Tunable ultra-wideband terahertz absorber based on graphene disks and ribbons

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

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.

Recent Advances in the Development of Materials for Terahertz Metamaterial Sensing

Design of a polarization-insensitive triple-band metamaterial absorber

This paper presents a graphene-based tunable polarization-insensitive metamaterial absorber (MMA) at terahertz (THz) frequencies. The absorber consists of top patterned gold (Au) layer followed by single layer of graphene, dielectric spacer, and Au layer at bottom. The proposed MMA demonstrates multi-band absorption with the characteristics of both broad- and dual-band absorption by optimizing dimensions (parametric analysis). Broad-band absorption reaches over 90% for the range of 4.57–6.45 THz with the relative absorption bandwidth of 34%, and the absorption peak at 6.86 and 7.20 THz having 98.9 and 95.2% absorption. The normalized impedance and constitutive electromagnetic parameters of the MMA are calculated using the Nicolson–Ross–Weir (NRW) method to validate the absorption rate. Furthermore, proposed absorber is polarization-insensitive upto 90° for transverse electric wave. The tunable characteristic of MMA is achieved by tuning the Fermi energy of graphene with the application of bias voltage. Accordingly, the proposed multi- and broad-band absorbers find its potential applications in spectroscopy detection, imaging, and sensing.

Graphene-based tunable multi-band metamaterial polarization-insensitive absorber for terahertz applications

Design of a five-band terahertz perfect metamaterial absorber using two resonators

Design and optimization of terahertz metamaterial sensor with high sensing performance

As one of the common diseases, hollowing deterioration destroys the structure and shortens the life of stone relics. The hollowing deterioration samples for the stone relics were nondestructive tested and studied by terahertz time-domain spectroscopy (THz-TDS) in this paper. The hollowing samples with different parameters can be distinguished by the THz spectra of the samples, which imply that THz nondestructive testing (THz NDT) method is applicable to test hollowing deterioration for stone relics. The THz NDT method not only can provide reliable reference data for repair and maintenance of stone relics, but also is an economic nondestructive detection technique with promising application prospects.

Experimental Study on THz Nondestructive Testing of Hollowing Deterioration for Stone Relics

Enhance sensitivity of the terahertz (THz) wave sensor by the THz wave control characteristic based on artificial electromagnetic meta-materials, is a hot spot in current research. The performance of split ring resonators (SRRs) THz sensor on Mylar substrate is numerical simulated with COMSOL Multiphysics software in this paper. The two key characteristic parameters of the THz sensor are analyzed with COMSOL Multiphysics software, which are the thickness of the Mylar substrate and the gap width of the gold SRRs. By comparing the relationship between different parameters and the corresponding resonance frequency curve, the optimal parameters of the THz sensor are obtained which are 10 microns for the Mylar substrate thickness, 2 microns for the gap width of gold SRRs. Then the optimized THz sensor model is used to test the different thickness and relative dielectric constant material with the COMSOL Multiphysics software. The results show that the resonant frequency (f0) move to lower frequency with the increase of the relative dielectric constant of tested materials, and has a good linear relationship between the f0 and the relative dielectric constant of tested materials. While the f0 also move to lower frequency as the thickness of tested materials are increase, but when the thickness are more than 5 microns, the resonance peak stay at near 1.997 THz. They are show that the SRRs THz sensor on flexible substrate has high measurement precision, sensitivity, and reliability when the tested materials are common metal, semiconductor and medium layer which layer thickness is less than 5 microns, and the relative dielectric constant for the range of 1-4 by the linear relationship between the resonance frequency and the different parameters of tested materials, as well as it can provide theory references for actual testing of such terahertz sensors.

Properties of split ring resonators metamaterials terahertz sensor on flexible substrates

A new non-destructive test method based on terahertz time domain spectroscopy technology (THz-TDS) was used to analyze the hollowing deterioration of Yungang Grottoes in this paper. The hollowing samples are strictly prepared and a series of experiments were designed in order to ensure the representativeness of the experimental results. The results show that this method can obtain the hollowing deterioration states to a certain extent with high reliability. At the same time, it can freely adjust the severity of the judgment standards. In particular, the same delay time interval was about 5 ps for the same thickness difference for hollowing deterioration, which effectively and accurately characterized the thickness hollowing deterioration for 1 mm, 2 mm and 3 mm. We can also established the hollowing thickness model by using the thickness correlation coefficient k. Detecting the hollowing deterioration surface diseases with nondestructive testing method based on THz-TDS, which has very important practical significance for the repairing and strengthening of Yungang Grottoes.

Tianhua Meng

Papers

Design of a five-band terahertz perfect metamaterial absorber using two resonators

Design and optimization of terahertz metamaterial sensor with high sensing performance

Experimental Study on THz Nondestructive Testing of Hollowing Deterioration for Stone Relics

Properties of split ring resonators metamaterials terahertz sensor on flexible substrates

Nondestructive testing of deterioration for Yungang Grottoes based on THz-TDS