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

Techniques for adjusting and controlling the polarization state of electromagnetic waves are of great importance in the optical and microwave regimes. In this letter, a dual-layer, via-free, polarization-rotating metasurface with wideband and effective asymmetric transmission properties is presented. Numerical and experimental results show that the metasurface can rotate the polarization of the incident electromagnetic wave by 90°, from 24.5 to approximately 30.9 GHz (relative bandwidth 23.10%). The simple structure and good performance of the proposed metasurface make it a promising candidate in quasimillimeter wave radar and communication applications and can be easily scaled to other frequency bands.

A 110 GHz quasi-optical ring resonator, designed for use with a 1 MW pulsed gyrotron, has been built and successfully tested using a 100 mW solid-state source. A low reflectance (2.4%) input coupler and a low-loss, four-mirror ring demonstrated a compression ratio, defined as the ratio of output to input power, of 36. The 6 ns output pulses were generated from the 2 m length ring using a silicon laser-driven semiconductor switch (LDSS). The quasi-optical ring resonator was designed with large waist sizes so that input pulses of up to 1 MW will stay under the 35 kV/cm electric field limit for ionization in ambient air. Maximum compression gain was achieved by matching the input coupling fraction to the round trip loss in the ring, achieving close to critical coupling. The experimental output pulse shape obtained after firing the LDSS was modeled using the reflectance, transmittance, and absorptance of the switch vs. time and vs. laser pulse fluence, with good agreement found with theory. The timing for the peak energy efficiency of 32% was found and the main loss mechanism limiting that efficiency was found to be the absorptance in the silicon wafer.

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.