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This work reports an ultra-low noise, multi-stage stagger-tuned low-noise amplifier (MS-ST-LNA) over the D-band performance and achieves a best trade-off between noise, bandwidth, and gain parameters. The ultra-low-noise is achieved in three ways: First, the high-gain 3-stage stagger tuned amplifier (STA) realizes a 3X gain compared to the conventional single-stage amplifier, which sets a low floor noise. Second, the stagger-tuned amplifier achieves 1.6 times lower noise than the traditional single-stage amplifier. Finally, the stagger tune realizes a high-order transfer function, which mitigates the high-frequency noise. The full LNA is implemented and fabricated using a commercial nano-manufacturing 9-nm graphene film FET on a silicon wafer using a 0.065-μm commercial process, occupying an area of 0.21 mm2. The proposed design achieves an optimum performance: a maximum measured gain of 20.5 dB and a minimum noise figure (NF) of 4.2 dB over 123.7 to 162.5 GHz. The proposed LNA consumes ultra-low power consumption of 21.3 mW under the power supply of 1.2 V. [ABSTRACT FROM AUTHOR]

In this paper, A Massive bandwidth High gain Compact 6G antenna is proposed. The antenna attains a massive bandwidth of 300 GHz with resonant at 148.6 GHz, 190.2 GHz, 257.8 GHz, 308.8 GHz, and 363.6 GHz covering 100 GHz to 400 GHZ which is otherwise termed as 0.1 THz to 0.4 THz spectrum. The reflections are observed to be below – 10 dB with the maximum reflection at – 65 dB. The maximum gain of 17 dBi and a minimum of 1 dBi is observed throughout the operating band. The gain at resonant points 148.6 GHz, 190.2 GHz, 257.8 GHz, 308.8 GHz, and 363.6 GHz are 6.600199 dBi, 16.30173 dBi, 8.14491 dBi, 6.260792 dBi, 13.33571 dBi respectively. The proposed design is embedded over a Rogers RT Duroid 5880 substrate material with a thickness of (t = 0.08 mm), dielectric constant (εr = 2.2), and loss tangent (0.0009) using a High-Frequency Structure simulator. Furthermore, the design steps and evolution of the antenna have been discussed. Supporting the parametric analysis which explains the impedance match at each stage of evolution such as development from Rectangular patch antenna (RPA) to Circular patch antenna (CPA). Configuration of inset feed with Full Ground being deployed, the proposed design becomes an eminent prototype for mobile communication in 6G Spectrum. [ABSTRACT FROM AUTHOR]

This paper considers a terahertz (THz) dual-function multi-input multi-output (MIMO) radar and communication system with the assistance of a reconfigurable intelligent surface (RIS) and jointly designs the constant modulus (CM) waveform and RIS phase shifts. A weighted optimization scheme is presented, to minimize the weighted sum of three objectives, including communication multi-user interference (MUI) energy, the negative of multi-target illumination power and the MIMO radar waveform similarity error under a CM constraint. For the formulated non-convex problem, a novel alternating coordinate descent (ACD) algorithm is introduced, to transform it into two subproblems for waveform and phase shift design. Unlike the existing optimization algorithms that solve each subproblem by iteratively approximating the optimal solution with iteration stepsize selection, the ACD algorithm can alternately solve each subproblem by dividing it into multiple simpler problems, to achieve closed-form solutions. Our numerical simulations demonstrate the superiorities of the ACD algorithm over the existing methods. In addition, the impacts of the weighting coefficients, RIS and channel conditions on the radar communication performance of the THz system are analyzed. [ABSTRACT FROM AUTHOR]

As the era of sixth-generation (6G) communications approaches, there will be an unprecedented increase in the number of wireless internet-connected devices and a sharp rise in mobile data traffic. Faced with the scarcity of spectrum resources in traditional communication networks and challenges such as rapidly establishing communications after disasters, this study leverages unmanned aerial vehicles (UAVs) to promote an integrated multi-hop communication system combining free-space optical (FSO) communication, terahertz (THz) technology, and intelligent reflecting surface (IRS). This innovative amalgamation capitalizes on the flexibility of UAVs, the deployability of IRS, and the complementary strengths of FSO and THz communications. We have developed a comprehensive channel model that includes the effects of atmospheric turbulence, attenuation, pointing errors, and angle-of-arrival (AOA) fluctuations. Furthermore, we have derived probability density functions (PDFs) and cumulative distribution functions (CDFs) for various switching techniques. Employing advanced methods such as Gaussian–Laguerre quadrature and the central limit theorem (CLT), we have calculated key performance indicators including the average outage probability, bit error rate (BER), and channel capacity. The numerical results demonstrate that IRS significantly enhances the performance of the UAV-based hybrid FSO/THz system. The research indicates that optimizing the number of IRS elements can substantially increase throughput and reliability while minimizing switching costs. Additionally, the multi-hop approach specifically addresses the line-of-sight (LoS) dependency limitations inherent in FSO and THz systems by utilizing UAVs as dynamic relay points. This strategy effectively bridges longer distances, overcoming physical and atmospheric obstacles, and ensures stable communication links even under adverse conditions. This study underscores that the enhanced multi-hop FSO/THz link is highly effective for emergency communications after disasters, addressing the challenge of scarce spectrum resources. By strategically deploying UAVs as relay points in a multi-hop configuration, the system achieves greater flexibility and resilience, making it highly suitable for critical communication scenarios where traditional networks might fail. [ABSTRACT FROM AUTHOR]

In this paper, a Substrate-Integrated Waveguide (SIW)–based Cylindrical Dielectric Resonator Antenna (CDRA) is designed for 6G THz applications. This antenna provides a Quad-band response at 2.14 THz, 3.41 THz, 5.61 THz, and 9.02 THz respectively. The unique feature of the proposed SIW-CDRA is its ability to exhibit Circular Polarization (CP) behavior across three frequency bands. Graphene material is added onto the top of the proposed CDRA to achieve tunability in the antenna's resonant frequency. CP tuning is also achieved by varying the graphene potential of the antenna. Furthermore, this proposed antenna shows both Right Hand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP) behavior at different resonant frequencies. The antenna exhibits a maximum gain of 6.97 dB and a maximum radiation efficiency of 84.53%. Notably, the antenna showcases a 3 dB Axial Ratio (AR) bandwidth of 11.05% (1.968–2.195 THz), 4.58% (5.483–5.734 THz), and 5.22% (8.843–9.313 THz) is achieved. Moreover, the CDRA generates two higher-order modes, specifically HEM11δ at 5.61 THz and HEM12δ at 9.02 THz. Additionally, the antenna exhibits a unique feature of converting multiband response to wideband response by changing the length of the aperture slots. All these results show that the proposed multiband SIW with CDRA is unique and suitable for THz applications. [ABSTRACT FROM AUTHOR]

This study introduces an ultrathin metamaterial-based sensor designed for the accurate detection of microorganisms and pesticides displaying enhanced sensing capabilities. The innovative design incorporates of polyimide thin film act as dielectric layer while a single square gold patch featuring four uniformly sized notches act as sensing surface. The outcome of simulation reveals a single resonance peak with absorption rate equal to 100%. Furthermore, the design sensor sensing effectiveness has also been examined and analyzed by manipulating the refractive index and thickness of analyte layer. The sensor exhibits remarkable sensitivity with sensor sensitivity increases up to 0.175 THz/ RIU within 1 to 1.8 RI range. This increased sensitivity makes the sensor notably capable to detect microorganisms such as bacteria and pesticides revealing a significant frequency shift of 100 GHz (high sensitivity) for pesticides that has not been previously apparently in the literature. The novelty of work lies in remarkable sensing capabilities in the detection of microorganisms such as bacteria and various pesticides in terms of notable frequency shift making it significant for applications in agriculture and food products industry. The proposed research work can also be significant in other sensing applications such as chemical and bio- sensing industry applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a unified model for gallium arsenide (GaAs) based on ab initio simulations which characterizes its terahertz (THz) properties when excited by optical pump. We use density functional perturbation theory to calculate the dielectric properties of GaAs, and investigate the relaxation time of photo-excited GaAs through electron–phonon interactions. In light of the complexities arising from the mixed absorption mechanisms and the sensitivity of GaAs to laser parameters, we have developed a method that leverages time-dependent density functional theory and Boltzmann transport theory. This approach enables us to establish an accurate relationship between the pump laser intensity and the carrier concentration by introducing the percentage of excited electrons, facilitating the quantitative characterization of GaAs's response under different optical pump intensities. Using the microscopic material parameters solved by first principles, we develop a unified Drude model to describe the macroscopic electromagnetic responses of photo-excited GaAs. We simulate several reported numerical examples of photo-excited GaAs, including a GaAs wafer and GaAs-based THz metamaterial modulators, to validate the proposed unified model as a reliable approach for predicting the THz properties of GaAs. The good agreement between the simulation and measurement results demonstrates that our model successfully captures the dynamic responses of photo-generated carriers and provides guidance for the design of optoelectronic devices based on GaAs. Furthermore, our modeling approach based on ab initio simulations is free from empirical parameters, providing a solid THz modeling method for other photo-excited semiconductor materials. [ABSTRACT FROM AUTHOR]

In this study, we explored the manipulation of optical properties in the terahertz (THz) frequency band of radio-frequency (RF) sputtered indium tin oxide (ITO) thin films on highly resistive silicon substrate by rapid thermal annealing (RTA). The optical constants of as-deposited and RTA-processed ITO films annealed at 400 °C, 600 °C and 800 °C are determined in the frequency range of 0.2 to 1.0 THz. The transmittance can be changed from ~27% for as-deposited to ~10% and ~39% for ITO films heat-treated at different annealing temperatures (Ta's). Such variations of optical properties in the far infrared for the samples under study are correlated with their mobility and carrier concentration, which are extracted from Drude–Smith modeling of THz conductivity with plasma frequency, scattering time and the c-parameters as fitting parameters. Resistivities of the films are in the range of 10−3 to 10−4 Ω-cm, confirming that annealed ITO films can potentially be used as transparent conducting electrodes for photonic devices operating at THz frequencies. The highest mobility, μ = 47 cm2/V∙s, with carrier concentration, Nc = 1.31 × 1021 cm−3, was observed for ITO films annealed at Ta = 600 °C. The scattering times of the samples were in the range of 8–21 fs, with c-values of −0.63 to −0.87, indicating strong backscattering of the carriers, mainly by grain boundaries in the polycrystalline film. To better understand the nature of these films, we have also characterized the surface morphology, microscopic structural properties and chemical composition of as-deposited and RTA-processed ITO thin films. For comparison, we have summarized the optical properties of ITO films sputtered onto fused silica substrates, as-deposited and RTA-annealed, in the visible transparency window of 400–800 nm. The optical bandgaps of the ITO thin films were evaluated with a Tauc plot from the absorption spectra. [ABSTRACT FROM AUTHOR]

Aiming at the limitations of single-functionality, limited-applicability, and complex designs prevalent in current metasurfaces, we propose a terahertz multifunctional and multiband tunable metasurface utilizing a VO2-metal hybrid structure. This metasurface structure comprises a top VO2-metal resonance layer, a middle polyimide dielectric layer, and a gold film reflective layer at the bottom. This metasurface exhibits multifunctionality, operating independently of polarization and incident angle. The varying conductivity states of the VO2 layers, enabling the metasurface to achieve various terahertz functionalities, including single-band absorption, broadband THz absorption, and multiband perfect polarization conversion for linear (LP) and circularly polarized (CP) incident waves. Finally, we believe that the functional adaptability of the proposed metasurface expands the repertoire of options available for future terahertz device designs. [ABSTRACT FROM AUTHOR]

In the field of integrated sensing and communication, there is a growing need for advanced environmental perception. The terahertz (THz) frequency band, significant for ultra-high-speed data connections, shows promise in environmental sensing, particularly in detecting surface textures crucial for autonomous systems' decision-making. However, traditional numerical methods for parameter estimation in these environments struggle with accuracy, speed, and stability, especially in high-speed scenarios like vehicle-to-everything communications. This study introduces a deep learning approach for identifying surface roughness using a 140-GHz setup tailored for such conditions. A high-speed data acquisition system was developed to mimic real-world scenarios, and a diverse set of rough surface samples was prepared for realistic high-speed datasets to train the models. The model was trained and validated in three challenging scenarios: random occlusions, sparse data, and narrow-angle observations. The results demonstrate the method's effectiveness in high-speed conditions, suggesting terahertz frequencies' potential in future sensing and communication applications. [ABSTRACT FROM AUTHOR]

A high gain D‐band hybrid integrated on‐chip antenna (OCA) based on a low‐cost printed circuit board (PCB) packaging technology is analyzed and designed in a standard 40‐nm CMOS process in this paper. The proposed OCA is a hybrid structure of a slotted patch OCA with off‐chip PCB ground and off‐chip dielectric resonator (DR). The proposed OCA exhibits a simulated gain of 3.5 dBi and 53% radiation efficiency at 150 GHz. The simulated impedance bandwidth is 20 GHz. The radiation performance and impedance bandwidth of the OCA are observably improved with the proposed techniques. The proposed OCA occupies 0.52 × 0.56 mm2, and addresses the highly desirable yet challenging overall design of future low‐cost integrated millimeter‐wave (mm‐Wave) and terahertz (THz) systems, which hit the mark on cost and compatibility. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hebei University of Science & Technology is the property of Hebei University of Science & Technology, Journal of Hebei University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High thermal conductivity and a high breakdown field make diamond a promising candidate for high-power and high-temperature semiconductor devices. Diamond also has a higher radiation hardness than silicon. Recent studies show that diamond has exceptionally large electron and hole momentum relaxation times, facilitating compact THz and sub-THz plasmonic sources and detectors working at room temperature and elevated temperatures. The plasmonic resonance quality factor in diamond TeraFETs could be larger than unity for the 240–600 GHz atmospheric window, which could make them viable for 6G communications applications. This paper reviews the potential and challenges of diamond technology, showing that diamond might augment silicon for high-power and high-frequency compact devices with special advantages for extreme environments and high-frequency applications. [ABSTRACT FROM AUTHOR]

A metamaterial wave absorber (MWA) optimized for high-performance absorbers to harvest electromagnetic energy is designed for operation within the terahertz (THz) frequency range using renewable palm oil frond graphitic carbon (POFGC). The structural composition of the MWA consists of double split-ring resonators configured in rotational symmetry. The fundamental component of the design has three distinct layers: (1) the bottom layer, composed of a metallic substance with gold that exhibits a lossy metal characteristic; (2) the middle layer, made of a lossy dielectric material referred to as silicon dioxide (SiO2); and (3) the top layer crafted from POFGC. The findings reveal that the absorber achieves a broad absorption spectrum, with simulated results from CST software indicating absorption peaks at 414, 708, 981, and 1242 THz. These results demonstrate high absorption levels of 99.989, 99.999, 99.988, and 99.999% for typical incident electromagnetic waves. The structural dimensions (590 × 590 nm2) are designed to deliver remarkable performance across the visible spectrum and infrared frequency ranges. The energy harvester exhibits independent polarization at various angles, including 0°, 45°, 90°, 135°, 180°, and 225°. It has excellent harvesting capabilities across multiple angles of incidence from 0° to 80°, including the whole operational spectrum. A comparative investigation of the circuit indicates enhanced performance of the metamaterial wave absorber, demonstrating its potential for exceptional functionality inside the advanced design system (ADS) software. Furthermore, the structures under consideration, which were simulated using the HFSS (high-frequency structure simulator) tool, demonstrate strong agreement with the highest level of absorption seen at each resonance peak in the CST simulation outcomes. This paper introduces an alternative protocol, expressed in terms of the phase velocity of the mode, for use with the restricted asymmetric structure to find optimum dispersion. The study highlights the exceptional properties of POFGC, including its high absorption capacity, insensitivity to angles, and effective dispersion properties. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of e & i Elektrotechnik und Informationstechnik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A completely embedded, planar, dual-element dielectric based antenna directly fed by a substrate integrated insulated guide within the same layer in Sub-THz band is presented in this paper. A dielectric layer is employed to make the structure stable. The proposed structure is compatible with the standard planar millimeter-wave and terahertz manufacturing technologies. To minimize the reflection loss, matching air holes inside the guiding channel of the waveguide and air holes with a smaller perforation radius surrounding the antenna are created. The proposed compact antenna, which has been successfully tested, covers the frequency range of 234.5-278.1 GHz with a measured impedance bandwidth of 17.01%, a proper simulated average radiation efficiency of 93.6%, and a maximum gain as well as average gain of 16.08 dBi and 12.56 dBi from measurement results, respectively. Because of these features, the suggested antenna would be a great candidate for short-range wireless applications in Sub-THz frequency bands.

Terahertz (THz) radar is well-suited for dynamic mobile target surveillance due to its high frame rates, minimal delay, and superior resolution. However, the defocusing problem caused by the motion of targets in the scene and the nonideal motion of the airborne platform severely affect synthetic aperture radar (SAR) imaging, particularly in the THz wave band. To address this issue, this article proposes a high-resolution imaging algorithm for THz-SAR ground-moving targets using the equalized alternating direction method of multipliers (ADMM). First, the range-Doppler algorithm is employed to generate a coarse image and extract the moving target region as the region of interest. Then, the range profile can be obtained by applying the inverse, which serves as input for the ADMM solving algorithm. Finally, the 2-D image of the target is reconstructed iteratively. The algorithm fully exploits the low-rank and sparse characteristics of moving targets in the SAR image to separate them from the background. It updates the azimuthal matched filter iteratively by minimizing image entropy and designs the equalization factor to retain target details while maintaining image sparsity. This approach significantly improves focusing accuracy compared with conventional algorithms while maintaining high imaging speed without estimating Doppler parameters.

In this study, a novel coarse-to-fine image registration algorithm based on feature matching using the Gabor filters is provided for repeat-pass SAR interferometry (InSAR). In the coarse registration, we propose a feature-based algorithm developed using the Gabor odd filter ratio-based operator (GOFRO), and the innovative feature based on the GOFRO (GOFRO-F) consists of the improved nonlinear scale space and the descriptor. The establishment of nonlinear scale spaces informed by the GOFRO enhances the stability of feature detection. Also, an improved 64-dimensional descriptor based on the GOFRO is presented to optimize the capability of feature matching. In the fine registration, we employ the normalized correlation coefficient algorithm (NCCA) and the random consensus sample (RANSAC) for determining offsets and the sub-pixel projection model calculation. The datasets of interferograms are derived from the 0.3 THz stepped-frequency radar. Compared to other algorithms, registration experiments of both simple and complex scatters show that GOFRO-F is more suitable for high precision image registration because of its enhanced robustness to the speckle noise. Furthermore, the three-dimensional (3D) reconstruction is conducted based on our proposed algorithm. The results demonstrate that our proposed algorithm facilitates the attainment of millimeter-level spatial resolutions for InSAR in THz band (THz InSAR).

Terahertz (THz) communication is envisioned as one of the candidate technologies for future wireless communications to enable achievable data rates of up to several terabits per second (Tbps). However, the high pathloss and molecular absorption in THz band communications often limit the transmission range. To overcome these limitations, this paper proposes intelligent reconfigurable surface (IRS)-aided THz networks with imperfect channel state information (CSI). Specifically, we present an angle-based trigonometric channel model to facilitate the performance evaluation of IRS-aided THz networks. In addition, to maximize the sum rate, we formulate the transmitter (Tx)-IRS-receiver (Rx) matching problem, which is a mixed-integer nonlinear programming (MINLP) problem. To address this non-deterministic polynomial-time hard (NP-hard) problem, we propose a Gale-Shapley algorithm-based solutions to obtain stable matching between transmitters and IRSs, and receivers and IRSs, in the first and second sub-problems, respectively. The impact of the transmission power, the number of IRS elements, and the network area on the sum rate are investigated. Furthermore, the proposed algorithm is compared to an exhaustive search, nearest association, greedy search, and random allocation to validate the proposed solution. The complexity and convergence analysis demonstrate that the computational complexity of our algorithm is lower than that of the ES method.

Low efficiency of Terahertz (THz) radiation and radiation power have limited the development of THz Science and Technology. Thus, with the aims of achieving greater photoconductive current and improving radiation characteristics of THz photoconductive antenna (PCA), this study utilized Extraordinary Optical Transmission (EOT) of light passing through various subwavelength metal structures to control and restrain the light wave in subwavelength scale. Furthermore, by grooving the grating electrode structure, the influence of metal grating's EOT on the transmission field of PCA were investigated and analyzed. Simulation results show that the effect of local electric field enhancement is significant. When the incident power is 0.1 W, the peak value of the local electric field reaches 7. 0 4 × 1 0 7 V/m. In addition, comparing to the grating electrode with no groove structure in which the field intensity was less than 4. 2 8 × 1 0 6 V/m, the local electric field increased by 16.4 times, respectively. Correspondingly, the photocurrent intensity of the improved photoconductive plasmonic structure is increased by 72.3 times. In conclusion, the improved plasma photoconductive structure was shown to obviously enhance the transmission field strength of semiconductor materials and the current of the PCA, and accordingly, to improve the THz radiation capability. [ABSTRACT FROM AUTHOR]

A 2-bit encoder based on the plasmon-induced transparency (PIT) effect was proposed and investigated in the range from 2 to 7 THz. The Lorentz oscillation coupling model was utilized to confirm the simulation. By tuning the Fermi levels of cross1 and cross2, the 2-bit encoder was achieved. And the minimum MD was 94.73 %, the minimum ER was 12.77 dB, and the maximum IL was 0.32 dB. As a sensor, the structure had a sensitivity of up to 2.33 THz/RIU. In addition, due to the insensitivities to incidence angle and polarization angle, the encoder could be utilized to complex environments. Therefore, these results reveals that our work is significant in terahertz encoders, optical switches, sensors, slow light devices, and modulators.

This paper considers a terahertz (THz) dual-function multi-input multi-output (MIMO) radar and communication system with the assistance of a reconfigurable intelligent surface (RIS) and jointly designs the constant modulus (CM) waveform and RIS phase shifts. A weighted optimization scheme is presented, to minimize the weighted sum of three objectives, including communication multi-user interference (MUI) energy, the negative of multi-target illumination power and the MIMO radar waveform similarity error under a CM constraint. For the formulated non-convex problem, a novel alternating coordinate descent (ACD) algorithm is introduced, to transform it into two subproblems for waveform and phase shift design. Unlike the existing optimization algorithms that solve each subproblem by iteratively approximating the optimal solution with iteration stepsize selection, the ACD algorithm can alternately solve each subproblem by dividing it into multiple simpler problems, to achieve closed-form solutions. Our numerical simulations demonstrate the superiorities of the ACD algorithm over the existing methods. In addition, the impacts of the weighting coefficients, RIS and channel conditions on the radar communication performance of the THz system are analyzed.

Aiming at the limitations of single-functionality, limited-applicability, and complex designs prevalent in current metasurfaces, we propose a terahertz multifunctional and multiband tunable metasurface utilizing a VO2-metal hybrid structure. This metasurface structure comprises a top VO2-metal resonance layer, a middle polyimide dielectric layer, and a gold film reflective layer at the bottom. This metasurface exhibits multifunctionality, operating independently of polarization and incident angle. The varying conductivity states of the VO2 layers, enabling the metasurface to achieve various terahertz functionalities, including single-band absorption, broadband THz absorption, and multiband perfect polarization conversion for linear (LP) and circularly polarized (CP) incident waves. Finally, we believe that the functional adaptability of the proposed metasurface expands the repertoire of options available for future terahertz device designs.

Here, we report on numerical modelling of AlGaN/GaN HEMT terahertz detectors using a two-dimensional solver based on three Boltzmann transport equation (BTE) moments and the Poisson equation. We use the Synopsys TCAD Sentaurus program package, which offers a wide material database and the possibility to include traps and polarization charges for the formation of the channel without any doping. The implications of different levels of model simplifications are addressed both analytically and numerically. We calculated the current responsivity ℜI to THz radiation on the drain voltage in the frequency range 0.01-3.0 THz for three AlGaN layer thicknesses d = 15, 20 and 25 nm and different gate lengths. We demonstrate that only a hydrodynamic model can reproduce the change in the sign in current responsivity at the gate voltage UG0 (ℜI = 0 at UG = UG0). The energy flux factor in the energy balance equation determines this effect. For the simulated structures, we find that the noise equivalent power may be as low as 0.1 pW/√Hz at 0.04 THz and 10 pW/√Hz at 3.0 THz. [ABSTRACT FROM AUTHOR]

This paper presents a promising solution to address the scarcity of spectrum resources and enhance spectrum efficiency in the context of cognitive radio (CR)-based soft-switching free-space optical (FSO)/terahertz (THz) radio frequency (RF) dual-hop amplify-and-forward (AF)–non-orthogonal multiple access (ROMANO) links. The impact of maximum tolerable interference power in the primary network, transmit power in the secondary transmitter, and maximum relay transmission power on the link are thoroughly studied. The numerical results ultimately validate the effectiveness of this link in improving performance, and a comparative analysis is conducted with the without-CR scheme, highlighting the distinctive characteristics of the proposed link. [ABSTRACT FROM AUTHOR]

This article is aimed at designing an inventive compact-size quad-port antenna that can be operated within terahertz (THz) frequency spectra for a 6G high-speed wireless communication link. The single-element antenna comprises a lotus-petal-like radiating patch and a defected ground structure (DGS) on a 20 × 20 × 2 µm3 polyamide substrate and is designed to operate within the 8.96–13.5 THz frequency range. The THz antenna is deployed for a two-port MIMO configuration having a size of 46 × 20 × 2 µm3 with interelement separation of less than a quarter-wavelength of 0.18λ (λ at 9 THz). The two-port configuration operates in the 9–13.25 THz frequency range, with better than −25 dB isolation. Further, the two-port THz antenna is mirrored vertically with a separation of 0.5λ to form the four-port MIMO configuration. The proposed four-port THz antenna has dimensions of 46 × 46 × 2 µm3 and operates in the frequency range of 9–13 THz. Isolation improvement better than −25 dB is realized by incorporating parasitic elements onto the ground plane. Performance analysis of the proposed antenna in terms of MIMO diversity parameters, viz., envelope correlation coefficient (ECC) < 0.05, diversity gain (DG) ≈ 10, mean effective gain (MEG) < −3 dB, total active reflection coefficient (TARC) < −10 dB, channel capacity loss (CCL) < 0.3 bps/Hz, and multiplexing efficiency (ME) < 0 dB, is performed to justify the appropriateness of the proposed antenna for MIMO applications. The antenna has virtuous radiation properties with good gain, which is crucial for any wireless communication system, especially for the THz communication network. [ABSTRACT FROM AUTHOR]

In the field of integrated sensing and communication, there is a growing need for advanced environmental perception. The terahertz (THz) frequency band, significant for ultra-high-speed data connections, shows promise in environmental sensing, particularly in detecting surface textures crucial for autonomous systems’ decision-making. However, traditional numerical methods for parameter estimation in these environments struggle with accuracy, speed, and stability, especially in high-speed scenarios like vehicle-to-everything communications. This study introduces a deep learning approach for identifying surface roughness using a 140-GHz setup tailored for such conditions. A high-speed data acquisition system was developed to mimic real-world scenarios, and a diverse set of rough surface samples was prepared for realistic high-speed datasets to train the models. The model was trained and validated in three challenging scenarios: random occlusions, sparse data, and narrow-angle observations. The results demonstrate the method’s effectiveness in high-speed conditions, suggesting terahertz frequencies’ potential in future sensing and communication applications.

High thermal conductivity and a high breakdown field make diamond a promising candidate for high-power and high-temperature semiconductor devices. Diamond also has a higher radiation hardness than silicon. Recent studies show that diamond has exceptionally large electron and hole momentum relaxation times, facilitating compact THz and sub-THz plasmonic sources and detectors working at room temperature and elevated temperatures. The plasmonic resonance quality factor in diamond TeraFETs could be larger than unity for the 240–600 GHz atmospheric window, which could make them viable for 6G communications applications. This paper reviews the potential and challenges of diamond technology, showing that diamond might augment silicon for high-power and high-frequency compact devices with special advantages for extreme environments and high-frequency applications.

This paper presents a novel periodic grounded coplanar waveguide (GCPW) leaky-wave antenna implemented in an Indium Phosphide (InP) process. The antenna is designed to operate in the 220 GHz–325 GHz frequency range, with the goal of integrating it with an InP uni-traveling-carrier photodiode to realize a wireless transmitter module. Future wireless communication systems must deliver a high data rate to multiple users in different locations. Therefore, wireless transmitters need to have a broadband nature, high gain, and beam-steering capability. Leaky-wave antennas offer a simple and cost-effective way to achieve beam-steering by sweeping frequency in the THz range. In this paper, the first periodic GCPW leaky-wave antenna in the 220 GHz–325 GHz frequency range is demonstrated. The antenna design is based on a novel GCPW leaky-wave unit cell (UC) that incorporates mirrored L-slots in the lateral ground planes. These mirrored L-slots effectively mitigate the open stopband phenomenon of a periodic leaky-wave antenna. The leakage rate, phase constant, and Bloch impedance of the novel GCPW leaky-wave UC are analyzed using Floquet's theory. After optimizing the UC, a periodic GCPW leaky-wave antenna is constructed by cascading 16 UCs. Electromagnetic simulation results of the leaky-wave antenna are compared with an ideal model derived from a single UC. The two design approaches show excellent agreement in terms of their reflection coefficient and beam-steering range. Therefore, the ideal model presented in this paper demonstrates, for the first time, a rapid method for developing periodic leaky-wave antennas. To validate the simulation results, probe-based antenna measurements are conducted, showing close agreement in terms of the reflection coefficient, peak antenna gain, beam-steering angle, and far-field radiation patterns. The periodic GCPW leaky-wave antenna presented in this paper exhibits a high gain of up to 13.5 dBi and a wide beam-steering range from − 60 ° to 35 ° over the 220 GHz–325 GHz frequency range. [ABSTRACT FROM AUTHOR]

This paper presents a 220 GHz × 2 amplifier–doubler chain composed of a rat-race balun, a 6-stage driver amplifier, and a frequency doubler. The presented amplifier–doubler chain was fabricated in commercial 40 nm bulk CMOS technology. The maximum cutoff frequency fmax for the NMOS transistor produced by this manufacturing process was 290 GHz. The saturation output power of the six-stage driver amplifier at 110 GHz was 11.5 dBm. The transistor of the frequency doubler consisted of a single-row interleaved Poly-Diffusion Contact balancing structure. Theoretically, the single-row interleaved Poly-Diffusion Contact balancing structure was able to effectively avoid parasitic components. The simulated results demonstrate that the presented structure achieves a higher output than the conventional designs. Based on these measured results, the presented amplifier–doubler chain provides a peak output power of 7.9 dBm at 200 GHz and a 3-dB bandwidth of 30 GHz. Based on the comparison with other reported results, the presented amplifier–doubler chain provides the highest output power among reported frequency doublers fabricated in CMOS technology. [ABSTRACT FROM AUTHOR]

Terahertz (THz) is a promising technology for future wireless communication networks, particularly for 6G and beyond. The ultra-wide THz band, ranging from 0.1 to 10 THz, can potentially address the limited capacity and scarcity of spectrum in current wireless systems such as 4G-LTE and 5G. Furthermore, it is expected to support advanced wireless applications requiring high data transmission and quality services, i.e., terabit-per-second backhaul systems, ultra-high-definition streaming, virtual/augmented reality, and high-bandwidth wireless communications. In recent years, artificial intelligence (AI) has been used mainly for resource management, spectrum allocation, modulation and bandwidth classification, interference mitigation, beamforming, and medium access control layer protocols to improve THz performance. This survey paper examines the use of AI in state-of-the-art THz communications, discussing the challenges, potentials, and shortcomings. Additionally, this survey discusses the available platforms, including commercial, testbeds, and publicly available simulators for THz communications. Finally, this survey provides future strategies for improving the existing THz simulators and using AI methods, including deep learning, federated learning, and reinforcement learning, to improve THz communications. [ABSTRACT FROM AUTHOR]

This work reported a novel terahertz sensor based on metamaterial absorber. The proposed structure is composed of rectangular metallic resonator made of gold placed above on dielectric medium of a polyimide and a metallic board at the bottom. Due to high-intensity field energy confinement in the sensing regime, two resonance peaks occur at 1.355 THz and 2.785 THz with absorption nearly 100% is achieved. The proposed structure represents sharp resonances with a highest Q factor of 69.6 in the dual-band absorption spectra. The proposed structure is highly sensitive to the change of refractive index (RI) of the surrounding medium at fixed analyte. Furthermore, the proposed sensor exhibits high sensitivity of 0.735THz/RIU, and high FOM of 18.4 RIU−1 in the refractive index ranging from 1 to 2 with fixed analyte thickness of 35 μm. Moreover, the sensitivity and absorption strength influence of the sensor on the sample thickness covered by the sensor surface is also analyzed. Due to high Q factor and sensitivity, the design RI sensor is successfully employed in sensing and detection. [ABSTRACT FROM AUTHOR]

In this paper, a newly developed 300 GHz channel sounder is presented followed by a detailed description of test measurements and the subsequent results obtained to validate its working. An elucidation of the high-resolution double-directional channel measurement in a typical conference room scenario precedes the comparison of the results obtained for the current campaign to that obtained from an earlier campaign at 60 GHz for a similar setup. It is observed that a similar number of clusters for both the bands under investigation for all the transmitter (Tx) and receiver (Rx) positions are obtained from the generated power spectra. Any deviation is theorized to be caused either due to the usage of lower measurement bandwidth in the 60 GHz campaign or due to limited elevation expanse in the 300 GHz measurement. To identify the interacting objects (IOs) causing the clusters, environment-embedded angular power spectra (APS) and ray tracing simulations are used. The large-scale parameters (LSPs) are also evaluated for both campaigns. It is observed that signal propagation at 300 GHz is dominated more by the line-of-sight (LoS) path compared to 60 GHz. The results are also compared with other similar results from the literature.

Quantum key distribution (QKD) can provide unconditional security to next-generation communication networks guaranteed by the laws of quantum physics. This article studies the secret key rate (SKR) of a continuous variable QKD (CV-QKD) system using multiple-input multiple-output (MIMO) transmission and operating at terahertz (THz) frequencies. Distinct from previous works, we consider a practical “restricted” eavesdropping scenario in which Eve can collect only a fraction of photons lost in the environment. We propose a system model for the MIMO THz CV-QKD system that accounts for restricted eavesdropping via a lossy wireless channel between Alice and Eve. We derive for this system new SKR expressions for both coherent-state-based and squeezed-state-based CV-QKD protocols. Our results show that previous analysis assuming unrestricted eavesdropping leads to overly pessimistic SKRs, and that in practice, the achievable SKR can be significantly increased under restricted eavesdropping. The increase in the SKR is quantified by the simplified SKR expansions derived in this article. Our results also reveal that squeezing is beneficial for improving the SKR only for unrestricted eavesdropping. However, in a practical setting with restricted eavesdropping, increased squeezing leads to a reduction in the SKR.

All-dielectric metasurfaces, which are periodic 2D gratings on slab waveguides, are designed to obtain angular-dependent polarization-insensitive guided-mode resonance filters operating in the terahertz region. The effect of the metasurface grating periods along the x- and y-axis on the filter's performance is systematically studied via the rigorous coupled-wave analysis method. When the grating periods along the x-axis are 380 $\mu$m, 400 $\mu$m, and 420 $\mu$m, the polarization-independent resonances of the split bands occur at 0.517 THz, 0.498 THz, and 0.481 THz, respectively. When the grating periods along the y-axis are adjusted to the above values, such polarization-independent resonances show good robustness, which means the polarization-independent resonance frequency of the split bands is mainly determined by the grating periods along the x-axis and is in an inverse proportion. Meanwhile, there are additional polarization-independent resonances formed by the intersection of the split and degenerate bands for the two unequal grating periods. This kind of component provides potential applications for narrowband filtering in emerging terahertz devices and systems for communication or sensing.

The abundant spectrum resources and low beam divergence of the terahertz (THz) band, can be combined with the orthogonal propagation property of orbital angular momentum (OAM) beams to multi-fold the capacity of wireless communication systems. Here, a reflective metasurface (RMTS) is utilized to enhance the coverage of the high gain THz OAM beams by enabling the non-line-of-sight (NLoS) component by reshaping the planar wavefront of the incident wave into the helical wavefront, so that it is re-directed towards the direction of interest. This can contribute to alleviating the concern of the small aperture size, since improving the channel capacity can be achieved at the low spectrum blocks of the THz band (larger aperture size). For validation, three $90 \times 90$ mm RMTSs are simulated, fabricated, and tested in the frequency range 90–110 GHz, to re-direct single and dual OAM beams towards the desired location.

This letter proposes a simple and compact circularly polarized (CP) conical horn antenna structure for sub-millimeter/THz band (75 − 110 GHz) applications. The proposed horn antenna is fabricated by a computer numerical control (CNC) milling technique approach to streamline the manufacturing process and increase the accuracy and the reduce time-consuming fabrication process. The horn antenna has a measured |S11 |< − 10 dB bandwidth that matches the W-band frequency range of 75 − 110 GHz (37.8%), whereas the CP feature operates within the 3 dB axial ratio (AR) bandwidth of 95.9 − 104.4 GHz (8.5%) and beyond this range is the active region of the linearly polarized (LP) feature and high right-hand CP (RHCP) gain that exceeds 24.2 dBic on the CP bandwidth. In addition, the antenna has a low sidelobe level (SLL < − 24 dB) and high aperture efficiency (> 70%) on the CP bandwidth. Experimental results of the proposed horn antenna demonstrate excellent gain and CP performance outcomes and are in good agreement with the simulation results. Therefore, the proposed horn antenna can be a reasonable candidate for the Sub-millimeter-wave and future 6G applications used in high-speed wireless and space communication systems. [ABSTRACT FROM AUTHOR]

We propose and investigate a graphene periodic subsurface structure consisting of a coplanar pair of graphene ring resonators and a graphene ribbon. The Fano-like interference can be actively regulated by the applied magnetic field, incident angle and Fermi energy. Since the excited charges of graphene monolayer have cyclotron properties in the external magnetic field, the transmittance and line-shape can be effectively controlled. At a certain frequency, different magnetic fields have different effects on the conductivity tensor of graphene, which affects the metallic properties of graphene, leading to changes in the transmittance. The Fano-like line-shape can be regulated by adjusting the incident angle to delay the phase between adjacent graphene sheets. In addition, the resonance frequency can be electrically regulated through Fermi energy. Finite element method is introduced to analyze the graphene periodic structure and the results are demonstrated by multimode interference coupled mode theory. The Faraday rotation angle exceeding 85° are observed in a small magnetic flux density B of about 0.5 T. Moreover, a plasma-optic switching with high ON/OFF ratio and large modulation depth (MD) is designed, whose ON/OFF ratio (η) and MD are 19.921 dB and 98.982%, respectively. Notably, combining the influence of magnetic flux density on transmittance and the modulation of resonance frequency by Fermi energy, optical switching can be implemented at any frequency within the frequency range studied. These results provide methods for active regulation of electromagnetic waves in the terahertz field and have potential applications in optical switching and integrated photonic circuit. [ABSTRACT FROM AUTHOR]