Magnetic Intensity Research Articles

A correction method of magnetic gradient tensor system to improve magnet localization accuracy

The magnetic gradient tensor systems using vector magnetic sensors are easily affected by single sensor error and sensor array misalignment, significantly affecting target localization accuracy. To address this problem, based on the differential measurement theory of magnetic gradient tensor, a vector sensor error model was established, and the single sensor errors were corrected using the total least square (TLS) ellipsoid fitting method. Besides, a misalignment error correction model for the sensor is obtained by constructing a rotation matrix for the magnetic sensor's three-axis orthogonal coordinate system transformation, and the tensor system can be aligned by performing the TLS estimation of the rotation angle. After calibration, the experimental results show that the outputs of each sensor have high coincidence and coaxiality. The root mean square error (RMSE) of the total magnetic intensity (TMI) is reduced to within 100 nT, and the RMSE of the tensor component is reduced to within 85 nT/m. Within a range of 5 m, the magnetic target positioning error is reduced to less than 25.1 cm. This technology can improve the measurement accuracy of the magnetic gradient tensor system with high stability and reliability.

The Studying of Magnetic Anomalies Due to Shallow Underground Targets and the Environmental Applications.

The magnetic method of investigation is a well-known and dependable technique for detecting underground ferro-materials. However, the application of the magnetic method to identify the exact position of underground targets such as buried explosive devices (BED), illegally buried waste (IBW), metallic storage tanks, utility pipes, and communication cables is quite challenging in both civil and environmental engineering. This article presents the results of the investigation performed at a 55m by 55m area within the Ahmadu Bello University Geophysical Test Site (ABUGTS) to study the signals generated by similar buried targets to simulate situations encountered in environmental engineering. The total magnetic intensity (TMI) of the site without buried targets was obtained to identify the possible existing underground materials or faults that could generate false geophysical data. The magnetic susceptibility of the buried targets was determined in the laboratory before the burial to validate the field results. The influence of the buried materials over the magnetic signature of the site was examined, showing the TMI values vary between 34966 nT and 44510 nT before burial and 351607 nT to 49795 nT after burial. The Euler deconvolution (ED) and residual maps alongside the signal enhancement maps like analytical signal and first vertical derivative (FVD) were employed to study the magnetic anomalies due to buried targets. The results of the data interpretation confirmed the existence of cluster anomaly source bodies due to buried targets. The ED delineates the depth of the buried targets varying between 0.7m – 3.3m corresponding with the actual depth of burial. The analytical signal map produced a perfect behaviour of the magnetic anomalies to buried targets, capturing all the buried targets buried at the site. However, the shape of the anomaly signal is almost independent of the buried target orientation with a spherical pattern of anomalies. However, the exact size and shape of the buried targets were not achieved. Nevertheless, the FVD and analytical signal maps perform better than the residual and TMI maps due to the substantially smaller magnetic anomalies of the buried targets similar to expected. In addition, stronger magnetic anomaly signals occur maximally around buried larger ferro-materials with precise prediction of the buried target position. The magnetic method is a very powerful, convenient, cheap, and time-saving geophysical tool for investigating underground targets, which is highly applicable in engineering and environmental contexts.

A Multibranch Deep Neural Network for the Superresolution of Solar Magnetograms

The existing superresolution (SR) models for solar magnetograms are mostly borrowed from the SR models for natural images. They are less effective for processing solar magnetograms with a very large dynamic range and very rich image features. In this paper, a multibranch superresolution (MBSR) model is specially designed for solar magnetograms. First, we split a low-resolution magnetogram into a group of overlapping image patches, and classify them into three categories according to magnetic flux intensity, namely simple, medium, and complex. Then, image patches of each category are fed into the corresponding branch of the MBSR network, the lightweight branch for simple image patches and the heavyweight one for complex image patches. The advantage of such a strategy is twofold. On the one hand, active regions are allocated more computational resources to train a heavyweight branch more fully, while quiet regions are allocated fewer computational resources to train a lightweight branch for saving computational resources. On the other hand, a lightweight network with a simple nonlinear function is preferable to simple regions, while a heavyweight one may be underfitting. Additionally, to verify the effectiveness of the proposed model, a magnetic field structure similarity metric is proposed to measure the artifacts of the generated high-resolution (HR) magnetograms. Experimental results show that the proposed MBSR model generates HR magnetograms highly consistent with the HMI ones, and achieves the best performance over five objective metrics, including peak signal-to-noise ratio and structure similarity, etc.

Steel Fiber Orientation Efficiency Factor Model for a Magnetically Treated Cement-Based Composite

In typical steel fiber-reinforced concrete, the fibers are randomly distributed and oriented throughout the matrix, and a magnetic field can effectively align these randomly oriented fibers. To predict the extent to which the steel fibers contained in mortar can be aligned by a magnetic field, an analytical steel fiber orientation efficiency factor model was proposed as a function of the magnetic induction intensity and exposure time. To verify the applicability of the proposed model, experiments were conducted for various magnetic induction intensities and exposure times with normal mortars and mortars in which some or all the sand was replaced with steel slag. The experimental results demonstrate that the proposed model allows predicting the degree of alignment of steel fibers under magnetic fields. However, this model can only be applied to a normal mortar. In the case of mortar containing steel slag, it is confirmed that the steel slag, which is a ferrous material, reduces the magnetic induction intensity, reducing the degree of alignment of steel fibers in the mortar.

Electromagnetic Environment Assessment and Safety Research of Electrified High-Speed Railway Carriages

With the advent of modern, high-speed electrified rail systems, there has been increasing concern about electromagnetic safety in rail carriages. The aim of this study was to assess the electromagnetic safety of passengers on trains by utilizing advanced 3D electromagnetic simulation software. A comprehensive model of the electromagnetic environment experienced by passengers on a CR400AF train, specifically under the influence of catenary radiation, was constructed. We analyzed the magnetic field strength, electric field strength, and current density in the brains of 20 passengers in various positions in the train. The findings revealed that among the 20 passengers analyzed, the maximum and minimum magnetic induction intensity recorded in the brain were 8.41 and 0.01 μT, respectively. The maximum and minimum induced electric field intensities were 1110 and 10 μV/m, respectively. Lastly, the maximum and minimum induced current densities were 1200 and 10 μA/m2, respectively. The results show that when people ride on the CR400AF train, the magnetic induction intensity, induced electric field strength, and induced current density in the brain are below the recommended basic limits of exposure to power frequency electromagnetic fields in the guidelines of the International Committee on Non-Ionizing Radiation Protection. The power frequency magnetic field generated by the catenary can be effectively shielded by the aluminum alloy car body. The final result of this study indicates that the electromagnetic exposure from the contact wire at the level 25 kV does not pose a threat to the health of passengers on the CR400AF train.

Research on transmission characteristics of sleeve type electromagnetic hybrid governor

Aiming at the shortcomings of the traditional permanent magnet governor air gap speed regulation, a sleeve-type electromagnetic hybrid governor is proposed by controlling the current instead of adjusting the air gap, the structural characteristics and working principle of the speed regulation model are introduced, and the electromagnetic torque mathematical expression is derived based on the equivalent magnetic circuit method, and the key parameters affecting the transmission performance of the governor are obtained, and the simulation model of the sleeve electromagnetic hybrid governor is established by using the finite element analysis method to analyze the electromagnetic field change law in the governor under the transient field. The change curve of air gap magnetic inductance intensity under different currents was obtained, and the influence of speed difference under different currents on the output torque was revealed, and finally, an experimental platform was built for testing, and the maximum error of torque simulation and the test was obtained by analyzing the results to verify the accuracy of the simulation method, on this basis, two structural schemes were proposed to improve the amplitude of the torque regulation of the governor by the current, under the structure of scheme 1, the adjustment amplitude of the torque increased from 35% of the original structure to 96%, and the improvement effect was ideal. Its laws and conclusions can provide a reference for the further design and optimization of sleeve electromagnetic hybrid governor.

Coupling effect between magnetic wires and its influence on high gradient magnetic separation performance

High gradient magnetic separation (HGMS) is effective for the separation of weakly magnetic minerals, and this method is achieved through the use of matrix, which is made of huge numbers of rod wires. So that the coupling effect of magnetic field and flow field between wires has a marked effect on the HGMS performance. In the investigation, the coupling effect between magnetic wires and its influence on high gradient magnetic separation performance were theoretically described and simulated using COMSOL Multiphysics. It is found that the magnetic field round a wire would be affected by the neighboring wires, and then a coupling effect of magnetic field between wires was produced, increasing the magnetic induction intensity on the upstream and downstream of wire surface. And the coupling effect of flow field could increase the slurry velocity at the regions of the wire surface with azimuth angles of 0° and 90°, which is beneficial for the selective capture of wire. These simulated results were basically validated with the experimental separation, using an innovative Magnetic Capture Analysis Method. It is found that the wire spacing has significant effect on the coupling effect of magnetic wires, and a critical spacing for wires could achieve an excellent coupling effect, which is beneficial for the improvement of HGMS performance. This investigation contributes to improve HGMS performance in concentrating fine weakly magnetic ores.

A novel hybrid magnetic material based on three-phase saturated core fault current limiter

Installing a three-phase saturated core fault current limiter (TSFCL) is an effective method to limit the increasing short-circuit current in high-voltage alternating current (HVAC) systems. However, the traditional TSFCL uses silicon steels as its working material for the iron core, resulting in poor current-limiting effects, requiring a large DC excitation current, and having a slow response speed. Nanocrystalline alloys have advantages such as a lower saturation point, higher permeability in the unsaturated zone, and a steep B–H curve, making them highly suitable for TSFCL’s applications. However, their poor capability which withstands fault hindered their large-scale commercialization. Therefore, this paper proposes a novel hybrid magnetic material based on TSFCL (HMTFCL), where the materials of the working limbs are replaced by nanocrystalline alloys. Compared to TSFCL, the DC excitation current of HMTFCL decreases by 60.5%. And, the HMTFCL reduces the peak short-circuit current by 23%. Last, the magnetic flux intensity inside the working limb of HMTFCL is reduced to zero more quickly.

Portable Intelligent Electromagnetic Flowmeter Controlled by Magnetic Induction Intensity

In this paper, we propose a portable intrinsically safe, intelligent electromagnetic flowmeter for the application of coal mines and provide a detailed description of its working principle. In terms of hardware circuit design, several important modules, including electromagnetic flow rate sensor, excitation circuit, core control circuit, signal conditioning circuit, and air traffic control detection circuit, were analyzed and designed in sequence. It adopts a high-performance, low-power MCU STM32407ZET6 and high-precision chips, ensuring measurement accuracy and reducing power consumption. The excitation method using low-frequency rectangular waves dynamically adjusts the sampling interval time, further prolonging the battery life. Finally, the performance of the electromagnetic flowmeter was measured, and the experimental data showed that the measured flow rate was basically linear with the output voltage. The relative indication error of the electromagnetic flowmeter was within 0.3%, and the repeatability fluctuated within the range of 0.03%. The flowmeter has good measurement accuracy, which is suitable for long-term use in coal mining environments.

Geomagnetic paleointensity dating of mid-ocean ridge basalts from the neo-volcanic zone of the Central Indian Ridge

Describing the evolution of the neo-volcanic zone in the spreading ridge is essential for understanding the dynamics and environments of abyssal basins. However, the absolute dating of ocean floor basalts is generally difficult. As a characteristic age indicator, absolute intensity of past geomagnetic field (absolute paleointensity, API) is useful to date ocean floor basalts. In this study, we adopted the Tsunakawa–Shaw method to measure APIs of whole-rock seafloor basalts collected from a conical cone on the Central Indian Ridge and performed rock magnetic experiments. We conducted the experiments on a total of 18 specimens (two or three specimens from each of eight lava sites). Six specimens from two lava sites with different morphologies (pillow and sheet), three for each, passed the acceptance criteria. API means at site level are 33.0 ± 1.0 and 35.8 ± 1.7 μT, respectively. The similarity of API site means suggests that they erupted within a short period. These site-level API means are approximately 0.7 to 0.8 times the present geomagnetic intensity of 46.0 μT at the sampling sites. The accepted specimens show higher Curie temperature, lower initial intensity of natural remanent magnetization, higher ratio of saturation remanence to saturation magnetization (Mrs/Ms), and signal of harder magnetic mineral than rejected ones. Our primary comparison between the two site-level API means and the 1590–present high-resolution IGRF-13 + gufm1 model constrains that the eruption timing of the conical cone to be < 1590 CE. When we compared the two site-level API means with the paleointensity curves calculated from the BIGMUDI4k.1 and ArchKalmag14 k.r, we found that they overlap in the period of − 7575 to −1675 CE or − 25 to 1590 CE, which may be the eruption timing of the conical cone. We concluded that timing of recent volcanic eruption in abyssal environment could be investigated by using appropriate rock magnetic selection and carefully examined API.Graphical

Mapping of geological structures and sediment thickness from analysis of aeromagnetic data over the Obudu Basement Complex of Nigeria

Abstract In this study, geologic structures, as well as attendant orientations and sediment thickness, in the Nigerian Obudu Complex were delineated using the Centre for Exploration Targeting (CET), and depth determination methods such as source parameter imaging (SPI) and standard Euler deconvolution (SED). The CET, SPI, and SED procedures were applied on the total magnetic intensity data. Also, the enhanced TMI data using analytic signal, first-vertical derivative, total-horizontal derivative, and tilt-angle derivative filters were further subjected to CET operation, with the aim of mapping both subtle and prominent lineaments. In general, mapped geologic structures trends in the NE–SW, NNE–SSW, E–W, and N–S directions. Overall, the dominant geologic structural orientations of NE–SW and NNE–SSW reflect the regional strike orientation. The regional striking of the lineation, which is caused by the Pan-African orogeny and subsequent post-orogenic processes, has an impact on these orientations. The N–S and E–W structural deviations from the main NE–SW and NNE–SSW trends are initiated by the YGS of the post-orogenic events. Overall, these complex geologic structures are probable sites for metallogenic minerals.

Effect of Gradient Heat Conduction on Secondary Recrystallization of Grain-Oriented Silicon Steel

The grain-oriented silicon steels were subjected to gradient heat conduction during high-temperature annealing by using thermal insulation cotton. The macrostructures of samples subjected to circumferential gradient heat conduction showed a “petal-like” morphology with peripheral columnar grains and central equiaxed grains, while samples subjected to transverse gradient heat conduction showed a morphology with approximately 50% columnar grains and 50% equiaxed grains. The grain orientations, magnetic domains as well as magnetic properties in different regions were detected. Results showed that the magnetic induction intensity of cylindrical grains was better than that of equiaxed grains while the iron loss was worse, which indicated that a fast heating rate during high-temperature annealing was conducive to the accuracy of Goss grains. The magnetic domains in columnar grains were wider than the equiaxed grains, which resulted in poorer iron loss. A theory of the competitive growth among secondary Goss grains was proposed. Under the condition of gradient heat conduction, once the Goss grains with the fastest heat conduction grew up abnormally, they would compete with other Goss grains which were supposed to survive in traditional processes and swallow up them until adjacent to the secondary equiaxed grains which were later developed.

Free vibration of ferromagnetic functionally graded cylindrical shells subjected to magnetic and temperature fields

The free vibration characteristics of functionally graded cylindrical shells under magnetic and temperature fields are investigated. According to Donnell’s theory, the kinetic energy, deformation energy, and their variational expressions are obtained. Based on the electromagnetic elasticity theory, the eddy current electromagnetic and magnetization force models are established. Using Hamilton’s principle, the magneto-thermo-elastic free vibration partial differential equations are derived. The modal frequency differential matrix equation with diverse boundary conditions is derived from the Galerkin integral technique. Through numerical examples, the curves and three-dimensional surface diagrams depicting the variations for the natural frequency with diverse parameters are obtained. The feasibility of the proposed solution method in this paper is supported by literature examples. The influence of magnetic induction intensity, temperature, power-law index, wave number, and shell dimension on the natural frequencies are determined.

Polycarboxylate functionalized magnetic nanoparticles Fe3O4@SiO2@CS-COOH: Preparation, characterization, and immobilization of bovine serum albumin

Magnetic nanoparticles with increasing superparamagnetism and magnetic targeting have found widespread application in fields such as food and medicine. In this study, polycarboxylated magnetic nanoparticles (Fe3O4@SiO2@CS-COOH) were prepared by surface functionalizing iron tetraoxide (Fe3O4) nanoparticles with ethylenediaminetetraacetic acid (EDTA) as a modifier. The appropriate degree of functionalization modification was obtained by adjusting the EDTA concentration and the ratio of cross-linking agents. The prepared magnetic nanoparticles were analyzed with structural and property characterization. The results showed that the Fe3O4@SiO2@CS-COOH magnetic nanoparticles prepared with 4 % EDTA and cross-linking agents at a molar ratio of 3:4 were uniform in particle size, with an average size of roughly 7 nm, and possessed an abundant carboxylate content (310.8064 μmol/g) and a high magnetization intensity (35.05 emu/g). As a model protein, bovine serum albumin (BSA) was immobilized on the surface of magnetic particles. The largest amount of immobilized protein was 500.4376 mg BSA/g at pH 4.0 and no extra salt ions. According to molecular docking simulations, its immobilization was due to the interaction of amino and carboxyl groups at the Fe3O4@SiO2@CS-COOH/BSA interface. Fe3O4@SiO2@CS-COOH possesses a large number of carboxyl groups, strong protein immobilization, and magnetic responsiveness, which may have potential applications in biomedical and food fields.

Fast Magnetization Vector Inversion Method with Undulating Observation Surface in Spherical Coordinate for Revealing Lunar Weak Magnetic Anomaly Feature

The three-dimensional magnetic vector structure (magnetization intensity and direction) of the planet can be effectively used to analyze the characteristics of its formation and operation. However, the quick acquisition of a large region of the magnetic vector structure of the planet with bigger observation surfaces undulation is hard and indispensable. We firstly proposed a fast magnetization vector inversion method for the inversion of a magnetic anomaly with the undulating observation surfaces in the spherical coordinate system, which first transforms the data to a plane when the data are distributed on a surface. Then, it uses a block-Toeplitz-Toeplitz-block (BTTB)-FFT to achieve fast inversion with the constraint that the magnetization intensities of the grids between the transformed observation surfaces and the terrain are zero. In addition, Gramian constraint term is used to reduce the ambiguity of the magnetic vector inversion. The theoretical model tests show that the proposed method can effectively improve the computational efficiency by 23 times in the 60 × 60 × 10 grid division compared to the conventional inversion method, and the accuracy of the two computation methods is comparable. The root-mean-square error of the magnetization intensity is only 0.017, and the angle error is within 1°. The magnetization vector structure shows that the largest crater diameter does not exceed 340 km in the Mare Australe region, the amplitude of the magnetic anomaly is much higher than the current meteorite impact simulation results, and the depth of the magnetic source is less than 10 km, which cannot be explained by the impact simulation experiments. In addition, the magnetization directions of adjacent sources differ by 122° (or 238°), and the high-frequency dynamics of the Moon as well as the short-lived dynamics may be responsible for this phenomenon. The magnetization directions of the three adjacent sources in the Mare Crisium region are close to each other and differ in depth with different cooling times, making it difficult to record the transient fields produced by meteorite impacts. In addition to the above characteristics, the magnetization direction of the magnetic sources in both regions is uniformly distributed without reflecting the dispersion of the magnetization direction of the meteorite impact magnetic field. Therefore, it can be inferred that the magnetic anomalies in these two regions are related to the generator hypothesis.

Staged magnetic concentration of complex rare earth ores containing niobium and zirconium

ABSTRACT The Balzhe rare earth deposit, located in Inner Mongolia, China, is a complex deposit that also contains niobium and zirconium. However, it remains undeveloped. One notable challenge is the low grades of the main valuable minerals, including xinganite, zircon, niobite, ilmenorutile, pyrochlorite, eschynite, monazite, and bastnaesite. These minerals are either weakly magnetic or associated with ilmenite, a paramagnetic mineral. To overcome this, a high-intensity magnetic method can be employed to separate these valuable minerals from the gangue minerals, thereby generating enriched products to lower the cost of the following flotation. In this study, the first step involved utilizing a high-intensity magnetic separation to enrich particles in different size fractions. It was observed that the size fraction of −0.5 + 0.02 mm was particularly suitable for effective separation. Subsequently, staged magnetic pre-concentration was conducted to obtain products with varying specific magnetization coefficients. To optimize the applied magnetic field intensity, a combination of a high-intensity magnetic separator and a superconducting magnetic separator was employed at different magnetic induction intensities. This proposed technique not only reduces reagent costs but also enhances the operational efficiency of subsequent flotation processes. By implementing this approach, it is anticipated that the Balzhe rare earth deposit can be effectively processed, overcoming the challenge of low-grade valuable minerals. This would contribute to improved economic viability and operational efficiency in the extraction of rare earth elements, niobium, and zirconium from the deposit.

Study on Magnetic and Plasmonic Properties of Fe3O4-PEI-Au and Fe3O4-PEI-Ag Nanoparticles.

Magnetic-plasmonic nanoparticles (NPs) have attracted great interest in many fields because they can exhibit more physical and chemical properties than individual magnetic or plasmonic NPs. In this work, we synthesized Au- or Ag-decorated Fe3O4 nanoparticles coated with PEI (Fe3O4-PEI-M (M = Au or Ag) NPs) using a simple method. The influences of the plasmonic metal NPs' (Au or Ag) coating density on the magnetic and plasmonic properties of the Fe3O4-PEI-M (M = Au or Ag) NPs were investigated, and the density of the plasmonic metal NPs coated on the Fe3O4 NPs surfaces could be adjusted by controlling the polyethyleneimine (PEI) concentration. It showed that the Fe3O4-PEI-M (M = Au or Ag) NPs exhibited both magnetic and plasmonic properties. When the PEI concentration increased from 5 to 35 mg/mL, the coating density of the Au or Ag NPs on the Fe3O4 NPs surfaces increased, the corresponding magnetic intensity became weaker, and the plasmonic intensity was stronger. At the same time, the plasmonic resonance peak of the Fe3O4-PEI-M (M = Au or Ag) NPs was red shifted. Therefore, there was an optimal coverage of the plasmonic metal NPs on the Fe3O4 NPs surfaces to balance the magnetic and plasmonic properties when the PEI concentration was between 15 and 25 mg/mL. This result can guide the application of the Fe3O4-M (M = Au or Ag) NPs in the biomedical field.

Mapping stony rise landforms using a novel remote sensing, geophysical, and machine learning approach

A basalt lava plain covers much of central and western Victoria in Australia. Many of the younger flows (<1 Ma) have hummocky surfaces with abundant tumuli and lava rises, known locally as stony rises due to the protruding basalt boulders. Stony rises are noteworthy geologically but have ecological importance and are culturally significant to Aboriginal Australians. Ecologically, stony rises host many native plant species. Culturally, stony rises provide evidence of Aboriginal land use and occupation through the presence of artefact deposits. Currently, mapping of stony rises is carried out by conducting field surveys on a study-by-study basis. This could be performed more rapidly using remote sensing datasets such as LiDAR, satellite and aerial imagery, and geophysical data. This research mapped stony rises in an area that is experiencing rapid urban development using a combination of remotely sensed datasets that characterise the morphology of stony rises through a Machine Learning approach that utilises Object Based Image Analysis (OBIA) segmentation and Random Forests (RF) classification techniques. The research successfully identified stony rises in the landscape to an accuracy of 89.97 %, with 314 potential new stony rise sites identified. The research identified the most important predictor variables were slope, local elevation, the concentrations of thorium and uranium (obtained from airborne radiometric data), aeromagnetic data (total magnetic intensity), the Normalised Difference Water Index (NDWI), and the Clay Mineral Ratio. The results from this study lay a foundation for standardising the definition of a stony rise within Australia. Furthermore, by utilising various predictor variables, this study highlights the success of a multi-faceted approach into detecting a specific landform at a landscape level.

Charge injection characteristics and charge migration mechanism of magnetic particle-modified EBA-based semi-conductive shielding layers

The space charge accumulation problem within insulation layer of high voltage direct current (HVDC) cable in engineering applications has attracted much attention. The inner semi-conductive shielding layer is located between the conductor and the insulation layer, which is the only way for charge injection into the insulation layer. The performance of the inner semi-conductive shielding layer has an important influence on the charge accumulation of the insulation layer. In this paper, the matrix resin EBA of high voltage grade DC cable shielding material is used as the research object. The magnetic particle SrFe12O19 is used to modify the EBA-based shielding material. The semi-conductive composites of CB/SrFe12O19/EBA with different SrFe12O19 concentrations (with different Lorentz Forces) are prepared. The mechanism of the influence of Lorentz Forces on the space charge injection characteristics of insulation layers and the mechanism of the charge migration are investigated. The trajectories of space charges in shielding layers are simulated using the finite element method. The experimental results show that SrFe12O19 can significantly reduce the space charge accumulation of the insulation layer. When SrFe12O19 is 5%, the shielding layer has the most obvious inhibition effect on the charge injection of the insulation layer. The simulation results show that the critical value of magnetic induction intensity is B′= 0.6 T when space charge moves in the shielding layer. This work provides a new way to solve the problem of space charge accumulation in HVDC cables, and has important reference significance for the development of HVDC cables.

The Effect of Stress on Paleomagnetic Signals: A Micromagnetic Study of Magnetite's Single‐Vortex Response

AbstractIn this study we use micromagnetic modeling to show that the magnetizations of magnetically single‐vortex particles rotate toward the stress axis on the application of a differential compression stress. This is the exact opposite response to magnetically single‐domain particles, which previously provided the theoretical underpinning of the effect of stress on the magnetic signals of rocks. We show that the magnetization directions of single‐vortex and equant single‐domain particles are altered by much lower stresses than previously predicted, c.f., 100 versus 1,000 MPa; where a change in magnetization is defined as a rotation of &gt;3° after the removal of stress. The magnetization intensity of assemblages also drops by ∼20%–30% on the application and removal of stress of ∼100 MPa. Given that single‐vortex particles are now thought to dominate the magnetization of most rocks, future studies should account for paleomagnetic directional uncertainties and potential underestimation of the ancient magnetic field intensity.