Dual-Resonance Split Ring Resonator Metasurface for Terahertz Biosensing

In this article, the ‘terahertz gap’ has been addressed by designing a novel THz metasurface for potential use in biosensing applications. The metasurface sensor employs surface plasmon resonance (SPR). It operates in the 0–1 THz band. Two sharp reflection dips are provided by the sensor, which serve as indicators of analyte refractive index variations. Geometrical as well as compositional parameters of the biosensor design have been studied to optimize the performance in the targeted frequency band. The sensor design shows compatibility with different metals. The performance of the metasurface with gold, copper, and aluminum has been investigated. The metasurface geometry is decently resilient to fabrication tolerances. The sensor maintains its resonance conditions when the angle of incidence is changed with minor deviations in the spectral response, but the polarization state of the incident terahertz beam clearly disturbs the absorption peak. Therefore, the sensing performance is restricted to a maximum allowable incidence angle of 20° and circularly polarized terahertz beams. The resonance conditions for the metasurface appear around 0.4 and 0.7 THz. Both resonances have been investigated with respect to changes in the analyte refractive index. The chosen refractive index range is 1 to 1.5. The sensor response is calibrated by plotting the resonance frequency versus the refractive index. Least squares regression technique has been used to extract a data model for sensor response. Comparison of the proposed design with contemporary works has been incorporated into the article. The sensor provides sensitivities of 0.1614 and 0.23 THz/RIU. The electromagnetic simulations have been carried out through the finite element method (FEM).