High Frequency Field Research Articles

High-frequency electric field intensity sensor based on double-slot waveguides filled with electro-optical polymer

We consider the structure of a high-frequency external electric field sensor based on microring resonators using waveguides with two horizontal or vertical slots filled with an electro-optical polymer. The method of lines is used to calculate the propagation constants and mode field distributions of such waveguides. It is shown that double-slot waveguides filled with an electro-optical polymer exhibit higher optical radiation intensity in the slot region compared to single-slot waveguides, which makes it possible to increase the sensor sensitivity. The distances between the slots and the values of their widths at which a maximum sensor sensitivity is achieved are determined. The sensor allows alternating electric fields with frequencies up to 10 GHz to be measured in the range of 100−16 × 106 V m−1 with an accuracy of 150 V m−1.

Floquet transitions “Insulator – Semimetal – Insulator” in 2D crystals with displaced Dirac points

The Floquet spectrum of charge carriers of ac-driven Dirac 2D material has been calculated by averaging over the incident radiation period. The possibility of ac-tuned transitions between semimetallic and Floquet insulator states has been shown. The dependence of energy gap induced by high frequency field on the radiation power has been derived. This dependence has been shown to be nonmonotoneous. The density of states in conditions of ac-driving has been analyzed.

A new way to generate a rotating magnetic field in the high frequency range

The article describes a new method of generating a rotating magnetic field of high frequency. This new measuring system is built of a magnetic circuit consisting of a ferrite torus, inside of which there are three LP windings wound on ferrite cores connected in parallel with CP capacitors. Between the three rectangular voltage signals shifted by 120 angular degrees and the LPCP circuits, three serial LSCS circuits that constitute the band-pass filter circuit are connected. In this way, the system can be powered by both sinusoidal and square signals. This significantly reduces the cost of the entire device. The necessary conditions for thermal energy release in a magnetic fluid placed in a high-frequency rotating magnetic field are given. The author presents the preliminary results of the calorimetric effect in a magnetic fluid caused by a rotating (RMF) and alternating (AMF) magnetic field. The same sample of the magnetic fluid with magnetite nanoparticles dispersed in the oil (as a carrier liquid) was studied by both methods. The heating rate temperature (dT/dt)t=0 and its dependence on the intensity and the frequency of the magnetic field was determined. Taking into account the fact that both experiments were carried out under slightly different conditions, the intrinsic loss power (ILP) was calculated in order to compare the results. They indicate that the thermal effect in RMF is more than two times greater than in AMF. This allows a significant reduction in the mass of the magnetic material needed to produce a similar thermal effect in medical applications.

Enhanced dynamically assisted pair production in spatial inhomogeneous electric fields with the frequency chirping

Chirped dynamically assisted pair production in spatial inhomogeneous electric fields is studied by the Dirac-Heisenberg-Wigner formalism. The effects of the chirp parameter on the reduced momentum spectrum, the reduced total yield of the created pairs for either low or high frequency one-color field and two-color dynamically assisted combinational fields are investigated in detail. Also, the enhancement factor is obtained in the later two-color field case. It is found that for the low frequency field, no matter whether it is accompanied by the other high frequency field, its chirping has a little effect on the pair production. For the one-color high frequency field or/and two-color fields, the momentum spectrum exhibits incomplete interference and the interference effect becomes more and more remarkable as chirp increases. We also find that in the chirped dynamically assisted field, the reduced total yield is enhanced significantly when the chirps are acting on the two fields, compared with that the chirp is acting only for the low frequency strong field. Specifically, by the chirping, it is found the reduced pair number is increased by more than one order of magnitude in the field with a relative narrow spatial scale, while it is enhanced at least two times in other case of field with larger spatial scales or even in the quasi-homogeneous region. We also obtain some optimal chirp parameters and spatial scales for the total yield and enhancement factor in different scenarios of the studied external field. These results may provide a theoretical basis for possible experiments in the future.

Solvent-mediated forces in protein dielectrophoresis.

DEP is an established method to manipulate micrometer-sized particles, but standard continuum theories predict only negligible effects for nanometer-sized proteins despite contrary experimental evidence. A theoretical description of protein DEP needs to consider details on the molecular scale. Previous work toward this goal addressed the role of orientational polarization of static protein dipole moments for dielectrophoretic effects, which successfully predicts the general magnitude of dielectrophoretic forces on proteins but does not readily explain negative DEP forces observed for proteins in some experiments. However, contributions to the protein chemical potential due to protein-water interactions have not yet been considered in this context. Here, we utilize atomistic molecular dynamics simulations to evaluate polarization-induced changes in the protein solvation free energy, which result in a solvent-mediated contribution to dielectrophoretic forces. We quantify solvent-mediated dielectrophoretic forces for two proteins and a small peptide in water, which follow expectations for protein-water dipole-dipole interactions. The magnitude of solvent-mediated dielectrophoretic forces exceeds predictions of nonmolecular continuum theories, but plays a minor role for the total dielectrophoretic force for the simulated proteins due to dominant contributions from the orientational polarization of their static protein dipoles. However, we extrapolate that solvent-mediated contributions to negative protein DEP forces will become increasingly relevant for multidomain proteins, complexes and aggregates with large protein-water interfaces, as well as for high electric field frequencies, which provides a potential mechanism for corresponding experimental observations of negative proteinDEP.

Schwinger pair production in inhomogeneous electric fields with symmetrical frequency chirp

Pair production in inhomogeneous electric fields with symmetrical frequency chirp is studied numerically using the Dirac-Heisenberg-Wigner formalism. We investigate high- and low-frequency modes and consider two carrier envelope phases. Momentum spectrum is sensitive to chirp causing different interference effect for different spatial scales as well as the carrier phase of the external field. The reduced particle number is in general enhanced with increasing chirp. The effect of spatial scale of the field on the reduced particle number is also examined. It is found that it is enhanced at small spatial scale but is almost unchangeable at large spatial scales for the considered field parameters. On the other hand, at small spatial scale, the reduced particle number is enhanced by one or two orders when chirp is applied with the exception of cosine low-frequency field which is only a few times larger. Moreover it is found that the reduced particle number is further increased by symmetrical chirp at about two times by comparing to the usual asymmetrical chirp in high frequency field.

Effects of frequency and thermal conductivity on dielectric breakdown characteristics of epoxy/cellulose/BN composites fabricated by ice-templated method

Epoxy resin has been extensively used in the electrical systems and electronic devices. However, it is still a challenge to fabricate highly thermally conductive but electrically insulating epoxy composites. In this work, epoxy/cellulose/BN (EP/C-BN) composites were fabricated by ice-templated method. More importantly, the effects of frequency and thermal conductivity on dielectric breakdown characteristics, supported by the experiments of dielectric breakdown characteristics, infrared thermal imaging and finite simulation analysis, were studied. The as-prepared EP/C-BN composites exhibit a maximum thermal conductivity of 1.19 W/(m·K), and notably improved breakdown time at high frequency (324% higher than that of EP at 44 kHz). This work gives significant insight into the design of the thermal management polymers working at high frequency and high voltage fields.

Subharmonics and superharmonics of the weak field in a driven two-level quantum system: Vibrational resonance enhancement.

We consider a quantum two-level system in bichromatic classical time-periodic fields, the frequency of one of which far exceeds that of the other. Based on systematic separation of timescales and averaging over the fast motion a reduced quantum dynamics in the form of a nonlinear forced Mathieu equation is derived to identify the stable oscillatory resonance zones intercepted by unstable zones in the frequency-amplitude plot. We show how this forcing of the dressed two-level system may generate the subharmonics and superharmonics of the weak field in the stable region, which can be amplified by optimization of the strength of the high frequency field. We have carried out detailed numerical simulations of the driven quantum dynamics to corroborate the theoretical analysis.

High-intensity longwall mining-induced ground subsidence in Shendong coalfield, China

Ground subsidence caused by underground coal mining is one of the challenging environmental issues in mining engineering. This paper presents a field monitoring study of longwall mining-induced ground subsidence in Shendong coalfield, China. The paper includes the subsidence data of four longwall panels, with mining and geological conditions varied. All the longwall faces have a high mining height (4.5-7 m) and extraction speed (9.0–13.3 m/day), but with shallow mining depth (180-210 m). High-frequency field observations allow the dynamic characteristics of the ground subsidence caused by high-intensity longwall mining to be captured and revealed. Results show that, for a longwall panel with a width to depth ratio of 1.35–1.6, the subsidence ratio is generally between 51.1–54.3%, and the maximum subsidence speed can reach 0.4 m/day. Furthermore, the overlying goaf considerably increases the subsidence ratio, and the instability of the boundary coal pillars decreases the ground surface deformation but increases the range of influence. Results also suggest the use of dynamic surface subsidence to infer the breakage and movement laws of the strata in the high-intensity longwall mining condition. Finally, the practical implications of the results and the associated environmental effects are briefly discussed.

Electromagnetic properties of curved HTS trapped field stacks under high-frequency cross fields for high-speed rotating machines

Superconducting electric propulsion systems, characterized by high power densities and efficiencies, provide a possibility to zero carbon emission for future aviation. Stacks of high temperature superconducting (HTS) coated conductors (CCs) have become an alternative for high field magnets applied to superconducting machines, given their excellent field trapping ability and thermal stability. High-frequency ripple fields always exist in high-speed electric machines. Most research work regarding HTS trapped field stacks (TFSs) was focused on their magnetization methods and amplitude of trapped flux density; however, their performance in the high-frequency environment remains unclear. Despite several numerical models established for flat HTS TFSs, a comprehensive analysis of curved ones is still lacking, which possess geometrical applicability for cylindrical rotating shafts. Aimed at exploring the electromagnetic properties of curved HTS TFSs applied to high-speed rotating machines, a 3D numerical model considering both the multilayer structure and the Jc (B) dependence of HTS CCs has been built. Current and magnetic flux density distributions, as well as loss properties of a curved HTS TFS have been studied in detail, under perpendicular and cross fields with varying frequencies ranging from 50 Hz to 20 kHz. Results have shown that, the widely adopted two-dimensional-axisymmetric models are inapplicable to study the electromagnetic distributions of TFSs because of the emergence of the electromagnetic criss-cross defined in this paper. High-frequency ripple fields can drive induced current towards the periphery of the HTS TFS due to the skin effect, leading to a fast rise of AC loss and even an irreversible demagnetization of the stack. This paper has qualified and quantified the high-frequency electromagnetic behaviours of curved HTS TFSs, providing a useful reference for their loss controlling and anti-demagnetization design in high-speed propulsion machines.

Design and analysis of a quasi-TM03 mode G-band extended interaction radiation source

A disk-loaded coupled cavity structure operating in the quasi-TM03 mode has been used here to develop a high electron efficiency, high output power terahertz radiation source, demonstrating that it is possible to concentrate the axial field energy along the source’s central axis within a large cavity. Compared with traditional extended interaction devices operating at the same frequency band, the operating mode of this present device provides a sizable beam tunnel capacity that can support efficient energy conversion between the electron beam and the high frequency field. The developed electron optical system is based on a cylindrical electron beam of 0.3 mm radius and is capable of producing a beam current of 0.65 A at a bias of 16.4 kV. Particle in cell simulations show that such new design approaches can achieve kilowatt-level output power at 0.22 THz with a high electron efficiency of 11.5%.

External light control of three-dimensional ultrashort far-infrared pulses in an inhomogeneous array of carbon nanotubes

We present a study of the propagation of three-dimensional (3D) bipolar electromagnetic ultrashort pulses in an inhomogeneous array of semiconductor carbon nanotubes (CNTs) in the presence of a control high-frequency (HF) electric field. The inhomogeneity is present in the form of a layer with an increased concentration of conduction electrons, which acts as a barrier for the propagation of ultrashort electromagnetic pulses through the CNT array. The dynamics of the pulse is described by a nonlinear equation for the vector potential of the electromagnetic field (it takes the form of a 3D generalization of the sine-Gordon equation), derived from the Maxwell's equations and averaged over the period of the HF control field. By means of systematic simulations, we demonstrate that, depending on the amplitude and frequency of the HF control, the ultrashort pulse approaching the barrier layer either passes it or bounces back. The layer's transmissivity for the incident pulse is significantly affected by the amplitude and frequency of the HF control field, with the reflection coefficient nearly vanishing in intervals that make up a discrete set of transparency windows, which resembles the effect of the electromagnetically-induced transparency. Having passed the barrier, the ultrashort pulse continues to propagate, keeping its spatiotemporal integrity. The results may be used for the design of soliton valves, with the transmissivity of the soliton stream accurately controlled by the HF field.

Electrophysiological field potential identification of an intact GABAergic system in mouse cortical slices

In brain slice experiments there’s currently no validated electrophysiological method for differentiating viability between GABAergic and glutamatergic cell populations. Here we investigated the neurophysiology of high frequency field potential activity — and its utility for probing the functional state of the GABAergic system in brain slices.Field potentials were recorded from mouse cortical slices exposed to 50 mM potassium (“elevated-K”) and the induced high frequency (>20 Hz) response characterized pharmacologically. The elevated-K responses were also related to the high frequency activity imbedded in no-magnesium seizure-like events (SLE) from the same slices.The elevated-K response, comprising a transient burst of high frequency activity, was strongly GABAA-dependent. The size of the high frequency response was reduced by 71% (p = 0.001) by picrotoxin, but not significantly attenuated by either APV or CNQX. High frequency activity embedded in no-magnesium SLEs correlated with the elevated-K response. The success rate for generating an elevated-K response — and high frequency SLE activity — declined rapidly with increasing time since slicing.These findings support the hypothesis that in cortical slices, a functioning synaptic GABAergic system is evidenced by a strong high frequency component to no-magnesium SLE activity — and that the integrity of the GABAergic system degrades quicker than the excitatory glutamatergic system in this preparation.

Velocity profiles of ferrofluids in a cylindrical container and in the presence of external rotating magnetic fields of high strength and frequency

Velocity profiles of ferrofluids in a cylindrical container and in the presence of external rotating magnetic fields of high strength and frequency

Limited Sensitivity of Hippocampal Synaptic Function or Network Oscillations to Unmodulated Kilohertz Electric Fields

Understanding the cellular mechanisms of kilohertz (kHz) electrical stimulation is of broad interest in neuromodulation including forms of transcranial electrical stimulation, interferential stimulation, and high-rate spinal cord stimulation (SCS). Yet, the well-established low-pass filtering by neuronal membranes suggests minimal neuronal polarization in respond to charge-balanced kHz stimulation. The hippocampal brain slice model is among the most studied systems in neuroscience and exhaustively characterized in screening the effects of electrical stimulation. High-frequency electric fields of varied amplitudes (1–150 V/m), waveforms (sinusoidal, symmetrical pule, asymmetrical pulse) and frequencies (1 and10 kHz) were tested. Changes in single or paired-pulse field EPSPs (fEPSP) in CA1 were measured in response to radial-directed and tangential-directed electric fields, with brief (30 s) or long (30 min) application times. The effects of kHz stimulation on ongoing endogenous network activity were tested in carbachol-induced γ oscillation of CA3a and CA3c. Across 23 conditions evaluated, no significant changes in fEPSP were resolved, while responses were detected for within-slice control direct current (DC) fields; 1-kHz sinusoidal and pulse stimulation (≥60 V/m), but not 10 kHz, induced changes in oscillating neuronal network. We thus report no responses to low-amplitude 1-kHz or any 10-kHz fields, suggesting that any brain sensitivity to these fields is via yet to be-determined mechanism(s) of action which were not identified in our experimental preparation.

Vibro-impact model and validation of the axial dynamics of a vibration-assisted drilling tool

A lumped parameter vibro-impact model is proposed to describe the axial dynamics of a vibration-assisted drilling tool prototype, developed to improve the drilling efficiency in hard-rock drilling applications. The purpose of this work is twofold: to develop a new mathematical model that represents the axial dynamics of a vibration-assisted drilling tool, and to validate the proposed mathematical model with field data. The proposed model has seven degrees-of-freedom model with four impact surfaces. High-frequency field data, measured at multiple locations, are used to validate the mathematical model. The results show an overall good match between field data and model outputs, as the vibro-impact model is capable of capturing and reproducing the main dynamic behavior of the vibration-assisted drilling tool. Furthermore, the proposed model is able to reproduce complex dynamic behavior with little computational cost, due to the low number of degrees-of-freedom.

Physical modeling and experimental verification of magneto-rheological damper under medium and high frequency excitation

As a promising semi-active device, magneto-rheological damper has been widely used in low-frequency vibration isolation fields (within 20 Hz) such as bridge damping and building seismic resistance. Recently, the application of magneto-rheological damper has extended to medium and high frequency fields such as satellite and power engine vibration control, accompanied with an urgent need of detailed understanding of its output characteristics. In this paper, a comprehensive physical model is established to analyze dynamic performance of the magneto-rheological damper. The model, derived from both Poiseuille and Couette flow, aims to describe the relationship between the flow rate and pressure difference. The compressibility of the magneto-rheological fluid, the inertia of both the fluid and piston assembly, and the friction are involved to capture the medium and high frequency dynamics of the damping force. Theoretical calculation and simulation verification of magnetic circuit are conducted. Then the experiment based on a self-made prototype is carried out. The results show that the damping force calculated by proposed physical model matches well with the experimental results across the predefined range of frequency and coil current levels.

Rainstorm events shift the molecular composition and export of dissolved organic matter in a large drinking water reservoir in China: High frequency buoys and field observations

Rainstorm events can flush large amounts of terrestrial organic-rich material into lakes that are used for drinking water. To date, few studies have been carried out to investigate how rainstorm events change the molecular composition, bio-lability, and flux of upstream-imported dissolved organic matter (DOM), which can impact the odor and taste of drinking water as well as the efficiency of wastewater treatment. We undertook high-frequency buoy monitoring and point sample collection (n = 495), during high, moderate, and low inflow discharge, in Lake Qiandao, a key drinking water source for about 10 million people. Data from two online fluorescent DOM sensors deployed and field samples collected at the river site, Jiekou, and the lake site, Xiaojinshan, showed that rainstorm events increased the specific UV absorbance (SUVA254), humification index (HIX), humic-like components (C1-C2), and FT-ICR MS derived condensed aromatic and polyphenolic compounds (p < 0.001) and decreased the spectral slope of DOM (S275–295), spectral slope ratio (SR), biological index (BIX), and highly bio-degradable peptide-like and aliphatic substances (p < 0.001). Our results suggest that rainstorm events enhanced the export to the lake of colored, hydrophobic, and aromatic DOM. Upstream-derived dissolved organic carbon (DOC) concentrations decreased (p < 0.001), while DOC bio-availability (BDOC) increased only slightly (p < 0.05) during rainstorm events. The loss rate of DOC in Lake Qiandao is 0.82 × 104 t C yr−1, of which 0.30 × 104 t C yr−1 is highly bio-labile, and higher occurrences of both ≥ 25 mm d − 1 and ≥ 50 mm d − 1 rainfall events are anticipated by linear fittings for this region in the future. The application of in situ fluorescence sensors provides an early warning of DOC surge incidents caused by rainstorm events and may be useful in advising drinking water treatment plant managers of changes in raw water DOM quality and treatability.

RESEARCH ON THE EFFECT OF SUPER HIGH FREQUENCY FIELD ON GREEN TEA EXTRACTION AND EXTRACT QUALITY

The article characterises non-brick green tea as a product of mass consumption. It has been described how practical it is to produce liquid extracts based on it and use them further in the non- alcoholic drinks technology. Achieving high yields of extractives from tea requires intensification of the mass transfer process. The analysis of scientific sources has shown that pre-treatment of raw materials is one of the most promising methods for this purpose. The article presents comparative characteristics of green tea extracts obtained using pre- treatment in the super high frequency field and of ones produced without it. The optimal power of the super high frequency field for extracts heated up to 60°С has been selected and analysed. If the energy of super high frequency is applied to a fresh mixture of tea and an extractant, with its further extraction in a rotary extractor IKA-RV-10 at the dilution 280 mBr, the yield of extractives doubles. The action of the microwave field leads to a 40% increase in the content of extractives in the resulting extract: the yield of phenolic substances increases by 44%, of caffeine by 45%, of substances with vitamin P activity by 23%, compared with the extracts produced without additional treatment. However, the chlorophyll and aldehyde content decreases. Pre-treatment with super high frequency energy in the course of green tea extraction helps effectively extract phenolic compounds like catechins that affect the taste of final beverages. This technique allows doubling the yield of catechins. Besides, it has been confirmed that the chemical composition (namely the quantity of hydroxyl groups in the catechin structure) determines the intensity of the transition of catechins into the composition of the extract. The findings on the safety of the extracts obtained have allowed establishing that though the contents of mercury, arsenic, lead, copper, and iron increase, they do not exceed the maximum permissible concentrations. This proves the safety of the extracts produced. The research results obtained make it possible to intensify the plant extract production technology without using any special extractors.

Framing the Impacts of Highly Oscillating Magnetic Field on the Ferrofluid Flow Over a Spinning Disk Considering Nanoparticle Diameter and Solid–Liquid Interfacial Layer

Abstract This article communicates on the ferrofluid flow over a spinning disk in the presence of highly oscillating magnetic field. The flow is presumed to be unsteady. Ferrous nanoparticles are suspended within base medium water. This investigation reveals how presence and absence of oscillating magnetic field influence the hydrothermal basis of the flow. Also, the effects of particles diameter and solid–liquid interfacial layer have been precisely incorporated to reveal the thermal integrity of the system. Shliomis theory is introduced to frame the leading equations of the system. Resulting equations have been solved using innovative spectral quasi-linearization method (SQLM). Residual error analysis is included to explore the advantage of such computational scheme. The influence of dynamic parameters on the velocities and temperature is deliberated through graphs and tables. Several 3D pictures and contour plots are depicted to extract the key points of the flow. The results exhibit that heat transfer is reduced for nanoparticle diameter but amplifies for base liquid nanolayer conductivity ratio and elevated field frequency enhances the temperature. Relative magnetization reduces for high field frequency, but increases for angular displacement. SQLM exhibits an accurate computational scheme with fast convergence.