Search Results (615)

Aiming to address the problems of low accuracy in coal–rock identification during coal mining, which lead to energy waste and safety hazards, a high-precision coal–rock medium identification method combining terahertz time-domain spectroscopy technology and multiple machine learning algorithms is proposed. By preparing coal–rock samples with a gradient change in coal content, terahertz time-domain spectroscopy data of coal–rock mixed media are collected, and optical parameters such as the refractive index and absorption coefficient are extracted. Principal component analysis is used to reduce the dimensionality of the terahertz data, and machine learning algorithms such as support vector machine, least squares support vector machine, artificial neural networks, and random forests are adopted for classification and identification. The study found that terahertz waves are more sensitive to coal–rock media in the 0.7–1.3 THz frequency band, and that the refractive index and absorption coefficient of coal–rock mixed media are significantly positively correlated with coal content within the range of 0–30%. After feature extraction and K-fold cross-validation, the random forest model achieved a coal–rock classification accuracy of over 96% on the test set, significantly outperforming other comparison algorithms. The research verifies the efficiency and practicality of terahertz technology combined with multiple machine learning algorithms in coal–rock identification, providing a new method for fields such as mineral separation. This method has, to a certain extent, broken through the accuracy bottleneck of traditional coal–rock identification technologies within its applicable range, providing a new solution for real-time detection of coal–rock interfaces and is expected to further reduce the risks of ineffective mining and roof accidents in the future. Full article

A terahertz multifunctional metasurface based on vanadium dioxide (VO₂) and graphene that can switch between waveplate and absorber functionalities is proposed. As the temperature is below 300 K, by electrically controlling the Femi energy of the graphene it can realize half-wave plate (HWP) and quarter-wave plate (QWP) functionalities in the operating bandwidths of both 1.39–2.34 THz and 0.92–2.68 THz, respectively. While the temperature is above 340 K, the dipole resonance between VO₂ and a gold reflector induces absorption. Furthermore, by applying the voltage to graphene, dual-parameter modulation of the amplitude of the transverse electric (TE) waves and the resonance frequency of the transverse magnetic (TM) waves is achieved, the absorption bandwidths of which are 3.65–3.78 THz and 1.41–3.12 THz, respectively. The operating frequencies for HWP, QWP, TE and TM waves can be tuned by changing the electrical field and working temperature. In addition, the incident angles are not sensitive to the performance of the metasurface, confirming its effectiveness even under large-angle incidence. The metasurface with simplicity in design, mature fabrication processes, and comprehensive functionality, has certain promising applications in terahertz optical switches, terahertz spectroscopy systems, modulators, and communication systems. Full article

Biochemical detection is fundamental to various scientific disciplines, yet conventional methods still face inherent bottlenecks in achieving rapid, ultrasensitive, and simultaneous multi-target analysis. Terahertz (THz) waves, characterized by their unique spectral fingerprinting capabilities and non-destructive properties, have emerged as a compelling platform for advanced biochemical sensing. This review outlines the evolution of THz biochemical sensing over the past two decades, tracing its progression from passive identification toward intelligent perception. We structure this technological trajectory around four core themes: sensitivity enhancement, specific recognition, multi-target visualization, and system intelligence. We first evaluate the fundamental limitations of direct detection techniques, such as THz time-domain spectroscopy (THz-TDS). Building on this, we examine how metamaterial-assisted architectures utilize high-quality-factor resonances to achieve trace-level detection, pushing the limits of detection (LOD) down to the ng/mL or even pg/mL scale, and how surface chemical functionalization provides a molecular lock mechanism for selective targeting in complex samples. Furthermore, we highlight the paradigm shift from single-point spectral measurements to spatially resolved multi-target imaging using pixelated metasurfaces. Finally, the review addresses emerging directions, including dynamically tunable intelligent metasurfaces, multimodal on-chip integration platforms, and the growing integration of artificial intelligence (AI) in inverse design and data interpretation, which achieves classification accuracies exceeding 95% even in complex matrices. By synthesizing these developments, this review provides a comprehensive perspective on the future trajectory of THz sensing technologies. Full article

Rectangular waveguides, serving as a standardized versatile platform for manipulating terahertz radiation within controlled environments, have been extensively employed across a broad range of terahertz systems. However, conventional fabrication methods encounter significant challenges in realizing such submillimeter-scale structures within a monolithic integration, particularly when subwavelength features or intricate geometries are incorporated for advanced functionalities. In this work, we propose a fabrication route integrating stereolithography 3D printing and electroless plating, and demonstrate its broad applicability, intrinsic benefits and limitations through the realization of various high-performance D-band terahertz rectangular waveguides and antennas. The resulting rectangular waveguides achieve an insertion loss below 0.3 dB and a return loss above 15 dB across the D-band, while remaining stable across extreme temperatures (−50 °C to 150 °C) and offering a weight reduction of over 60%. A monolithically fabricated smooth-walled conical horn antenna exhibits beam-shaping characteristics that closely align with theoretical expectations. Attempts on corrugated horn antennas in conventional design reveal degraded performance, primarily arising from the inherent staircase effect associated with 3D printing. A novel design featuring obliquely oriented corrugations is developed, effectively mitigating uncontrolled deformation in periodic subwavelength features. Compared with the classical corrugated design (θ = 90°), the proposed obliquely oriented corrugations (θ = 30°) improve the agreement between experimental and theoretical radiation patterns, reducing the gain deviation from 1.45 dB to less than 0.5 Db—a quantitative improvement of over 60% in pattern fidelity. We believe that this fabrication route together with the process-adaptive design paradigm establishes a robust technical foundation for realizing high-performance, lightweight, and design-flexible terahertz waveguide components and holds significant promise for advancing the development of next-generation integrated terahertz systems. Full article

With ongoing advancements toward 6G networks, the terahertz (THz) band is expected to serve as an essential platform for realizing integrated sensing and communication (ISAC). In particular, maintaining high-data-rate communication while ensuring highly responsive, real-time radar operation in dynamic environments is a critical requirement. This study presents a THz-band ISAC architecture that utilizes a high-speed wavelength-tunable laser for photomixing, enabling simultaneous generation of a fast frequency-swept frequency-modulated continuous-wave (FMCW) radar signal and amplitude-shift keying (ASK) communication. The wavelength-tunable laser enables sub-microsecond frequency sweeps and supports high repetition rates suitable for real-time operation. To address the limitations in waveform design efficiency in conventional time-division ISAC, we experimentally investigate two transmission strategies for simultaneous operation. The first is a frequency-division scheme that reduces mutual interference between radar and communication signals, and the second is a joint-waveform scheme in which both functions share the same THz carrier. Using a single THz transmitter, the proposed system achieves sub-centimeter ranging accuracy together with 15-Gbit/s data transmission. These findings demonstrate that the presented ISAC approach enables efficient integration of radar and communication functions while lowering overall system complexity and implementation cost, offering substantial potential for deployment in future 6G infrastructures. Full article

We present a checkerboard metasurface integrating interleaved Helmholtz resonator arrays with distinct geometrical parameters, enabling decoupled dual-band coherent perfect absorption (CPA) in both in-phase and anti-phase excitation conditions. Full-wave simulations confirm that the proposed structure achieves absorption rates exceeding 99% at 2.904, 3.024, 3.788 and 3.856 THz, corresponding to two pairs of resonant modes enabled by the asymmetric transmission characteristics. Notably, by actively manipulating the relative phase difference between the two excitation modes, the absorption frequencies associated with each CPA channel can be independently and continuously tuned. Benefiting from the planar checkerboard configuration, which combines compact geometry, suppressed mutual coupling, and balanced energy distribution, the metasurface achieves stable and independent dual-band absorption characteristics. The proposed design provides a promising pathway for the development of terahertz coherent absorbers with enhanced frequency stability and spectral flexibility of dual-mode operations, offering strong potential for practical photonic and electromagnetic applications. Full article

Topological edge and corner states show great promise for manipulating electromagnetic waves, but their limited mode area restricts practical applications. Here, we propose a topological terahertz photonic crystal with a three-layer heterostructure, in which the middle Dirac photonic crystal layer that exhibits Dirac-like dispersion supports large-area terahertz waveguide states. Quantitative analysis shows that valley-momentum-locked states maintain high transmission even at sharp bends and in the presence of defects. Additionally, we demonstrate topological large-area corner modes. The mode area scales with the number of photonic crystal layers that exhibit Dirac-like dispersion, as confirmed by numerical calculations. This work advances the flexible control of terahertz waves and holds significant potential for practical applications in topological photonics. Full article

One of the strongest electromagnetic engineering approaches for enhancing antenna performance is the use of photonic crystal (PhC) substrates. This technique can be efficiently applied to antenna design and offers notable advantages, such as gain improvement, increased bandwidth, and frequency-dependent beam scanning. In this paper, a bow-tie dipole antenna has been developed for terahertz operation over the 0.39–1.3 THz band, presenting a novel structure capable of producing strong ultra-wideband (UWB) field enhancement within its feed gap. The feed gap between the two metallic arms has a slot width of 1.24 λ0 (λ0 is the wavelength in free space at a center range of 0.8 THz), which facilitates the generation of an enhanced electric field. The PhC substrate enables surface-wave control through dispersion engineering, thereby enhancing the radiation efficiency of the antenna. The proposed antenna exhibits a radiation efficiency of approximately 73–93% over the entire UWB frequency band. Furthermore, the PhC substrate antenna achieves a maximum gain of 21 dB, exceeding that of a homogeneous-substrate THz bow-tie antenna by at least 3.3 dB. The results indicate that the antenna achieves |S₁₁| < −10 dB impedance matching over the bandwidth of 105.9%, ranging from 0.4 to 1.3 THz. The proposed bow-tie dipole antenna integrated with a PhC substrate demonstrates a wide beam-scanning capability from −54° to +74° across the 0.39–1.16 THz band, while maintaining a compact footprint of 14.9 λ₀ × 22.4 λ₀. This combination of wide scanning, broad bandwidth, and ultra-low profile represents a notable advancement in the development of compact THz radiating structures. Full article

Metasurfaces offer an unprecedented avenue to facilitate light-matter interactions. However, traditional design methodologies rely on computationally intensive trial-and-error processes. Moreover, existing deep learning (DL) schemes are predominantly hindered by their massive data requirements and limited exploration of freeform design spaces. To overcome these challenges, a multi-model-driven generative-evolutionary strategy (GES) is proposed, for the on-demand inverse design of bespoke Terahertz (THz) metasurface sensors. By leveraging a Conditional Diffusion Generator (CDG) and an Attention-Enhanced Residual Network (ARN), this framework enables the exploration of an expansive design space encompassing $2^{100}$ possible configurations. The GES effectively overcomes the data bottleneck by selectively generating high-potential data in stages. Full-wave simulations confirm that the inversely designed metasurfaces exhibit high-contrast resonance peaks and exceptional sensitivity across low, mid, and high THz bands. This work provides a versatile paradigm for the efficient design of high-performance functional metamaterials, significantly accelerating the advancement of application-specific THz sensing. Full article

This paper presents the concept of a 2D m × n waveguide-based power combiner (PC) that is scalable with respect to the operating frequency band and number of input ports. To our knowledge, this work reports the first planar (2D) power combiner, where the input waveguide ports are distributed in two spatial dimensions to form an array, rather than arranged along a single linear (1D) axis as in conventional corporate or cascaded waveguide combiners. The novelty of the approach relies on using H-plane rectangular waveguide T-junctions and low-loss polarization twisters in between vertically stacked T-junctions to facilitate scalability. The work is motivated by the aim to coherently combine the output power of multiple modified uni-traveling carrier (MUTC) terahertz (THz) waveguide photodiodes (PDs) in a 2D array configuration. In the manuscript, the design of a 2 × 2 planar waveguide power combiner for the WR3 band (220–320 GHz) is reported, and it is also shown that this block can be further extended to m × n input ports. Full-wave numerical analysis of the proposed 2 × 2 power combiner shows a return loss of 11 dB at the output port and an average transmission coefficient of about −6.5 dB, i.e., an overall power combining efficiency of ~90%. Furthermore, to enable 2D photodiode array integration, the manuscript presents a new slot-bow tie antenna integrated MUTC photodiode for radiating the optically generated THz power from each PD vertically into the rectangular waveguide. The simulation results of reflection loss and insertion loss for the slot bow-tie antenna are shown to be better than 10 dB and 1.4 dB over the full WR3 band, respectively. To prove scalability of the power combiner concept w.r.t. the number of input ports, a 2 × 4 power combiner is also analyzed. Results reveal a return loss better than 10 dB from 225 to 318 GHz and a transmission coefficient of approximately −9.7 dB at 300 GHz, i.e., a power combining efficiency of ~85%. Full article

This study proposes a new fabrication process for terahertz Fresnel zone plates on high-resistivity silicon substrates. It involves ion implantation surface modification, ultra-precision diamond turning, and magnetron sputtering, followed by polishing. Ductile-regime cutting is used to form smooth microgrooves, which are selectively metallized to create alternating opaque and transparent zones for terahertz waves. Finite-element simulations are performed to design the zone structure and to evaluate the effect of process-induced radius errors. A 3 μm amorphous layer is formed via ion implantation, which significantly enhances the ductile-to-brittle transition depth of silicon from 55 nm to about 535 nm while causing only minor changes in terahertz transmittance. The results demonstrate that the proposed method can produce high-quality Fresnel zone plates on silicon and offers a practical route to compact diffractive terahertz components. Full article

We present an investigation of the thermal damage threshold of passivated Bi₂Se₃ films upon laser illumination, with a focus on their employment in terahertz (THz) spectroscopic applications. Passivation was achieved by depositing a thin 3 nm Al capping layer which, exposed to the ambient, forms a natural oxide. In THz transient emission experiments, the samples were exposed to a train of 100 fs wide laser pulses with 800 nm wavelength at 78 MHz repetition rate and peak power density up to 295 mW/µm². For the sake of comparison, the films were also exposed to continuous wave laser light with a wavelength of 532 nm in the average optical power density range from 5 × 10⁻² mW/µm² to 50 mW/µm². In both cases, changes in film appearance, detected by optical microscopy, or even film removal in a small area close to the center of the illuminated spot could be induced. Raman spectroscopy provided evidence that the crystalline phase of Bi₂Se₃ films is present in areas that have been exposed but not damaged. Conversely, in the film region illuminated with the highest peak power density no Raman signal was detected in the range under investigation which we ascribe to material removal. At the perimeter of this ablated area, we observed a dominant Raman mode at approximately 255 cm⁻¹ that we can attribute to selenium and indicates partial Bi₂Se₃ decomposition. In contrast, we observed Raman spectra corresponding to as-deposited Bi₂Se₃ only a few micrometers away from the laser-damaged area. Hence, the observed THz radiation originates from this illuminated but undamaged region. This detailed knowledge is expected to serve as a guide for designing the emitter’s thermal management and choosing laser parameters for optimal operation. Full article

With the deepening of fifth-generation mobile communication technology (5G) commercialization and the surge in demand for intelligent connectivity of all things, the sixth-generation mobile communication technology (6G) has entered a phase of technological breakthroughs. The innovation in antenna design will determine the upper limits of 6G communication. This paper systematically reviews the research progress on antenna technology for 6G communications, focusing on operating frequency bands, antenna structure design, and materials and packaging technologies. The development of 6G communication technology drives antenna research toward higher-frequency bands, with the current research focus extending from the millimeter wave (mmWave) band to the terahertz (THz) band. Compared to the traditional mmWave band, the THz band shows significant advantages in performance indicators. At the antenna structure level, its development trend is mainly reflected in the following three aspects: size miniaturization, scale expansion and distributed deployment, and expansion of frequency bands and functions. New materials and advanced packaging have become key enabling technologies: materials with low-loss characteristics and tunable surface conductivity have become research focuses. Meanwhile, advanced packaging processes achieve miniaturization and high-performance integration of antenna systems. This review aims to provide a systematic technical reference for the research and engineering development of next-generation 6G antennas. Full article

This paper examines the secrecy performance of a decode-and-forward (DF) relay-assisted device-to-device (D2D) communication system operating over Terahertz (THz) channels in multi-cluster two-wave (MTW) fading environments. Eavesdroppers are located near the relay and the receiver, intercepting their respective signals. Co-channel interference (CCI) affecting the relay, receiver, and eavesdroppers is also considered. To counter fading, both the relay and the receiver employ Maximal Ratio Combining (MRC). The analysis uses a characteristic function (CF)-based approach to derive key secrecy metrics, such as secrecy outage probability, secrecy success probability, the probability of strictly positive secrecy capacity, and intercept probability. The derived expressions are dependent on the characteristics of the THz, MTW fading, and CCI parameters. Finally, the system’s performance is then evaluated numerically for a range of channel and interference parameters. Full article

Since the thermal reliability issues of terahertz traveling wave tubes (THz TWTs) severely limit their power capacity, we propose a thermal analysis and optimization process for THz TWTs in this paper. The measurement results from the accessible test points exhibited good consistency with those of the thermal analysis. Based on the analysis of the heat generation mechanisms of each component of the THz TWT, two novel thermal conduction structures were introduced that decreased the operating temperature of the output window from 81 °C to 34 °C and decreased the operating temperature of the slow wave structure (SWS) from 103 °C to 56 °C. According to the simulation results for the maximum allowable internal power dissipation under the optimized structure, these novel optimization strategies theoretically double the power capacity of the SWS. This work demonstrates an experimentally validated full-tube thermal model and establishes a transferable optimization principle based on identifying and eliminating thermal bottlenecks through a strategic heat conduction path design. This study provides an effective approach for improving the thermal reliability and power capacity of THz TWTs, providing technical support for the engineering application of high-power THz TWTs. Full article