Metamaterial absorbers are used in the terahertz frequency regime as photo-detectors, as sensing elements, in imaging applications, etc. Narrowband absorbers, on account of their ultra-slender bandwidth within the terahertz frequency spectrum, show a significant shift in the absorption peak when an extrinsic entity relative to the absorber, like refractive index or temperature of the encircling medium, is altered. This property paves the path for the narrowband absorbers to be used as potential sensors to detect any alterations in the encircling medium. In this paper, a novel design of a terahertz metamaterial (MTM) absorber is proposed, which can sense the variations in the refractive index (RI) of the surrounding medium. The effective permeability of the structure is negative, while its permittivity is positive; thus, it is a μ-negative metamaterial. The layout involves a swastika-shaped design made of gold on top of a dielectric gallium arsenide (GaAs) substrate. The proposed absorber achieved a nearly perfect absorption of 99.65% at 2.905 terahertz (THz), resulting in a quality factor (Q-factor) of 145.25. The proposed design has a sensitivity of 2.12 THz/RIU over a range of varied refractive index from n = 1.00 to n = 1.05 with a step size of 0.005, thereby achieving a Figure of Merit (FoM) of 106. Furthermore, the sensor was found to have a polarization-insensitive characteristic. Considering its high sensitivity (S), the proposed sensor was further tested for gas sensing applications of harmful gases. As a case study, the sensor was used to detect chloroform. The proposed work can be the foundation for developing highly sensitive gas sensors.

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Metamaterial absorbers, on account of their inherent property of electromagnetic radiation absorption, have become a center of attraction for many researchers in recent times. This paper proposes a unique design of a terahertz metamaterial absorber that can be used to sense biomedical samples. The proposed design consists of two identical circular ring resonators (CRRs) made of aluminum on top of a gallium arsenide (GaAs) substrate. On account of its high field confinement in the sensing regime, a near-to-perfect absorption rate of 99.50% is achieved at a frequency of 2.64 THz, along with a large quality factor (Q-Factor) of 44. The design is highly sensitive to the refractive index changes in the encompassing medium. Hence, the proposed absorber can be used as a refractive index sensor exhibiting a reasonable sensitivity of 1500 GHz/RIU and a figure of merit (FoM) of 25. The refractive index range has been varied in the range of 1.34 to 1.39. As many biomedical samples, including cancerous cells, reside within this range, the proposed sensor can be used for biomedical sensing applications.

This research introduces a novel design of a metamaterial absorber having the range in terahertz, capable of sensing changes in the refractive index of the encircling medium. The layout includes adjoining rectangular patches in the form of a plus symbol along with four circular patch resonators (CPRs) on the pinnacle of a Gallium Arsenide (GaAs) substrate. The proposed design comes up with three consecutive absorption peaks, with an absorptivity of 99.0%, 99.75%, and 98.0% at three different resonant frequencies of 2.36 THz, 2.675 THz, and 2.97 THz, respectively, and a Full Width Half Maximum (FWHM) of 0.08, 0.04, and 0.05. This structure's quality factor (Q-factor) at the three resonant frequencies is 29.5, 66.8, and 59.4 together with 6.75, 17.5, and 30 as figure of merit (FoM), respectively. The proposed design offers a sensitivity of 0.54 THz/RIU, 0.7 THz/RIU, and 1.5 THz/RIU in those three absorption bands. To support the selection of design parameters, parametric assessment was done. The designed sensor can find its applications in terahertz sensing.

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