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

Rainfall can reduce the radar signal through a radome. The effects of different water layers on the radome transmission are studied using quasi-optical measurement from 26 to 330 GHz including water permittivity characterization. The water is deposited as drops of different sizes or as a uniform layer while keeping a constant volume, highlighting the importance of the control of the total wet surface for radar applications. A compact model is proposed to predict the signal loss due to water on the radome depending on the rain flow.

Abstract

This research presents the design and analysis of a compact MIMO antenna tailored for 5G millimeter-wave applications, specifically targeting bands N257, N260, and N262. The antenna, characterized by its straightforward design, maintains compact dimensions of 10 mm × 16 mm while delivering exceptional performance with high gain. Employing Rogers RT/Duroid 5880 substrate material with a thickness of 0.508 mm, the antenna consists of two crescent-shaped radiating elements (patches) situated on the top surface of the dielectric material, complemented by a slotted ground on the bottom. The radiating elements are fed through a 50-Ω microstrip line. Operating across three distinct bands, the antenna’s capabilities are outlined as follows: the first band spans from 27.2 to 29 GHz, centering around 28 GHz; the second band encompasses the frequency range from 34 to 40.2 GHz, with a center frequency of 39 GHz achieved through slotting crescent-shaped radiating elements; the third band, ranging from 47.5 to 51.3 GHz with a center frequency of 48.7 GHz, is attained by engraving circular slots on the ground. To validate simulation outcomes, a hardware prototype of the antenna is manufactured, showcasing excellent agreement between simulations and measurements. The antenna design is implemented using the CST Microwave Studio software tool and is benchmarked against existing literature. Key attributes of the proposed antenna include its compact size, simple geometry, wide bandwidth, and high gain. The antenna’s favorable MIMO parameters (ECC, TARC, DG, and CCL), coupled with minimal spacing between elements, position it as a promising candidate for forthcoming 5G millimeter-wave communication applications.

Terahertz frequency domain spectroscopy provides a superior resolution in the broad range from 50 GHz to 5 THz. However, temporal frequency drift and the standing wave pattern in the spectrometer, which often act simultaneously, produce intensive coherent noise in the transmittance spectra of the measured samples. The paper presents a spectrum processing method allowing to reduce the coherent noise and thus significantly enhance the accuracy of spectral data analysis. The idea of the method is to remove the small-period (0.25 GHz) oscillations in the standing wave pattern of the measured signal by applying the windowed Fourier filtering. The large-period (4 GHz) oscillations in the measured spectra are broadened and then used to compensate the frequency drift of the two consecutive measurements of the signal with the sample and without it. The proposed approach is tested on the measured spectra of metamaterial and silicon wafer. Its advantage over the classical method based on the averaging of adjacent data points is confirmed. Our work benefits to optimization of the frequency domain terahertz systems and paves the way for fast and accurate analysis of spectral data.

This paper presents the design and experiment results for a W-band sheet beam electron gun of the extended interaction oscillator (EIO). A 3D simulation has been performed, and then, the structure parameters of the electron gun have been optimized. The simulation results show that the beam waist (BW) and transmission ratio are extremely sensitive to the distance between the cathode and the focus electrode. By observing the beam waist and the beam range, the maximum beam range is up to 46 mm, which is measured at the beginning of the beam-wave interaction cavity. In addition, the thickness of the beam waist decreases rapidly when the cathode is moved along the positive axial direction by 0.03 mm. Moreover, the voltage on the focus electrode has a significant impact on the beam trajectory. At last, by considering the deviation, experiment results show that the transmission is improved to 98%.

The detection of pollutant dyes in the environment, particularly in waterways, can be extended and potentially simplified using terahertz spectroscopy. The use of hydrogels to absorb these contaminants from water and create solid samples with moderate transparency at terahertz frequencies evidently facilitates spectroscopic analysis. In this study, we demonstrate that chitosan and poly(vinyl alcohol) hydrogels, as well as their cross-linked and nanocomposite hybrid blends, efficiently capture the acid blue 113 azo dye (AB113). We show that terahertz transmittance and refractive index measurements conducted on these hydrogel materials offer an effective alternative method for detecting water contaminants, especially azo dyes. The terahertz transmittance spectra provide evidence of azo dye molecules within the hydrogel membranes. Additionally, considering the alterations in the hydrogels’ refractive index due to the sorption of AB113 dye molecules, we derived an analytical model to accurately estimate the amount of dye sorbed by the polymeric networks. The findings of this study establish a practical and promising approach for both qualitative and quantitative terahertz detection of AB113 dye using hybrid hydrogels. A detailed comparison with optical and infrared spectroscopy is also provided for reference.

We have developed a cryogenic characterization platform for ultrafast photodiodes, whose time domain responses are extracted by electro-optic sampling using femtosecond laser pulses in a pump-probe configuration. The excitation of the photodiodes with the pump beam and the electro-optic sampling crystals with the probe beam are realized in a fully fiber-coupled manner. This allows us to use the characterization platform at different temperatures, ranging from cryogenic to room temperature. As an application example, we characterize the time-domain response of commercial p-i-n photodiodes with a nominal bandwidth of 20 GHz and 60 GHz at temperatures of 4 K and 300 K and in a large parameter range of photocurrent and reverse bias. For these photodiodes, we detect frequency components up to approximately 250 GHz, while the theoretical bandwidth of our sampling method exceeds 1 THz. Our measurements demonstrate a significant excitation power and temperature dependence of the photodiodes’ ultrafast time responses, reflecting, most likely, changes in carrier mobilities and electric field screening. Since our system is an ideal tool to characterize and optimize the response of fast photodiodes at cryogenic temperatures, it has a direct impact on applications in superconducting quantum technology such as the enhancement of optical links to superconducting qubits and quantum-accurate waveform generators.

We directly observed terahertz (THz) waves generated in a cascading manner under noncollinear phase-matching conditions in a THz parametric generator. Although cascading induced by collinear phase matching has been extensively studied, cascading featuring noncollinear phase matching, using devices such as our injection-seeded THz parametric generator (is-TPG), has received less attention. However, an understanding of is-TPG cascading is required not only for the further development of THz-wave sources but also for THz-range parametric detection and amplification; direct observations are essential. Here, we used a high-power seed beam to induce cascading efficiently; when the crystal was tilted, we detected new higher-order THz waves near the end face. To the best of our knowledge, no previous study has described THz waves generated by cascading under noncollinear phase-matching conditions. We present empirical data that will greatly aid the theoretical exploration of parametric TH-wave generation. Our work paves the way toward enhancement of the output powers of THz sources.