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Terahertz Active Metamaterials Based on Stacked Closed-Ring Resonator Arrays
摘要： Metamaterials, which can show novel optical functionalities beyond conventional optics, has been actively studied in recent years. As one of approaches to add tunability on resonant characteristics of metamaterials, slightly shifting relative position of stacked metamaterials or metasurfaces has been reported. In this study, based on numerical simulation we have designed stacked closed-ring resonator (CRR) arrays that show relatively large spectral shift with a small lateral shift of the stacked layers in terahertz (THz) range. We also show that changing dielectric constant of the dielectric media between CRR arrays is also effective to obtain large spectral shift of the resonant responses. Our findings may be utilized to develop novel type of THz active devices and also sensing devices.
关键词： terahertz,metamaterial,closed-ring resonator
更新于2025-09-23 15:22:29
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Continuous-wave Terahertz Imaging Applied to Detect Infestations Caused by Insects in Grain
摘要： Detection infestations caused by insects in grain are important control measures for ensuring storage longevity, seed quality and food safety. The efficiency of the continuous wave terahertz imaging method to detect infestations caused by insects in wheat kernels was determined in this study. A continuous wave terahertz experimental setup was designed for recording of THz images corresponding to different infestations caused by different life stages of insects. The experimental results indicate that the absorbance is generally highest for un-infested wheat kernels and decreased at later growth stages from THz pseudo-color images. Our study intended to demonstrate how the method of continuous wave Terahertz imaging could be applied to detect Infestations Caused by Insects in Grain.
关键词： terahertz imaging,wheat grain,infestation,insect,Detection
更新于2025-09-23 15:22:29
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Dual-prism based terahertz time-domain attenuated total reflection spectroscopy and its application to characterise the hydration state of L-threonine in solution
摘要： To investigate the hydration state of amino acids, terahertz time-domain attenuated total internal reflection (THz TD-ATR) spectroscopy is often adopted to measure the complex permittivity. However, the classical THz TD-ATR spectroscopy system has only a single ATR prism and requires prism cleaning for different measuring modes, increasing the time consumed and easily introducing errors due to the changing environment. To accelerate the measurements and avoid the influence of environmental fluctuations, in this paper, we designed and built a dual-prism based THz TD-ATR spectroscopy: two ATR prisms with and without samples setting on the optical rail can be sequentially switched to optical systems for easily and rapidly collecting both sample and reference ATR spectra. According to the measurements of deionised water, the dual-prism based THz TD-ATR spectroscopy system can measure the sample complex permittivity rapidly and with high accuracy. The complex permittivity of L-threonine in aqueous solution is measured and analysed via the proposed system, and the hydration numbers of L-threonine solutions in different concentrations are quantitatively characterised. It is believed that the dual-prism based THz TD-ATR technique is a powerful tool for quickly and accurately investigating the hydration of amino acids.
关键词： Terahertz spectroscopy,Complex permittivity,Time-domain attenuated total internal reflection,Amino acid hydration
更新于2025-09-23 15:22:29
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Polarization dependent five-band terahertz metamaterial using two resonators
摘要： In this paper, we present a multi-band terahertz metamaterial composed of two hexagonal shaped metallic resonators supported by a Teflon dielectric substrate. The performance characteristics of the proposed structure are evaluated numerically using CST Microwave Studio software. The design has polarization sensitive and angle independent operational nature. The designed structure resonates at five frequencies: 0.19 THz, 0.3 THz, 0.47 THz, 0.5 THz, and 0.61 THz in transverse electric mode. The underlying concept of multi-band resonances has been understood by obtaining the electric field.
关键词： multi-band,terahertz,metamaterial,imaging,polarization
更新于2025-09-23 15:22:29
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Modal transmission line theory of plane wave excited layered media with multiple conductive anisotropic sheets at the interfaces
摘要： A succinct and efficient transmission line formulation is presented for the analysis of plane wave excited planar multilayered uniaxial media comprising multiple conductive sheets at the interfaces. The conductive sheets may be anisotropic with a fully populated conductivity tensor, which results in the coupling the transverse-magnetic and transverse-electric waves. The transmission line formalism is thus extended to accommodate this hybrid mode of propagation. Three different algorithms for the solution of the transmission line network are developed and compared, including a numerically stable and efficient scattering matrix procedure. Numerical examples are included that validate the theoretical method.
关键词： Anisotropic conductive sheet,Terahertz,Transmission line network,Transition matrix,Graphene,Scattering matrix,Plane wave,Planar multilayer
更新于2025-09-23 15:22:29
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Design of a six-band terahertz metamaterial absorber for temperature sensing application
摘要： We present a simple design of a six-band terahertz metamaterial absorber (MMA). The unit-cell of the MMA consists of a metallic cross-cave-patch (CCP) structure and an InSb dielectric spacing layer stands on a ground-plane. The permittivity of the InSb dielectric layer can be adjusted efficiently by the variation of external temperature. The numerical simulation results show that the MMA has six distinct absorption peaks from 0.4 THz to 2.2 THz, and the absorption peak frequencies can be tuned easily by changing the external temperature. The surface current distributions of the top layer and back layer of the unit-cell structure are studied to better understand the physical mechanism of the proposed MMA. The six-band strong absorption of the MMA is originated from the excitations of high-order magnetic resonance. In addition, the sensitivity S is investigated to explore temperature sensing performance of the device, and the value of S is 10.3 GHz/K, 8.1 GHz/K, 6.7 GHz/K, 6.4 GHz/K, 5.5 GHz/K and 5.4 GHz/K, respectively. The design of the MMA could find potential applications in temperature sensing or other optoelectronic related areas in terahertz region.
关键词： InSb,Terahertz metamaterial absorber,Temperature sensing,Six-band
更新于2025-09-23 15:22:29
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Simulations of some physical parameters of homologous series of nBT and nCHBT at 0.3–20.0 THz
摘要： In this work, the terahertz (THz) absorption of homologous series of isothiocyanobiphenyls (nBT) and 4-(trans-4?-n-alkylcyclohexyl)isothiocyanato-benzene (nCHBT) are simulated by using the density functional theory (DFT) method. Numerical results show that absorption of the tested nematic liquid crystals (NLCs) varies up to 0.04 in the broad range of 0.3–20.0 THz and takes maximum value in the range of 9–14 THz. In addition, the values of molecular polarisabilities (αo, αe) increase with the increase in the number of carbon atoms in the alkyl chain, while refractive indices (no, ne) decreases. The calculated birefringence (Δn) values for nCHBT are approximately twice as large as the birefringence value for nBT. It is crucial to examine these series of nematic liquid crystals at THz frequencies due to the role of soft matter in various switchable THz components.
关键词： Numerical calculations,refractive index,terahertz radiation,birefringence,nematic liquid crystals
更新于2025-09-23 15:22:29
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High-frequency breakdown of the integer quantum Hall effect in GaAs/AlGaAs heterojunctions
摘要： The integer quantum Hall effect is a well-studied phenomenon at frequencies below about 100 Hz. The plateaus in high-frequency Hall conductivity were experimentally proven to retain up to 33 GHz, but the behavior at higher frequencies has remained largely unexplored. Using continuous-wave terahertz spectroscopy, the complex Hall conductivity of GaAs/AlGaAs heterojunctions was studied in the range of 69–1100 GHz. Above 100 GHz, the quantum plateaus are strongly smeared out and replaced by weak quantum oscillations in the real part of the conductivity. The amplitude of the oscillations decreases with increasing frequency. Near 1 THz, the Hall conductivity does not reveal any features related to the filling of Landau levels. Similar oscillations are observed in the imaginary part as well; this effect has no analogy at zero frequency. This experimental picture is in disagreement with existing theoretical considerations of the high-frequency quantum Hall effect.
关键词： integer quantum Hall effect,GaAs/AlGaAs heterojunctions,terahertz spectroscopy,high-frequency Hall conductivity,quantum oscillations
更新于2025-09-23 15:22:29
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The Transitional Transmittance Response of ZIF-8 Gas Adsorption Observed Using Terahertz Waves
摘要： In this study, we recorded the transitional response in terms of terahertz transmittance of zeolitic imidazole framework-8 [Zn(2-methylimidazolate)2, ZIF-8] at 2.0 THz as a function of exposure time to gaseous propane and n-butane. The transmittance at 2.0 THz increased as gas adsorbed onto the ZIF-8. Conversely, during a nitrogen purge, transmittance decreased as the alkane gas desorbed. We estimated time constants for the adsorption and desorption of the two gases by comparing the plots of their responses. We also demonstrated the potential of using a combination of ZIF materials and terahertz technology as a novel gas analyzer.
关键词： Adsorption kinetics,Terahertz vibration,Metal-organic frameworks,Porous solids,Infrared absorption spectroscopy
更新于2025-09-23 15:22:29
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Different Types of Field-Effect Transistors - Theory and Applications || Quantum Confinement in High Electron Mobility Transistors
摘要： Modulation-doped semiconductor nanostructures exhibit extraordinary electrical and optical properties that are quantum mechanical in nature. The heart of such structures lies in the heterojunction of two epitaxially grown semiconductors with different band gaps. Quantum confinement in this heterojunction is a phenomenon that leads to the quantization of the conduction and the valence band into discrete subbands. The spacing between these quantized bands is a very important parameter that has been perfected over the years into device applications. Most of these devices form low-dimensional charge carriers that potentially allow optical transitions between the subbands in such nanostructures. The transition energy differences between the quantized bands/levels typically lie in the infrared or the terahertz region of the electromagnetic spectrum and can be designed according to the application in demand. Thus, a proper understanding and a suitable external control of such intersubband transitions (ISTs) are not only important aspects of fundamental research but also a necessity for optoelectronic device applications specifically towards closing the terahertz gap.
关键词： HEMT,intersubband transition,infrared,heterojunction,terahertz
更新于2025-09-23 15:22:29