Triple band terahertz absorption based fractal ring shaped ultrathin mustard oil adulteration sensor.

A tri-band terahertz (THz) absorber for sensing the adulteration percentage in mustard oil is proposed in this paper. It consists of a gold based metallic resonating geometry and metallic ground plane on the top and bottom layers of the dielectric material respectively. It has three absorption peaks with peak absorptivity of 99.74%, 99.96% & 99.94% and Full Width at Half Maxima (FWHM) of 0.57, 0.862 & 1.112 THz at 4.6296, 8.295 & 12.6309 THz respectively. The proposed absorber's unit cell volume has an overall volume of 10 μ m × 10 μ m × 1. 61 μ m (0.15432 λ L × 0. 15432 λ L × 0. 024846 λ L where λ L is wavelength at lowest operating frequency i.e. 4.6296 THz). It has polarization insensitive absorption performance under normal incidence and incident angle (θ ∘) stability up to 50° for A ≥ 90%. The proposed structure is simulated through by using CST & HFSS. The results are validated by developing an equivalent circuit model (ECM). The results of CST, HFSS and ECM are found to be in good agreement. A sensitivity varying from ∼ 0.23 THz/RIU to ∼ 1.62 THz/RIU is achieved for Refractive Index (RI) sensing case, whereas a high sensitivity in the range of ∼ 0.4 THz/RIU to ∼ 2 THz/RIU is achieved for mustard oil adulteration sensing case by mounting the absorber's top surface with a polyimide based container filled with an analyte (either refractive index material or mustard oil). During the validation, a maximum ∼ 0.16% error in mustard oil adulteration estimation is achieved. The proposed sensor has advantages of simple & ultra compact dimensions, high sensitivity and minimal error in impurity concentration estimation with respect to other absorber-based sensors. • Unit cell volume 0.15432 λ L × 0. 15432 λ L × 0. 024846 λ L where λ L = λ at 4.6296 THz • Peak absorption of ∼ 99.9% at 4.6296, 8.295 and 12.6309 THz • Polarization independent and Incident angle (θ °) stability up to 50°for A ⩾ 90% • Used as Mustard oil adulteration sensor with maximum sensitivity of ∼ 2 THz/RIU. • Maximum 0.16% error in estimation of unknown refractive indices (avg. calc. RI) [Display omitted] [ABSTRACT FROM AUTHOR]