Frequency Interval Research Articles

Reducing industrial noise by the use of damping alloys when manufacturing mining equipment parts

The existing experience of noise and vibration specialists has shown that the problem of noise reduction is very relevant, especially for the mining industry. Traditional methods of dealing with industrial noise are not effective enough. In solving this issue, it is advisable to reduce the noise level at the source of its occurrence through the use of metal alloys with enhanced dissipative properties. The article presents the results of experimental studies of developing steels with increased damping properties for manufacturing perforator parts: bit bodies and drill rods. In this article, the sound pressure level of alloys dependence on the type of heat treatment has been studied, and the optimal content of alloying elements has been established to ensure the development of the ferrite-pearlite structure. This structure is characterized by an increased dislocation density and is the reason for reducing the noise of the drill rod and the body of the perforator bit by 10–12 dB A. In addition, the article establishes the pattern of noise intensity at different frequency intervals for standard and developed alloys.

Wavelet Transform Method for the Evaluation of the Seismic Response of One Isolated Building in the Lima Metropolitan Area

Structural health monitoring based on vibration measurements is a process that implements the instrumentation of sensors and methodologies to provide information regarding the condition of a structure, which allows the evaluation of the safety and integrity of structural systems. Because of this, in the past decades, several algorithms have been developed; among them, the wavelet transform is considered an efficient method for the elimination of the error contained in the acceleration recorded by the sensors. However, due to the complex nature of earthquakes and the particularity of the structural systems, the parameters used by the wavelet transform for error elimination in the seismic response are frequently variable. This paper proposes a method to get the seismic response of a base-isolated building subjected to ground-strong motions through numerical simulations of a mathematical model of the structure, using synthetic records based on historical seismic events occurring in Peru. In this way, the research found that the optimal intrinsic parameters of the building correspond to an approximate frequency interval of 0.20 to 6.25 Hz. Finally, the results show that this method is valid and can be reliably applied in structural health monitoring systems.

Internal gravity waves in massive stars

Stars that are over 1.6 solar masses are generally known to possess convective cores and radiative envelopes, which allows for the propagation of outwardly travelling internal gravity waves (IGWs). Here, we study the generation and propagation of IGWs in such stars using two-dimensional, fully non-linear hydrodynamical simulations with realistic stellar reference states from the one-dimensional stellar evolution code, Modules for Stellar Astrophysics. Compared to previous similar works, this study utilises radius-dependent thermal diffusivity profiles for five different stellar masses at the middle of the main sequence: 3 M⊙, 5 M⊙, 7 M⊙, 10 M⊙, and 13 M⊙. From the simulations, we find that the surface perturbations are larger for higher masses, but no noticeable trends are observed for the frequency slopes with different stellar masses. The slopes are also similar to the results from previous works. We compared our simulation results with stellar photometric data from a recent survey and we found that for frequency intervals above 8 μHz, there is a good agreement between the temperature frequency slopes from the simulations and the surface brightness variations of these observed stars. This indicates that the brightness variations are caused by core-generated IGWs.

Flexible channel selection method based on optical combs for broadband signals receiving.

A flexible channel selection method based on optical combs is proposed for reconfigurable optical channels in this paper. Optical-frequency combs with a large frequency interval are used to modulate broadband radio frequency (RF) signals, and an on-chip reconfigurable optical filter [Proc. of SPIE, 11763, 1176370 (2021).10.1117/12.2587403] is used to perform periodic carrier separation of wideband and narrowband signals and channel selection. In addition, flexible channel selection is achieved by presetting the parameters of a fast-response programmable wavelength-selective optical switch and filter device. Channel selection only relies on the combs through the Vernier effect of the combs and the passbands for different periods and does not require the use an additional switch matrix. Finally, flexible switching between and selection of specific channels for 13 GHz and 19 GHz broadband RF signals are experimentally verified.

Coherent dual-frequency signal generation in an optoelectronic oscillator.

Coherent dual-frequency microwave signal generation using an optoelectronic oscillator (OEO) is presented and demonstrated. In the proposed OEO, a dual-band bandpass filter (DB-BPF) is utilized to select two oscillation modes. An external signal is injected into the OEO loop with its frequency equaling the frequency interval of the two oscillation modes. Owing to the modulation nonlinearity of the Mach-Zehnder modulator, the two oscillation frequencies interact with the injection frequency. When the phase and gain conditions are satisfied within the loop, injection locking between the two oscillation signals will be established, and their phases will be synchronized. The effect of gain competition in the OEO loop, which leads to single-frequency oscillation, is suppressed. An experiment is carried out, and two frequencies, of 16.083 GHz and 9.998 GHz, are generated at the same time. The phase noise values are -140.1 and -141.0 dBc/Hz @ 10 kHz, respectively. The coherence between the generated signals and sidemode suppression performance are evaluated.

Inter-annual morphological evolution and volume changes of a meso- to macrotidal beach exhibiting multiple intertidal bars (MITB)

Although morphologically persistent in the long term, Multiple Intertidal Bar Systems (MITBs) display short-term, especially seasonal, morphodynamic behaviour. Analysis of high-density, monthly DGPS surveys conducted at Murlough and Ballykinler beaches, inter- and supratidal sediment volumes and hydrodynamic forcing (wave conditions and water levels), demonstrates a link between strong seasonality in wave climate and MITB beach behaviour. Summer, low-energy conditions limit cross-shore sediment exchange during which MITB beach morphology tends to stabilise throughout the season. With the onset of high-energy winter conditions cross-shore sediment exchanges occur between inter- and supratidal areas. Sediment transport is then enhanced during storm conditions that are coincident with spring tides, leading to high total water levels (TWL). Ultimately the storm sequencing, (frequency, magnitude and inter-storm interval), is the key parameter driving the beach morphological response. Major erosional patterns occur when the most energetic event, combined with spring high tide, occurs at the beginning of the winter season. Subsequent, less energetic storms then promote bar recovery until another extreme event occurs.Seasonality is also evident in alongshore dynamics. Cross-shore drainage channels that dissect the intertidal bars migrate alongshore, driving alongshore sediment transport and MITB longshore migration patterns. In summer migration of drainage channels is limited, whereas the winter high-energy forcing enhances channel migration rates and resulting sediment transport. Differences in dynamics between the two study sites are attributed to differences in local geology, beach morphology and sediment size, but in both locations, drainage channels are in fine migrating toward the inlet and associated ebb delta that divides the bay. Subsequent transport vectors are unknown, but the observations highlight the primary role of the inlet in the sediment circulation dynamics in the system as a whole.

Intrinsic optical absorption in Dirac metals

A Dirac metal is a doped (gated) Dirac material with the Fermi energy (EF) lying either in the conduction or valence bands. In the non-interacting picture, optical absorption in gapless Dirac metals occurs only if the frequency of incident photons (Ω) exceeds the direct (Pauli) frequency threshold, equal to 2EF. In this work, we study, both analytically and numerically, the role of electron–electron (ee) and electron–hole (eh) interactions in optical absorption of two-dimensional (2D) and three-dimensional (3D) Dirac metals in the entire interval of frequencies below 2EF. We show that, for Ω≪EF, the optical conductivity, ℜσ(Ω), arising from the combination of ee and certain eh scattering processes, scales as Ω2lnΩ in 2D and as Ω2 in 3D, respectively, both for short-range (Hubbard) and long-range (screened Coulomb) interactions. Another type of eh processes, similar to Auger–Meitner (AM) processes in atomic physics, starts to contribute for Ω above the direct threshold, equal to EF. Similar to the case of doped semiconductors with parabolic bands studied in prior literature, the AM contribution to ℜσ(Ω) in Dirac metals is manifested by a threshold singularity, ℜσ(Ω)∝(Ω−EF)d+2, where d is the spatial dimensionality and 0<Ω−EF≪EF. In contrast to doped semiconductors, however, the AM contribution in Dirac metals is completely overshadowed by the ee and other eh contributions. Numerically, ℜσ(Ω) happens to be small in almost the entire range of Ω<2EF. This finding may have important consequences for collective modes in Dirac metals lying below 2EF.

Stable directional amplification in one-dimensional non-Hermitian single-band systems

We investigate the directional amplification of non-Hermitian single-band systems in one dimension by using two models. The first model is the Hatano-Nelson model with added cavity decay and the second model is a linear lattice with fully asymmetric next-nearest-neighbor hopping. Based on the Dyson equation, we calculate the Green's functions of the two models analytically and investigate the directional amplification of a weak probe field. We find that, although the periodic-boundary spectrum of the two models determines the frequency interval in which the probe field can be directionally amplified, the open-boundary spectrum influences not only the bandwidth of the amplification curve but also the shape of the transmission curves. The bandwidth and the gain can be tuned independently by the parameters of the system. We also find that, for lattices with finite size, the frequency interval of the directional amplification shrinks due to the finite-size effects. Our thorough analysis is expected to provide a deeper insight into the directional amplification in non-Hermitian single-band systems and a tool for designing directional amplifiers and sensors.

RF measurement and tuning for an Alvarez-type drift tube linear accelerator without post couplers

Alvarez-type Drift Tube Linacs (DTLs) are commonly adopted to accelerate the proton or heavy ion beam with the speed range about 0.04∼0.4 times of the light speed in vacuum. Acquisition of appropriate frequency and distribution of the electromagnetic field, and the field stability inside the Alvarez-type DTL cavity are essential to achieve good beam characteristics. The field requirement can be achieved through tuning by tuners and post couplers when the cavity is off-line. The field stability of cavity is usually measured by the tilt sensitivity and the minimum frequency interval between the operation mode and the nearest neighbor mode. The frequency interval will increase with the reduction of the number of the acceleration units (cells) inside the cavity, which is beneficial to fulfill the tilt sensitivity requirement. If the field stability condition is naturally satisfied, the post couplers inside the DTL cavity are not needed, and the cavity frequency and field distribution can be tuned merely by tuners. In this paper, the tuning method based on the pseudo-inverse matrix is applied to the Alvarez-type DTL cavity without post couplers in Xi’an 200 MeV proton application facility (XiPAF). The method is improved by an expanded matrix algorithm and the tuning process is optimized to expedite the iteration during the tuning. The XiPAF DTL cavity has 23 cells and 5 tuners. By adjusting the insertion depths of the tuners, the tuning was achieved in merely one round of iteration. After tuning, the relative error of the peak field distribution and resonant frequency of the cavity reached to within ±3% and 325 ± 0.007 MHz (25°C, vacuum), respectively. It was verified that the field stability meets the requirement from the physical design both before and after tuning.

Effects of control fields on pair creation and vacuum information transmission

The effects of control fields on the energy spectra of particle pairs created from vacuum, the pair yield, and the transmission of information by Dirac vacuum modes are investigated using computational quantum field theory. The study reveals that oscillation structures of the energy spectrum are unstable and highly sensitive to the direction, width, and temporal profile of the control fields and can provide a more practical and detailed way to control or optimize the yield of the created particles with a certain energy. The information about the field direction, frequency, and time interval between two laser pulses can also be encoded in the control fields, embodied by vacuum modes, and reflected in the pair creation rate over time. In addition, the receiver and detector in the information transmission device can form a new remote, contactless detector for measuring laser field parameters. These findings may pave the way for future experiments and applications.

Spatiotemporal Evolution of Orbital Angular Momentum (OAM) Beams Based on a Uniform Circular Frequency Diverse Array (UC-FDA)

Radar imaging based on orbital angular momentum (OAM) beams has become a significant approach to realize high resolution and multidimensional target detection. The irradiation of a target area with OAM beams with different modes has been proven to be a feasible solution to improve the azimuthal resolution of the target. This article is the first to propose and validate novel spatiotemporal OAM beams generated by a uniform circular frequency diverse array (UC-FDA). Unlike the conventional uniform circular array (UCA), signals with frequency intervals need to be fed to the antennas in the UC-FDA structure. The mode of the spatiotemporal OAM beam can be switched automatically with spatial transmission, which enhances the flexibility of mode switching and reduces the switching time. The evolution characteristics of the OAM beam are fully demonstrated. Meanwhile, the intrinsic spatiotemporal evolution rules and influence parameters are analyzed and summarized. Furthermore, an optimized dynamic decomposition (DMD) algorithm is proposed and used to implement mode detection. Finally, the spatiotemporal evolution of OAM beams is applied to a rudimentary exploration of radar imaging. The measured results indicate that azimuth imaging of targets can be successfully accomplished. Spatiotemporal OAM beams may unlock promising potential for new-tech radar scenarios.

Microscale Searching Algorithm for Coupling Matrix Optimization of Automated Microwave Filter Tuning.

Automated tuning can significantly improve productivity and save the costs of manual operation in the microwave filter manufacturing industry. This article proposes a mathematical model of scattering data optimization to find the accurate coupling matrix for multiple-version microwave filters, a core step of automated microwave filter tuning. For the large-scale problem of coupling coefficient combination, we propose a decision set decomposition strategy that evenly divides the entire frequency interval into several subintervals according to the correlation between scattering data. With this strategy, we design a microscale (small-size subsets of the decomposed decision set) searching algorithm, which solves each suboptimization problem by searching the decision subset instead of the entire decision set. To verify the validity of the proposed algorithm for multiple-version microwave filters, experiments are conducted on three versions of microwave filters from a real-world production line, including the two-port eighth-order, ninth-order, and tenth-order microwave filters. Experimental results show that the proposed model is feasible within the industrial error for the multiversion microwave filter tuning problem. Besides, the proposed algorithm outperforms the state-of-the-art optimization algorithms in the coupling matrix optimization problem.

Comparison of bicoherence on the ensemble of realizations and a selective evaluation of the bispectrum of the dynamics of dangerous parameters of the gas medium during fire

The object of the study is the bicoherence of the bispectrum assessment of the dynamics of dangerous parameters of the gas environment during the ignition of materials. The subject is a measure of bicoherence of the bispectrum estimation from the ensemble of realizations and selective bispectrum estimation for the dynamics of hazardous parameters of the gas environment. The practical importance of the research is the use of the measure of bicoherence of the bispectrum for the early detection of fires. The measure of bicoherence of the dynamics of hazardous parameters of the gas environment is substantiated, which allows them to be numerically compared for the studied bispectrum estimates. As such measure, it is proposed to use the integral value of bicoherence for a given frequency interval, which makes it possible to numerically compare the bicoherence of bispectrum estimates for arbitrary time intervals of the dynamics of hazardous parameters of the gas environment. On the basis of the proposed measure for the frequency range of 0.2–2 Hz, a comparison of the integral bicoherence of the bispectrum estimates was made. The numerical value of the measure was determined for three fixed time intervals of the dynamics of hazardous parameters of the environment, corresponding to the absence of ignition, the occurrence of ignition, and the subsequent burning of test materials in the laboratory chamber. According to the results of the comparison of such values, it was established that the bicoherence of the bispectrum estimation from the ensemble of realizations is the most appropriate for detecting fires. When ignited, the numerical value of the measure for all test materials is about 90°. This means that the nature of the dynamics of hazardous environmental parameters in the event of fires becomes random. In this regard, the proposed measure is recommended to be used as a test for early detection of fires.

SARS-CoV-2 reinfection with different SARS-CoV-2 variants in children, Ohio, US.

Beginning in late 2021 we observed a significant increase in SARS-CoV-2 reinfections in pediatric patients evaluated at our institution. We aimed to characterize the children with SARS-CoV-2 reinfection, to determine the number of SARS-CoV-2 reinfections and characterize the intervals between two infections in our patient population. From March 2020 to September 2022, we identified children ≤ 21 years old who had ≥2 SARS-CoV-2 infections using laboratory reports. We then defined the type of SARS-CoV-2 variant in the first and subsequent infections by mutation specific typing or local epidemiology data. Clinical outcomes and interval between SARS-CoV-2 infections were assessed. We identified 541 children with ≥ 2 SARS-CoV-2 infections. The median interval between two infections was 229 days. The hospitalization rate was lower in the second infection. Reinfection counts were higher during the periods that Omicron variants predominated. Reinfection occurred more rapidly when Omicron variants were circulating with some occurring in less than 90 days. As SARS-CoV-2 continues to evolve, there is a need for ongoing surveillance to identify the frequency and time interval between reinfections and to re-evaluate the definition of SARS-CoV-2 reinfections.

Analyses of negative real permittivity behavior, AC conductivity and impedance properties of (YxEu1-x)Ba2Cu3O6.5 ceramics

In the present study, the dielectric, ac conductivity, and complex impedance properties of (YxEu1-x) Ba2Cu3O6.5 perovskite ceramics where x: 0; 0,4; 0,6; 1 have been examined from room temperature to 523 K between 1 Hz and 20 MHz frequency range. The ceramics have been synthesized by solid-state reaction method. The XRD analyses of the samples pointed out that they crystallize in an orthorhombic structure. While the highest orthorombicity factor has been observed for YBa2Cu3O6.5 ceramic, the reduced orthorhombicity in the other ceramics has been associated with the Eu substitution. On the other hand, the dielectric analyses of the samples have revealed a negative real permittivity (NRP) property of all ceramics regardless of the Eu substitution ratio and temperature. The origin of the NRP phenomenon has been explained based on the Drude model. However, it has been reported that the frequency interval at which the NRP is valid is maximum for x≥0.6 at high temperatures (T > 500 K). Additionally, both impedance and loss tangent spectra of the samples have been evaluated by establishing a correlation between NRP and the inductive character of the ceramics. The dc conductivity and the real component of complex impedance analyses imply the semiconducting nature and the negative thermal coefficient (NTC) of resistance of the ceramics. Ac conductivity analyses also indicate a pre-dominant CBH charge transport mechanism in the ceramics except for EuBa2Cu3O6.5.

Electrical Bioimpedance Analysis for Evaluating the Effect of Pelotherapy on the Human Skin: Methodology and Experiments.

Pelotherapy is the traditional procedure of applying curative muds on the skin's surface-shown to have a positive effect on the human body and cure illnesses. The effect of pelotherapy is complex, functioning through several mechanisms, and depends on the skin's functional condition. The current research objective was to develop a methodology and electrodes to assess the passage of the chemical and biologically active compounds of curative mud through human skin by performing electrical bioimpedance (EBI) analysis. The methodology included local area mud pack and simultaneous tap water compress application on the forearms with the comparison to the measurements of the dry skin. A custom-designed small-area gold-plated electrode on a rigid printed circuit board, in a tetrapolar configuration, was designed. A pilot study experiment with ten volunteers was performed. Our results indicated the presence of an effect of pelotherapy, manifested by the varying electrical properties of the skin. Distinguishable difference in the measured real part of impedance (R) emerged, showing a very strong correlation between the dry and tap-water-treated skin (r = 0.941), while a poor correlation between the dry and mud-pack-treated skin (r = 0.166) appeared. The findings emerged exclusively in the frequency interval of 10 kHz …1 MHz and only for R. EBI provides a promising tool for monitoring the variations in the electrical properties of the skin, including the skin barrier. We foresee developing smart devices for promoting the exploitation of spa therapies.

Dirac-Weyl semimetal in photonic metacrystals.

Dirac-Weyl semimetal is a novel type of topological phase that features the coexistence of Dirac and Weyl points in momentum space. In this study, a photonic Dirac-Weyl semimetal is proposed by introducing screw rotation symmetries into a spatial inversion symmetry-lacking system. A realistic metacrystal structure is designed for experimental consideration. The screw rotation symmetries are crucial for the existence of Dirac points, whose Z2 topology is revealed by the (010) surface states. Meanwhile, two pairs of ideal Weyl points at the same frequency are protected by D2d point group symmetries. The Dirac points and Weyl points reside in a clean frequency interval. The proposed photonic Dirac-Weyl semimetal provides a versatile platform for exploring the interaction between Dirac and Weyl semimetals and exploiting possible photonic topological devices.

Wireless and Flexible Tactile Sensing Array Based on an Adjustable Resonator with Machine‐Learning Perception

AbstractIntelligent soft robotics and wearable electronics require flexible, wireless radio frequency (RF) pressure sensors for human‐like tactile perception of their moving parts. Existing devices face two challenges for array extension: the construction of sensitive units over a limited area and the handling of resonant peaks overlapping within the channel width. Herein, a simply adjustable RF‐resonator‐based tactile array (RFTA) is reported, in which the initial frequency of each resonator unit is regulated by doping polydimethylsiloxane (PDMS) dielectric layers with various concentrations of multiwalled carbon nanotubes (MWCNTs). An array is constructed using four sensor units with a frequency interval of 15 MHz and a multi‐layer micropyramid structure is employed to obtain a low detection limit (&lt;1 Pa) and high sensitivity (17.49 MHz kPa‐1 in the low‐pressure range). A machine‐learning‐based strategy identifies tactile positions precisely via a one‐time S11 reading, achieving 98.5% accuracy with six stimulation modes. Furthermore, the RFTA distinguishes six objects during the grasping process when installed on a soft manipulator. The device shows considerable potential to be extended for flexible moving scenarios and high‐integrated tactile sensing systems for soft robotics.

Grade-control outdoor turning flight of robo-pigeon with quantitative stimulus parameters.

The robo-pigeon using homing pigeons as a motion carrier has great potential in search and rescue operations due to its superior weight-bearing capacity and sustained flight capabilities. However, before deploying such robo-pigeons, it is necessary to establish a safe, stable, and long-term effective neuro-electrical stimulation interface and quantify the motion responses to various stimuli. In this study, we investigated the effects of stimulation variables such as stimulation frequency (SF), stimulation duration (SD), and inter-stimulus interval (ISI) on the turning flight control of robo-pigeons outdoors, and evaluated the efficiency and accuracy of turning flight behavior accordingly. The results showed that the turning angle can be significantly controlled by appropriately increasing SF and SD. Increasing ISI can significantly control the turning radius of robotic pigeons. The success rate of turning flight control decreases significantly when the stimulation parameters exceed SF > 100 Hz or SD > 5 s. Thus, the robo-pigeon's turning angle from 15 to 55° and turning radius from 25 to 135 m could be controlled in a graded manner by selecting varying stimulus variables. These findings can be used to optimize the stimulation strategy of robo-pigeons to achieve precise control of their turning flight behavior outdoors. The results also suggest that robo-pigeons have potential for use in search and rescue operations where precise control of flight behavior is required.

Behavioral Model of G3-Powerline Communication Modems for EMI Analysis

G3-powerline communication (G3-PLC) is a robust communication protocol originally developed for smart metering in low-voltage power distribution networks. Modeling G3-PLC modems is an essential task to investigate electromagnetic compatibility (EMC) issues related to the coexistence of the PLC signal with the high-frequency noise affecting low-voltage networks, mainly due to the presence of power converters and non-linear loads. Since detailed information on the modem internal architecture is usually not available to the end-user, this work investigates the possibility of developing behavioral (black-box) models of G3-PLC modems, whose parameters can be estimated starting from measurements carried out at the modem output ports. To this end, suitable test benches are set up and used for model-parameter extraction as well as for validation purposes. Experiments have proven that an equivalent representation involving non-ideal voltage sources (i.e., in terms of extended Thevenin/Norton equivalent circuits) is no longer feasible for the transmitting modem, since the presence of a closed-loop control system invalidates the linearity assumption. Hence, while the receiving modem is still modeled through an impedance matrix (since it behaves as a linear device), an alternative representation is proposed for the transmitting modem, which resorts to the use of two ideal voltage sources in accordance with the substitution theorem. Experimental results prove that the proposed modeling strategy leads to satisfactory predictions of the currents propagating on the PLC system in the frequency interval of interest. Hence, it could be used in combination with high-frequency models of the other components in the network to investigate EMC and the coexistence of the PLC signal with the high-frequency noise generated by power converters.