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Future networks communication scenarios by the 2030s will include notable applications are three-dimensional (3D) calls, haptics communications, unmanned mobility, tele-operated driving, bio-internet of things, and the Nano-internet of things. Unlike the current scenario in which megahertz bandwidth are sufficient to drive the audio and video components of user applications, the future networks of the 2030s will require bandwidths in several gigahertzes (GHz) (from tens of gigahertz to 1 terahertz [THz]) to perform optimally. Based on the current radio frequency allocation chart, it is not possible to obtain such a wide contiguous radio spectrum below 90 GHz (0.09 THz). Interestingly, these contiguous blocks of radio spectrum are readily available in the higher electromagnetic spectrum, specifically in the Terahertz (THz) frequency band. The major contribution of this study is discussing the substantial issues and key features of THz waves, which include (i) key features and significance of THz frequency; (ii) recent regulatory; (iii) the most promising applications; and (iv) possible open research issues. These research topics were deeply investigated with the aim of providing a specific, synopsis, and encompassing conclusion. Thus, this article will be as a catalyst towards exploring new frontiers for future networks of the 2030s.

Time domain THz spectroscopy measurements were performed on a series of undoped and Mg-doped congruent lithium niobate crystals with 1.2, 6.1, and 8.4 mol% Mg concentrations and on undoped and Mg-doped stoichiometric lithium niobate crystals with 0.7, 1.5, and 4.2 mol% Mg concentrations with polarization parallel (extraordinary) and perpendicular (ordinary) to the z axis of the crystal at 300 K. The absorption coefficient and refractive index spectra were determined in the THz frequency range from 0.25 to ~2.5 THz. In the case of congruent samples for both polarizations, both the refractive index and the absorption coefficient have minimal values for compositions close to the photorefractive threshold. In the case of stoichiometric samples, similar tendencies close to the photorefractive threshold at lower Mg concentration were observed but only for extraordinary polarization, while for ordinary polarization the measured values, especially for the absorption coefficient, were only weakly dependent on the Mg content.

Measurements of terahertz absorption spectra of pharmaceutical hydrate samples are achieved under a normal humidity condition by combining terahertz frequency-domain spectroscopy with a newly proposed method for suppressing absorption peaks caused by water vapor. In this method, only simple mathematical operations such as subtraction, thresholding, interpolation, and smoothing are applied to extinction (or absorbance) data obtained by locating samples under a normal humidity condition. By considering the difference in spectral line width between narrow absorption peaks caused by water vapor and the relatively wide absorption peaks caused by active pharmaceutical ingredients (APIs) in solid forms, the absorption peaks caused by water vapor can be effectively suppressed without affecting the absorption peaks of the APIs in the samples. In the present study, levofloxacin hydrates were used as samples to investigate the performance of the proposed method. Spectra were obtained under both dry and normal humidity conditions. The temperature of the samples was raised from 300 to 363 K to dehydrate them and brought back to 313 K to observe hydration under the normal humidity condition. Spectra obtained under the normal humidity condition were processed with the proposed method. The spectra of the hydrates obtained under the dry condition were slightly different from those obtained under the normal humidity condition and processed by our method. Dehydration during the measurements under the dry condition was suggested. Stable and reliable results are expected by measuring spectra under normal humidity conditions and applying the proposed method to suppress absorption peaks by water vapor.

In this study, the frequency down-conversion of terahertz waves is analytically and experimentally demonstrated at the temporal boundaries within a GaAs waveguide. The temporal boundary is established by photoexciting the top surface of the waveguide, thereby instantaneously increasing its electrical conductivity. This photoexcited waveguide supports a transverse electromagnetic (TEM) mode with a frequency lower than those of the transverse magnetic (TM) modes present in the original waveguide. At the temporal boundary, the incident TM mode couples with the TEM mode, resulting in frequency down-conversion. Subtracting the propagation loss from the frequency-converted components indicates that the frequency conversion occurs with an efficiency consistent with the analytical predictions. The propagation loss is primarily due to ohmic loss, caused by the finite electrical conductivity of the photoexcited region. Given that the frequency of transverse electric modes is up-converted at the temporal boundary, our findings suggest that the direction of frequency conversion (upward or downward) can be controlled by manipulating the incident polarization. The polarization-dependent frequency conversion in waveguides holds significant potential for applications in devices designed for the interconversion of terahertz signals across various frequency channels. This capability is instrumental in the development of frequency-division-multiplexed terahertz wave communication systems, thereby enabling high data transfer rates.

A planar nanodevice, known as the self-switching diode (SSD), has a non-linear current-voltage characteristic that resembles a typical diode behaviour. Unlike other conventional diodes that depending on barrier junction or gate, SSD utilized its L-shaped trenches to exhibit non-linear I-V behaviour, which can be exploited for high-frequency operations. This paper presents technology computer-aided design (TCAD) rectification studies of two InGaAs-based SSDs connected in parallel with similar/different length operating at sub-terahertz frequencies and at zero bias. As expected, the combination of SSDs with the shortest length possess the highest cut-off frequency, and in this case, at approximately 0.35 THz. This is comparable with the recent proposed hybrid structure of SSD and planar barrier diode (SSD/PBD). In fact, it has lower leakage current than SSD/PBD which can reflect to a better rectification performance.

In order to replace millimetre wave communication for extremely fast terabit wireless local and personal area network connectivity, researchers have been looking into the possibilities of the terahertz band for establishing wireless data communication at terabit rates. The IEEE 802.15 WPAN Terahertz Interest Group (IGTHz) has been created to encourage research in the terahertz bands and set standards for their use, in order to facilitate progress and advancement in this area. The specific objective of this study is to design and analyze a microstrip antenna working at 3.5 THz resonant frequency. The proposed novel antenna includes three layers: a top layer that represents the patch, a second layer that represents the substrate, and a bottom layer that represents the ground plane. It is designed using a 32 nm thin FR-4 substrate with a permittivity of 4.4. Using HFSS simulations, it was found that the proposed antenna has an overall efficiency greater than 85% within the working frequency range of 3.5 THz. Additionally, it exhibited an extremely low reflection coefficient (S11) of -43.61 dB at 3.5 THz, with an efficiency exceeding 80%. This simple and broadband antenna design could have relevance in high-speed data transmission networks.

The terahertz (THz) band contributes significantly to high-speed data rates in short-distance communication. This article proposes a unique design of the trigonal microstrip patch antenna on photonic crystal (PhC) substrate in THz communication. The PhC design structure employs unique air-hole shapes such as L, H, T, I and upturned L instead of regular periodic latitude holes. The proposed antenna substrate uses Rogers RO4350 material, which helps to attain high gain and almost negligible return loss at THz frequency. The antenna performance is investigated with different PhC air-hole shapes. The I-shaped air-hole PhC antenna offered a meager return loss of − 58.99 dB with a high gain of 9.1 dB and directivity of 10.7 dBi. The CST studio tool helps to simulate the parametric analysis of the proposed antenna design. This compact PhC antenna structure is apt for wireless communication, particularly in THz applications.

In this paper, we present a terahertz transmission frequency-selective quasi surface (FSQS) that exhibits strong absorption lines and a periodic band-pass characteristic. The FSQS structure is created by laterally combining Fabry-Pérot resonators with different thicknesses. The transfer function of the FSQS can serve as a broadband reference for testing the signal integrity of the transmission path for broadband terahertz systems. The transfer function achieves a combination of band-pass characteristics and sharp resonances with a theoretical attenuation of over 80 dB and with quality factors of more than 40,000 for a combination of 36 resonators. A single FSQS made up of four resonators is 3D printed by fused deposition modeling using a low-loss cyclic olefin copolymer (COC) filament. Finally, the 3D-printed FSQS is characterized using both frequency-domain and time-domain terahertz spectroscopy. The results show an attenuation of over 42 dB and a quality factor above 100.

This study represents the development and analysis of the types of metamaterial structures for terahertz frequency. Recently, investigations about unique coding metamaterial have become well-known among the scientific community since it can manipulate electromagnetic (EM) waves by utilizing various coding sequences. Therefore, several coding and tailored metamaterial designs were compared and numerically analyzed the performances in this research work. The 1-bit coding metamaterial made up of only “0” and “1” elements by adopting two types of unit cells with 0 and π phase responses were analyzed for the coding metamaterial. Moreover, for the numerical simulation analyses, the well-known Computer Simulation Technology (CST) Microwave Studio software was adopted. This investigation focused on the frequency ranges from 0 to 5 THz. On the other hand, the proposed designs were simulated to find their scattering parameter behavior. The comparison of coding and tailored metamaterial revealed slight differences in the RCS values. The coding metamaterial designs manifested RCS values less than −50 dBm2, while tailored metamaterial designs exhibited less than −60 dBm2. Furthermore, the proposed designs displayed various transmission coefficient result curves for both types of metamaterial. Moreover, the bistatic far-field scattering patterns of both metamaterial designs were presented in this work. In a nutshell, the 1-bit coding metamaterial with a unique sequence can influence the EM waves and realize different functionalities.

The present study has been performed with the purpose of designing a highly sensitive biosensor for cervical cancer cell detection. The structure of the proposed design for biosensor includes a hollow core, four-quarter circular-type airholes spread through the cladding region, and Zeonex (R.I.-1.53) as background fiber material. Further, guiding properties of the proposed waveguide have been studied. The suggested photonic crystal fiber structure has been operated in the THz frequency regime. COMSOL Multiphysics 5.6a software based on finite element method and MATLAB 17b software have been used to examine various guiding properties of the sensor. Various performance parameters such as effective refractive index 1.3414, effective area 8.4733 × 10 −9 µm 2 , nonlinearity 9.9468W −1  km −1 , propagation constant 2.5703 × 10 −26 , relative sensitivity 78.68%, and confinement loss 5.1406 × 10 −26  cm −1 have been evaluated for cervical cancer cells. The simplified design reduces fabrication complexity and makes it cost-effective. It enhances the optical sensing capabilities of the proposed sensor model. The proposed design will add new opportunities in the field of bio photonics. Moreover, it leads to better applications in medical field for detecting and diagnosing cervical cancer cells disease.