High Frequency Field Research Articles

Electromagneto-fluid Coupling Simulation of Arc Rapid Prototyping Process with External High-frequency Magnetic Field

Electromagneto-fluid Coupling Simulation of Arc Rapid Prototyping Process with External High-frequency Magnetic Field

English

This paper outlines the data on the possibility of applying the Coronal gas discharge effect in modeling non-equilibrium conditions with gas electric discharge simulating conditions occurring in the primary atmosphere (electric sparks, lightning). The physical basis and technique of visualization of gas discharge (GD) glowing of water drops in alternating electric fields of high electrical voltage (5–30 kV) and frequency (10–150 kHz) as well as possible electrosynthesis of organic molecules from a mixture of inorganic substances as hydrogen (H 2 ), methane (CH 4 ), ammonia (NH 3 ) and carbon monoxide (CO) in aqueous solutions of water exposed under electrical discharge, UV-radiation and thermal heating was examined. The colour coronal spectral gas discharge analysis, IR-spectroscopy, and NES-, and DNES-spectral analysis were applied for investigation of water samples of various origin, the samples of hot mineral, sea and mountain water obtained from various sources of Bulgaria, as well as cactus juice and Mediterranean jellyfish Cotylorhiza tuberculata obtained from the Aegean Sea (Chalkida, Greece). As a main parameter was measured the average energy of hydrogen bonds between H 2 O molecules in the process of cluster formation (dimmer, trimmer) and the function of the distribution of energies ∆f between individual H 2 O molecules compiles –0.1067±0.0011 eV. These data indicate that the origination of life and living matter depends on the structural and physical chemical properties of water, as well as the temperature and pH value. Keywords : Color gas discharge effect, IR-spectroscopy, primary atmosphere, water, origin of life, S. Miller’s experiments.

Investigations and advanced concepts on gyrotron interaction modeling and simulations

In gyrotron theory, the interaction between the electron beam and the high frequency electromagnetic field is commonly modeled using the slow variables approach. The slow variables are quantities that vary slowly in time in comparison to the electron cyclotron frequency. They represent the electron momentum and the high frequency field of the resonant TE modes in the gyrotron cavity. For their definition, some reference frequencies need to be introduced. These include the so-called averaging frequency, used to define the slow variable corresponding to the electron momentum, and the carrier frequencies, used to define the slow variables corresponding to the field envelopes of the modes. From the mathematical point of view, the choice of the reference frequencies is, to some extent, arbitrary. However, from the numerical point of view, there are arguments that point toward specific choices, in the sense that these choices are advantageous in terms of simulation speed and accuracy. In this paper, the typical monochromatic gyrotron operation is considered, and the numerical integration of the interaction equations is performed by the trajectory approach, since it is the fastest, and therefore it is the one that is most commonly used. The influence of the choice of the reference frequencies on the interaction simulations is studied using theoretical arguments, as well as numerical simulations. From these investigations, appropriate choices for the values of the reference frequencies are identified. In addition, novel, advanced concepts for the definitions of these frequencies are addressed, and their benefits are demonstrated numerically.

Expressions for the high frequency fields in the focal region of symmetrical hyperboloidal focusing lens placed in chiral medium

In this article, Geometric method (GO) and Maslov's method have been used to obtain the expressions for high frequency field refracted by a hyperboloidal focusing lens placed in homogenous and reciprocal chiral medium. High frequency focal region problems are transformed into focal free domain. The high-frequency field expressions that include the focal region obtained from GO method fail at the focal region, so Maslov's method has been used to find the field expressions which are also valid around the focal point. By using hybrid space, Maslov's method combines the simplicity of ray theory and the generality of Fourier transform method. Using the derived expressions numerical results around the focal region are plotted using MATLAB. These results show the effect of chirality parameter β on the focal region fields of hyperboloidal focusing lens placed in chiral medium.

Focal region field expressions for a spherical reflector backed by chiral substrate

High frequency field expression at the focal region of a spherical reflector antenna backed by isotropic and homogeneous chiral substrate is derived using Maslov's method. As Geometrical Optics (GO) solution fails at the focal point, so Maslov's method is used to overcome this problem. Field patterns are calculated numerically and the results are plotted. Analysis is done to show the effects of thickness (d) of chiral substrate, chirality parameter (β) of the chiral substrate and permittivity (ɛ) of the medium.

Low-amplitude, high-frequency electromagnetic field exposure causes delayed and reduced growth in Rosa hybrida

It is now accepted that plants perceive high-frequency electromagnetic field (HF-EMF). We wondered if the HF-EMF signal is integrated further in planta as a chain of reactions leading to a modification of plant growth. We exposed whole small ligneous plants (rose bush) whose growth could be studied for several weeks. We performed exposures at two different development stages (rooted cuttings bearing an axillary bud and 5-leaf stage plants), using two high frequency (900MHz) field amplitudes (5 and 200Vm−1). We achieved a tight control on the experimental conditions using a state-of-the-art stimulation device (Mode Stirred Reverberation Chamber) and specialized culture-chambers. After the exposure, we followed the shoot growth for over a one-month period. We observed no growth modification whatsoever exposure was performed on the 5-leaf stage plants. When the exposure was performed on the rooted cuttings, no growth modification was observed on Axis I (produced from the elongation of the axillary bud). Likewise, no significant modification was noted on Axis II produced at the base of Axis I, that came from pre-formed secondary axillary buds. In contrast, Axis II produced at the top of Axis I, that came from post-formed secondary buds consistently displayed a delayed and significant reduced growth (45%). The measurements of plant energy uptake from HF-EMF in this exposure condition (SAR of 7.2 10−4Wkg−1) indicated that this biological response is likely not due to thermal effect. These results suggest that exposure to electromagnetic field only affected development of post-formed organs.

High frequency characteristics for W-band multiple beam staggered double-vane traveling wave tube amplifier

A new micro-structure scheme was proposed by using three parallel pencil beams instead of the sheet beam for the W-band staggered double vane traveling wave tube amplifier,and detailed analysis and optimization were given for the high frequency characteristic with its input / output couplers. The results show that the structures have a good dispersion characteristic and very broad working bandwidth,the strong component of longitudinal electric field is very benefit to the interaction and exchange of the energy between the electron beam and the high frequency field. Keep the diameter of the pencil beam tunnel as the same of the height of the sheet beam tunnel,the interaction impedance of the structures can achieve 2- 3 times as high as the sheet beam scheme to obtain the high interaction efficiency and high output power. In order to match the staggered double-vane high frequency system,we present a more simple and easy input / output coupler structure. Just using three periods of transition structures,the input / output structures of the traveling wave tube amplifier can achieve a low reflection loss below the- 20 d B in a broad bandwidth with more suitable application in the devices later.

Analysis of NdFeB Bonded Magnet Behaviors Within High-Frequency Field and High Temperature Using Micromagnetic Simulator

Motors of hybrid vehicles and electric vehicles are anticipated to become smaller and have higher rotational speed. However, the small motors with high rotational speed may demagnetize the permanent magnets of motors by applying a high-frequency field of $\sim 10$ kHz at temperatures over 400 K. This demagnetization also depends on a static dc-field $\sim 3$ –4 kOe. We call this demagnetization phenomena magnetic fatigue. In this paper, magnet behaviors within a high-frequency field and at high temperature were simulated using a micromagnetic simulator.

Microwave-Assisted Shingled Magnetic Recording

Simulations of shingled, microwave-assisted magnetic recording were carried out. First, a simplified model of the head field near the corner of the main pole of a write head was used to understand the effect of the spin torque oscillator (STO) position relative to the head. Next, shingled tracks were written and evaluated for two different write head and STO geometries. For shingled recording, locating a rotated STO on the side of the main pole may provide some advantages in that medium grains experience the high-frequency (HF) field for a longer time and the chirality of the HF field does not change as the grains pass by the STO. Recording simulations show that the rotated STO writes smoother track edges at lower densities, but there is little difference in signal-to-noise ratio at high linear densities.

Wakefield potentials of corrugated structures

A corrugated structure, which is used in ``dechirper'' devices, is usually a pipe or two plates with small corrugations (bumps) on the walls. There is a good single-mode description of the wake potentials excited by a relativistic bunch if the wave length of the mode is much longer than the distance between the bumps in the pipe. However, ultrashort bunches, which are now used in free electron lasers, excite much higher frequency fields and the corresponding wake potentials will be very different from the single-mode description. We have made analyses of these wake potentials based on a numerical solution of Maxwell's equations. It was confirmed that the behavior of the wakefields of ultrashort bunches in corrugated structures is not much different from the fields excited usually in accelerating structures where the wake potentials are described by the exponential function. For a practical application we present results for the SLAC ``dechirper.'' We also carried out calculations for a similar device, that was installed and measured at the Pohang Accelerator Laboratory, Korea. We find very good agreement with the experimental results.

Influence of X-ray and polar cap absorptions on vertical and oblique sounding ionograms on different latitudes

High frequency (HF) radio band is important for the long-range communications and over-the-horizon surveillance, particularly in the polar cap region where the ground infrastructure may be limited. However, the space weather events drastically affect the high frequency radio wave propagation so that the ability to provide now-casting and forecasting of HF radio wave absorption is important for users relying on the HF communications. During the space weather events such as solar proton events and X-ray flares the high-latitude ionosphere becomes a particularly efficient absorber of HF radio waves. There is therefore a need to develop accurate HF propagation prediction services. Absorption of the HF field caused by the X-ray flux, Solar Ultra-Violet flux and proton precipitations is investigated in this paper for the event of the solar flare observed on 11 April 2013. The effects of the X-ray flux and proton precipitations on the structure of the vertical and oblique ionograms for different latitudes are estimated. The simulation of the vertical and oblique ionograms was performed on the basis of the computational model of the ionosphere oriented to applications into the high frequency wave propagation problems. The absorption effects induced by the proton precipitations and X-ray flux are calculated according to the algorithm elaborated by Sauer and Wilkinson and D-region Absorption Model (D-RAP) available from the NOAA Space Weather Prediction Center. The simulated vertical and oblique ionograms with the absorption effects taken into account and the measured ionograms exhibit a fairly good similarity.

A one-dimensional study of the evolution of the microwave breakdown in air

The microwave breakdown in air is simulated numerically within a simple 1D model taking into account a perturbation of electromagnetic field by plasma. The simulations were performed using two qualitatively different codes. One of these codes is based on computation of Maxwell equations, whereas the other one utilizes an approximation of quasi-monochromatic electromagnetic field. There is a good agreement between simulation results obtained by using both codes. Calculations have been carried out in a wide range of air pressures and field frequencies; also varied were initial spatial distributions of plasma density. The results reveal strong dependence of the breakdown evolution on the relation between the field frequency and the gas pressure as well as on the presence of extended rarefied background plasma. At relatively low gas pressures (or high field frequencies), the breakdown process is accompanied by the stationary ionization wave propagating towards the incident electromagnetic wave. In the case of a high gas pressure (or a relatively low field frequency), the peculiarities of the breakdown are associated with a formation of plasma filament array. The extended background plasma can suppress formation of the plasma filament array completely even at high pressures (or low frequencies).

Ion heating, burnout of the high-frequency field, and ion sound generation under the development of a modulation instability of an intense Langmuir wave in a plasma

The development of one-dimensional parametric instabilities of intense long plasma waves is considered in terms of the so-called hybrid models, with electrons being treated as a fluid and ions being regarded as particles. The analysis is performed for both cases when the average plasma field energy is lower (Zakharov's hybrid model—ZHM) or greater (Silin's hybrid model—SHM) than the plasma thermal energy. The efficiency of energy transfer to ions and to ion perturbations under the development of the instability is considered for various values of electron-to-ion mass ratios. The energy of low-frequency oscillations (ion-sound waves) is found to be much lower than the final ion kinetic energy. We also discuss the influence of the changes in the damping rate of the high-frequency (HF) field on the instability development. The decrease of the absorption of the HF field inhibits the HF field burnout within plasma density cavities and gives rise to the broadening of the HF spectrum. At the same time, the ion velocity distribution tends to the normal distribution in both ZHM and SHM.

Modeling Tumor Treating Fields (TTFields) application in single cells during metaphase and telophase.

Effects of electric fields on biological cells have been extensively studied but primarily in the low and high frequency regimes. Low frequency AC fields have been investigated for applications to nerve and muscle stimulation or to examine possible environmental effects of 60 Hz excitation. High frequency fields have been studied to understand tissue heating and tumor ablation. Biological effects at intermediate frequencies (in the 100-500 kHz regime) have only recently been discovered and are now being used clinically to disrupt cell division, primarily for the treatment of recurrent glioblastoma multiforme. In this study, we develop a computational framework to investigate the mechanisms of action of these Tumor Treating Fields (TTFields) and to understand in vitro findings observed in cell culture. Using Finite Element Method models of isolated cells we show that the intermediate frequency range is unique because it constitutes a transition region in which the intracellular electric field, shielded at low frequencies, increases significantly. We also show that the threshold at which this increase occurs depends on the dielectric properties of the cell membrane. Furthermore, our models of different stages of the cell cycle and of the morphological changes associated with cytokinesis show that peak dielectrophoretic forces develop within dividing cells exposed to TTFields. These findings are in agreement with in vitro observations, and enhance our understanding of how TTFields disrupt cellular function.

Observations and Predictions of Wave Runup, Extreme Water Levels, and Medium-Term Dune Erosion during Storm Conditions

Monitoring of dune erosion and accretion on the high-energy macrotidal Vougot beach in North Brittany (France) over the past decade (2004–2014) has revealed significant morphological changes. Dune toe erosion/accretion records have been compared with extreme water level measurements, defined as the sum of (i) astronomic tide; (ii) storm surge; and (iii) vertical wave runup. Runup parameterization was conducted using swash limits, beach profiles, and hydrodynamic (Hm0, Tm0,–1, and high tide water level—HTWL) data sets obtained from high frequency field surveys. The aim was to quantify in-situ environmental conditions and dimensional swash parameters for the best calibration of Battjes [1] runup formula. In addition, an empirical equation based on observed tidal water level and offshore wave height was produced to estimate extreme water levels over the whole period of dune morphological change monitoring. A good correlation between this empirical equation (1.01Hmoξo) and field runup measurements (Rmax) was obtained (R2 85%). The goodness of fit given by the RMSE was about 0.29 m. A good relationship was noticed between dune erosion and high water levels when the water levels exceeded the dune foot elevation. In contrast, when extreme water levels were below the height of the toe of the dune sediment budget increased, inducing foredune recovery. These erosion and accretion phases may be related to the North Atlantic Oscillation Index.

High frequency synchrony in the cerebellar cortex during goal directed movements.

The cerebellum is involved in sensory-motor integration and cognitive functions. The origin and function of the field potential oscillations in the cerebellum, especially in the high frequencies, have not been explored sufficiently. The primary objective of this study was to investigate the spatio-temporal characteristics of high frequency field potentials (150–350 Hz) in the cerebellar cortex in a behavioral context. To this end, we recorded from the paramedian lobule in rats using micro electro-corticogram (μ-ECoG) electrode arrays while the animal performed a lever press task using the forelimb. The phase synchrony analysis shows that the high frequency oscillations recorded at multiple points across the paramedian cortex episodically synchronize immediately before and desynchronize during the lever press. The electrode contacts were grouped according to their temporal course of phase synchrony around the time of lever press. Contact groups presented patches with slightly stronger synchrony values in the medio-lateral direction, and did not appear to form parasagittal zones. The size and location of these patches on the cortical surface are in agreement with the sensory evoked granular layer patches originally reported by Welker's lab (Shambes et al., 1978). Spatiotemporal synchrony of high frequency field potentials has not been reported at such large-scales previously in the cerebellar cortex.

Hysteretic dynamics of active particles in a periodic orienting field.

Active motion of living organisms and artificial self-propelling particles has been an area of intense research at the interface of biology, chemistry and physics. Significant progress in understanding these phenomena has been related to the observation that dynamic self-organization in active systems has much in common with ordering in equilibrium condensed matter such as spontaneous magnetization in ferromagnets. The velocities of active particles may behave similar to magnetic dipoles and develop global alignment, although interactions between the individuals might be completely different. In this work, we show that the dynamics of active particles in external fields can also be described in a way that resembles equilibrium condensed matter. It follows simple general laws, which are independent of the microscopic details of the system. The dynamics is revealed through hysteresis of the mean velocity of active particles subjected to a periodic orienting field. The hysteresis is measured in computer simulations and experiments on unicellular organisms. We find that the ability of the particles to follow the field scales with the ratio of the field variation period to the particles' orientational relaxation time, which, in turn, is related to the particle self-propulsion power and the energy dissipation rate. The collective behaviour of the particles due to aligning interactions manifests itself at low frequencies via increased persistence of the swarm motion when compared with motion of an individual. By contrast, at high field frequencies, the active group fails to develop the alignment and tends to behave like a set of independent individuals even in the presence of interactions. We also report on asymptotic laws for the hysteretic dynamics of active particles, which resemble those in magnetic systems. The generality of the assumptions in the underlying model suggests that the observed laws might apply to a variety of dynamic phenomena from the motion of synthetic active particles to crowd or opinion dynamics.

DISTRIBUTION OF LECTIN RECEPTORS OF PEANUT (ARACHIS HYPOGAEA) IN HISTOCHEMICAL CHARACTERISTICS OF TESTICLES IN RATS AFTER THEIR EXPOSURE TO ELECTROMAGNETIC FIELD AND THE USE OF ECHINACEA PURPUREA TINCTURE

The performed scientist research determined certain data concerning accumulating of PNA+receptors to peanut (Arachis hypogaea) lectin in the structures of rat testicles ,which were irradiated by electromagnetic field of high voltage and low frequency with following immune stimulation by 7% alcohol tincture of Echinacea purpurea. The influence of Echinacea purpurea was found to cause activation of spermatogenesis process in testicles of irradiated rats.

Nonlinear energy dissipation of magnetic nanoparticles in oscillating magnetic fields

The heating of magnetic nanoparticle suspensions subjected to alternating magnetic fields enables a variety of emerging applications such as magnetic fluid hyperthermia and triggered drug release. Rosensweig (2002) [25] obtained a model for the heat dissipation rate of a collection of non-interacting particles. However, the assumptions made in this analysis make it rigorously valid only in the limit of small applied magnetic field amplitude and frequency (i.e., values of the Langevin parameter that are much less than unity and frequencies below the inverse relaxation time). In this contribution we approach the problem from an alternative point of view by solving the phenomenological magnetization relaxation equation exactly for the case of arbitrary magnetic field amplitude and frequency and by solving a more accurate magnetization relaxation equation numerically. We also use rotational Brownian dynamics simulations of non-interacting magnetic nanoparticles subjected to an alternating magnetic field to estimate the rate of energy dissipation and compare the results of the phenomenological theories to the particle-scale simulations. The results are summarized in terms of a normalized energy dissipation rate and show that Rosensweig's expression provides an upper bound on the energy dissipation rate achieved at high field frequency and amplitude. Estimates of the predicted dependence of energy dissipation rate, quantified as specific absorption rate (SAR), on magnetic field amplitude and frequency, and particle core and hydrodynamic diameter, are also given.

Analog electro-optical readout of SiPMs achieves fast timing required for time-of-flight PET/MR

The design of combined positron emission tomography/magnetic resonance (PET/MR) systems presents a number of challenges to engineers, as it forces the PET system to acquire data in a space constrained environment that is sensitive to electro-magnetic interference and contains high static, radio frequency and gradient fields. In this work we validate fast timing performance of a PET scintillation detector using a potentially very compact, very low power, and MR compatible readout method in which analog silicon photomultipliers (SiPM) signals are transmitted optically away from the MR bore with little or even no additional readout electronics. This analog ‘electro-optial’ method could reduce the entire PET readout in the MR bore to two compact, low power components (SiPMs and lasers). Our experiments show fast timing performance from analog electro-optical readout with and without pre-amplification. With 3 mm × 3 mm × 20 mm lutetium–yttrium oxyorthosilicate (LYSO) crystals and Excelitas SiPMs the best two-sided fwhm coincident timing resolution achieved was 220 +/− 3 ps in electrical mode, 230 +/− 2 ps in electro-optical with preamp mode, and 253 +/− 2 ps in electro-optical without preamp mode. Timing measurements were also performed with Hamamatsu SiPMs and 3 mm × 3 mm × 5 mm crystals. In the future the timing degradation seen can be further reduced with lower laser noise or improvements SiPM rise time or gain.