Search Results (86)

Grout voids in external tendons of post-tensioned bridges are a critical issue, as they may result in the corrosion of the steel strands and significantly reduce tendon strength. Therefore, preventing tendon failure necessitates thorough inspection for these voids during both construction and operation. Terahertz electromagnetic wave testing is an effective method for detecting voids between the protective duct and the grout in external tendons, as terahertz waves can penetrate through the protective duct. This study introduces a D-band electronic frequency-modulated continuous-wave terahertz A-scanner for enhanced real-time inspection. The proposed method offers key advantages such as miniaturization, cost-effectiveness, and robustness, while providing effective detection of voids beneath the duct in external tendons. It is indicated that voids with a thickness of approximately 2.5 mm or greater can be detected using the D-band THz A-scanner. Full article

The emergence of 6G wireless systems marks a paradigm shift toward intelligent, context-aware networks that can adapt in real-time to their environment. Within this landscape, Sensing-Assisted Communication (SAC) emerges as a key enabler, integrating perception into the communication control loop to enhance reliability, beamforming accuracy, and system responsiveness. Unlike prior surveys that treat SAC as a subfunction of Integrated Sensing and Communication (ISAC), this work offers the first dedicated review of SAC in Millimeter-Wave (mmWave) and Sub-Terahertz (Sub-THz) systems, where directional links and channel variability present core challenges. SAC encompasses a diverse set of methods that enable wireless systems to dynamically adapt to environmental changes and channel conditions in real time. Recent studies demonstrate up to 80% reduction in beam training overhead and significant gains in latency and mobility resilience. Applications include predictive beamforming, blockage mitigation, and low-latency Unmanned Aerial Vehicle (UAV) and vehicular communication. This review unifies the SAC landscape and outlines future directions in standardization, Artificial Intelligence (AI) integration, and cooperative sensing for next-generation wireless networks. Full article

In recent years, electromagnetic waves (terahertz waves) with frequencies between 0.1 and 10 THz, which exist between radio waves and light waves, have attracted much attention. These electromagnetic waves have both the linearity of light waves and the transparency of radio waves and are expected to be applied to the field of human non-destructive testing. While it is known that terahertz waves can be used to detect foreign matter inside an object, we thought that by irradiating terahertz waves to the object to be measured from various directions, it would be possible to analyze the location and direction of contamination by comparing the scattering of the terahertz waves irradiated to the foreign matter. The samples were biomass resources in a jar with an opening of 53 mm and a diameter of 66.8 mm, and an aluminum plate 76 × 50 mm. When terahertz waves were irradiated from the side of the jar with the biomass resources in it, and the aluminum plate inserted, the transmission was higher when the metal plate was parallel to the light source and detector. This indicates that the transmission tendency of terahertz waves changes depending on the position and angle of the metal strip inside with respect to the direction of terahertz wave irradiation. This transmission tendency enables us to locate the position of a foreign object by irradiating terahertz waves from multiple directions, which is expected to be applied not only to the removal of foreign objects but also to various non-destructive inspections. Full article

A feasibility study was conducted on the detection of corroded rebars inside concrete using sub-THz waves. In this study, spectral measurements were performed with a reflection-type system in the 20–50 GHz frequency range. Measurements were conducted on steel plates corroded in salt water and on concrete specimens containing these corroded plates. The results confirmed that reflectance decreases as corrosion progresses. Furthermore, it was demonstrated that the presence or absence of internal steel plates and corrosion can be detected up to a cover thickness of 20 mm. The frequency spectral peaks and their periodicity also provided a means to estimate the cover thickness. Full article

Deep learning techniques are increasingly being incorporated into the inspection and maintenance of social infrastructure. In this study, we show that when supervised deep learning was applied to imaging data obtained from sub-THz waves, the average recall exceeded 80% for all cover thicknesses of steel plate inside concrete and more than 90% for rebar inside concrete with a cover thickness of up to 20 mm. Unsupervised deep learning enabled the classification for both steel plate and rebar, even at large cover thicknesses. These results are expected to improve the exploration depth, which has been limited in previous studies. Full article

Next-generation wireless communication networks are developing across the world day by day; this requires high data rate transportation over the systems. Millimeter-wave (mm-wave) spectrum with terahertz (THz) bands is a promising solution for next-generation systems that are able to meet these requirements effectively. For such networks, designing new waveforms, providing high-quality service, reliability, energy efficiency, and many other specifications are taking on important roles in adapting to high-performance communication systems. Recently, artificial intelligence (AI) and machine learning (ML) methods have proved their effectiveness in predicting. and optimizing nonlinear characteristics of high-dimensional systems with enhanced capability along with rich convergence outcomes. Thus, there is a strong need for the use of these intelligence-based methods to achieve higher bandwidths along with the targeted outcomes in comparison with the traditional designs. In this work, we provide an overview of the recently published works on the utilization of mm-wave and THz frequencies for designing and implementing various designs to carry out the targeted key specifications. Moreover, by considering various newly published works, some open challenges are identified. Hence, we provide our view about these concepts, which will pave the way for readers to get a general overview and ideas around the various mm-wave and THz-based designs with the use of AI methods. Full article

Millimeter-wave (mmWave) and terahertz (THz) communications are susceptible to frequent link disruptions and severe performance degradation due to high directionality, significant path loss, and sensitivity to blockages. These challenges are particularly acute in highly dynamic and densely populated user environments. The issues present significant obstacles to ensuring reliability and quality of service (QoS) in future space–air–ground integrated networks. To address these challenges, this paper proposes an adaptive transmission control scheme designed for space–air–ground integrated multi-hop networks operating in the mmWave/THz bands. By analyzing the intermittent connectivity inherent in such networks, the proposed scheme incorporates an incremental factor and a backlog indicator into its congestion control mechanism. This allows for the accurate differentiation between packet losses resulting from network congestion and those caused by channel blockages, such as human body occlusion or beam misalignment. Furthermore, the scheme optimizes the initial congestion window during the slow-start phase and dynamically adapts its transmission strategy during the congestion avoidance phase according to the identified cause of packet loss. Simulation results demonstrate that the proposed method effectively mitigates throughput degradation from link blockages, improves data transmission rates in highly dynamic environments, and sustains more stable end-to-end connectivity. Our proposed scheme achieves a 35% higher throughput than TCP Hybla, 40% lower latency than TCP Veno, and maintains 99.2% link utilization under high mobility. Full article

Terahertz (THz) wireless communications can support ultra-high data rates and secure wireless links with miniaturized devices for unmanned aerial vehicle (UAV) communications. In this paper, a three-dimensional (3D) non-stationary geometry-based stochastic channel model (GSCM) is proposed for multiple-input multiple-output (MIMO) communication links between the UAVs in the THz band. The proposed channel model considers not only the 3D scattering and reflection scenarios (i.e., reflection and scattering fading) but also the atmospheric molecule absorption attenuation, arbitrary 3D trajectory, and antenna arrays of both terminals. In addition, the statistical properties of the proposed GSCM (i.e., the time auto-correlation function (T-ACF), space cross-correlation function (S-CCF), and Doppler power spectrum density (DPSD)) are derived and analyzed under several important UAV-related parameters and different carrier frequencies, including millimeter wave (mmWave) and THz bands. Finally, the good agreement between the simulated results and corresponding theoretical ones demonstrates the correctness of the proposed GSCM, and some useful observations are provided for the system design and performance evaluation of UAV-based air-to-air (A2A) THz-MIMO wireless communications. Full article

THz communication stands as a pivotal technology for 6G networks, designed to address the critical challenge of data demands surpassing current microwave and millimeter-wave (mmWave) capabilities. However, realizing Tbps and kilometer-range transmission confronts the “dual attenuation dilemma” comprising severe free-space path loss (FSPL) (>120 dB/km) and atmospheric absorption. This review comprehensively summarizes our group′s advancements in overcoming fundamental challenges of long-distance THz communication. Through systematic photonic–electronic co-optimization, we report key enabling technologies including photonically assisted THz signal generation, polarization-multiplexed multiple-input multiple-output (MIMO) systems with maximal ratio combining (MRC), high-gain antenna–lens configurations, and InP amplifier systems for complex weather resilience. Critical experimental milestones encompass record-breaking 1.0488 Tbps throughput using probabilistically shaped 64QAM (PS-64QAM) in the 330–500 GHz band; 30.2 km D-band transmission (18 Gbps with 543.6 Gbps·km capacity–distance product); a 3 km fog-penetrating link at 312 GHz; and high-sensitivity SIMO-validated 100 Gbps satellite-terrestrial communication beyond 36,000 km. These findings demonstrate THz communication′s viability for 6G networks requiring extreme-capacity backhaul and ultra-long-haul connectivity. Full article

As solid-state devices continue to advance, vacuum electron devices maintain critical importance due to their superior high-frequency power handling, long-term reliability, and operational efficiency. Among these, traveling-wave tubes (TWTs) excel in high-power microwave (HPM) applications, offering exceptional bandwidth and gain. However, developing THz-range TWT slow-wave structures (SWSs) presents significant design challenges. This work systematically outlines the SWS design methodology while addressing key obstacles and their solutions. As a demonstration, a staggered double vane (SDV) SWS operating at 1 THz (980–1080 GHz) achieves 650 mW output power, 23.35 dB gain, 0.14% electronic efficiency, and compact 21 mm length. Comparative analysis with deformed quasi-sine waveguide (D-QSWG) SWS confirms the SDV design’s superior performance for THz applications. Full article

The transition to 5G and beyond has highlighted the need for efficient devices that operate at mm-wave frequencies, which require new structures and pose fabrication challenges. This paper proposes a novel non-linear antenna that combines the well-established substrate-integrated cavity (SIC) radiators and time-varying graphene for generating harmonic frequencies in the mm-wave spectrum. Graphene is represented as having a dispersive surface conductivity, while time modulation of the conductivity is introduced by varying the applied bias electric field. A modified FDTD algorithm is, additionally, used to simulate the time-varying graphene behaviour under different modulation schemes. The final antenna design involves an SIC resonator with a graphene-covered slot aperture for radiation. The numerical study highlights the effective generation of harmonics using the modulated graphene at the mm-wave regime. Finally, different modulation schemes are applied to enhance certain higher-order harmonics, demonstrating the potential of this non-linear antenna design for future mm-wave and THz frequency applications. Full article

The transition from 5G to 6G wireless systems introduces new challenges at the physical layer, including the need for higher frequency operations, massive MIMO deployment, advanced beamforming techniques, and sustainable energy harvesting mechanisms. A plethora of feature articles, review and white papers, and roadmaps elaborate on the perspectives and research challenges of wireless systems, in general, including both unified physical and cyber space. Hence, this paper presents a comprehensive review of the technological challenges and recent advancements in wireless communication hardware that underpin the development of next-generation networks, particularly 6G. Emphasizing the physical layer, the study explores critical enabling technologies including beamforming, massive MIMO, reconfigurable intelligent surfaces (RIS), millimeter-wave (mmWave) and terahertz (THz) communications, wireless power transfer, and energy harvesting. These technologies are analyzed in terms of their functional roles, implementation challenges, and integration into future wireless infrastructure. Beyond traditional physical layer components, the paper also discusses the role of reconfigurable RF front-ends, innovative antenna architectures, and user-end devices that contribute to the adaptability and efficiency of emerging communication systems. In addition, the inclusion of application-driven paradigms such as digital twins highlights how new use cases are shaping design requirements and pushing the boundaries of hardware capabilities. By linking foundational physical-layer technologies with evolving application demands, this work provides a holistic perspective aimed at guiding future research directions and informing the design of scalable, energy-efficient, and resilient wireless communication platforms for the Future Internet. Specifically, we first try to identify the demands and, in turn, explore existing or emerging technologies that have the potential to meet these needs. Especially, there will be an extended reference about the state-of-the-art antennas for massive MIMO terrestrial and non-terrestrial networks. Full article

The industrial scenario is indispensable for ubiquitous 6G coverage, which demands hyper-reliable and low-latency communication for full automation, control, and operation. To meet these demands, it is widely believed that it is necessary to introduce not only the conventional sub-6 GHz bands but also high-frequency technologies, such as millimeter wave (mmWave), terahertz (THz), and visible light bands. In this paper, we conduct a channel characterization and comparison in the industrial scenario from the sub-6 GHz to visible light bands. The channel characteristics, including the path loss (PL), root mean square (RMS) delay spread (DS), and angle spread (AS), were analyzed with respect to the frequency dependence and the distance dependence. On the one hand, the visible light band exhibited significant differences in channel characteristics compared to the electronic wave band. Due to the line-of-sight transmission of VLC, the visible light band had a higher path loss, and the path loss exponent reached 3.84. Due to the Lambertian radiation pattern, which has a wide range of reflection angles, the AS of the visible light band was much larger than that of the electronic wave band, which were 1.73 and 0.80 for the visible light and THz bands, respectively. On the other hand, the blockage effect of the metal instruments in the industrial scenario will greatly affect the channel characteristics. As the transceiver distance grows large, signals from both sides of the receiver will be blocked by metal instruments, resulting in a decreasing trend in the RMS DS for the electronic wave band. Moreover, the statistical characteristics of the channel properties were modeled and compared with the 3GPP TR 38.901 standard. It was found that the height of the receiver caused the difference between the proposed model and the 3GPP model and needs to be taken into account when modeling. Furthermore, we extended the 3GPP model to the THz and VLC bands and provided the statistical parameters of the channel characteristics for all frequency bands. This study can provide insights for the evaluation and standardization of multi-frequency communication technology in the industrial scenario. Full article

The general objective of the work is to propose, examine, and study the innovations needed, providing a roadmap in order to place the next generation of wireless communication vision and concepts into technological reach. The main trends and directions are identified; relative challenges are addressed; and needed solutions are anticipated, proposed, and evaluated. In detail, to address the role of the antenna system in the wireless communication evolution, in the work at hand, we examine the challenges addressed by the increase in the degrees of freedom of the radiator systems. Specifically, we study the increase in the degrees of freedom provided by gMIMO, reconfigurable intelligence surfaces (RIS), holographic metasurfaces, and orbital angular momentum (OAM). Then, we thoroughly examine the impact that those potent technologies deliver to the mmWave, satellite, and THz wireless communications systems. Full article

Most of the traditional rod antennas in the literature are in the shape of a cylinder or are conical, which are not suitable shapes for planar PCB technology or planar integrated CMOS or BiCMOS technology. In this paper, we present a 24 GHz planar end-fire rod antenna based on an SIW (substrate integrated waveguide) suitable for planar PCB technology or planar integrated circuit technology. The antenna is made of PCB Rogers 4350 and utilizes the SIW to realize the end-fire rod antenna. The measurement results of the antenna are presented: its gain is 8.55 dB and its S11 bandwidth is 6.2 GHz. This kind of planar end-fire rod antenna possesses the characteristics of high gain, wide bandwidth, compactness, and simple design and structure. This type of antenna can also be used as a PCB antenna in other frequency bands, and it could also possibly be utilized in mm-wave and THz integrated antenna design in the future due to its very simple architecture. Full article