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Thermally tunable terahertz metasurface absorber based on all dielectric indium antimonide resonator structure
摘要： In this paper, we present a novel design of temperature tunable metasurface absorber (MSA) based on all dielectric indium antimonide (InSb) resonator structure in terahertz (THz) region. The permittivity of the InSb dielectric is dependent on the variation of temperature. Based on the perfect impedance-match (Re(z)?1) to the free space, the absorbance of the proposed MSA is up to 99.9% at 1.43 THz and the Q-factor is about 26.9 when temperature is 285 K. The perfect absorption of the MSA is mainly from excitation of fundamental dipolar mode. In addition, the MSA is polarization-insensitive for both transverse electric (TE) and transverse magnetic (TM) waves. Furthermore, the absorption properties of the MSA can be adjusted by changing the geometric parameters of the unit-cell structure and temperature. The design offers a new route for control of THz absorption with potential applications in imaging, energy harvesting, sensing, and detecting.
关键词： Terahertz,Tunable,Metasurface absorber,Indium antimonide (InSb)
更新于2025-09-23 15:19:57
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Coherently controlled generation of single-cycle terahertz pulses from a thin layer of nonlinear medium with low-frequency resonances
摘要： We propose a scheme to generate single-cycle terahertz (THz) pulses via reflection of an optical femtosecond pulse train from a thin layer of nonlinear resonant medium. Our method is based on the coherent control of low-frequency oscillations and free induction decay in the medium. The specific single-cycle shape of generated THz pulses requires a plane wave front and detection in the near field. Our theoretical results pave the way to a new, simple, and highly efficient way to generate single-cycle waveshape-tunable THz pulses.
关键词： nonlinear resonant medium,coherent control,single-cycle waveshape-tunable,free induction decay,terahertz pulses
更新于2025-09-23 15:19:57
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[IEEE NAECON 2019 - IEEE National Aerospace and Electronics Conference - Dayton, OH, USA (2019.7.15-2019.7.19)] 2019 IEEE National Aerospace and Electronics Conference (NAECON) - Development of Optically Controlled Tunable/Reconfigurable Terahertz Waveguide Circuits/Components For Advanced Sensing and Adaptive Wireless Communications
摘要： We report our recent progress toward the development of optically controlled tunable/reconfigurable THz circuits/components in waveguide configurations for advanced sensing and adaptive wireless communications. The development and demonstration of a modified WR-4.3 variable waveguide attenuator based on photo-excited Si with 60-dB range and 0.7-dB insertion loss will first be reviewed. Then the investigation of a WR-5.1 reconfigurable band-stop filter (BSF) prototype based on photo-induced electromagnetic band gap (PI-EBG) structures using semiconductor mesa arrays will be presented. The center frequency of the BSF can be reconfigured from 166-200 GHz with adjustable stop-band rejection and bandwidth. Finally, the development of high-performance THz integrated switches using the same optical control methodology will be envisioned, investigated and discussed. Preliminary results reveal that the optically controlled RF figure-of-merit (evaluated by RonCorr constant) of 153 THz, allowing them to outperform both conventional solid-state-device-based (e.g., HEMTs) and emerging phase-changing-material-based (e.g., VO2) counterparts, and therefore promising to compete with MEMS switches in the mmW-THz region for a novel class of tunable/reconfigurable circuits/components.
关键词： Terahertz,tunable/reconfigurable,imaging,waveguides,optical tuning,wireless communication,THz devices
更新于2025-09-23 15:19:57
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Thermal expansion of α-nitrogen ice in terahertz spectroscopy
摘要： The volumetric thermal expansion coef?cient of a-nitrogen (N2) ice is calculated for temperatures between 10 and 25 K using its terahertz transmission data and a phonon model. The observed dip in terahertz transmission around 1.45 THz is modeled as phonon absorption based on an intermolecular potential which is sum of the Lennard-Jones potential and quadrupole–quadrupole interaction term. Using this model and our experimental data, the lattice parameters of a-N2 ice were obtained.
关键词： Thermal expansion,Terahertz,Time-domain spectroscopy,a-Nitrogen ice
更新于2025-09-23 15:19:57
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Terahertz Metalens for Multifocusing Bidirectional Arrangement in Different Dimensions
摘要： Metasurface lenses are typically investigated for a lot of characteristics, but the design method for conventional devices is comparatively simple in terms of controlling the quantity, position, and size of focal spots. Herein, ultra-thin-phase metasurface structures based on complementary square-split-ring (SSR) nanoantennas have been proposed to achieve terahertz (THz) optical metalenses with multidimensionality and multifocusing. The principle of beam propagation and efficient transmission can be effectively explained through the Fabry–Pérot resonance mode. The THz metalens can efficiently transfer linear cross-polarization under the effects of gratings in the incident plane. By locally tailoring edge lengths and opening the angles of the split rings, full control over abrupt phase changes can be achieved. Two symmetrically distributed parallel focal spots and two vertical focal spots with arbitrary distance can be obtained by arranging the SSR units on the metalenses. Furthermore, we apply the concept of a partitioned-phase mode to realize a double-focusing metalens in the longitudinal direction, which provides a flexible and convenient method to achieve the desired focusing properties. The simulation results are expected to pave the way for practical use of metasurfaces in optical holography, optical-information coding, and parallel-particle trapping.
关键词： nanoantenna,phase shift,Multifocusing metalens,Fabry-Pérot-like resonance,terahertz
更新于2025-09-19 17:15:36
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Nondestructive imaging of hidden defects in aircraft sandwich composites using terahertz time-domain spectroscopy
摘要： Aircraft sandwich composites are superior to ordinary composites and have been largely used in the manufacture of military aircraft. This study attempts to investigate the efficacy of terahertz (THz) time-domain spectroscopy (TDS) imaging technology in detecting hidden defects in aircraft glass fiber (GF) sandwich composites. The defects of various sizes, such as debonding, delamination, and multi-delamination, at different depths in GF A-sandwich structure composites with foam core, C-sandwich structure composites with honeycomb core, and sheet-to-sheet cementing structure composites were evaluated. The THz frequency-domain amplitude and time-domain amplitude imaging algorithms were used to visualize the defects simulated by ultrathin double-layer Teflon inserts. And the suitable image processing methods which include wavelet-based fusion and multiscale edge representation were employed. With a combination of high-resolution THz C-scan and B-scan imaging, both the horizontal size and location, and the vertical depth and thickness of the defects were obtained in three dimensions. This study experimentally demonstrated that THz imaging technology can clearly detect various hidden defects in aircraft GF sandwich composites through reflection or transmission imaging mode.
关键词： image processing,debonding,multi-delamination,Aircraft sandwich composites,terahertz time-domain spectroscopy,nondestructive testing
更新于2025-09-19 17:15:36
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Computational phantom study of frozen melanoma imaging at 0.45 terahertz
摘要： Terahertz radiation (THz) is highly absorbed by liquid water. This creates the possibility of medical imaging on the basis of the water content difference between normal and diseased tissue. The effective penetration of THz is limited, however, to a tissue depth of 0.2–0.3 mm at body temperature. A unique feature of the 0.1–2.0 THz frequency is that there is a high disparity between liquid water absorption and ice absorption, with ice being 100 times more permeable to the radiation than liquid water. This results in 90% of the radiation surviving to 1.0 mm in ice, permitting the imaging of frozen tissues to a depth of 5.0 mm. This method is practical as an in vivo procedure before or during surgical excision. Finite difference time domain (FDTD) computational modeling of frozen normal skin and frozen melanoma was undertaken using tissue phantoms. The study suggests that sufficient contrast exists to differentiate normal frozen skin and melanoma on the basis of the difference of water content alone. When the melanin pigment in melanomas is modeled as a significant absorber of THz, the contrast changes. Based on the modeling, further exploration of the “THz-skin freeze” imaging technique is justified. In the modeling, the boundary between the frozen tissue and non-frozen tissue is shown to be strongly reflective. If the reflective properties of the boundary are substantiated, the “THz-skin freeze” technique will have applications in other areas of skin diagnostics and therapeutics.
关键词： imaging,freezing,melanoma,skin,terahertz
更新于2025-09-19 17:15:36
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[IEEE 2018 11th Global Symposium on Millimeter Waves (GSMM) - Boulder, CO, USA (2018.5.22-2018.5.24)] 2018 11th Global Symposium on Millimeter Waves (GSMM) - High-Resolution Antenna Near-Field Imaging and Sub-THz Measurements with a Small Atomic Vapor-Cell Sensing Element
摘要： Atomic sensing and measurement of millimeter-wave (mmW) and THz electric fields using quantum-optical EIT spectroscopy of Rydberg states in atomic vapors has garnered significant interest in recent years towards the development of atomic electric-field standards and sensor technologies. Here we describe recent work employing small atomic vapor cell sensing elements for near-field imaging of the radiation pattern of a Ku-band horn antenna at 13.49 GHz. We image fields at a spatial resolution of λ/10 and measure over a 72 to 240 V/m field range using off-resonance AC-Stark shifts of a Rydberg resonance. The same atomic sensing element is used to measure sub-THz electric fields at 255 GHz, an increase in mmW-frequency by more than one order of magnitude. The sub-THz field is measured over a continuous ±100 MHz frequency band using a near-resonant mmW atomic transition.
关键词： atom,microwave,electric field,metrology,quantum sensing,millimeter-wave,THz,antenna,mmW,Rydberg,terahertz,Atomic sensors,antenna characterization
更新于2025-09-19 17:15:36
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Design of terahertz photoconductive antenna arrays based on defective photonic crystal substrates
摘要： In this paper, arrays of two different terahertz (THz) antennas based on defective photonic crystal (DPC) substrates are proposed and their radiation characteristics are investigated by using full-wave simulation. We show that employing DPC substrates in THz photoconductive antenna (PCA) arrays reduces the amount of power coupled to the substrate surface waves and, as a result, decreases the mutual coupling between the elements of the antenna array and increases the directivity in the boresight direction. By studying 1 × 2 arrays of bowtie and four-leaf-clover-shaped antennas, we show that either the improvement of directivity in a broad bandwidth or the enhancement of photomixer antenna impedance at a resonant frequency can be considered in the design of the DPC substrate. Therefore, the proposed approach can significantly improve the efficiency and radiation performance of THz photomixer antennas resulting in an improved effective THz radiated power in the desirable direction. The proposed DPC substrate can be considered as a way to realize sub-millimeter-sized dielectric resonator antennas at terahertz frequencies. In addition, this cost-effective technique can reduce the necessity of exploiting hyper-hemispherical Si lenses by overcoming the adverse effects of the thick substrate which is of prime importance in PCA arrays from a practical viewpoint.
关键词： Arrays,Defective photonic crystal substrate,Propagation waves,Terahertz antennas
更新于2025-09-19 17:15:36
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A novel analytical method for designing a multi-band, polarization-insensitive and wide angle graphene-based THz absorber
摘要： In this paper, we propose a simple and analytical method to design a multi-band tunable graphene-based absorber using circuit model. The presented paper provides a flowchart and equations to design a multi-band absorber which tremendously simplifies the design procedure of a multi-band absorber. This paper only investigates the disk shape graphene-based absorber, but we believe the proposed method is extendable to all presented shapes of graphene which previously designers provided with a circuit model. To verify the accuracy of the presented method; we have designed several multi-band absorbers and used Full-wave numerical modeling of the structure to approve our method. Also, this paper studies the reliability of our proposed model by investigating the fabrication sensitivity of the structure. Lastly, this paper investigates to see how a multi-band absorption spectra behave, in case there are any errors during the fabrication phase. The designed absorbers have potential applications in various fields of active THz metamaterials, tunable filters, and sensors. The graphene-based disk-shaped absorber has the advantage of polarization insensitivity, wide-angle absorption and ease of implementation due to its simple shape. Another advantage of using graphene in the absorber structure is that with the availability of changing the Fermi energy level, it is possible to tune the absorption frequency of the multi-band absorbers.
关键词： Circuit model,Absorber,Graphene Terahertz,Tunable bandwidth,Transmission line method
更新于2025-09-19 17:15:36