Design and Simulation of THz Metasurface Sensor Based on Transmission and Reflection Modes for Aqueous Solution Detection

Aqueous solutions can strongly absorb terahertz (THz) waves, and THz sensing signal would be severely diminished. This can be potentially avoided by attenuated total reflection (ATR) in THz sensing because the associated evanescent field decays exponentially with increasing depth from the metasurface, and the influence of the aqueous solution on the signal will be greatly reduced. This paper presents a comparison of resonance peaks in reflection and transmission modes, The simulation of reflection and transmission mode, including variations in the shape, size and materials of the metasurface, was conducted by finite element simulation (FEM) through CST STUDIO SUITE software. The sensitivities of the transmission and reflection mode are compared for different solution concentrations. Results of the simulation show that the FOM factor of ATR and transmission mode were 0.5822 and 0.5336 separately, indicating that the ATR mode is superior to the transmission mode in terms of detecting sample solution components by a tail sensor. This paper presents a novel metasurface pattern to more effectively identify the concentration of aqueous solutions. The theoretical sensitivity of the biosensor is evaluated up to 66.7 GHz/ RIU (refractive index units). The pattern provides higher detection sensitivity and FOM than conventional open-ring metasurface patterns. The biosensor shows great potential in the detection of liquid substances, especially for biochemical medical testing.