Magnetic Current Distribution Research Articles

Enhanced Joule heat release at surface irregularities

The heat release that occurs in a cylindrical conductor carrying an alternating current is analyzed for the cases when the conductor has axisymmetric surface irregularities of one of three types: local bumps, local pits, and sequences of alternating bumps and pits (wavy irregularities). The magnetic field and current density distributions over the conductor cross section have been simulated. The simulation parameters were chosen to match the conditions of experiments on the generation of strong magnetic fields. However, due to the analysis of the initial heating stage, the problem is solved neglecting the temperature dependence of the resistivity of the material. A multiple increase in heat release power in the vicinity of a surface irregularity has been revealed for the three types of irregularities.

A Compact, Portable Device for Microscopic Magnetic Imaging Based on Diamond Quantum Sensors

AbstractMagnetic imaging based on ensembles of diamond nitrogen‐vacancy quantum sensors has emerged as a useful technique for the spatial characterization of magnetic materials and current distributions. However, demonstrations have so far been restricted to laboratory‐based experiments using relatively bulky apparatus and requiring manual handling of the diamond sensing element, hampering broader adoption of the technique. Here a simple, compact device that can be deployed outside a laboratory environment and enables robust, simplified operation is presented. It relies on a specially designed sensor head that directly integrates the diamond sensor while incorporating a microwave antenna and all necessary optical components. This integrated sensor head is complemented by a small control unit and a laptop computer that displays the resulting magnetic image. The device is tested by imaging a magnetic sample, demonstrating a spatial resolution of 4 µm over a field of view exceeding 1 mm, and a best sensitivity of 45 µT per (5 µm)2 pixel. The portable magnetic imaging instrument may find use in situations where taking the sample to be measured to a specialist lab is impractical or undesirable.

Numerical simulation of bulk superconductor during pulsed field magnetization based on multi-field coupled analysis

High-temperature bulk superconductors are widely used in various superconducting devices due to their high critical current density, which enables them to trap high magnetic fields. However, the critical current density of bulk superconductors is influenced by magnetic field, temperature and stress, and both increase of stress and temperature can lead to a decrease in the critical current density. And the influence of magnetic field, current, stress are interactional. In this paper, the multi-field coupled analysis is employed to investigate the electromagnetic and mechanical behavior on bulk superconductor during pulsed field magnetization. The simulation results were compared with the present experimental results. The results showed a good agreement between the simulation and experimental results, further validating the reliability of the numerical simulation method. The magnetic field, current, temperature, and stress distribution and variation within the bulk sample during the pulsed magnetization process were calculated and analyzed. Additionally, the influence of the central crack and edge crack in the bulk superconductor was investigated. The results indicate that the region near the crack experiences a variation in current flow direction, resulting in local temperature rise and significant electromagnetic forces. The tip of the crack exhibits stress concentration, leading to a decrease in critical current density. Bulk supercondutor with edge crack case exhibits greater stress concentration compared to those with central crack case. The impact of crack length on maximum stress was analyzed, revealing that as the crack length increases, both the maximum hoop stress and radial stress within the bulk sample rise.

Optimization of double-wire X-pinch using prepulse current

The radiation properties including size, intensity, and pulse width of the double-wire X-pinch were optimized using prepulse current. The optimization mechanism was investigated using optical diagnostics. The X-pinch driven by a current with a peak intensity of ∼250 kA and a rise rate of 0.95 kA/ns was difficult to produce strong radiation. The application of prepulse effectively enhances the current rise rate and intensity of the radiation source. The radiation source also exhibited reduced spatial dimensions and radiation duration, thereby improving spatial and temporal resolution while used in x-ray projection shadow radiography. The magnetic field and current distribution were measured using Faraday rotation. During the early stage, the current predominantly flows in the corona plasma at a larger radius generated by the prepulse current, consequently reducing the load inductance. As the time delay between the main and prepulse current increased, the intensity of the radiation source further increased. This study provides an approach for controlling radiation sources and enables different applications of X-pinches with adjustable prepulse current.

An electromagnetic-thermal-mechanical analysis model for high temperature superconducting magnets

High temperature superconducting magnets are the core component of superconducting power devices, and their stability is the key factor that restricts the safe operation of superconducting power devices. In order to accurately and effectively evaluate the stability of superconducting magnets during operation, an electromagnetic-thermal-mechanical numerical simulation method for high temperature superconducting magnets is studied in this paper. Based on the model, the 150 kJ SMES magnet as case is studied, the magnetic field and current density distribution are solved during its operation, and its temperature rise, AC loss and stress analysis of the magnet are achieved. In addition, this work further analyses the critical current degradation of superconducting tapes in the 150 kJ HTS magnet under multi-field coupling, the dangerous region in operation is obtained and suggestions are put forward to avoid quench. The electromagnetic-thermal-mechanical model may provide an appropriate stability assessment with rapid and real-time calculations for high temperature superconducting magnets.

Radiation pattern reshaping designs for slot antenna based on the third-order mode

Based on radiation pattern reshaping technology, two slot antennas (SAs) operating on the third-order mode are designed. Both of them obtain high-gain characteristic and stable bidirectional radiation. The radiation characteristic of the SA three-order mode is analyzed. Then, the influence of the finite ground edge’s diffraction on radiation pattern of SA is considered. By using the finite ground with a suitable size, the main lobe in radiation direction can be effectively regulated. On this basis, according to the equivalent magnetic current distribution in slot, this paper proposes two radiation pattern reshaping design schemes (a. Folding rectangular slot; b. Loading C-shaped slots). Both design schemes can suppress the side lobes and regulate the main lobe in the radiation pattern. Two proposed SAs can achieve stable bidirectional radiation and obtain high-gain response. Finally, two SAs are fabricated and measured. The measured results show that two SAs achieve bidirectional radiation. The peak gains of two SAs are 6.88 dBi and 7.51 dBi, respectively.

Experimental study of the magnetic field and current distribution in double-wire Z-pinch

This paper investigates the two-dimensional magnetic field structure of a double-wire Z-pinch during the ablation stage using Faraday rotation diagnosis. The experimental results intuitively display the two-dimensional magnetic field distribution and reveal the process of the global magnetic field spreading towards the load axis as the ablation progresses. The radial current component is determined based on the axial non-uniformity of the magnetic field structure, which further confirms the two-dimensional current path within the ablation stream. Additionally, the significantly enhanced magnetic field intensity and opposing magnetic field direction on both sides of the precursor plasma column indicate the existence of magnetic reconnection and the current layer within the precursor. This process also explicitly reveals the current transfer process from the wire to the precursor column. Through this structured investigation, we facilitate experimental validation of existing simulation outcomes and offer a more intuitive demonstration.

Scanning SQUID-on-tip microscope in a top-loading cryogen-free dilution refrigerator.

The scanning superconducting quantum interference device (SQUID) fabricated on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile tool for the nanoscale imaging of magnetic, thermal, and transport properties of microscopic devices of quantum materials. We present the design and performance of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight cell mounted at the bottom of the probe and is suspended by springs to suppress vibrations caused by the pulse tube cryocooler. Two capillaries allow for the in situ control of helium exchange gas pressure in the cell that is required for thermal imaging. A nanoscale heater is used to create local temperature gradients in the sample, which enables quantitative characterization of relative vibrations between the tip and the sample. The spectrum of the vibrations shows distinct resonant peaks with a maximal power density of about 27 nm/Hz1/2 in the in-plane direction. The performance of the SQUID-on-tip microscope is demonstrated by magnetic imaging of the MnBi2Te4 magnetic topological insulator, magnetization and current distribution imaging in a SrRuO3 ferromagnetic oxide thin film, and thermal imaging of dissipation in graphene.

Optically transparent triple and dual band terahertz metamaterial absorber based on indium tin oxide and PET substrate

A simple optically transparent polarization and angular insensitive triple and dual band Terahertz (THz) Metamaterial Absorber (MMA) is designed and analysed in this paper. The MMA consists of three layers, dielectric layer is placed in-between the ground plane and top metallic patch. Without using stacked layers, doping and multiple resonators the absorber is designed here. The metal and substrate used here is Indium Tin Oxide (ITO) and Polyethylene Terephthalate (PET). The ITO with PET combination produces the optical transparency. The important thing in this work is the same design produces the triple and dual band operation while changing the top patch radius value. The absorber produces the triple band operation when the radius of the top circle is 65 μm and it produces the dual band when the radius of the top circle is 55 μm. It covers the frequency ranges from 0.3 THz to 1.4 THz. The designed structure is analysed by electric field, magnetic field distribution and surface current distributions. This structure is polarization and angle independent up to 90 degrees. From the parametric analysis, we found this absorber will work in both triple and dual band operation. So, this bifunctional working absorber will find more applications in optically transparent devices, sensing and imaging.

Observation of filaments in mega-ampere dense plasma focus within pure deuterium by means of simultaneous schlieren and interferometry diagnostics

Fifteen-frames interferometric diagnostics at the PF-1000 facility was enhanced by adding four frames of the schlieren diagnostics and by splitting of four channels in the optical delay line. This setup enabled the visualization of gradients in the plasma density perpendicular to the direction of the diagnostic laser beam, and their relationship with larger structures visualized by using laser interferometry. The schlieren pictures showed filamentary structures of submillimeter 200–300 μm diameter in shots performed with pure deuterium filling. Filaments were observed in a thin (millimeter-thick) lateral-boundary layer, in lobules, and in internal fast transforming regions of the dense plasma column. Their high-density gradients and location in the regions of recorded (or inferred) currents indicated local concentrations of the magnetic field and current distribution. Millimeter- and submillimeter-size sources of fast charged particles, which were identified in the recorded ion pinhole pictures, have been conjectured to be a manifestation of high local concentrations of the magnetic energy.

IFFERENTIAL TRANSFORMER SENSORS WITH SIMPLE STRUCTURE OF MAGNETIC CIRCUITS METHODS FOR INCREASING THE DISTRIBUTION LINEARITY OF MAGNETIC CURRENTS

In the article differential transformer sensors measuring shifts the magnetic capacitance of the air gap between two long ferromagnetic cores, which allows the linear distribution of magnetic currents in ordinary structural scattered parameter differential magnetic circuits along the length of the chain, the expressions of the change of the magnetic circuit length of the compare values of the magnetic driving forces located longitudinal. Based on the analysis of differential magnetic chains with the proposed simple structure according to these analytical expressions, it was determined that the construction of a magnetic chain is technologically relatively simple and does not require an excess of non-ferrous metal (copper) due to the fact that the air gap between two long ferromagnetic cores changes the compare value of the magnetic.

A Standing-Wave Microstrip Leaky-Wave Antenna on EH₁/EH₃ Modes With Enhanced Broadside Gain

A conventional microstrip EH1-mode bidirectional leaky-wave antenna (LWA) usually works as a traveling wave antenna, and its typical maximum broadside gain is commonly obtained when the phase and leakage constants of the used EH1-mode are exactly equal to each other. In this article, it is, for the first time, revealed that this bidirectional LWA can alternatively operate under standing-wave states when its terminations may be open-circuited. Under some of these states, the open-terminated LWA attains higher efficiency due to the extremely small leakage constant. However, it is unfortunately illustrated that split beams are generated at these concerned states owing to the inherent opposite directions of equivalent magnetic current distributions along the two edges of the strip conductor. In order to transform the unwanted split beams into a single high-gain beam at the broadside, a novel standing-wave bidirectional LWA is presented under the operation of the hybrid EH1 and EH3 propagating modes. By analyzing the transversal electric fields of EH1- and EH3-modes, respectively, it is demonstrated that their leaky electric fields can be crucially made in an antiphase manner. Next, the EH3-mode electric field is employed to periodically replace the original EH1-mode counterpart, so as to reshape the electric fields along the two parallel radiating edges toward a desired in- phase pattern. In such a way, the appealing high-gain beam can be successfully achieved. As an example, such a hybrid-mode standing-wave bidirectional LWA is designed, simulated, and tested. The measured and simulated far-field radiation performances show excellent agreement, and they both powerfully indicate that our reported antenna has enhanced its radiation gain at the broadside compared to the conventional EH1-mode traveling-wave bidirectional LWA

Development of Self-Discharge Point Visualization Technique inside Lithium-Ion Battery

With the rapid spread of electric vehicles and hybrid vehicles in recent years, the energy density of lithium-ion batteries, which are the power sources of them, tends to increase.This means that the risk of ignition is further increased as represented by some fire accident case of an EV vehicle that had taken long time to extinguish, and thus eventually makes the requirement of safety management in the battery manufacturing process be expected stricter.To prevent ignition due to internal short circuit of battery, and eliminate a short-life battery product, we have been developing a technology to non-destructively visualize the self-discharged part inside the storage battery. In this technology, on the first, electric current is applied to the battery from external power source, and the leakage magnetic field that generated due to the internal electric current in the battery is sensed on outside of the battery. Next, the electric current density distribution inside the battery can be reconstructed and visualized three-dimensionally by using the spatial distribution of the measured magnetic field as the boundary condition and solving the inverse problem analytically.To measure leakage magnetic field with high sensitivity, it is necessary to take steps against disturbances as like DC magnetic field derived from magnetism or magnetic materials (often Ni is used for the collector foil), and AC magnetic fields generated from external circuits. In this method, two steps are used in combination for detection sensitivity of the pico-tesla order;(1) An AC current is applied to the battery, and the AC magnetic field generated in synchronization is phase-detected.(2) Install a small coil near the sensor and generate a DC cancel magnetic field by feedback control.By this method, it is possible to detect only the AC magnetic field corresponding to the applied current with high sensitivity in the linear operating region of the magnetic sensor. In actual detection of the leakage magnetic field, a DC voltage that balances with the output voltage of the battery is applied to the AC output of the AC current source connected to the battery so that the SOC of the storage battery is kept constant voltage. In addition to the above, the frequency of the AC output is usually set to 10 Hz or less to avoid the shielding effects of electrodes and the metallic package of the battery.By these steps and scanning two-dimensional of magnetic sensors or using a sensor array in which magnetic sensors are arranged two-dimensionally, the spatial distribution of the two-dimensional magnetic field outside the storage battery can be obtained. Since the sensor detects only one direction component of magnetic field, changing the direction of the sensor by 90 ° is needed.On data processing, some realistic structural assumptions are required to solve the inverse problem.(1) Defining that the plane parallel to the storage battery electrode plane is the XY plane, the Z component of the magnetic field vector is zero around the battery, and only X component and Y component remains as magnetic field vector components generated from internal current of the battery.(2) The thickness of the battery is sufficiently smaller than the size of the battery in the plane direction, that is, the three-dimensional current in the battery is confined in the thin two-dimensional plane.In the first step of the reconstruction, under the fact of (1), Laplace's equation is analytically solved in the "free space from the measurement surface to just above the electrode surface in the battery, without a magnetic source", and derive the two-dimensional magnetic field distribution directly above the electrode surface. In the next step, it is possible to obtain a three-dimensional current distribution inside the battery by analytically solving the Poisson-type equation and the electric current continuity equation under the realistic structural assumption of (2) with first calculation result as the boundary condition.In the presentation, we will introduce in detail the experiment and data processing for identifying the self-discharge point with this technology, including examples of visualizing the magnetic field distribution and current density distribution inside a battery after aging test.

Simulation of the Electro-Superconducting System Based on the H Equation

In order to reduce the levitation energy consumption and increase the levitation air gap, a simulation study of the electrochemistry superconducting magnetic levitation system based on the H equation is proposed. Through finite element simulation, the magnetic field distribution, current distribution, force, and other characteristics of the magnetic suspension system in the superconducting gravimeter are obtained; the relationship between the force of the superconducting ball in the magnetic field and the height of the suspension body and the current of the suspension coil is analyzed; and the penetration rate, the magnetic gradient, penetration depth, and maximum magnetic induction intensity of the superconducting spherical surface of the single-coil electrochemistry superconducting magnetic levitation system are obtained by simulation calculation. Simulation results show that, at 1 s, we start to use 0.2 s, 0.4 s, 0.6 s, and 0.8 s time, respectively, to pass current into the floating coil until it reaches 4.4 A. The magnetic gradient of the electrochemistry superconducting magnetic levitation system using a single coil is too large to meet the requirements of gravity measurement, the penetration depth is much smaller than the thickness of the superconducting sphere, and the maximum magnetic field on the surface of the superconducting sphere is much smaller than the critical magnetic field value of the superconducting material, and no loss will occur. The critical magnetic field value of the superconducting sphere is much smaller than that of the superconducting sphere. The critical magnetic field value of the material will not quench, which verifies that the H equation can simulate the superconducting magnetic levitation system well and has a high simulation accuracy and efficiency.

Pulsed Electromagnetic Field Transmission through a Small Rectangular Aperture: A Solution Based on the Cagniard–DeHoop Method of Moments

Pulsed electromagnetic (EM) field transmission through a relatively small rectangular aperture is analyzed with the aid of the Cagniard–deHoop method of moments (CdH-MoM). The classic EM scattering problem is formulated using the EM reciprocity theorem of the time-convolution type. The resulting TD reciprocity relation is then, under the assumption of piecewise-linear, space–time magnetic-current distribution over the aperture, cast analytically into the form of discrete time-convolution equations. The latter equations are subsequently solved via a stable marching-on-in-time scheme. Illustrative examples are presented and validated using a 3D numerical EM tool.

Realization of tunable dual-type quasi-bound states in the continuum based on a Dirac semimetal metasurface

In this study, two types of tunable quasi-bound states in the continuum (BIC) based on Dirac semimetal metamaterial (DSM) in the terahertz (THz) band are proposed in the same metasurface. The symmetry-protected BICs are achieved by altering the structural symmetry. The accidental BICs are realized by adjusting the structural parameters, and the quality factor (Q factor) of the corresponding quasi-BICs can be as high as 175. To better understand the excitation mechanism of the quasi-BIC, we investigated the magnetic field distribution and current distribution of the BIC and quasi-BIC, respectively. The results showed that the accidental BIC and the symmetry-protected BIC have a common resonance mode, and the two LC resonance modes are coupled with each other, which causes a strong resonance. The dynamic modulation of the transmission amplitude is achieved by changing the Fermi energy of the DSM at a nearly constant resonant frequency, and the difference in amplitude modulation is about 46%. Based on the idea of amplitude modulation, the design of the Dirac semimetal film (DSF) metasurface array for stereoscopic graphic display is realized.

Parametric Modeling and Characterization of Leakage-Integrated Planar Transformer for CLLC DC–DC Converter

With an objective to accurately characterize the leakage inductances and winding resistances of a high-frequency planar transformer (HFPT) for a 500 kHz resonant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> converter, this article elucidates the correlation between various specifications involved in hardware fabrication of various winding configurations and their structural dependence on the resultant parameters. A precise analytical model is developed using 3-D finite element analysis (FEA) to synthesize the effective magnetic field and current density distribution in fabricated winding structures. Furthermore, a thorough analysis to study the interdependence of the resultant parameters on specifications such as printed circuit board (PCB) thickness and its fabrication layout, air gaps, and conductor thickness is presented for various winding configurations, thus elucidating various design-based tradeoffs. Also, frequency dependence of the obtained parameters is described which validates the optimal selection of winding configuration based on the effective gain magnitude for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> converter topology. Detailed comparison between the developed analytical model with simulation model developed in Maxwell3-D and fabricated winding structures is presented, and the results validate the model accuracy, portraying an average mismatch of 3.8% and 6.2%, respectively.

Magnetic Field Modeling and Current Distribution of Magnetic-Driven Laser Steering for Endoscopic Microsurgery

Magnetic-driven laser scanner for laser steering and ablation has demonstrated its clinical significance in transoral microsurgery. However, the limited steering range restricts its usability of the magnetic laser scanner in the clinical setting. To this end, this paper improves the design of the magnetic-driven scanner and expands its steering range to 11 mm &#x00D7; 11 mm. Compatible with the optimized laser scanner, an improved magnetic field model is established by taking both the length and thickness of the coil into consideration, and the numerical solution of the magnetic field model is derived via a Gauss-Legendre quadrature. After calibration, the proposed model appears to be consistent with the real magnetic field of the coil which incorporates a magnetic core inside. The RMSE of magnetic field model within 10 mm &#x00D7; 10 mm different plane are 1.3404 Gs, 4.1706 Gs and 0.4236 Gs, respectively. In addition, the current equation is derived from the proposed model to estimate the associated current while the desired magnetic field needs to be yielded. In order to avoid coil overload, this paper enforces the constraint of balancing current distribution to the current equation, and defines the effective workspace to intuitively adjust the coefficients of the current equation. The results demonstrate that when the coefficient a_<i>x</i> = a_<i>y</i> = 1, the corresponding effective workspace is optimal, reflecting that the laser scanner could yield the desired magnetic field within the maximum steering range while ensuring safety.

Rapid Analytical Calculation of Magnetic Field and Critical Current Distributions in HTS Magnets

For the design of superconducting magnets, the magnetic field and critical current distributions are usually calculated based on finite element software such as COMSOL, ANSYS, etc. These software are necessary for accurate structure modeling and field calculation, but they occupy large memory space and comsume long simulation time. Furthermore, they are not easy to use. To achieve an easy-to-implement solution for rapid magnet field and critical current calculations, this paper investigates three types of analytical calculating methods, and builds an autonomously-operated calculating application program (APP) for the uses in various superconducting magnets.

Numerical Simulation of Multispecies Vacuum Arc Subjected to Actual Spatial Magnetic Fields

A three-dimensional (3-D) model for multispecies vacuum arc considering ionization and recombination process has been built in this article. With the model, the arc behaviors and species characteristics subjected to actual spatial magnetic fields of cup-shaped axial magnetic field (AMF) contact and transverse magnetic field-axial magnetic field (TMF-AMF) contact are investigated and compared. Furthermore, the validity of the model is verified by comparing with the experiments. Simulation results show that contact structures affect the species distributions of the arc by changing magnetic field and current density distributions. More triple charged ions are generated through ionization under higher electron temperature so that the triple charged ions gather where current constricts. The heat flux density is large in the current contraction region, where the contribution from triple charged ions is large as well. Spatial magnetic field distribution affects the Lorentz force acting on ion components. The force distribution is relatively uniform and the species are subject to inward force on the arc edge under cup-shaped AMF contact. For TMF-AMF contact, the double charged ions are subject to the force pointing to the TMF contact arms, whereas the triple charged ions are subject to the force pointing to the arc center. In addition, the consideration of arc species can improve the accuracy of the simulation results of the heat flux distribution, leading to a good agreement of the erosion condition between experiments and simulation.