A Plasmonic Refractive Index Sensor Using a Water-Based Metamaterial Absorber

A structure for refractive index sensing application in THz band is proposed and analyzed in this paper. This structure is comprised of a golden plasmonic metamaterial absorber in which water is used as a dielectric and a thin TOPAS layer-which does not have a significant effect on the performance of the sensor- is used for the separation of analyte and water. This structure has an absorption of 99.2% at resonance frequency of 2.8725 THz. Lateral absorption frequency shift occurs due to variation in the refractive index (RI) of the analyte. This structure can be used for refractive index measurement in the range of 1-1.4 with full-width half maximum (FWHM), sensitivity (S), the figure of merit (FoM), and quality factor (Q-factor) in the ranges of 0.01647 THz, 427-644 GHz per refractive index unit (RIU), 6.3-26.5 and 26.23-175.5, respectively. It is worth mentioning that for a limited refractive index range of 1.1 to 1.15, the values of FWHM, Q-factor, and FoM enhance to 0.0053327 THz, 516, and 90, respectively. The simplicity, compactness, and ease of fabrication due to the use of water as a dielectric along with appropriate refractive index sensitivity and FoM help this structure to be used in biological, medical, and environment sensing applications.