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As the standardization of 5G New Radio (NR) systems operating in micro- and millimeter-wave frequency bands is over, scientific and industrial communities have begun to address the question of what 6G communications systems might or should be. While technological specifics are still in their early development phase, there is a common agreement that these systems will utilize the lower part of the terahertz band, namely, 100-300 GHz. This band poses a number of specific challenges for system designers, including the effects related to channel characteristics and the conceptually new requirements for electronics. This paper aims to report the current state-of-the-art channel characterization and communications system design. With respect to the former, we consider dynamic human body blockages and micromobility impairments. For the latter, we mainly concentrate on the physical layer devices for direct conversion schemes and the design of the so-called reconfigurable intelligent surfaces that will potentially serve as a cost-efficient blockage mitigation technique.

The development of electronic fuze has placed higher demands on encapsulation resins, which are required to provide not only insulation and protection, but also higher impact resistance and good electromagnetic shielding performance. A new composite material consisting of hollow glass microspheres (HGM) and modified epoxy resin was developed. This material exhibits significant electromagnetic shielding capabilities for terahertz (THz) waves, as well as superior impact energy absorption properties. Bisphenol A‐type epoxy resin (E‐44) was modified using Al(OH)3, red phosphorus, carbon black, and SiO2, and the material properties were optimized by adjusting the HGM content. The electromagnetic shielding effectiveness and impact energy absorption of the composite material in the THz band were comprehensively tested using THz time‐domain spectroscopy and split Hopkinson pressure bar testing systems. Additionally, a comprehensive evaluation of the mechanical and dielectric properties, thermal conductivity, and thermal stability of the material was conducted. The results showed that the electromagnetic shielding effect of 60 vol.% HGM hybrid‐modified resins was the best, reaching 43.78 dB. The 20 vol.% HGM hybrid‐modified resins not only has a specific absorption energy of 18.51 J/cm3, but also has the best overall performance. This work has advanced the design and development of multifunctional and impact‐resistant potting epoxy resins. [ABSTRACT FROM AUTHOR]

Advancement in miniaturization of electronics devices and nano sensors has led to sophistication of Internet of things (IoT) devices. The improved fabrication technology of recent time makes it feasible for nano sensors to be positioned within the human body, and the terahertz (THz) band is seen as compatible frequency band for in vivo applications within millimeter scale. This paper presents the investigative analysis for nano communication operating at the terahertz frequency band. Link quality and capacity of in vivo comm has been examined using pathloss model where the losses due to absorption and spreading are generalized along with additional permittivity for a considered human model, precisely for skin, water, plasma, RBCs, and whole blood in wireless body area network (WBAN). The variations in link quality matrices such as bit error rate (BER), signal to noise ratio (SNR) and channel capacity have been obtained as these parameters are affected by change in path loss. For the considered scenario, maximum path loss has been observed in plasma with least in the skin. This change in pathloss affects the other link parameters in similar manner. Therefore, the complete analysis of different body components to obtain SNR, BER, and channel capacity relaying on absorption loss plus spreading loss has been realized. The channel capacity is observed least in plasma, increasing of 2.5% in whole blood, 6.5% in water, 6.7% in RBCs, and maximum of 12.5% in skin. Similarly, the SNR is least in plasma, and maximum in skin. Whereas the BER has been noticed maximum in plasma, and least in skin. [ABSTRACT FROM AUTHOR]

This article presents a compact, planar, and circularly polarized array antenna operating in the W-band (84.5–110 GHz), with all its prototypes fabricated using a low-cost, traditional, microwave printed circuit board composed of Rogers RT/duroid 5880 (ɛr = 2.2, tanδ = 0.009). The final design that was fabricated and measured was a 4 × 4 array antenna having an overall size of 9 mm × 20 mm × 0.254 mm that used series feeding to reduce its sidelobes. Measurements of the 4 × 4 patch antenna array showed approximately 6.9% 3-dB axial ratio bandwidth along with 15.2 dBi maximum right-hand circularly polarized (RHCP) antenna gain at 100 GHz. The array antenna yielded RHCP radiation characterized by a low profile, low cross-polarization levels (91%). Additionally, a two-port MIMO antenna system was investigated by considering side-by-side and front-to-front configurations, both of which achieved good isolation and considerable envelope correlation coefficient and diversity gain values. Therefore, the proposed series array and MIMO antennas can be reasonable candidates for 6G applications of the sub-THz band (100–110 GHz) in ultra-high-speed wireless and satellite communication systems.

Combined with the light absorption from molecular vibration, photonic crystal (PhC) cavity structures have gradually shown great potential in gas detection, particularly for toxic gases. We proposed a PhC cavity with a high-quality factor of 1.24 × 106 and a small mode volume of 2.3 × 10−4 (λ/n)3, which was used for carbon monoxide detection. To reduce the interference of other gases, we set the resonance frequency in the terahertz band. The numerical analysis shows that the structure has good selectivity and high sensitivity, and the linear fitting of the results provides the possibility to realize the application, which has great competitiveness in the same type of sensor structure. Additionally, we also proved that the interference of H2O and CO2 on the CO sensing can be ignored, and it supports the detection of CO without pre-drying.

The method by which a photonic crystal is manufactured fiber is detailed throughout the subsequent undertaking, containing a hexahedron core and hazardous dietary additives using a hexagonal cladding. Saccharine, sorbitol, and butyl acetate are used as analytes for sensing purposes. The sensor contains five tiers of circular ventilation holes within the hexagonal framework, as well as two tiers of hexahedron circles in the central area. FEM (Finite Element Method) is implemented in the sensor design of COMSOL software version 4.2. We noticed the response of the PCF sensor to the specific substances. We examined key optical metrics encompassing specifications including V-parameter, Relational sensitivity, effective refractive index, and power fraction to assess the suitability of the sensor for precisely and effectively detecting various food additives. The revised model attains sensitivity values of 90.10%, 91.30%, and 86.60%, respectively, at a frequency of 1 THz, the identification of saccharine (1.550 in the index of refraction), sorbitol (1.375 in the index of refraction), and butyl acetate (1.394 in the index of refraction) is performed. Furthermore, the compositions of saccharine (1.550 in the index of refraction), sorbitol (1.375 in the index of refraction), and butyl acetate (1.394 in the index of refraction) demonstrate losses from confinement of 6.15 × 10−8 dB/m, 7.25 × 10−8 dB/m, and 6.35 × 10−8 dB/m, which are comparatively minimal, and 0.0235 cm−1 is an insignificant effective material loss. These structures are studied at the terahertz frequency spectrum. Owing to its superior wave-guiding properties, this proposed sensor can be used for polarization-preserving terahertz wave applications and detecting dangerous food additives. Besides, because of simple fabrication, high sensitivity, and low confinement loss, we strongly believe this optimized geometrical structure will contribute to real-life applications that lead to safer food and support a circular economy in developing countries.

This paper presents an innovative approach for terahertz (THz) band communications, utilizing reconfigurable intelligent surfaces (RISs) to implement an angular-based hybrid beamforming (AB-HBF). This study examines two significant THz channel scenarios with cost-efficient solutions utilizing RISs to enhance performance. The first scenario ensures reliable communication in the presence of obstacles blocking the direct path, where RISs offer an alternative transmission path. The second scenario leverages multiple-RIS in line-of-sight dominant or sparse environments to increase the rank of the channel matrix, consequently improving the achievable rate. By introducing an innovative HBF design for multiple-RIS-assisted THz massive MIMO systems, a three-stage design is proposed based on a geometry-based THz channel model. This design encompasses the transmit and receive radio frequency (RF) beamformers, transmit/receive baseband (BB) precoder/combiner, and RIS phase shift matrix. A particle swarm optimization-based solution is employed to design the RIS phase reflections. This design methodology is extended to the multiple-RIS-aided scenario, optimizing the phase shift matrices of each RIS. We also provide sub-connected AB-HBF configuration by offering a remarkable reduction in the total number of phase shifters compared to the fully-connected AB-HBF. Additionally, a deep learning-based phase shift design is incorporated to effectively optimize the RIS configurations, significantly reducing the computational time required for system calibration in dynamic THz environments. Extensive numerical experiments demonstrate the significant enhancement in the achievable rate of THz AB-HBF systems by incorporating RISs, mitigating the wireless propagation disruptions as well as reducing hardware cost/complexity and power consumption for massive MIMO systems.

Nano-networks are envisioned to allow several nanoscale devices to transmit and receive information. One form of such networks is electromagnetic nano-networks working within the THz band. However, high overall path loss and molecular noise experienced in the THz band, as well as limited energy storage capabilities, restrict the communication range of nano-nodes and impact network efficiency. Therefore, optimizing the nano-network resources is necessary. In this paper, we present an optimization framework employing mixed-integer linear programming (MILP) to determine the most energy-efficient routing, bandwidth, and sub-band allocation for each nano-node in an electromagnetic nano-network operating within the THz band. Our model was tested for two different scenarios related to the priority of energy saving. We also compare our proposed optimal bandwidth, routing, and sub-band allocation against less complex designs where sub-bands with fixed bandwidth are employed in nano-nodes. Furthermore, we investigate the impact of nano-node’s processing and sensing units on the overall network energy consumption and the associated optimal bandwidth allocation and routing strategy. Given the considered parameters and the model’s assumptions, the results show that using the optimal multi-hops paths with higher bandwidth allocation for the considered sub-bands can be more energy efficient than sending the traffic using a single hop and lower bandwidths, especially when the transmission power dominates in the nano-network. On the other hand, when the processing and sensing unit’s energy consumption is dominant, then single hop schemes with lower bandwidth allocation result in the minimum network energy consumption. Finally, we discuss the limitations of the proposed energy-efficient strategies and point toward possible future research directions to which the model can be adapted.

A highly sensitive graphene-based metamaterial biosensor is proposed and analyzed for early cancer detection. The sensor design employs three circular graphene split ring resonators to achieve polarization-insensitive performance. The finite element method simulation results confirm that the designed biosensor exhibits a tunable sensing capability. The material under test covers the surface of the biosensor, where resonance occurs with high absorption. The resonance frequencies of the sensor are dependent on the optical properties of the analyte sample, enabling the device to differentiate between various cancer cell types, including skin, blood, cervical, adrenal gland, and breast cancer. Graphene's tunability is leveraged to study the effects of chemical potential, relaxation time, and temperature, with the aim of maximizing the sensor's sensitivity. The designed biosensor, which detects variations in refractive index, exhibits a maximum sensitivity of 3.880 THz/RUI, a Q-factor of 8.948, and a figure-of-merit of 8.146 RUI$^{-1}$ for healthy and cancerous cell samples. The spatial patterns of electric and magnetic fields, surface current distribution, and power flow of the proposed biosensor have been thoroughly analyzed to ensure its sensitivity and suitability for biomedical applications. The results demonstrate the potential of the THz sensor for early cancer detection.

A broadband waveguide-to-differential-line transition with a triple stacked patch is proposed for use in 300 GHz band. This transition consists of differential signal lines inserted into the waveguide region from both broad walls of the waveguide. A triple circular stacked patch element was used for broadband transmission from the waveguide to the planar differential line formed in a multi-layer substrate. Concurrently, the optimized arrangement of via holes can prevent electric field leakage efficiently and improve the transmission characteristic in a high-frequency band. The geometry of the transition was optimized through electromagnetic simulations using the finite element method. Measurements and simulations were implemented to evaluate the performance of the transition. The measured result of the transition shows the bandwidth of the $S_{11}$ below −10 dB was over 100 GHz.

Wireless Network-on-Chip (WNoC) incorporating on-chipantennas has emerged as a promising alternative to overcome the communication bottleneck due to high frequency operation, propagation delay, crosstalk delay, noise and need for repeaters inwired interconnects in chip-multiprocessors (CMPs). Recent advancements in nano materials, such as graphene have enabled the development of novel plasmonic graphene devices, which intrinsically operate in THz band. This ultra-low power andcompact graphene-based nano-antennas (GNA) establishes ultra-high bandwidth THz-on-chip wireless links for intra/inter-chip communication. In this article, we design and simulate a novel fork-shaped planarplasmonic nano-patch antenna using grapheneon SiO2/Si substrate that can be integrated into transceivers working at THz frequencies operating from 0.5 THz to 2.6 THz. By simulation at THz band, proposed antenna performance as a wireless inter/intra-chip link is investigated by numericallyobtaining itssignal transmission coefficient characteristics between the two on-chip antennas, acting as transmitter and receiver or vice-verse for short-range THz communication among wireless NoC based multi-core processors integrated on same substrate. Theresults are obtained by placing the antennas in broadside orientation, that can communicate with intra-chip transmission coefficients ranging from − 20 dB to − 60 dB while sustaining bandwidths upto 0.13–0.2 THz. Further, the effect of transmission and radiation performance of proposed antennas with increase in distance dlink is studied along with reconfigurable nature of graphene with varying chemical potentials from 0.1 eV − 0.5 eV. Proposed antenna has obtained maximum gain and radiation efficiency of 3.89 dB and 58% at 1.83 THz when chemical potential of 0.1 eV is applied. This concept can broadly be applied to future systems as it can be directly integrated into transceivers as graphene is compatible with CMOS processes.Fabrication process steps of proposed on-chip antenna and its feasibility as a real device in chip environment isalso discussed. [ABSTRACT FROM AUTHOR]

In a wireless communication system, a microstrip patch antenna is gaining importance as a most powerful technology trend and it is applicable for the development of low-cost, minimal-weight, low-profile and high-performance antenna. This paper presents the design and the analysis of 1 × 2, 1 × 4 and 2 × 8 rectangular microstrip patch antenna (RMPA) arrays based on the photonic crystals for improved gain performance and high radiation characteristics compared to ones that are designed based on the homogeneous substrate in the frequency range of 0.25 - 0.55 THz. The design of the proposed antenna arrays based on the photonic band gap (PBG) and the homogeneous substrate structures is made by using the designed single-element RMPA as the basic building element, and then, they were fed by the parallel feeding structure. The designed antenna arrays were simulated using CST Microwave Studio software and validated with the aid of Ansoft HFSS simulator. For high radiation characteristics, the proposed antenna arrays resonated around 0.35 THz which is a low loss frequency window in the terahertz band. The main results showed that the designed antenna arrays based on the PBG substrate structure outperform the antenna arrays based on the homogeneous substrate in terms of return loss, bandwidth, gain and directivity. The best directivity was achieved by the 2 × 8 RMPA array of 17.40 dBi, whereas the 1 × 4, 1 × 2 RMPA arrays and single-element RMPA achieved the directivity of 13.54 dBi, 9.87dBi and 7.76 dBi, respectively. Hence, the designed antenna arrays can be used for medical imaging, threat detection and wireless surveillance communication. [ABSTRACT FROM AUTHOR]

Terahertz (THz) metasurfaces have emerged as powerful tools to modulate the wavefronts of THz radiation fully. Smart designs and fabrication are essential for enhancing the flexibility and encryption security of THz metasurfaces. In addition to digital coding metasurfaces and microelectromechanical systems, one method to realize dynamic THz metasurfaces is to utilize an active material. In this paper, a dynamic THz metasurface, which is combined with the phase‐change material VO2 and can be thermally controlled to achieve optical encryption, is proposed. Based on the electromagnetically induced transparency effect and by arranging the antennas in advance according to a specific hologram, a secret image can be encoded into the metasurface. At room temperature, the transmitted light field is an irregular light spot with no useful information. If the temperature increases above the phase‐change temperature, the encrypted hologram can be reconstructed. Moreover, owing to the distinct characteristics of VO2, the phase‐change temperature required during decryption is not very high, and the entire process is reversible. It is expected that, in combination with updated processing technology, such metasurfaces can be practically applied to the next generation of optical encryption or optical anticounterfeiting in the future. [ABSTRACT FROM AUTHOR]

Channel state information in millimeter wave (mmWave) and terahertz (THz) communications systems is vital for various tasks ranging from planning the optimal locations of BSs to efficient beam tracking mechanisms to handover design. Due to the use of large-scale phased antenna arrays and high sensitivity to environmental geometry and materials, precise propagation models for these bands are obtained via ray-tracing modeling. However, the propagation conditions in mmWave/THz systems may theoretically change at very small distances, that is, 1 mm–1 μ m, which requires extreme computational effort for modeling. In this paper, we first will assess the effective correlation distances in mmWave/THz systems for different outdoor scenarios, user mobility patterns, and line-of-sight (LoS) and non-LoS (nLoS) conditions. As the metrics of interest, we utilize the angle of arrival/departure (AoA/AoD) and path loss of the first few strongest rays. Then, to reduce the computational efforts required for the ray-tracing procedure, we propose a methodology for the extrapolation and interpolation of these metrics based on the convolutional long short-term memory (ConvLSTM) model. The proposed methodology is based on a special representation of the channel state information in a form suitable for state-of-the-art video enhancement machine learning (ML) techniques, which allows for the use of their powerful prediction capabilities. To assess the prediction performance of the ConvLSTM model, we utilize precision and recall as the main metrics of interest. Our numerical results demonstrate that the channel state correlation in AoA/AoD parameters is preserved up until approximately 0.3–0.6 m, which is 300–600 times larger than the wavelength at 300 GHz. The use of a ConvLSTM model allows us to accurately predict AoA and AoD angles up to the 0.6 m distance with AoA being characterized by a higher mean squared error (MSE). Our results can be utilized to speed up ray-tracing simulations by selecting the grid step size, resulting in the desired trade-off between modeling accuracy and computational time. Additionally, it can also be utilized to improve beam tracking in mmWave/THz systems via a selection of the time step between beam realignment procedures. [ABSTRACT FROM AUTHOR]

Next-generation wireless communication requires high-performance antennas that can support high-speed data transmission while meeting the requirements for low weight, low cost, and low profile. This article introduces a graphene-based wideband microstrip patch antenna at 2.96 THz resonant frequency for terahertz application. The proposed antenna is mounted on a polyimide substrate with dielectric constant of 3.5. The periodic arrangement of photonic band gap structure has been etched on the polyimide substrate to enhance radiation characteristics. The result of this research has been investigated in respect of reflection coefficient (S11), gain, voltage standing wave ratio (VSWR), radiation efficiency, and radiation pattern for both E and H plane. The proposed antenna achieved minimal return loss of icrostrip50.98 dB, VSWR of 1.022, Gain of 5.40 dB, and impedance bandwidth of 797 GHz at 2.96 THz resonant frequency. All the simulation has been carried out by using EM simulator CST microwave studio with the finite integration technique. The proposed antenna has many applications are medical imaging, airport security analysis, explosive detection, material characterization, etc. [ABSTRACT FROM AUTHOR]

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Due to their low energetic photons and lack of ionization damage, terahertz (THz) waves are recognized as suitable for various wireless innovative applications with high-speed data rates. This paper proposes the design and analysis of a microstrip patch antenna based on a dual-ply hexagonal split ring resonator (HSRR). The suggested antenna resonates at 1.9 THz and is suitable for recent advancements in wireless communication. Furthermore, the HSRR structure has been investigated for various spacing Rs values between the rings, and the optimized HSRR structure performance is compared with conventional antennae. The computer simulation technology studio suite was used to model the planned HSRR and to study the antenna properties. The optimized HSRR structure produces − 47.09 dB return loss with a voltage standing wave ratio of 1.008. The structure exhibits a gain of 8.649 dB and a directivity of 8.696 dB at 1.992 THz. THz light's capability to react differently with innocuous and threatening materials as a function of the THz band provides a highly flexible base for spectroscopic THz scanning and security checks. This suggested HSRR antenna is appropriate for all THz applications with high-speed data rates, such as wireless satellite communication, the biomedical detection of malignant tissue, THz imaging, and spectrometers. [ABSTRACT FROM AUTHOR]

Terahertz (THz) communications systems have been considered as one of the enabling technologies for beyond 5G mobile networks, with the ability to offer higher capacity and lower latency compared to the current systems. In this paper, we develop a new THz channel model that captures rough surface scattering while considering attenuation due to molecular absorption of the atmosphere. The main advantage of the proposed model is that it conserves the energy of the channel impulse response, regardless of the number of launched rays in the ray-tracing simulator, or the size of the tiles for the scattering surface. Using the proposed model, a simple propagation scenario for the indoor environment has been analyzed, and the improvement over other models discussed in detail.

In this letter, a new nanocommunication modulation scheme termed multi-level pulse position modulation (ML-PPM) is proposed. The ML-PPM approach will boost the link capacity of a nanocommunication system while achieving a processing gain in reception. The bit error rate and link capacity of the scheme are evaluated using a non-coherent energy detection nanoreceiver. Simulation results show that the proposed scheme has a substantially greater link capacity than the existing schemes including time-spread on–off keying (TS-OOK) and M-ary pulse position modulation (PPM).

Terahertz band gap is the range of frequency lying between the microwave band and the optical band, its range spectrum starts from 0.1 THz to 10 THz. This band provides unallocated wide bandwidth as well as very high-speed communication in the futuristic applications. This article presents a broadband microstrip 1 x 2 array antenna powered by hybrid coupler in terahertz band (around 2.45 THz). To reach this Broadband antenna, at first, a wideband 3 dB hybrid coupler is designed and optimized. After that, two basic elements of square shaped with slots are fed by the two output ports of the coupler. The results obtained reports that the suggested antenna offers – 10 dB wide bandwidth equals to 846 GHz (from 1.91 to 2.77 THz) with good impedance matching, maximum directivity equals to 8.86 dBi at the operating frequency 2.45 THz. Additionally, it offers the capability of beam steering which can be obtained by switching of the input ports of the coupler. Thus, the antenna can produce two beams at ±30°. The structure and simulation results of the proposed antenna have been done on Rogers RT/duroid 5880 substrate. The total size of the proposed microstrip array antenna is 110 x 112 x 1.56 μm³. Due to its capability of beam steering and broadband characteristic, the proposed antenna is a potential candidate for Terahertz band applications such as materials characterization in the THz band, medical imaging and future high-speed wireless communication. [ABSTRACT FROM AUTHOR]

Sixth generation (6G) wireless networks require very low latency and an ultra-high data rate, which have become the main challenges for future wireless communications. To effectively balance the requirements of 6G and the extreme shortage of capacity within the existing wireless networks, sensing-assisted communications in the terahertz (THz) band with unmanned aerial vehicles (UAVs) is proposed. In this scenario, the THz-UAV acts as an aerial base station to provide information on users and sensing signals and detect the THz channel to assist UAV communication. However, communication and sensing signals that use the same resources can cause interference with each other. Therefore, we research a cooperative method of co-existence between sensing and communication signals in the same frequency and time allocation to reduce the interference. We then formulate an optimization problem to minimize the total delay by jointly optimizing the UAV trajectory, frequency association, and transmission power of each user. The resulting problem is a non-convex and mixed integer optimization problem, which is challenging to solve. By resorting to the Lagrange multiplier and proximal policy optimization (PPO) method, we propose an overall alternating optimization algorithm to solve this problem in an iterative way. Specifically, given the UAV location and frequency, the sub-problem of the sensing and communication transmission powers is transformed into a convex problem, which is solved by the Lagrange multiplier method. Second, in each iteration, for given sensing and communication transmission powers, we relax the discrete variable to a continuous variable and use the PPO algorithm to tackle the sub-problem of joint optimization of the UAV location and frequency. The results show that the proposed algorithm reduces the delay and improves the transmission rate when compared with the conventional greedy algorithm. [ABSTRACT FROM AUTHOR]

Terahertz (THz) band will play an important role in enabling sixth generation (6G) envisioned applications. Compared with lower frequency signals, THz waves are severely attenuated by the atmosphere temperature, pressure, and humidity. Thus, designing a THz communication system must take into account how to circumvent or diminish those issues to achieve a sufficient quality of service. Different solutions are being analyzed: intelligent communication environments, ubiquitous artificial intelligence, extensive network automation, and dynamic spectrum access, among others. This survey focuses on the benefits of integrating intelligent surfaces (ISs) and THz communication systems by providing an overview of IS in wireless communications with the scanning of the recent developments, a description of the architecture, and an explanation of the operation. The survey also covers THz channel models, differentiating them based on deterministic and statistical channel modeling. The IS-aided THz channels are elucidated at the end of the survey. Finally, discussions and research directions are given to help enrich the IS field of research and guide the reader through open issues.

Abstract In a world where communication requires ever faster data transmission capable of transmitting high speeds. In order to reach and transmit this high speed, it is necessary to increase the frequency that carries the information. For this, scientists are interested in the terahertz (THz) range which, thanks to its high frequencies between 0.1 THz and 30 THz, offers the possibility of increasing the data rate. This letter presents the inclusion of Dodecagon Split Ring Resonator (D-SRR) in rectangular microstrip patch antenna and its effect in the performance of the proposed antenna. The metamaterial design employs two types of SRRs resonators shapes such as the Dodecagon Broadside Coupled Split Ring Resonator (DBC-SRR) and Dodecagon Split Ring Resonator (D-SRR). The model applied uses a local field approach and allowed to obtain the dispersion characteristics of discrete negative magnetic permeability. The proposed antenna substrate uses Arlon AD1000 material, which helps to attain high gain and good directivity at THz frequency. The antenna performance is investigated with and without superstrate. The operating frequencies of the proposed antenna vary in the range of 0.66 - 0.69 THz and shows maximum gain of 10.4 dB and maximum directivity of 9.84 dB. HFSS software tool helps to simulate the parametric analysis of the proposed antenna design. This novel structure may find applications in terahertz imaging, remote systems and may find manifold possibilities in the medical field.

In this paper, a monolayer graphene-based metasurface that can achieve plasma-induced transparency (PIT) is proposed. This metasurface consists of a horizontal strip and a pair of vertical ribbons. The simulation results of Finite-Difference Time-Domain (FDTD) method perfectly match with the theoretical results based on Coupled-mode Theory (CMT). Based on the dynamic modulation characteristics of graphene, an optical switch is studied with a vibration amplitude of 94.7%, 89.59% and 89.58%, corresponding to frequencies of 3.34 THz, 3.86 THz and 4.36 THz, respectively. The proposed graphene-based metasurface has potential applications in mid-infrared photoconducting devices, this work has a certain theoretical significance for the development of terahertz dynamic integrated photonic devices. • Stable PIT window with a transmittance greater than 90%. • Simple structural design and a wide tuning range. • Multi-frequency modulated optical switch with low loss. • The PIT physical mechanism analyzed by two theories: bright-dark mode theory and Coupled-mode Theory. [ABSTRACT FROM AUTHOR]

Nanomachines are submicrometer-scale devices led by nanotechnology that can perform simple sensing, local actuation, limited data processing, storage, and communication tasks in the terahertz (THz) band, that is, from $\mathrm {0.1~}$ - $\mathrm {10~ \text {T} \text {Hz} }$ . Electromagnetic nanocommunication among nanomachines results in a nanonetwork which could breakthrough promising applications in multiple domains such as software-defined metamaterials, in-body communication, and on-chip communication. This study adopts a modulation scheme for nanomachine communication based on multilevel pulse position modulation (ML-PPM). The multilevel scheme uses several orthogonal codes and is combined with PPM to generate the final transmit signal consisting of several multilevels. In this paper, we propose a more advanced scheme called level trimming to further boost the data rates of the ML-PPM scheme. Employing level-trimming, we transmit a fewer number of levels than required in ML-PPM, which will result in an spectral efficiency gain at the nanoreceiver. The simulation results reveal that the link capacity of the proposed scheme can be increased more than twofold using the level-trimming approach while the error rate performance remains better than the conventional ML-PPM. For instance, ML-PPM with level trimming achieves a data rate of approximately 4.5 terabits per second (Tbps) when trimming the levels from seven to one compared to ML-PPM that achieves around $\mathrm {1~Tbps}$ under the same network conditions. At the same time, a $\mathrm {2~dB}$ gain in BER performance is achieved with level trimming. Moreover, the computational complexity of nanotransceivers is reduced with the transmission of fewer levels. Furthermore, although level-trimming causes artificial errors, it improves the decoding performance by reducing the number of levels. We believe that the potential impact of this study will open doors for further investigations on various possible modulation formats for THz nanocommunication.

In this study, a novel photonic crystal fiber (PCF) based drug sensor has been introduced. The core and cladding area of the hexagonal fiber structure (H-PCF) has round air holes. We examined the model in the THz regime using the FEM and the COMSOL Multiphysics Software platform. With this updated model, the sensitivity to detect amphetamine (n = 1.518), cocaine (n = 1.5022), and ketamine (n = 1.562) at 1 THz is 89.50%, 90.20%, and 85.50% accordingly. Furthermore, the suggested fiber, operating at 1 THz, generated a vast effective area of Ketamine (n = 1.562), cocaine (n = 1.5022), and amphetamine (n = 1.518) of 1.37 × 10−7 m2, 1.40 × 10−7 m2, 1.39 × 10−7 m2 and relatively low confinement loss of 6.40 × 10−8 dB/m, 7.10 × 10−8 dB/m, 6.20 × 10−8 dB/m and negligible effective material loss of the structure of 0.02 cm−1. After all, we can say that abuse of drugs produces not only short-term effects but also long-term, catastrophic consequences for human health, including the potential for death. Therefore, it is essential to identify illegal drugs with high efficiency and precision. So, this H-PCF structure that we have proposed will be ideal for illegal drug detection.

In this paper, two different types of graphene-based rectangular patch antennas are designed for broadband terahertz applications. First, a patch antenna is modeled using copper metal for terahertz applications. The simulation results show a degraded reflection coefficient due to the use of copper. Therefore, the reflection coefficient is above -10 dB at 4.6 THz, then a VSWR is less than 3 dB when we used copper for the top patch. The patch antenna results are improved when graphene material is used, which has good conductivity, as demonstrated through simulations. Furthermore, an increasing band-width of 1 THz instead to 0.8 THz when we used the graphene material, due to a better impedance match. On the other hand, we achieved a slight increase in gain and the VSWR is less than 2 dB inside the available bandwidth.The time-domain solver of CST MWS software is used to evaluate the performance of the SIW (Substrate Integrated Waveguide) patch antennas. The SIW, PBG technology and the graphene material makes the antenna very important due to performance, such as the gain increases to about 7 dB, the bandwidth is about 1.6 THz duo to increase the chemical potential of the graphene material. The results obtained with CST are compared with simulations using HFSS to validate the design further. In addition, the 10 g peak skin SAR values of the antenna are 1.726e7 W/Kg instead of 9.55e5 W/Kg. In these results we conclude the antenna can detect tumor presence.

Two promising technologies cosidered for the Beyond 5G networks are the terahertz and nano-technologies. Besides other possible application areas they hold the commitment to numerous new nano-scale solutions in the biomedical field. Nano-technology, as the name implies, examines the construction and design of nano-sized materials. These two interconnected emerging technologies have the potential to find application in quite many areas, one of the most importan being healthcare. This overview paper discusses the specifics of these technologies, their most important characteristics and introduces some of the trends for their application in the healthcare sector. In the first section terahertz frequency radio waves and their specific properties depending on the surrounding environment are discussed, followed by an introduction to nano-scale communications. Terahertz waves mandate the use of nano-scale antennas, which in turn brings us to the concept of nano-scale nodes. Nano-scale nodes are units that can perform the most basic functions of nano-machines and inter-nano-machine communications, which allow distributed nano-machines to perform more complex functions. Beyond 5G the development of these nano-communications is expected to lead to the emergence of new complex network systems. In the second part of this paper the paradigms of the Internet of Nano Things, molecular commnications and the Internet of Bio-Nano Things are discussed followed by details on their integration in healthcare related applications. The main goal of the article is to provide an introduction to these intriguing issues discussing advanced nano-technology enablers for Beyond 5G networks such as terahertz and molecular communications, nano-communications between nano-machines and the Internet of Bio-Nano-Things in light of health related applications. [ABSTRACT FROM AUTHOR]

In this paper, the authors have emphasized on the perspectives of the Terahertz channel modeling in Internet of multimedia nano things (IoMNT) networks. A modulation technique targeting body-centric network is discussed. An analogy of a real Terahertz antenna is developed within a terahertz multi-layer modelling channel for a human skin tissue. As a result, the investigation of how signals at THz frequency band interact and transmit within the skin biomaterial. The human skin model used to collect data was selected to have four layers: epidermis, dermis, blood, and hypodermis, with the depth of the layers varying between normal human body values. It is revealed from the literature that the frequency and content have a substantial impact on path failure. The estimated path loss could thus differ considerably, but for a human skin model with depths of 0.21 mm, 1.23 mm, 1.38 mm, and 3.76 mm, the frequencies of 0.5-1.5 THz at the end distance resulted in a path loss estimated about 250-350 dB. [ABSTRACT FROM AUTHOR]

Channel state information in millimeter wave (mmWave) and terahertz (THz) communications systems is vital for various tasks ranging from planning the optimal locations of BSs to efficient beam tracking mechanisms to handover design. Due to the use of large-scale phased antenna arrays and high sensitivity to environmental geometry and materials, precise propagation models for these bands are obtained via ray-tracing modeling. However, the propagation conditions in mmWave/THz systems may theoretically change at very small distances, that is, 1 mm–1 μm, which requires extreme computational effort for modeling. In this paper, we first will assess the effective correlation distances in mmWave/THz systems for different outdoor scenarios, user mobility patterns, and line-of-sight (LoS) and non-LoS (nLoS) conditions. As the metrics of interest, we utilize the angle of arrival/departure (AoA/AoD) and path loss of the first few strongest rays. Then, to reduce the computational efforts required for the ray-tracing procedure, we propose a methodology for the extrapolation and interpolation of these metrics based on the convolutional long short-term memory (ConvLSTM) model. The proposed methodology is based on a special representation of the channel state information in a form suitable for state-of-the-art video enhancement machine learning (ML) techniques, which allows for the use of their powerful prediction capabilities. To assess the prediction performance of the ConvLSTM model, we utilize precision and recall as the main metrics of interest. Our numerical results demonstrate that the channel state correlation in AoA/AoD parameters is preserved up until approximately 0.3–0.6 m, which is 300–600 times larger than the wavelength at 300 GHz. The use of a ConvLSTM model allows us to accurately predict AoA and AoD angles up to the 0.6 m distance with AoA being characterized by a higher mean squared error (MSE). Our results can be utilized to speed up ray-tracing simulations by selecting the grid step size, resulting in the desired trade-off between modeling accuracy and computational time. Additionally, it can also be utilized to improve beam tracking in mmWave/THz systems via a selection of the time step between beam realignment procedures.

A novel methodology to perform mode conversion from rectangular fundamental TE10 mode to circular TE $_{n1}$ ($n $ = 2, 3, $4, \ldots $)/TE $_{0p}$ ($p $ = 1, 2, $3, \ldots $)/TE $_{1q} (q $ = 2, 3, $4, \ldots $) modes with similar topologies is presented in this article. The mode converter consists of two sections: a novel H-plane T-junction-based rectangular TE $_{m0}$ ($m $ = 2, 3, $4, \ldots $) mode launcher and a rectangular TE $_{m0}$ -circular TE $_{n1}$ /TE $_{0p}$ /TE $_{1q}$ mode converter. This kind of mode converter possesses good comprehensive performance and is highlighted by three primary advantages: 1) it is flexible to produce various circular TE modes and rectangular TE $_{m\mathrm {0}}$ modes; 2) the mode converter has a relatively simple and easy-to-fabricate geometry, making it especially suitable for the terahertz-band operation; and 3) it possesses a high mode conversion efficiency over a wide bandwidth, which is adequate to satisfy most of the application requirements. The analysis of mode conversion principle, numerical simulations, microfabrication, and experimental measurement of two H-band (220–325 GHz) prototypes are described. Back-to-back measurement results exhibited good agreement with simulation predictions having considered the conductor loss. A 3-dB transmission bandwidth of 56.7 GHz (231.4–288.1 GHz)/42.1 GHz (244.0–286.1 GHz) was experimentally obtained for the ${\mathrm {TE}}^{\square}_{10}-{\mathrm {TE}}_{01}^{\circ}/{\mathrm {TE}}_{31}^{\circ}$ mode converter. [ABSTRACT FROM AUTHOR]

• Tunable suspended core THz PCF polarization rotator (PR) is reported. • By applying an external voltage, the polarization conversion ratio can be adjusted. • At a device length of 2023 µm and f = 0.6 THz, polarization conversion ratio of 99 % is attained with crosstalk of −19.76 dB. • The crosstalk is better than −10 dB within a tolerance of ±0.1 THz around the operating frequency. Tunable suspended core photonic crystal fiber (SC-PCF) is designed and investigated as a polarization rotator (PR) in the Terahertz (THz) band. In the proposed THz-SC-PCF-PR device, the backgrounds used are the air and TOPAS polymer. In order to enhancing the modal hybridity of the two polarized modes, the nematic liquid crystal (NLC) is used to increase the polarization conversion ratio. So, the core is filled with NLC type E7 material in the proposed THz-SC-PCF-PR design. Furthermore, the conversion ratio of the polarization can be adjusted by applying an external voltage. The modal and propagation analysis of the THz-SC-PCF-PR is studied using full vectorial finite difference approach. To reduce the device length while maintaining low crosstalk, the geometrical parameters are studied. At a conversion length of 2023 µm and a frequency of 0.6 THz, high conversion ratio of 99 % is attained with a minimum crosstalk of −19.76 dB. Furthermore, crosstalk is still less than −10 dB at a 0.1 THz bandwidth around the working frequency. Further, the proposed THz-SC-PCF-PR has a good fabrication tolerance for the geometrical parameters and temperature, ensuring the described design's viability in the THz domain. [ABSTRACT FROM AUTHOR]

This paper provides a broadband perfect absorber with tunable function in terahertz frequency range based on vanadium dioxide metamaterial structure. The absorber regulates and controls the conductivity of vanadium dioxide through temperature tuning, thus realizing the dynamic tuning function of the absorber. Initial numerical results show that the absorption efficiency of the absorber under normal incidence conditions from 6.6 THz to 18.2 THz can reach more than 90% with a bandwidth of 11.6 THz. when the vanadium dioxide has a conductivity of 200000 S/m and the absorption peak of the absorber can be dynamically adjusted to 99.8% by adjusting the conductivity of vanadium dioxide. Vanadium dioxide serves as a functional material for the absorber, and the physical mechanism of the absorber is explained using three theories: impedance matching, equivalent circuit modeling, and electromagnetic resonance. By adjusting the angle of incident light, it is confirmed that the absorber still has good efficiency in the range of 0° to 50° of incident light. With the introduction of liquid layer modulation, the absorption of the device can be adjusted by the temperature and depth of the water, and the bandwidth of the device can be further extended to 18.3 THz. The symmetric structure, simple fabrication, polarization insensitivity, dynamic modulation, and ultra-wide bandwidth of the device can be applied in the direction of liquid temperature storage and optical switching. • The device is a metamaterial absorber with a simple structure for stable ultra-broadband absorption and regulation, and can work in an aqueous environment. • The bandwidth is 11.6 Terahertz in the initial state and up to 18.3 Terahertz in a water environment. The absorber can absorb up to 50° wide angle and can be adjusted for temperature or water conditions. • The three theoretical systems of impedance matching, equivalent circuit modeling and electric field distribution work together to realize the argumentation. • The three theoretical systems of impedance matching, equivalent circuit modeling and electric field distribution work together to realize the argumentation. • The device has promising applications in terahertz-integrated optoelectronic devices, such as thermal emitters, liquid-temperature storage, and optical switches. [ABSTRACT FROM AUTHOR]

Sixth generation (6G) wireless networks require very low latency and an ultra-high data rate, which have become the main challenges for future wireless communications. To effectively balance the requirements of 6G and the extreme shortage of capacity within the existing wireless networks, sensing-assisted communications in the terahertz (THz) band with unmanned aerial vehicles (UAVs) is proposed. In this scenario, the THz-UAV acts as an aerial base station to provide information on users and sensing signals and detect the THz channel to assist UAV communication. However, communication and sensing signals that use the same resources can cause interference with each other. Therefore, we research a cooperative method of co-existence between sensing and communication signals in the same frequency and time allocation to reduce the interference. We then formulate an optimization problem to minimize the total delay by jointly optimizing the UAV trajectory, frequency association, and transmission power of each user. The resulting problem is a non-convex and mixed integer optimization problem, which is challenging to solve. By resorting to the Lagrange multiplier and proximal policy optimization (PPO) method, we propose an overall alternating optimization algorithm to solve this problem in an iterative way. Specifically, given the UAV location and frequency, the sub-problem of the sensing and communication transmission powers is transformed into a convex problem, which is solved by the Lagrange multiplier method. Second, in each iteration, for given sensing and communication transmission powers, we relax the discrete variable to a continuous variable and use the PPO algorithm to tackle the sub-problem of joint optimization of the UAV location and frequency. The results show that the proposed algorithm reduces the delay and improves the transmission rate when compared with the conventional greedy algorithm.

This article presents the design, microfab- rication, and measurement of a terahertz band ${\mathrm {TE}}^{\Box }_{20}$ mode input–output coupling structure for dual-sheet-beam traveling-wave tubes (TWTs). The proposed coupling structure is based on an $E$ -plane Riblet slot coupler with one shorted port and a ${\mathrm {TE}}^{\Box }_{10}$ – ${\mathrm {TE}}^{\Box }_{20}$ mode converter. Compared to the previously reported high-order mode (HOM) coupling structures, the proposed structure possesses superior electrical and mechanical performance, including better reflection/transmission properties and relatively easy-to-fabricate configuration with features insensitive to fabrication tolerances. For verification, two $H$ -band (220–325 GHz) identical ${\mathrm {TE}}^{\Box }_{20}$ mode coupling structures joined back-to-back were manufactured and measured. Good agreement between the experimental results and the simulated responses is observed. The fabricated prototype of the coupling structure exhibits good electromagnetic (EM) performance over a bandwidth of 52.1 GHz (243.2–295.3 GHz) with a transmission coefficient better than −1.5 dB and a port reflection lower than −15.0 dB. [ABSTRACT FROM AUTHOR]

Terahertz (THz)-band communications have been envisioned as a key technology to support ultra-high-data-rate applications in 5G-beyond (or 6G) wireless networks. Compared to the microwave and mmWave bands, the main challenges with the THz band are in its i) large path loss hence limited network coverage and ii) visible-light-like propagation characteristics hence poor support of mobility in blockage-rich environments. This paper studies quantitatively the applicability of THz-band communications in blockage-rich mobile environments, focusing on a new network scenario called FlyTera. In FlyTera, a set of hotspots mounted on flying drones collaboratively provide data streaming services to ground users, in the microwave, mmWave and THz bands. We first provide a mathematical formulation of the FlyTera control problem, where the objective is to maximize the network spectral efficiency by jointly controlling the flight of the drone hotspots, their association to the ground users, and the spectrum bands used by the users. To solve the resulting problem, which is shown to be a mixed integer nonlinear nonconvex programming (MINLP) problem, we design distributed solution algorithms based on a combination of echo state learning and reinforcement learning. An extensive simulation campaign is then conducted with SimBAG, a newly developed Simulator of Broadband Aerial-Ground wireless networks. It is shown that no single spectrum band can meet the requirements of high data rate and wide coverage simultaneously. Moreover, from the network-level point of view, THz-band communications can significantly benefit from the mobility of the flying drones, and on average $4 - 6$ times higher (rather than lower) throughput can be achieved in mobile than in static environments. [ABSTRACT FROM AUTHOR]

The recent demand for connections to a huge number of users with very high data rates have motivated research communities to investigate communications into the higher frequency bands, such as millimeter waves and TeraHertz (THz) bands. Moreover, Subcarrier Index Modulation (SIM) has recently received a significant research efforts analyzing its different performance aspects. In this paper, we propose a SIM system operating over the THz band and analyze its performance considering mobile users and different resource allocation schemes. Specifically, Random WayPoint (RWP) mobility model is considered for users’ mobility with different numbers of mobility dimensions, and three different spectrum resource allocation schemes, namely, fixed-order allocation, random allocation and distance-aware allocation are considered. Our analysis includes deriving mathematical expressions of both the average Bit Error Rate (BER) and the average Outage Probability (OP) for the three resource allocation schemes. Simulation results analyze different performance metrics like the BER and the OP and are shown to validate the accuracy of the derived expressions.

Herein, a dual‐band tunable ideal absorber based on graphene array, and the dynamic tuning performance of the perfect absorber in the terahertz band and its sensing properties based on graphene metamaterials are studied. The absorber shows two perfect absorption peaks at 1.01 and 1.86 THz, with an absorbance of 99.5% and 99.9%, respectively. With an elevation angle in the range of 0°–30° and a frequency in the range of 0.971–1.100 THz or 1.794–1.897 THz, the absorber designed herein can achieve an absorbance greater than 90%. Owing to the superior properties of graphene, dynamic tuning of the absorption frequency band, absorption bandwidth, and relative bandwidth of the absorber can be achieved by adjusting the Fermi level of graphene. In addition, adjusting the relaxation time realizes dynamic tuning of the absorption bandwidth and the absorbance with constant resonant frequency and fixed geometric parameters. Moreover, the sensitivity of the absorber reaches 492.5 GHz/RIU, which can achieve the sensing resolution required for the resonance frequency. This research provides a new concept for the development of high‐performance terahertz devices.