Detection of Benzoic Acid Additive Based on a Terahertz Metasurface Sensor

Benzoic acid and its derivative benzoate are widely utilized as food preservatives. This paper presents a highly sensitive method for detecting benzoic acid using a cross-shaped aluminum resonator integrated on top of a polyimide substrate. The resonance dip for benzoic acid was designed to be at 0.93 THz. The terahertz (THz) transmission spectrum was simulated using a designed structure with varying thicknesses of benzoic acid. Analysis of the spectral response of the THz resonance dips to the thickness of the benzoic acid layer shows that the amplitude of the resonance dips generally increases with an increase in the benzoic acid concentration. The spectral frequency shifts and transmission intensities both demonstrate high sensitivity of the metasurface sensor to trace benzoic acid thicknesses. The sensor exhibits a sensitivity of approximately 0.247 THz/RIU (Refractive Index Unit) and FOM (figure of merit) of 3.927/RIU. The THz metasurface sensor is a fast and accurate sensing tool that can detect trace substances, making it crucial in the field of food safety.