Substrate-etched terahertz metasurfaces with enhanced field and high sensitivity.

Terahertz metasurfaces have emerged as versatile platforms for diverse applications ranging from sensing to communications. Nevertheless, existing architectures struggle to generate the enhanced field required for highly sensitive sensing, as their native electromagnetic field confinement remains inherently limited. This work presents a substrate-etched terahertz metasurface structure exhibiting electromagnetically induced transparency effects. Through systematic numerical investigation, we elucidate the electromagnetically induced transparency formation mechanism and quantitatively characterize how substrate etching enhances sensor performance parameters. The studies demonstrate that substrate etching not only fully utilizes the penetrating electric field within the substrate but also reduces its effective dielectric constant, thereby significantly enhancing the localized electric field and substantially strengthening light-matter interactions. Numerical simulations reveal a remarkable sensitivity improvement, reaching 271.5 GHz/RIU, representing a 6.7-fold increase over the un-etched structure. These findings highlight the applicability of substrate etching in ultrasensitive biosensors.