Maximum Field Value Research Articles

Numerical Investigations of Stirring Induced Flow on Solidification and Interface Behavior in Continuous Casting Mold With Bifurcated Nozzle

Abstract Electromagnetic stirring (EMS) is a technique that has the potential to improve steel quality with fine microstructure by fragmentation of dendrites and enhancing the inclusion removal. The success of implementing the EMS lies in the selection of key input parameters such as position, frequency, and current density of the stirrer. In the present study, an integrated mathematical model consisting of liquid steel solidification and two phase interface is numerically developed with the use of EMS. The enthalpy porosity and volume of fluid (VOF) model are adopted for numerical modeling analysis of solidification and interface level fluctuation, respectively. The results reveal that on moving EMS downwards decreases the maximum magnetic field value, widens the mushy zone, and promotes the stability of the interface. Current intensity and frequency are seen to have the opposite effect on stirring intensity and interface fluctuation. With an increase in frequency, both stirring intensity and interface level fluctuations decrease while the high liquid fraction region increases. Moreover, current density enhances the swirling flow intensity and homogenizes the liquid fraction, thereby promoting equiaxed grain formation. Interface fluctuation is seen to increase with current density.

Optimizing the Effectiveness of Magnetic Lenses by utilizing the Electron Optical Design (EOD) Software

This paper introduces a computational analysis that discusses an approach for optimal synthesis in the design of magnetic lenses, specifically focusing on the analytical method. A widely employed approach for magnetic lens design involves utilizing an analysis optimization procedure, which makes use of the finite element method and is supported by Munro programs. In this study, this approach has been employed to explore magnetic lenses using the Electron Optical Design (EOD) software. The study offers insights into the role of the air gap in magnetic lens design, highlighting its importance in optimizing objective and projector properties. The analysis reveals that variations in the air gap (S) significantly influence the performance of magnetic lenses. Decreasing the air gap when it is set to (3) leads to substantial improvements in objective optical properties and focal length. Conversely, increasing the air gap when it is set to (12) enlarges the half-width of the axial magnetic field while reducing the maximum magnetic field value. These findings underscore the importance of carefully optimizing the air gap to achieve desired lens performance. The focal length is determined using this input data and coefficients of aberration (spherical and chromatic) of the objective. The study focuses on the influence of a crucial geometric parameter, specifically the air gap (S), on both objective and projector properties. Its importance stems from its capability to pinpoint the suitable geometry for magnetic lenses, thereby facilitating their efficient application.

A Modification of Magnetic Adaptive Testing: Progressive Method for Nondestructive Inspection of Microstructural Changes in Ferromagnetic Constructional Materials

Magnetic adaptive testing (MAT), thanks to its relative simplicity from the point of view of both hardware and software, appears to be very promising for non-destructive analysis of various ferromagnetic constructional materials used in many industrial applications. In order to make the inspection of tested objects faster, even more straightforward and the processing of data easier, we concentrated our effort both to improve the experimental procedure, based on specific way of the measurement of magnetization curves at piece-wise linear (triangular) exciting field with a constant field rate of change (i.e., slope) as well as to create a universal software tool for MAT data analysis. On contrary to the original implementation of MAT, the hysteresis loops are measured with decreasing maximum field values, starting at sample saturation region; therefore, time consuming sample demagnetization can be skipped completely. In addition, an advanced tool for the processing of experimentally obtained magnetization curves is presented. Using this application allows to find proper non-traditional magnetic parameters (e.g., the differential permeability) being the most sensitive to various types of industrial load (e.g., thermal, mechanical and/or neutron irradiation) and, at the same time, sufficiently correlated with other, traditional magnetic as well as non-magnetic parameters used routinely for the assessment of possible structural changes associated with applied, often long-term, load even on a microscopic scale, prior to any damage manifests on a macroscopic, visible level. The software capabilities were demonstrated on the data representing the material, whose response to acting thermal load is being difficult to analyze, since the dependence of observed parameters (differential permeability) upon defined artificial ageing was rather complicated. Nevertheless, the sensitivity of differential permeability to such a load was found being more than 8 times larger than in case of traditional hysteretic parameter, namely the remanent flux density while the correlation between them was high.

High Gain Improved Planar Yagi Uda Antenna for 2.4 GHz Applications and Its Influence on Human Tissues

Considering the technological enhancements nowadays, antennas tend to be smaller in order to be easily integrated in devices. The most used antennas today in small high-tech devices close to the human body are planar antennas. In this paper, a Yagi Uda planar antenna operating at a frequency of 2.4 GHz is HF analyzed and optimized by increasing its bandwidth and gain while maintaining its initial dimensions. The methods used to optimize the antenna’s operation are the use of different dielectrics, different numbers of directors, and different dimensions for directors, placing new conductor elements, all while keeping the same dimensions for its implementation on the planar device. The optimized structure of the planar Yagi Uda antenna has a 10% increase in bandwidth and a 30% increase in gain, reaching a peak value of 4.84 dBi. In our daily activities, we use devices with such antennas very often, so an analysis of the antenna’s influence on the human body is performed: the SAR, electric and magnetic field and radiation power density are determined, represented and reported to the standards in force. For the frequency considered, the SAR should be below 4 W/kg for the head/torso when the exposure is more than six minutes, which is a value exceeded by the antenna in its near vicinity. The calculated maximum electric field limit is 0.349 V/m and the maximum magnetic field value is 28.441 V/m for an exposure between 6 and 30 min values, which is also exceeded in the immediate vicinity of the antenna. The results allow us to suggest that such an antenna should be placed further from the human body, or some protection should be placed between the body and the antenna. From the radiation power density point of view for the modeled antenna, it can be said that a distance from the antenna greater than 0.5 m is considered to be safe.

Improvement of critical current density J c in powder-in-tube rapid heating, quenching and transformation Nb3Al wires by doping with nano-SnO2

We prepared Nb3Al superconducting wires doped with nano-size SnO2 (n-SiO2) particles through a multi-time rapid heating and quenching process and investigated their microstructure and superconducting properties. All the samples showed a highly homogeneous A15 Nb3Al phase. Compared with pure Nb3Al, the n-SnO2 doped Nb3Al wires presented a larger ΔT c value and a higher J c value. The best J c at 4.2 K was found in the 1 wt% n-SnO2 doped Nb3Al sample, with 3.37 × 105 A cm−2, 2.55 × 105 A cm−2 and 1.80 × 105 A cm−2 at 8 T, 10 T and 12 T, respectively. These results were an improvement of about 60% compared with pure Nb3Al at the same applied fields. The maximum irreversible field value was obtained in the 1 wt% SnO2-doped Nb3Al wire, with a result of 29.5 T at 4.2 K. The improvement of J c performance in the n-SnO2 doped Nb3Al wires might be attributed to the formation of artificial nanoparticles in the grain, which act as extra effective flux pinning centers.

Numerical analysis of nucleate boiling in rolling rod bundle with tilted axis using two-fluid modeling approach

In this study, an Eulerian-Eulerian two-fluid approach was applied to simulate nucleate boiling in a vertical rolling 2 × 2 rod bundle with a tilted axis. For this purpose, the standard multiphaseEulerFoam solver of OpenFOAM was modified to include the fictitious forces necessary in a non-inertial frame of the reference formulation. High-performance computing was then applied to analyze the effects of oscillation on boiling and the physics of the fluids inside the rod bundle. In particular, the effect of a tilted rolling axis was investigated for the first time. The results indicated that the space-averaged void fraction and surface-averaged heat transfer coefficient decrease in the rolling cases compared with the stationary case. Furthermore, it was found that while the tilt angle has a negligible effect on the space-averaged values, it may have a significant impact on the maximum value of the void fraction. The higher the tilt of the rolling axis, the higher the variation in the maximum field values. The results of this study will further improve our understanding of wall nucleate boiling, which is critical for the design, development, and safety of light water-cooled reactors (LWR).

Near-Field Scanning Based Shielding Effectiveness Analysis of System in Package

The electromagnetic interference (EMI) problems are crucial for system-in-package (SiP) due to the high demand of miniaturization and dense integration. Shielding methods are generally employed to protect SiP from EMI, through assessing the key performance index, i.e., shielding effectiveness (SE). In this article, the SE of a SiP is evaluated by using near-field scanning method. The SEs derived by using maximum near-field values and average near-field values are comparatively analyzed. The difference in near-field patterns of the unshielded and shielded SiPs may incur overestimation of the SE by using maximum field values. Both simulation and measurement results manifest that the gap between SiP and printed circuit board (PCB) will significantly change the radiation pattern of a shielded SiP, and thus has a great impact on the SE, especially when the frequency is above 1 GHz. However, a good correlation is found between the SE based on average near-field and the SE derived from the radiated power. This study has revealed the near-field shielding properties of SiP, which is helpful for building and analyzing the correlation among the SEs measured by different methods, including the near-field scanning, transverse electromagnetic (TEM) cell and reverberation chamber.

Численное моделирование наземного распределения напряженности поля бортового низкочастотного передатчика в ионосфере.

Projects of active experiments in the ionosphere and the magnetosphere of the Earth and planets often include powerful low-frequency transmitters installed on-board of a spacecraft. Such sources are very effective, but their radiation is extremely heterogeneous in space because of the anisotropy of the ionospheric plasma due to the presence of the magnetic field of the Earth. This paper is devoted to numerical modeling of a distribution of the wave field strength near the Earth surface. The work examines a specific active wave experiment with a 20 m loop as a transmitting antenna. The satellite is assumed to orbit with an inclination of 82.5 degrees at an average altitude of 1000 km. All calculations are performed in linear approximation using the cold magneto-active plasma model. The computation model uses ray approximation everywhere except for the highly heterogeneous lower ionosphere, where a full wave equations set is applied. It is shown that the maximum magnetic field value is decreased with increasing of the geomagnetic latitude value and the strength range is 1… 2 nA/m for frequency 10 kHz and loop current 100 A. The magnitude of the vertical component of the electric field lies in the range of 0.4 ... 0.8 μV/m. An average Doppler frequency shift is equal to ~0.4 Hz. A comparison is made between the data of the numerical experiment and the results of simple estimations of the values of the magnetic field strength at the maximum of the ground distribution.

Field reduction simulation based on covered conductors design in medium voltage lines

This research presents a numerical study of the economic design of the medium voltage overhead transmission lines based on the maximum reduction in the electric field in the studied domain using the Finite Element method (FEM). Seven different cases of bare and covered conductors with cross-link polyethylene (XLPE) material are used to investigate the field reduction. Three bare conductors – three covered conductors – and one bear with two covered conductors - one covered conductor with two bare are simulated using the concept of FEM considering the distance between the conductors to be 1 and 0.5 ​m. The ratio of the field reduction is comparing the maximum field value in the domain resulting from each case with the fundamental one. The fundamental is the case of three bare conductor. The results showed that the maximum value of the field reduction is existing in case of one bare and two covered conductors with distance 0.5 ​m. The field reduction in this case reaches 0.9646 of the fundamental value. The electric field is simulated by the concept of FEM using COMSOL Multiphysics with LiveLink™ for SOLIDWORKS system design.

The effect of heat treatment on the FeCo phase in Tb-Fe-Co thin films

Investigation of the magnetic behavior of nanostructured Tb-Fe-Co thin films before and after heat treatment below and above Fe-Co phase crystallization temperature has explored by electron microscopy (SEM), X-ray diffraction (XRD), temperature-dependent resistivity, magnetization (MOKE), magneto-resistivity, and Hall resistivity measurements. The thin films are composed of fine crystallites (from 10 to 75 nm) after heat treatment around the FeCo phase crystallization temperature obtained from XRD and SEM measurements. The nanostructured thin films show the unique perpendicular magnetic properties in the out-of-plane direction around the room temperature. The maximum squareness ratio value of as-deposited thin film with 10 nm crystallite size is 0.98, and the maximum coercive field value of 400∘C thin film with 60 nm crystallite size is 3897 Oe. Our findings offer a different perspective for synthesizing the nanostructured Tb-Fe-Co thin films for promising applications in the magnetic sensor technologies.

Robust Distributed Estimation of the Maximum of a Field

This paper deals with the problem of robust distributed sampling of a field in the presence of unreliable sensors/agents. An algorithm is devised to estimate the maximum of the field over the domain spanned by the agents where some of the sensors can sample wrong measurements over a finite time, higher than the maximum field value. Necessary and sufficient conditions are given to guarantee convergence to the maximum field value and a robust and redundant algorithm design is presented by combining an exhaustive ergodic search with multiagent consensus protocols. In this original setup, the presence of unilateral interactions and exogenous signals is considered, the latter representing the measures sampled by the agents. Representative examples are presented to illustrate the effectiveness of the proposed framework and conditions.

Magnetic phase tuning of diluted Fe-doped CuO nanoparticles through annealing temperature as characterized by first-order reversal curve analysis

Abstract Diluted magnetic semiconductors (DMSs) exhibit room temperature ferromagnetic behavior and have recently been used in a broad range of applications including spintronic devices. Here, we present a simple co-precipitation method to synthesize pure CuO and diluted Cu1−xFexO (x = 0.05 and 0.1) nanoparticles (NPs) with different annealing temperatures (Ta) ranging between 500 °C and 900 °C, achieving ferromagnetic DMSs with a monoclinic structure at room temperature. The mean NP size, evaluated using a field-emission scanning electron microscope, was found to increase with increasing Ta. A red shift was observed in UV–visible spectra and indicated the successful substitution of Fe ions in the CuO NPs, confirming the absence of impurity phases in the resulting structures. Investigating magnetic properties by hysteresis loop measurements, maximum saturation magnetization and coercive field values were obtained to be 4.8 emu/g and 325 Oe, respectively, for 10% Fe-doped CuO NPs at Ta = 900 °C. First-order reversal curve analysis was used to study detailed magnetic characteristics of the NPs. While a soft magnetic phase with superparamagnetic fractions ranging from approximately 41% to 53% dominated magnetic behavior at Ta = 700 °C, a strong hard phase determined the average magnetic properties of Fe-doped CuO NPs with nanocrystalline structure at Ta = 900 °C.

Surface Coil with an Inductively Coupled Wireless Surface and Volume Coil for Improving the Magnetic Field Sensitivity at 400-MHz MRI

This work presents the use of combinations between a wireless radio-frequency surface coil and a wireless 16-leg birdcage coil that are inductively coupled to improve the magnetic field sensitivity and uniformity. A single surface loop coil operating as transmission/reception (Tx/Rx) coil was designed for mouse head imaging at a magnetic field strength of 9.4-T. Numerical analyses using finite-difference time-domain were performed to compute the sensitivity and homogeneity of magnetic and electric flux density fields for each of the coil combinations. Maximum field values and standard deviation were used as statistical parameters to compare the sensitivity and homogeneity of the fields produced by the Tx/Rx surface coil for each case, when the wireless inductively coupled coils were used. The electromagnetic analyses were applied to a cylindrical oil-based phantom and a mouse model. The proposed combinations of the surface coil with the inductively coupled wireless surface and wireless volume coils offer an enhanced magnetic-flux sensitivity and RF excitation field distribution at 9.4-T. The modifications to the surface coil geometry by adding the inductively coupled radio-frequency coil combinations could be applied to the generally used transmit/receive surface coils and extended to parallel radio-frequency transmission array at ultra-high-field magnetic resonance imaging.

Finite Element Analysis of Maximum Electric Field for Air Breakdown under Various Electrode Configurations

<p>This paper describes the electric field behavior of air breakdown under various electrode configurations and gap length. By using COMSOL Multiphysics, a Finite Element Method (FEM) software, the values of maximum electric field can be determined based on the air breakdown voltage data obtained from the experiment under AC stress. The results show that R0.5-plane configuration provides a very high electric field upon breakdown, compared to R6-plane, R48-plane and plane-plane configurations. In addition, the comparison between the analytical and simulation results of maximum electrical field gives almost identical results for each electrode configuration except for R6-plane.</p>

English

Corona onset voltage is one of the most important factors that determine the charging toxic particle in an industrial application. Electrostatic precipitators (ESP) remove the suspended particle with a gas inlet. This paper developed Peek's formula to estimate the maximum electric field near the discharge wire in corona discharge models, the values of maximum electric field and corona onset voltage near the discharge wires have been calculated for different values of pressure and temperature for confined gas in a region between the electrodes in ESP. The model uses finite difference method (FDM) to solve governing equations (Poisson’s and current continuity equations) simultaneously. Computer simulation method uses FORTRAN program to estimate potential distribution and maximum electric field intensity. The calculated corona onset voltage values are compared with the calculated values of different models.    Key words: Corona onset voltage, corona discharge, electric field distribution, electrostatic precipitators.

Location of Shielding Material and Size of Radiation Field in Radiographic Procedures for Neurocranium Affect Entrance Surface Dose in Major Organs

Objectives: The purpose of this study was to determine the effect of the location of cylinder thyroid shielding materials and the size of radiation field in radiographic procedures for neurocranium on entrance surface dose in major organs.Methods/Statistical Analysis: Two SID (100cm and 70cm) of DR system with exposure conditions at 76 kVp and 25 mAs were used. ESD was measured by using OSLD and ART phantom with maximum radiation field of and 8 inch x 10 inch.Measurement points included the left, the right, the anterior and the posterior of the thyroid area using thyroid shielding. Findings: The ESD values of maximum field at the back shield were lower (SID 100cm and 70cm: 85.9% and 63.4% lower,respectively) than those at the front shield. For 8 inch x 10 inch field, the ESD values were lower by 64% and 54.3% for SID 100 cm and 70 cm, respectively. The ESD values when the cylinder device was used were lower by 67% and 27.6% for SID 100 cm and 70 cm, respectively. In addition, for SID 100 cm, the orbit ESD with maximum field was the highest (200.62uSV). Orbit ESD value was lower by 54.4% (91.57 uSV) for a field of 8 inch x 10 inch. It was also lower by 57% (86.28 uSV) when cylinder device was used. For SID of 70 cm, orbit ESD value with the maximum field was the highest (262.18 uSV).It was lower by 28% (188.87 uSV) than that for a field of 8 inch x 10 inch. It was also lower by 64% (94.59 uSV) when the cylinder was used. Improvements/Applications: Using cylinder device and back shielding for the thyroid could reduce ESD in sensitivity organs of patients.

Cathode fall measurement in a dielectric barrier discharge in helium

A method based on the “zero-length voltage” extrapolation is proposed to measure cathode fall in a dielectric barrier discharge. Starting, stable, and discharge-maintaining voltages were measured to obtain the extrapolation zero-length voltage. Under our experimental conditions, the “zero-length voltage” gave a cathode fall of about 185 V. Based on the known thickness of the cathode fall region, the spatial distribution of the electric field strength in dielectric barrier discharge in atmospheric helium is determined. The strong cathode fall with a maximum field value of approximately 9.25 kV/cm was typical for the glow mode of the discharge.

Microstructure and trapped field of Al-doped GdBCO–Ag bulk superconductors

The effect of Gd2Ba6Al4O15 powder addition on microstructure, field trapping capability and critical transition temperature, Tc, of GdBCO–Ag superconductors grown in air is reported. Single-grain GdBCO–Ag bulk superconductors with different amounts of Gd2Ba6Al4O15 powder were fabricated by the top seeded melt growth process. Addition of 0.3 wt% Gd2Ba6Al4O15 powder increased the maximum trapped field value, BZmax. Microstructure analysis confirmed that, up to 1.0 wt% addition of this powder, Al-based phase is not formed and Al is supposed to substitute Cu in the GdBa2Cu3O7−δ matrix. Addition of 2.0 wt% Gd2Ba6Al4O15 powder leads to formation of Pt, Al-based phase, which indicates that the solubility limit of Al in the studied system was exceeded. The critical transition temperature, Tc, decreases monotonically with increasing Gd2Ba6Al4O15 powder addition.

Comparison of dc and superconducting rf photoemission guns for high brightness high average current beam production

A comparison of the two most prominent electron sources of high average current high brightness electron beams, DC and superconducting RF photoemission guns, is carried out using a large-scale multivariate genetic optimizer interfaced with space charge simulation codes. The gun geometry for each case is varied concurrently with laser pulse shape and parameters of the downstream beamline elements of the photoinjector to obtain minimum emittance as a function of bunch charge. Realistic constraints are imposed on maximum field values for the two gun types. The SRF and DC gun emittances and beam envelopes are compared for various values of photocathode thermal emittance. The performance of the two systems is found to be largely comparable provided low intrinsic emittance photocathodes can be employed.

The peak effect in bulk Y–Ba–Cu–O superconductor withCeO2 doping by the infiltration growth method

In this study, large single grain Y–Ba–Cu–O (YBCO) superconductors withCeO2 addition were fabricated by the infiltration and growth (IG) technique. It is noticeable that theCeO2 doped IG-YBCO sample showed a superior critical current densityJc(H, T) with a peak effect. TheJc (3 T, 65 K) of theIG-YBCO sample with CeO2 addition reached 105 A cm − 2, which was two times higher than that of theCeO2 dopedtop-seeded melt texture (TSMT)-YBCO sample. Microstructure analysis indicated that the concentration ofSm in the CeO2 doped IG-YBCO sample was 0.2 mol%. The Sm which dissolved from the SmBCO seeddiffused into the bulk to form compositional fluctuations of (Y, Sm)BCO and wascorrelated to the effective pinning in high field regions (or peak effect) to improve theJc(H, T) in high fields. In addition, the maximum trapped field value of 0.23 T and trapped field profile of theCeO2 doped sample grown by IG are larger than that of 0.13 T grown by TSMT using the samediameter of precursor pellets.