Multi-resonances terahertz refractive index sensor based on a ring with embedded split rings metasurface array

Terahertz biosensors have gained significant attention due to their low energy and high penetrability, which enables them to interact with analytes without causing ionization damage. However, the weak interaction between terahertz waves and natural materials often results in poor sensing performance. To address this issue, various metasurface structures have been designed to enhance the light-matter interaction between the incident electromagnetic waves and the metasurface structure, thereby improving sensing performance. In this paper, we propose a metal-insulator-metal metasurface structure with a top metal consisting of a metasurface array that includes an outer ring with two embedded split rings. This structure generates three resonances at 0.732 THz, 1.916 THz, and 2.602 THz. Our simulation results show that the resonance formed by the mode coupling between the outer ring and the embedded split rings at 1.916 THz achieves the best sensing performance, with a sensitivity of 572 GHz/RIU, a quality factor of 22.8, and a figure of merit of 6.81. Our findings suggest that designing high-performance refractive index sensing with resonances generated from mode coupling is preferred. The remarkable sensing performance of the proposed metasurface structure enables the measurement of trace amounts of analytes in the terahertz region.