A New Design of a Terahertz Metamaterial Absorber for Gas Sensing Applications

Abstract

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.

High FoM quad‐band THz perfect metamaterial absorber‐based RI sensor for gas sensing applications

“…The effective permeability ( eff ) and effective permittivity (μ eff ) of the proposed structure are presented in Figure 2a to know the absorption character with enhanced clarity. These can be obtained with Equations ( 1) and (2) as stated below [14]:…”

Mechanism of formation and evolution of bound states in the continuum of split-hole all-dielectric metasurface under asymmetric displacement perturbation

“…All-dielectric metasurface with high refractive index [1] has been widely used in the design and fabrication of micro and nanophotonic devices, including holograms [2], ultra-narrow band absorbers [3], planar lenses [4], filters [5], sensors [6], and so on, due to their advantages of low loss, powerful light trapping capability, smaller volume, and good compatibility with nonlinear systems. The all-dielectric metasurface is known for supporting high-density electromagnetic energy localized and enhanced toroidal dipoles at tiny subwavelength scales [7,8], which has led the study of metasurface to focus on enhanced toroidal dipole responses, and subsequently to achieve toroidal dipole resonances at terahertz [9], infrared [10], and visible wavelengths [11].…”

Asymmetric Cross Metasurfaces with Multiple Resonances Governed by Bound States in the Continuum

“…Metasurfaces have attracted considerable attention due to their ability to control light propagation and light localization [ 1 , 2 , 3 ]. Using design methods for structural parameters of metacells, metasurfaces can be developed for many applications, such as beam splitters [ 4 ], holograms [ 5 ], ultra-narrow-band absorbers [ 6 , 7 ], filters, sensors [ 8 , 9 ], etc. A key concept is the generation of the high quality factor (Q factor).…”