approach for detecting trace amounts of biomolecules and chemical substances.