Ultrathin Multiband Polarization-Independent Terahertz Absorber as a Biosensor

A multiband electromagnetic terahertz (THz) absorber is proposed as a biosensor. The proposed design consists of a metallic resonator loaded with multiple ring-shaped slots, dielectric material, and a metallic ground plane. The dimension of the proposed absorber’s unit cell is
$9.6\times 9.6\,\,\mu \text{m}$
. It has six peaks at 2.8807, 7.6348, 14.4221, 20.5217, 23.5416, and 25.4552 THz with absorption of 98%, 99.5%, 99%, 99.9%, 95.14%, and 99.4%, respectively. The full width at half maxima (FWHM) for the first three resonant peaks is 0.28, 0.81, and 1.38 THz. The combined FWHM for the remaining three peaks is 6.97 THz. The symmetrical geometry of the proposed absorber results in polarization independency. An equivalent circuit model (ECM) for the validation of the proposed absorber’s simulated performance in the absence of any analyte is also presented. The effectiveness of the proposed absorber in the detection of malaria, cancer cells, and tumor cells located in different body parts is also presented. In all these biosensing applications, a peak sensitivity of ~3.7 THz/refractive index per unit (RIU) is achieved. The estimation of unknown refractive indices by using this absorber is also presented and a good estimation is achieved. The presence of multiple absorption peaks leads to the approximation of refractive index (RI) of any unknown sample with an accuracy of
${ < }0.5\%$
which may not be possible with single-peak and high-
${Q}$
sensor if the peak overlaps with that of some known RI. The proposed absorber dominates previously reported multiband THz absorbers in terms of the number of operating bands, FWHM, absorption peak values, overall volume, and sensitivity of the sensor.