Ultra-high Frequency Research Articles

Classification of Partial Discharge Sources in Ultra-High Frequency Using Signal Conditioning Circuit Phase-Resolved Partial Discharges and Machine Learning

This work presents a methodology for the generation and classification of phase-resolved partial discharge (PRPD) patterns based on the use of a printed UHF monopole antenna and signal conditioning circuit to reduce hardware requirements. For this purpose, the envelope detection technique was applied. In addition, test objects such as a hydrogenerator bar, dielectric discs with internal cavities in an oil cell, a potential transformer and tip–tip electrodes immersed in oil were used to generate partial discharge (PD) signals. To detect and classify partial discharges, the standard IEC 60270 (2000) method was used as a reference. After the acquisition of conditioned UHF signals, a digital signal filtering threshold technique was used, and peaks of partial discharge envelope pulses were extracted. Feature selection techniques were used to classify the discharges and choose the best features to train machine learning algorithms, such as multilayer perceptron, support vector machine and decision tree algorithms. Accuracies greater than 84% were met, revealing the classification potential of the methodology proposed in this work.

Enhanced breakdown strength of epoxy composites by constructing dual-interface charge barriers at the micron filler/epoxy matrix interface

For the advanced energy systems with ultra-high voltage and frequency, in order to improve the thermal conductivity, arc resistance and mechanical strength of epoxy-based dielectric materials, the addition of micron inorganic fillers is necessary. However, this will inevitably degrade their breakdown strength. In this work, the example of constructing dual-interface charge barriers by optimizing molecular structure at micron filler/epoxy matrix interface to capture charge and then enhance the breakdown strength of epoxy composites is reported. Results show that the Al2O3@PVDF-6/BPA system with optimized interfacial structure exhibits the breakdown strength of AC and DC voltages of 37.5 and 67.8 kV/mm, respectively, far outperforming current epoxy composites containing micron fillers. The charge trapping effects in the dual-interface charge barriers are comprehensively investigated, which is confirmed to be the reason for the improved breakdown strength. In particular, the construction of dual-interface charge barriers hardly sacrifices the thermal and mechanical properties of epoxy composites. This work unveils a scalable approach to exploring satisfied dielectric epoxy composites by dual-interface charge barriers construction at the micron filler/epoxy matrix interface.

Femtosecond laser ablation responses of kerogen-rich, argillaceous, and bituminous shale rocks

Shale rocks have become one of the major sources of natural gas and oil. Laser drilling has emerged as a promising technique that can be incorporated into horizontal drilling and hydraulic fracturing processes. In this study, we selected three types of shales (kerogen-rich, argillaceous, and bituminous) with distinct compositions and microstructures and performed femtosecond laser irradiation with different power and energy to investigate their ablation characteristics. Evidence of melting and solidification was observed in all samples, despite the ultra-high pulse frequency of the femtosecond laser. Among the three types of shale rocks, the kerogen-rich shale exhibited the highest ablation rate, while argillaceous and bituminous shale showed lower and comparable rates. The above observations highlight the significance of shale chemistry in influencing laser ablation characteristics under femtosecond laser irradiation. Furthermore, no ablation rate anisotropy was observed when irradiating the samples parallel with and perpendicular to the bedding direction, although shale rocks are microstructurally and mechanically anisotropic.

Gravitational waves from particle decays during reheating

Gravitational waves have become an irreplaceable tool for exploring the post-inflationary universe. Their cosmological and astrophysical origins have been attracting numerous attention. In this Letter, we point out a novel source of ultra-high frequency gravitational waves: the decay of particles produced during the reheating era. We highlight the decays of the inflaton and the Higgs bosons in the Standard Model and in the gauged B-L model as representative cases, showing how they yield a testable gravitational wave spectrum by future observations. We find that the peak frequency and the strain in the Higgs boson decay in the gauged B-L model, when the symmetry breaking scale is higher than the inflationary scale, can be greater than those in the inflaton decay scenario. Typically, the predicted spectrum lies beyond MHz in frequency and thus calls for non-interferometric experiments. Regardless of the shape of the spectrum, on the other hand, the total energy density of the produced gravitational waves can be reached by future Big Bang nucleosynthesis limits.

Ultrasound in Microsurgery: Current Applications and New Frontiers.

Ultrasound has revolutionized reconstructive microsurgery, offering real-time imaging and enhanced precision allowing for preoperative flap planning, recipient vessel identification and selection, postoperative flap monitoring, and lymphatic surgery. This narrative review of the literature provides an updated evidence-based overlook on the current applications and emerging frontiers of ultrasound in microsurgery, focusing on free tissue transfer and lymphatic surgery. Color duplex ultrasound (CDU) plays a pivotal role in preoperative flap planning and design, providing real-time imaging that enables detailed perforator mapping, perforator suitability assessment, blood flow velocity measurement, and, ultimately, flap design optimization. Ultrasound also aids in recipient vessel selection by providing assessment of caliber, patency, location, and flow velocity of recipient vessels. Postoperatively, ultrasound enables real-time monitoring of flap perfusion, providing early detection of potential flap compromise and improved flap survival rates. In lymphatic surgery, ultra-high frequency ultrasound (UHFUS) offers precise mapping and evaluation of lymphatic vessels, improving efficacy and efficiency by targeting larger dilated vessels. Integrating ultrasound into reconstructive microsurgery represents a significant advancement in the utilization of imaging in the field. With growing accessibility of devices, improved training, and technological advancements, using ultrasound as a key imaging tool offers substantial potential for the evolution of reconstructive microsurgery.

Atomic-Level Engineered Cobalt Catalysts for Fenton-Like Reactions: Synergy of Single Atom Metal Sites and Nonmetal-Bonded Functionalities.

Single atom catalysts (SACs) are atomic-level-engineered materials with high intrinsic activity. Catalytic centers of SACs are typically the transition metal (TM)-nonmetal coordination sites, while the functions of coexisting non-TM-bonded functionalities are usually overlooked in catalysis. Herein, the scalable preparation of carbon-supported cobalt-anchored SACs (CoCN) with controlled Co─N sites and free functional N species is reported. The role of metal- and nonmetal-bonded functionalities in the SACs for peroxymonosulfate (PMS)-driven Fenton-like reactions is first systematically studied, revealing their contribution to performance improvement and pathway steering. Experiments and computations demonstrate that the Co─N3C coordination plays a vital role in the formation of a surface-confined PMS* complex to trigger the electron transfer pathway and promote kinetics because of the optimized electronic state of Co centers, while the nonmetal-coordinated graphitic N sites act as preferable pollutant adsorption sites and additional PMS activation sites to accelerate electron transfer. Synergistically, CoCN exhibits ultrahigh activity in PMS activation for p-hydroxybenzoic acid oxidation, achieving complete degradation within 10min with an ultrahigh turnover frequency of 0.38min-1, surpassing most reported materials. These findings offer new insights into the versatile functions of N species in SACs and inspire rational design of high-performance catalysts in complicated heterogeneous systems.

Estimation of errors of the spectral method for measuring the concentration of water vapor and moisture reserves in the surface layer of the Earth’s atmosphere

A method for passive measurements of water vapor concentration in the atmosphere in the presence of solar radiation has been proposed and tested. The location of the measurements is the northeast of the Moscow region. When processing the results of measurements carried out on a single water absorption line, a coincidence of experimental data and data obtained from direct meteorological measurements with an error of no more than ~7.5 % was revealed. It was also found that on the water absorption line in the region of 1653 nm, the interfering factor is the nearby methane absorption line, which introduces a systematic error in the measurement results, and the results turn out to be underestimated. A possible reason is that the absorption cross section of methane molecules is ~4 orders of magnitude larger than that of water vapor molecules and light radiation is absorbed to a greater extent by methane, reducing the fraction of absorption of water vapor at a wavelength close to the methane absorption line. Compensatory corrections have been introduced to determine the concentration and moisture content in the atmospheric column with an accuracy of several percent at this wavelength. The proposed technique allows both long-term monitoring of concentration and moisture content in the atmosphere and obtaining operational information in real time. The results of the measurements performed are, on average, consistent with the results of measurements obtained using radiometers operating in the ultrahigh frequency range.

Folded Narrow-Band and Wide-Band Monopole Antennas with In-Plane and Vertical Grounds for Wireless Sensor Nodes in Smart Home IoT Applications

This article presents two monopole antennas with an endfire radiation pattern in the UHF band that can be installed on dry walls or metallic cabinets as a part of wireless sensor nodes, making them a suitable choice for smart home applications, such as the wireless remote control of house appliances. Two different antennas are proposed to cover the RFID bands of North America (902–928 MHz) and worldwide (860–960 MHz). The antennas have wide horizontal radiation patterns that provide great reading coverage in their communication with a base station placed at a certain distance from the antennas. The structures have two ground planes, one in-plane and the other vertical. The vertical ground helps the antenna to have a directive radiation and also makes it easily installed on walls. The antenna feeding line lies over the vertical ground substrate. The maximum dimensions of the narrow-band antenna are L × W = 0.3λ × 0.14λ, and those for the wide-band antenna are L × W = 0.39λ × 0.14λ. The measured results show that the bandwidth of the proposed antennas for the North America and worldwide RFID bands are from 902 MHz to 939 MHz and 822 MHz to 961 MHz, with maximum gains of 4.2 dBi and 4.9 dBi, respectively.

Boron/nitrogen-trapping and regulative electronic states around Ru nanoparticles towards bifunctional hydrogen production

Developing a straightforward and general strategy to regulate the surface microenvironment of a carbon matrix enriched with N/B motifs for efficient atomic utilization and electronic state of metal sites in bifunctional hydrogen production via ammonia-borane hydrolysis (ABH) and water electrolysis is a persistent challenge. Herein, we present a simple, green, and universal approach to fabricate B/N co-doped porous carbons using ammonia-borane (AB) as a triple functional agent, eliminating the need for hazardous and explosive functional agents and complicated procedures. The pyrolysis of AB induces the regulation of the surface microenvironment of the carbon matrix, leading to the formation of abundant surface functional groups, defects, and pore structures. This regulation enhances the efficiency of atom utilization and the electronic state of the active component, resulting in improved bifunctional hydrogen evolution. Among the catalysts, B/N co-doped vulcan carbon (Ru/BNC) with 2.1 wt% Ru loading demonstrates the highest performance in catalytic hydrogen production from ABH, achieving an ultrahigh turnover frequency of 1854 min−1 (depending on the dispersion of Ru). Furthermore, this catalyst shows remarkable electrochemical activity for hydrogen evolution in alkaline water electrolysis with a low overpotential of 31 mV at 10 mA cm−2. The present study provides a simple, green, and universal method to regulate the surface microenvironment of various carbons with B/N modulators, thereby adjusting the atomic utilization and electronic state of active metals for enhanced bifunctional hydrogen evolution.

High Performance Indium-Tin-Oxide Schottky Diodes for Terahertz Band Operation.

Schottky diode, capable of ultrahigh frequency operation, plays a critical role in modern communication systems. To develop cost-effective and widely applicable high-speed diodes, researchers have delved into thin-film semiconductors. However, a performance gap persists between thin-film diodes and conventional bulk semiconductor-based ones. Featuring high mobility and low permittivity, indium-tin-oxide has emerged to bridge this gap. Nevertheless, due to its high carrier concentration, indium-tin-oxide has predominantly been utilized as electrode rather than semiconductor. In this study, a remarkable quantum confinement induced dedoping phenomenon was discovered during the aggressive indium-tin-oxide thickness downscaling. By leveraging such a feature to change indium-tin-oxide from metal-like into semiconductor-like, in conjunction with a novel heterogeneous lateral design facilitated by an innovative digital etch, we demonstrated an indium-tin-oxide Schottky diode with a cutoff frequency reaching terahertz band. By pushing the boundaries of thin-film Schottky diodes, our research offers a potential enabler for future fifth-generation/sixth-generation networks, empowering diverse applications.

Empowering the Blind: Contactless Activity Recognition with Commodity Software-Defined Radio and Ultra-High-Frequency Radio Frequency Identification.

This study presents a novel computational radio frequency identification (RFID) system designed specifically for assisting blind individuals, utilising software-defined radio (SDR) with coherent detection. The system employs battery-less ultra-high-frequency (UHF) tag arrays in Gen2 RFID systems, enhancing the transmission of sensed information beyond standard identification bits. Our method uses an SDR reader to efficiently manage multiple tags with Gen2 preambles implemented on a single transceiver card. The results highlight the system's real-time capability to detect movements and direction of walking within a four-meter range, indicating significant advances in contactless activity monitoring. This system not only handles the complexities of multiple tag scenarios but also delineates the influence of system parameters on RFID operational efficiency. This study contributes to assistive technology, provides a platform for future advancements aimed at addressing contemporary limitations in pseudo-localisation, and offers a practical, affordable assistance system for blind individuals.

Modeling and radiation performance analysis of acoustically actuated magnetoelectric antennas

Bulk acoustic wave-mediated magnetoelectric (ME) antenna is the most promising acoustically actuated ultra-compact antenna scheme at ultrahigh frequency (0.3–3 GHz). However, the relevant research is still exploratory, and the antenna’s multi-field coupling modeling and performance analysis are imperfect. This work presents a cellular model based on finite element simulation to analyze the radiation characteristics of the ME antenna integrated on a thin-film bulk wave resonator (FBAR). Compared with the finite difference time domain (FDTD) method, the cellular model has the advantages of simplicity and high universality. The effects of mechanical and dielectric losses of piezoelectric (PE) material and mechanical and eddy current losses of magnetostrictive (MS) material on radiation efficiency are analyzed through the intensive research of unit cells of four different material combinations. Results show that the mechanical quality factors and piezomagnetic stress constant are the key parameters to determine the radiation efficiency. Besides conductivity and permeability, eddy current loss is also closely related to the thickness of the MS layer. This study provides a theoretical foundation for enhancing the radiation performance of ME FBAR antennas and identifying areas for further development.

Investigating three-dimensional vortex evolution in centrifugal pump under rotating stall conditions using tomographic particle image velocimetry

A rotating stall in centrifugal pumps commonly occurs under off-design operations, which is a detrimental phenomenon leading to flow instabilities, pressure fluctuations, and reduced performance. A time-resolved non-intrusive three-dimensional (3D) flow visualization method is developed for investigating complex vortex structures in centrifugal pumps based on Omega vortex identification and tomographic particle image velocimetry (tomo-PIV). A special-made centrifugal pump prototype was developed with acrylic glass allowing for optical access. This method enables both qualitative and quantitative analysis of high spatiotemporal resolution on flow behaviors and dynamics under various stall conditions. The ultra-high sampling frequency realized over 40 time-consecutive observations per revolution under 0.2 Qd, 0.4 Qd, 0.6 Qd, and 0.8 Qd. It captures the instantaneous evolution of vortex structures that undergoes a growth–breakup transition within 7–9 ms. The rotating stall mechanism is revealed experimentally from the evolution of the vortex structure. Our analysis shows the tomo-PIV's additional velocity component aids in understanding the 3D characteristics of the stall. A substantial region of reverse flow in the z-axis direction is observed under 0.2 Qd. Vortex structures are more prone to blockage at the impeller inlet, exacerbating the stall phenomenon. As the flow rate increases, the velocity distributions across different layers exhibit a laminar characteristic with a more uniform profile. The vortex structures extend radially and migrate toward the outlet. The evolutions of the stall vortex, wake vortex, and inlet vortex share the same dominant frequency components (4.75fn and 5.25fn), but the flow rate affects the proportion of different frequency components.

An ultrahigh frequency dielectric sensor for microdroplet detection using a split ring resonator-based microfluidic chip

An ultrahigh frequency dielectric sensor for microdroplet detection using a split ring resonator-based microfluidic chip

Propagation Analysis of an RFID System in the UHF Band in the Honeycomb Frame of a Beehive.

In recent years, communication systems, including RFID, have been used in intelligent beehives for beekeeping. RFID systems in the UHF frequency band offer reading distances of tens of centimetres, allowing the localisation and identification of the queen bee inside the hive. With this purpose, this work proposes an analysis of an environment of propagation that consists of a honeycomb frame, where the reader is placed within the frame, and the tag is placed in different positions over it. A honeycomb frame consists of a wooden box containing a honey wax panel, supported by metallic wires. The environment is modelled theoretically using its S-parameters and simulated in CST Studio. An analysis of these results and empirical measurements is performed. The results show that a periodicity in the received power of the tag is found with respect to the distance to the reader when the tag is located in a direction parallel to the wire, where local maximum and minimum values are found. Additionally, when the tag is placed over a wire of the frame, a higher received power is obtained compared to the case where the tag is placed between two wires. Furthermore, it has been observed that the reading range has increased with respect to free space, covering the full frame.

Study of the dielectric properties of decomposing materials during heating

The dielectric properties of materials when heated at ultrahigh frequencies are determined by methods based on the use of waveguide cavity resonators. However, as the sample is in the closed volume during measurements, the dielectric properties of destructive material thus determined can contain errors attributed filling of the resonator volume and depositing products of the sample decomposition on the internal conducting surfaces of the resonator. We present the results of studying the dielectric properties of destructive materials under heating in waveguide resonator cavity using methods that exclude the impact of destruction products on the accuracy of measurement. To reduce the influence of destructive vapors rising from the surface of the sample during the destruction process, additional thin quartz plates, placed on the sample surface were used. In addition, cuvettes with a lid were also used to prevent destruction products from entering the resonator volume. A method for taking into account the effect of plates and cuvettes in calculating the dielectric constant and dielectric loss tangent of a material sample when heated in a cavity resonator is presented. Changes in the dielectric properties of a composite material consisting of quartz fabric impregnated with an aluminochromophosphate binder and fiberglass laminate made of quartz fabric impregnated with a phenol-formaldehyde binder were studied in a temperature range above the onset of the destruction (up to temperatures at which loss of the structural strength of the material is observed). The developed method can be used in studying the thermophysical properties of destructive materials to assess changes in their dielectric characteristics under operation conditions of high-temperature heating.

Ultrahigh frequency primordial gravitational waves beyond the kHz: The case of cosmic strings

We investigate gravitational-wave backgrounds (GWBs) of primordial origin that would manifest only at ultrahigh frequencies, from kilohertz to 100 gigahertz, and leave no signal at LIGO, the Einstein Telescope, the Cosmic Explorer, LISA, or pulsar-timing arrays. We focus on GWBs produced by cosmic strings and make predictions for the GW spectra scanning over high-energy scale (beyond 1010 GeV) particle physics parameters. Signals from local string networks can easily be as large as the big bang nucleosynthesis/cosmic microwave background bounds, with a characteristic strain as high as 10−26 in the 10 kHz band, offering prospects to probe grand unification physics in the 1014–1017 GeV energy range. In comparison, GWB from axionic strings is suppressed (with maximal characteristic strain ∼10−31) due to the early matter era induced by the associated heavy axions. We estimate the needed reach of hypothetical futuristic GW detectors to probe such GWB and, therefore, the corresponding high-energy physics processes. Beyond the information of the symmetry-breaking scale, the high-frequency spectrum encodes the microscopic structure of the strings through the position of the UV cutoffs associated with cusps and kinks, as well as potential information about friction forces on the string. The IR slope, on the other hand, reflects the physics responsible for the decay of the string network. We discuss possible strategies for reconstructing the scalar potential, particularly the scalar self-coupling, from the measurement of the UV cutoff of the GW spectrum. Published by the American Physical Society 2024

Frequency multiplexing enables parallel multi-sample EPR

Electron paramagnetic resonance (EPR) spectroscopy stands out as a powerful analytical technique with extensive applications in the fields of biology, chemistry, physics, and material sciences. It proves invaluable for investigating the molecular structure and reaction mechanisms of substances containing unpaired electrons, such as metal complexes, organic and inorganic radicals, and intermediate states in chemical reactions. However, despite their remarkable capabilities, EPR systems face significant limitations in terms of sample throughput, as current commercial systems only target the analysis of one sample at a time. Here we introduce a novel scheme for conducting ultra-high frequency continuous-wave EPR (CW EPR) targeting the EPR spectroscopy of multiple microliter volume samples in parallel. Our proof-of-principle prototype involves two decoupled detection cells equipped with high qualty factor Q=104\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Q=104$$\\end{document} solenoidal coils tuned to 488 and 589 MHz, ensuring a significant frequency gap for effective radio frequency (RF) decoupling between the channels. To further enhance electromagnetic decoupling, an orthogonal alignment of the coils was adopted. The paper further presents an innovative radiofrequency circuit concept that utilizes a single physical RF channel to simultaneously conduct parallel EPR on up to eight cells. Parallel EPR experiments on two BDPA samples, each with a sample volume of 18.3 μL, registered signal-to-noise ratios of 255 and 252 for the two EPR measurement cells, with no observable coupling. The showcased prototype, built using cost-effective commercially available fabrication technology, is readily scalable and represents an initial step with promising potential for advancing sample screening with high-throughput parallel EPR.

Research on Miniaturized UHF Sensing Technology for PD Detection in Power Equipment Based on Symmetric Cut Theory.

In answer to the demand for high sensitivity and miniaturization of ultra-high frequency (UHF) sensors for partial discharge (PD) detection in power equipment, this paper proposes research on miniaturized UHF-sensing technology for PD detection in power equipment based on symmetric cut theory. The symmetric cut theory is applied for the first time to the miniaturization of PD UHF sensors for power equipment. A planar monopole UHF sensor with a size of only 70 mm × 70 mm × 1.6 mm is developed using an exponential asymptotic feed line approach, which is a 50% size reduction. The frequency-response characteristics of the sensor are simulated, optimized and tested; the results show that the standing wave ratio of the sensor developed in this paper is less than 2 in the frequency band from 427 MHz to 1.54 GHz, and less than 5 in the frequency band from 300 MHz to 1.95 GHz; in the 300 MHz~1.5 GHz band; the maximum and average gains of the sensor E-plane are 4.76 dB and 1.02 dB, respectively. Finally, the PD simulation experiment platform for power equipment is built to test the sensor's sensing performance; the results show that the sensor can effectively detect the PD signals; the sensing sensitivity is improved by about 95% relative to an elliptical monopole UHF sensor.

Ultrahigh frequency path loss prediction based on K-nearest neighbors

Abstract Path loss prediction (PLP) is an important feature of wireless communications because it allows a receiver to anticipate the signal strength that will be received from a transmitter at a given distance. The PLP is done by using machine learning models that take into account numerous aspects such as the frequency of the signal, the surroundings, and the type of antenna. Various machine learning methods are used to anticipate path loss propagation but it is difficult to predict path loss in unknown propagation conditions. In existing models rely on incomplete or outdated data, which can affect the accuracy and reliability of predictions and they do not take into account the effects of environmental factors, such as terrain, foliage, and weather conditions, on path loss. Furthermore, existing models are not robust enough to handle the real-world variability and uncertainty, leading to significant errors in predictions. To tackle this issue, a novel ultrahigh frequency (UHF) PLP based on K-nearest neighbors (KNNs) is developed for predicting and optimizing the path loss for UHF. In this proposed model, a KNN-based PLP has been used to predict the path loss in the UHF. This technique is used for high-accuracy PLP through KNN forecast route loss by determining the K-nearest data points to a particular test point based on a distance metric. Moreover, the existing models were not able to optimize path loss due to complex and large-scale machine learning models. Therefore, the stochastic gradient descent technique has been used to minimize the objective function, which is often a measure of the difference between the model’s predictions and the actual output that will fine-tune the parameters of the KNN model, by measuring the similarity between data points. This model is implemented using Python to make it a lot more convenient.