Dual-band tunable terahertz perfect absorber based on all-dielectric InSb resonator structure for sensing application

In this paper, we demonstrate a dual-band tunable absorber coupled with a nanoscale metal-dielectric-metal (MDM) structure for sensing applications in the near-infrared spectral region. This structure exhibits a dipole resonance mode in absorbance and reflectance spectra which results in the enhancement of absorbance over a wide range of incident angles for TE polarization. Using a numerical and analytical study, the performance parameters of the structure including sensitivity (SS), the figure of merit (FoM) and quality factor (Q) are investigated by changing the incident polarization, geometrical parameters, filling dielectric and plasmonic metasurface material. Moreover, we study the dependence of the sensitivity as a function of plasmonic metasurface shape to demonstrate a better response compared with other methods. Results show that, in terms of the refractive index unit (RIU), an ultra-high sensitivity and tunable sensor can be designed with a maximum sensitivity of 1240.8 nm/RIU for a refractive index change of Δn = 0.0458. In the optimum design of the proposed dual-band absorber, a Q-factor and FoM equal to 123.45 and 44.5 are obtained. Furthermore, the proposed structure can be utilized for controlling the light propagation. By considering silver as a plasmonic metasurface, a slow down factor as high as 680 is obtained. Our work will be applied to future sensors capable of ultra-high sensitivity.

Ultra high-sensitivity and tunable dual-band perfect absorber as a plasmonic sensor

In this letter, we design a terahertz (THz) multi-band absorber comprised of four square open/closed loops and a ring wall resonant metamaterial with a high absorption rate for TE and TM polarization. Based on resonant response of metamaterial, five different sizes of the metal rings could tune five absorption peaks to produce five-band absorbing performance in the frequency ranging from 0.1 to 1 THz. By comparing the absorber consisting of independent ring with multiple rings, the multi-band absorption could be demonstrated by increasing the number of metal rings. The simulation results are indicated that the multi-band absorbing of the THz absorber is independent of incident angle within a wide range. The design method of the absorber presented can not only provide a theoretical tool to perform diversity absorbing with multiple band and multi-absorption azimuth in terahertz communications, but also has potential for applications in THz imagers, detectors, sensors, and emitters.

Multi-Band Terahertz Absorber at 0.1–1 THz Frequency Based on Ultra-Thin Metamaterial

A technique is implemented for altering the multimodal resonance generated in an ultrathin silicon ring resonator-based terahertz (THz) absorber. The absorber provides the dual-band resonance with the excitation of magnetic and electric dipole in the lower and upper band, respectively. The field of magnetic and electric dipoles is altered using a non-resonant graphene ring placed in the center of the generated dipolar arrangement and the tunability and perfect absorption is achieved. A circuit model is prepared using transmission line method and absorber operation is verified. The proposed absorber can be utilized as a biosensor for the detection of malaria virus and glucose percentage in water. The sensor offers highest sensitivity as 0.29 and 0.27 THz per thickness unit change and quality factor as 117.53 and 245 in the lower and upper band, respectively during the sensing of analyte thickness. Also, it offers the sensitivity as 0.20 and 0.10 THz per refractive index unit change and quality factor as 105.28 and 211.84 in the lower and upper band, respectively during refractive index sensing. Moreover, the structure remains insensitive to polarization angle of the incident electromagnetic wave.

Altering the Multimodal Resonance in Ultrathin Silicon Ring for Tunable THz Biosensing

Terahertz metamaterial sensing (TMS) is a new interdisciplinary technology. A TMS system employs terahertz waves as the pumping source, these then interact with the sample and carry the substance information, e.g., refractive index, absorption spectra. These properties are relevant to the molecular rotation and vibration states produced by a surface-plasmon-polariton-like effect. TMS technology is usually characterized by large penetration depth and high sensitivity. Owing to these advantages, TMS may be used for ultratrace detection and consequently has a wide range of practical applications in biomedicine, food safety, environmental monitoring, industry and agriculture, material characterization, and safety inspection. Furthermore, TMS performance is determined not only by the structural topology of metamaterials, but also by their compositions and substrates. This paper reviews the essential fundamentals, relevant applications, and recent advances in TMS technology with a focus on the influence of material selection on TMS performance. This review is envisaged to be used as a key reference for developing TMS-based functional devices with enhanced characteristics.

A.T. Tenggara

Papers

Design of a metasurface-based dual-band Terahertz perfect absorber with very high Q-factors for sensing applications