Journal of Infrared, Millimeter, and Terahertz Waves最新文献

This study presents a planar dual-band multiple-input multiple-output (MIMO) antenna design for the prospective fifth-generation (5G) frequency bands of 28 and 38 GHz. The antenna element is designed by utilizing a rectangular patch with an offset microstrip feeding technique. A dual-band response is achieved by placing semi-circular slots on each side of the patch element. To tune the frequency response and improve impedance matching, vertical rectangular slits are etched in the rectangular patch and the ground plane, respectively. The results show that the single antenna element offers an impedance bandwidth of 2.52 GHz (26.32–28.84 GHz) and 7.5 GHz (34–41.5 GHz). In addition, a MIMO configuration based on pattern diversity using four antenna elements is designed and fabricated. The designed MIMO configuration achieves an impedance bandwidth of 3 GHz (27–30 GHz) and 5.46 GHz (35.54–41 GHz) at operating bands of 28 and 38 GHz. The peak realized gain for the single element at 28 and 38 GHz is noted to be 7.4 dBi and 7.5 dBi, respectively. Furthermore, the polarization diversity configuration illustrates an isolation of > 15 dB and > 25 dB for the 28 and 38 GHz frequency bands, respectively. Moreover, the MIMO configuration attains appropriate values for the envelope correlation coefficient (ECC) and diversity gain (DG), Total Active Reflection Co-efficient (TARC), Channel Capacity Loss (CCL) and Mean Effective Gain (MEG) for the operating frequency bands. The proposed MIMO system based on results seems to be potential choice for mmwave Ka Band Applications.

This paper presents the results of an experimental study of a new hybrid plasmatron scheme, which was used to realize a gas discharge at atmospheric pressure supported by continuous focused submillimeter radiation with a frequency of 263 GHz. The implemented design allowed organizing a self-consistent interaction between submillimeter radiation and the supercritical plasma in a localized area both in terms of gas flow and electrodynamic. It is experimentally shown that the gas discharge absorbs up to 80% of the introduced submillimeter radiation power.

LoS (Line of Sight) MIMO (Multiple Input Multiple Output) is considered the best way to deliver high-capacity channels for terahertz communications due to the severe attenuation suffered by reflected components. Unfortunately, terahertz links are easily blocked by any obstruction resulting in link breakage. Therefore, it is necessary to provide alternative paths via reflectors. A problem shared by LoS paths and reflected paths (via polished reflectors) is that the channel matrix is rank 1 in the far field. As a result, the achieved capacity is lower than what can theoretically be achieved in a rich multi-path environment. In this work, we simultaneously solve the channel rank problem and the coverage problem by using static reflective surfaces which provide limited scattering of the incident signal in a way that minimizes signal loss but provides multiple paths to the receiver with varying phase. We construct such a surface and characterize the received signal using a terahertz testbed. We show that using our surface, we can improve channel capacity for 2 × 2 LoS MIMO. We also develop a theoretical model for the received signal and show that the reflected capacity matches the measured capacity well.

Terahertz imaging is one of the most promising approaches for non-destructive control. An interesting approach to having cost-effective systems is to use frequency-modulated continuous wave (FMCW) radars with a raster scan configuration. Nevertheless, current systems using linear stages or robotic arms have the disadvantage of being heavy, requiring a long scan and not allowing a direct visualization of the result being measured. In addition, it is complex to evaluate the position of the measuring point on the real object, particularly if it is not flat. Here, we propose to solve these previous challenges with a portable system combining an FMCW radar with an augmented reality (AR) interface using a smartphone. This system achieves two goals: (i) first is to achieve data acquisition in the AR environment and (ii) the second is to make possible the visualization of data, even after post-processing, in the AR environment.

In pharmaceuticals, pseudo-polymorphism, e.g., the existence of hydrate and anhydrous forms, affects their physicochemical characteristics. Therefore, the evaluation of pseudo-polymorphism is one of the most important quality analyses. In this research, we investigate the real-time monitoring of the hydration reaction of theophylline using terahertz attenuated total reflection time domain spectroscopy (THz-attenuated total reflection (ATR)-TDS). We continuously measured a mixture of hydroxypropyl cellulose solution and theophylline anhydrous (TPA) while keeping it pressed to the ATR surface. We observed that the absorption peaks derived from TPA decreased and those derived from theophylline monohydrate (TPM) increased with time, demonstrating that the hydrate reaction of TPA can be monitored. Subsequently, we performed an accurate and quantitative evaluation of the hydration reaction by calculating the temporal changes in the crystal form ratio of TPM based on the changes in its second derivative peak intensity followed by a curve fitting. In addition, we performed real-time monitoring of the reaction using two different pressure mechanisms, finding that using a weight to apply pressure provided better reproducibility than using a screw. This study demonstrates that THz spectroscopy is a useful method for the evaluation of pseudo-polymorphism in pharmaceuticals.

In this article, the designing and analysis of a compact novel dual-port multiple-input multiple-output (MIMO) printed antenna are investigated for 30 GHz mm-wave applications. The single antenna unit is having modified C-shaped radiator and an attached rectangular stub with an overall dimension of 10 × 7 × 0.8 mm³. The dual-element MIMO antenna is achieved by creating a back mirror of the single antenna element around the x-axis. This back mirror composition of the MIMO antenna elements is introducing the high level of inter-element isolation (> 20 dB). The proposed antenna prototype is built on a Roger RT/duriod substrate with a loss tangent (tanδ) of 0.0009 and a relative constant (ε_rsub) of 2.2. As a way to determine the capabilities of the proposed MIMO antenna, many diversity parameters are computed, including the envelope correlation coefficient (ECC < 0.05), diversity gain (DG > 9.99 dB), channel capacity loss (CCL < 0.2 bits/s/Hz), mean effective gain (MEG < − 3 dB), and total active reflection coefficient (TARC). The suggested MIMO antenna is appropriate for 5G new radio frequency bands under mm-wave communication as it has 8.36% impedance bandwidth across the frequency range of simulated (29.04–31.57 GHz)/measured (28.82–31.30 GHz). The antenna under consideration is constructed, and the simulated outcomes are verified by the measurement results.

Terahertz (THz) backward wave oscillators (BWOs) hold immense potential for a broad range of industrial and military applications. This study presents a comparative analysis of 0.34 THz sheet beam (SB) and circular beam (CB) folded waveguide (FWG) BWOs. We examined the design, simulation (CST MWS and PS, HFSS), and performance, revealing that sheet beam BWO outperforms circular beam BWO in terms of interaction impedance, power, efficiency, and bandwidth. Under 20 kV beam voltage and 10 mA beam current conditions, sheet beam BWO achieves 0.47 (Omega ) (0.34 THz) interaction impedance, 0.65 W output power, and a bandwidth of approximately 12 GHz, surpassing the 0.18 (Omega ), 0.23 W, and 8.5 GHz values of circular beam BWO, respectively. Furthermore, this study encompasses the fabrication and thorough characterization of the sheet beam BWO’s slow-wave structure. Experimental validation confirms its effectiveness, with measured (S_{11}) demonstrating reflection below (-)10 dB and (S_{21}) exhibiting transmission above (-)2 dB.

Abstract

The present work proposes three MIMO antennas with different configurations for the future applications of wireless communications in the Q-band of the frequency to realize both spatial and polarization diversities. A circularly polarized (CP) printed antenna operating over two frequency bands at 37.8 and 50 GHz is utilized as a single element to construct the proposed MIMO antennas. Two-element MIMO antenna systems arranged in two configurations, side-by-side and face-to-face, are proposed to achieve spatial diversity. Also, a four-element MIMO antenna system is designed to achieve polarization diversity in addition to spatial diversity. The proposed MIMO antenna systems are designed with the aid of the CST simulator. The three MIMO antennas are fabricated and their performance is experimentally evaluated regarding the circular polarization, impedance matching, antenna gain, envelope correlation coefficient (ECC), and diversity gain (DG). The experimental results for the single-element as well as the MIMO antennas come in good agreement with simulation results showing high performance. Both the numerical and experimental investigations reveal that the mutual coupling between any two ports of the proposed MIMO antennas is below (-25 {text{dB}}) . Also, for any two ports it is shown that the ECC is below (1times {10}^{-7}) and the diversity gain is higher than (9.99) . The impedance matching bandwidths (for (left|{S}_{11}right|<-10 {text{dB}}) ) are shown to be (1.53) and (1.88) GHz at (37.8) and (50mathrm{ GHz}) , respectively, and the corresponding 3-dB axial ratio bandwidths are (700) and (130mathrm{ MHz}) , respectively.

This paper presents a full-wave method, based on the method of moments (MoM), to calculate the (bar{varvec{S}}) matrix from a two-dimensional complex sample in millimeter and submillimeter W and J bands. From the surface currents obtained by inverting the impedance matrix and from the Huygens principle, the reflection and transmission coefficients are computed. This allows us to obtain the four elements of the (bar{varvec{S}}) matrix. Firstly, the method is validated from canonical samples (a dielectric slab and a stack of two dielectric slabs) by applying the well-known Fresnel coefficients. Secondly, for the W (75 to 110 GHz) and J (220 to 330 GHz) bands, a PVC slab covered by water drops is considered, for which the (bar{varvec{S}}) matrix is compared with measurements made in quasi-optical free space. A satisfactory agreement is obtained between the measurements and the model.

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.