Magnetic Field Intensity Research Articles

Effect of an Applied Magnetic Field on Joule Heating-Induced Thermal Convection

Thermal convection induced by internal heating appears in different natural situations and technological applications with different internal sources of heat (e.g., radiation, electric or magnetic fields, chemical reactions). Thermal convection due to Joule heating in weak electrical conducting liquids such as molten salts with symmetric thermal boundary conditions is investigated using linear stability analysis. We show that, in the quasi-static approximation where the induced magnetic field is negligible, the effect of the external magnetic field consists of the delay in the threshold of thermal convection and the increase in the size of thermoconvective rolls for an intense magnetic field. Analysis of the budget of the perturbations’ kinetic energy reveals that the Lorentz force contributes to the dissipation of the kinetic energy.

The effect of magnetic nanofilm morphology on spintronic terahertz emission performance

Femtosecond laser-driven spintronic terahertz (THz) emitters based on magnetic nanofilms are poised to be the next-generation mainstream THz radiation devices due to their low cost, high performance, ultra-broadband, and easy integration. The radiation performance of spintronic THz emitters is related to the material characteristics, heterostructure interfaces, pump laser, and magnetic field intensity. Additionally, the THz emission performance is greatly reliant on the material surface morphology. Here, we employed ultrafast THz scattering-type scanning near-field optical microscopy with nanoscale spatial resolution to obtain the static THz scattering nano-imaging of ferromagnetic/antiferromagnetic heterostructures (W/Co20Fe60B20/IrMn3). We established the relationship between surface morphology and THz scattering intensity. Utilizing laser-induced THz emission technology, we achieve injection and detection of nanoscale ultrafast spin current without the external magnetic field. The strong consistency of the THz emission nanoscopy with the atomic force microscopy topography demonstrates that the sample surface morphology is critical to the THz radiation performance. This study serves as a valuable reference for the further optimization of spintronic THz emitters and promotes the development of high-performance, strong-field spintronic THz sources.

Study on the influence of high permeability magnetic iron on energy consumption reduction in high gradient magnetic separator

The green processing of weakly magnetic iron ore is inseparable from high-intensity and high-gradient magnetic separator (HGMS), which is one of the most energy-intensive magnetic separation equipment. Iron (Fe) armor serves as the key primary structure for enhancing magnetic field conduction efficiency within the magnetic system. The order of magnetic properties of commonly used magnetic yoke materials is: ordinary carbon structural steel < Q235 steel < DT4 electrical pure iron. But the utilization cost of DT4 electrical pure iron is the highest, especially the magnetic properties of DT4C super electrical pure iron are unstable and the yield is low. On the basis of ordinary pure iron materials, this article has developed a new type of 411 pure iron (411) upon controlling the levels of harmful elements, while increasing the concentration of beneficial elements.intensity Furthermore, through the utilization of magnetic field simulation software, the impact of 411 on the background magnetic field intensity of HGMS was analyzed. The results indicated that the newly developed 411 pure Fe exhibited a coercivity of 24.07 A/m, a saturation magnetization intensity of ∼ 1.69 T, a maximum relative magnetic permeability of 24.38 × 10-3H/m, demonstrating superior magnetic properties in comparison with Q235 and DT4C. When using 411 pure iron as the magnetic yoke material, the background magnetic field intensity of the HGMS can be increased by 6.85 % − 14.64 % compared with using DT4C super pure iron under the same excitation current conditions. The magnetic yoke with better magnetic conductivity will enhance the magnetic field utilization efficiency of the magnetic system, a reduce the excitation energy consumption, and improve the sorting performance of HGMS.

The Assessment of the Influence of Low-Frequency Electromagnetic Fields Originated from the Power Infrastructure on Humans’ Health

The objective of this study is to assess the impact of low-frequency electromagnetic fields (LF EMFs) generated by power infrastructure on the nearby environment. Measurements of electric (E) and magnetic (H) field intensities were conducted around high-voltage power lines, transformer stations and facilities related to them. Numerical simulations were also performed to model the distribution of the field values around real buildings in close proximity to power delivery systems. Given the ongoing scientific debate regarding the effects of EMFs on living organisms, the current analysis was based on the existing standards—particularly ICNIRP 2010 guidelines, which set the maximum allowable E and magnetic induction (B) values at 5 kV/m and 200 μT, respectively. Stricter national regulations were also examined, such as Poland’s 1 kV/m E limit in residential areas and Belgium’s 10 μT limit for B. The results showed that while most cases complied with ICNIRP 2010 standards, certain stricter local regulations were exceeded. Specifically, 9 of 14 cases exceeded Poland’s E limits, and 8 failed to meet Belgium’s B requirements. Only in one place—a warehouse near 110 kV power lines (in a critical case)—the ICNIRP limit B was exceeded. These findings underscore the variability in regulatory standards and highlight the need for localized assessments of EMF exposure.

Frequency Shift Caused by Magnetic Field and Light Intensity Inhomogeneity in Optically Detected Clock

Frequency Shift Caused by Magnetic Field and Light Intensity Inhomogeneity in Optically Detected Clock

Research on influence of stress concentration on metal magnetic memory signal for stress evaluation

Abstract Based on the magneto-mechanical effect and stress concentration effect, this paper takes the failure of ferromagnetic components caused by stress concentration as the research background, artificially creates stress concentration by prefabricating U-shaped defects, and discusses the Hp(y) signal distribution law of prefabricated U-shaped defect samples and the difference in Hp(y) signal between specimens with different tip SCFs. Results show that the Hp(y) signal has an apparent mutation in the stress concentration area, and when the stress concentration factor was the same, the magnetic field intensity gradient K becomes higher as tensile load increasing. As stress concentration factor increasing, the K value of the stress concentration area also increases gradually. Based on theoretical model of Hp(y) signal, it can be known that the K value can be used to judge the sample stress concentration degree with the results in this study.

Magnetic field improves the quality of frozen tilapia fillets by decreasing the ice crystals during freezing process

SummaryIn this study, the alternating magnetic field (AMF) with frequency of 50, 100, 150, 200 and 250 Hz at magnetic field intensity of 5 mT was used to assist the freezing of tilapia fillets, with no magnetic field (NMF) as a control group. The evaluation of thawed tilapia fillets encompassed an assessment of freezing curve, texture, microstructure, moisture state and protein structure, followed by a subsequent analysis of their correlation. The findings showed that the application of a magnetic field during the freezing process yielded favourable outcomes in enhancing the overall quality of tilapia fillets. Among them, 200 Hz had the best effect. Under the condition, the frozen tilapia fillets assisted by magnetic field showed the shortest freezing time, the least decrease in hardness and elasticity and the best chewiness after thawing. The size of the ice crystals generated during freezing was small and uniform, and the fractal dimension of the frozen sections was the highest. Muscle tissue was the least damaged, which led to the improvement of its water‐holding capacity. Magnetic field‐assisted freezing was found to maintain the α‐helix and β‐sheet in the secondary structure of proteins. The correlation analysis showed that cohesion, elasticity, fractal dimension, FD, A2, A22 and β‐turn were closely related to the quality changes of tilapia fillets after magnetic field treatment.

Residence time prediction in magnetically controlled biomolecular local rebinding-dissociation kinetics

The residence time of drug-target conjugates is a critical factor in drug screening and efficacy prediction. The local rebinding-dissociation kinetics gives insights into in-vivo drug-target interactions. A magnetic torque system (MTS) is designed to observe rebinding-dissociation kinetics for predicting residence time. The system utilizes an alternating magnetic field (AMF) to manipulate the magnetization motion of magnetically labeled biomolecules and the forces acting upon biomolecular bonds. The motion, sensed by a quartz crystal microbalance (QCM), reflects biomolecular interactions occurring at the particle surface. Meanwhile, the motion facilitates the separation of dissociated molecules from the surface, thereby obviating the necessity for fixed and mobile phases in common kinetics observations. The constant and static solution environment minimizes reagent consumption. The MTS was utilized to observe the local rebinding-dissociation of antibodies (PAB and MAB) to magnetic beads (MB) and to HER2 receptors. The residence times recorded by the MTS were larger than the results obtained via SPR method, due to the occurrences of rebinding-dissociation kinetics. Interaction behaviours can be meticulously regulated for varying affinities by modulating the intensity of magnetic field. A high intensity field (400 Oe) was applied for strong binding between antibody-MB (biotin-streptavidin), and a low intensity field (300 Oe) was applied for weak antigen-antibody interactions. An increase in AMF strength enhanced dissociation, with a shift from 300 Oe to 400 Oe resulting in a 1 ∼ 4-fold reduction in residence time. Overall, the MTS provides an interactive and customizable perspective on kinetics observations.

Electromagnetic force calculation within finite volume framework

ABSTRACT In this research, the comparison of force calculation methods in magnetostatic simulations within a cell-centered finite volume framework is presented. Various procedures for postprocessing of the magnetic vector potential field are laid out to obtain the surface and volume integrals of Maxwell’s stress tensor and the Lorentz force density. Two different magnetostatic problems with multiple operating points were modeled with the AVL FIRETM M. The force results have been verified by comparing them to the Ansys Maxwell and were validated on a benchmark case from a Testing Electromagnetic Analysis Methods (TEAM) workshop. The interpolation of the magnetic flux density on a multi-material interface is presented, and it is used in conjunction with the surface integral of Maxwell’s stress tensor for an efficient global force computation. For all observed cases, the calculated results correspond well to the results found in the literature. It was found that the accuracy of the volume integral of Maxwell’s stress tensor is dependent on the mesh quality and gradient calculation scheme. Employing the semi-structured mesh with Gauss’s gradient scheme results in force discrepancies of less than 3% between the surface and volume integral of Maxwell’s stress tensor. The convergence of the iterative solver is observed to be slower in the case of the materials with permeability jump, where discontinuities between the tangential component of the magnetic flux density and the normal component of the magnetic field intensity occur.

On-Demand Coalescence of Ferromagnetic Droplets in Microchannels Using an Oscillating Magnetic Field.

Droplet-based microfluidics exhibit remarkable potential in achieving high-throughput chemical reactions with minimal reagent consumption. However, a pivotal challenge lies in the selective coalescence of droplets for precise process control, particularly when dealing with droplets of varying amounts and volumes, which are difficult to trap and coalesce due to their tiny dimensions and incessant movement. Hence, we proposed a method for on-demand coalescence of ferromagnetic droplets using an oscillating magnetic field. Experimental results show that the ferromagnetic droplets can be trapped in different positions in the microchannels according to the applied magnetic field intensity. A high-intensity pulsed amplitude of the magnetic field enables the migration of trapped droplets toward the same position, facilitating their mutual contact and interaction. By programmable modulation of the oscillating magnetic field, a controllable reciprocation of droplets in microchannels was successfully realized, which enabled us to dynamically capture, coalesce, and release two or more (≥3) droplets on demand. The integrated ferromagnetic droplet-based microfluidic platform allows contact-free, easily monitored, and on-demand coalescence of ferromagnetic droplets in microchannels, which holds promise for a wide range of applications, such as microfluidic-based drug synthesis, biosensing, reaction kinetics, and paracrine signaling, particularly.

Features of 2D mapping technique of non-uniform magnetic fields using self-biased magnetoelectric composites based on “bidomain LiNbO3/Ni/Metglas” structures

Magnetoelectric (ME) composites are extensively researched for their ability to detect magnetic fields but are typically characterized by their interactions with homogeneous magnetic fields. However, practical applications often involve non-uniform magnetic fields (NMFs). In this study, we developed and validated a technique for 2D mapping of NMFs using sensor based on ME composite. The primary focus was on mapping the magnetic field generated by a single wire carrying an alternating current (AC). The experimental setup included a “bidomain LiNbO3/Ni/Metglas” ME structure, which demonstrated a ME coefficient of 0.83 V/(cm⋅Oe) without external biasing at 117 Hz. The ME structure was characterized using both quasi-static and dynamic methods, with the mapping performed at a frequency of 232 Hz, chosen to ensure a linear response and minimize resonance effects. Our measurements revealed that the position of maximum magnitude of the ME signal was consistently shifted from the position of the maximum integral magnetic field intensity of the wire. This shift was attributed to the deformation of the ME structure and the redistribution of the magnetic flux along the sample due to the magnetic layers, as confirmed through modeling. Further, the measured 2D mapping of the NMF from the wire closely matched the theoretical distribution, displaying axial symmetry but with a persistent shift of 2–3 mm along the length of the ME structure. These effects were linked to the linear dimensions and clamping methods of the ME structure. Overall, our experimental results closely correlated with theoretical data and the FEM model, demonstrating that ME composites are effective for NMF detection and mapping. Future work will aim to reduce the dimensions of the ME structure using MEMS technology to minimize the observed shift effects in the measurements.

Modeling magnetic field amplification in supernova remnants driven by laser

Abstract The origin of magnetic fields and their amplification have always been hot topics in fields such as astrophysics and high-energy-density physics. Among them, the turbulent dynamo effect is an important candidate mechanism, and the interaction between supernova remnants (SNRs) is an important carrier for studying the amplification effect of turbulent magnetic fields. In this paper, we use the radiation magnetohydrodynamic simulation program to carry out a scaling simulation study on the amplification effect of turbulent magnetic fields in the interaction of SNRs driven by powerful lasers. We investigate and compare the evolution of turbulence under different laser driving methods, different directions, and different intensities of initial external environmental magnetic fields. Here, we carefully identify the contributions of Biermann self-generated magnetic fields and environmental magnetic fields in the process of magnetic field amplification, present magnetic energy spectra, and magnetic field amplification factors, and analyze the influence of radiative cooling effect on turbulence and magnetic field evolution. The results show that the collision direction component of the environmental magnetic field dominates the process of magnetic field amplification, and the frequency spectrum of turbulence is consistent with Kolmogorov’s law. The research results are necessary for sorting out and elucidating the physical mechanism of magnetic field amplification in SNRs, and have reference significance for regulating turbulence in strong magnetic fields in the future.

Effect of physical field-assisted freezing on the quality attributes of frozen baked sweet potato and its optimization

Freezing plays a crucial role in ensuring the safety of foods over long storage periods. However, ice crystals within the cells can cause irreversible damages to tissue structures during the freezing process, resulting a significant problem on the quality. The present study aimed to investigate the effects of physical field-assisted freezing on the quality attributes of frozen baked sweet potato and identify the optimum operational parameters of quick-frozen process. Combination of magnetic field and ultrasound suggested the best results, with a 58.33% reduction in freezing time, 59.63% reduction in thawing loss, compared to IF. The hardness and the signal values of Sweetness and W2W of CF were 58.90%, 20.03%, and 27.07% higher than those of IF, which showed that CF have better maintenance of sample quality. Low field-nuclear magnetic resonance results showed that CF caused a decrease in the proportion of free water and an increase in the proportion of immobile water, and the water status are more similar to FB. Microscopic observations confirmed that the CF had the smallest and the most evenly distribution of ice crystals. Optimization of frozen baked sweet potato via response surface methodology, which revealed that the optimal conditions included a magnetic field intensity of 30 mT, an ultrasonic intensity of 320 W, and an ultrasonic time of 10 s. Therefore, treatment of combination with magnetic field and ultrasound is a promising novel method to improve the quality of frozen foods.

Durably Superhydrophobic Magnetic Cobalt Ferrites for Highly Efficient Oil-Water Separation and Fast Microplastic Removal.

Microplastic pollution has become a primary global concern in the 21st century. Recyclable magnetic particles with micro-nanostructures are considered an efficient and economical way to remove microplastics from water. In this study, superhydrophobic magnetic cobalt ferrite particles were prepared by using a simple coprecipitation method combined with surface functionalization. The micromorphology, chemical composition, hysteresis loop, and surface contact angle of the functionalized cobalt ferrite were characterized. The separation efficiency and absorption capacity of cobalt ferrite particles in water-oil separation and microplastic removal were investigated. The results showed that the saturation magnetic field intensity of cobalt ferrite was 65.52 emu/g, the residual magnetization intensity (Mr) was 18.79 emu/g, and the low coercivity was 799.83 Oe. Cobalt ferrites had stable superhydrophobicity in the pH range of 1-13. The separation efficiency of cobalt ferrite powder for four oil-water mixture separations was higher than 94.2%. The separation efficiency was as high as 99.6% in the separation of the hexane and water mixtures. Due to the synergistic effect of the hydrophobic effect and van der Waals force, the functionalized magnetic cobalt ferrite had a high and stable microplastic removal efficiency and capture capacity. The removal efficiency of microplastics was close to 100%, and the capture capacity was 2.56 g/g. After ten microplastic removal cycles, the removal efficiency reached more than 98%, and the surface contact angle was still greater than 150°.

Coupling nanoscopic tomography and micromagnetic modelling to assess the stability of geomagnetic recorders

The recording of planetary magnetic fields is often attributed to uniformly-magnetised nanoscopic iron oxides, called single-domain. Yet, the main magnetic constituents of rocks are more complex, non-uniformly magnetised grains in single or multi-vortex states. We know little about their behaviour due to limitations in defining their precise shape and internal magnetic structure. Here we combine non-destructive Ptychographic X-ray Computed Nano-tomography with micromagnetic modelling to explore the magnetic stability of remanence-bearing minerals. Applied to a microscopic rock sample, we identified hundreds of nanoscopic grains of magnetite/maghemite with diverse morphologies. Energy barrier calculations were performed for these irregularly shaped grains. For some grains, these morphological irregularities near the transition from single-domain to the single-vortex state allow for multiple domain states, some unstable and unable to record the field for significant periods. Additionally, some other grains exhibit temperature-dependent occupancy probabilities, potentially hampering experiments to recover the intensity of past magnetic fields.

Characterizing the Magnetic and Plasma Environment Upstream of Ganymede

AbstractWe present an application of the latest UCL‐AGA magnetodisc model (MDISC) to the study of the magnetic and plasma conditions in the near‐Ganymede space. By doing this, we provide a comparison with measurements from Juno's most recent flyby of the Jovian moon, perijove 34 (PJ34). We find good agreement between the model results and the magnetometer data, pointing toward a hot plasma index value (2.7190.024)107 Pa m T−1 and an effective magnetodisc radius (79.51.1) Jupiter radii for the Jovian magnetosphere, for the duration of the trajectory, suggesting a configuration with middling levels of expansion. We also predict the plasma conditions observed by Juno during the same flight‐path, as well as the typical conditions over the orbit of Ganymede, with the magnetic and hot plasma pressures assuming dominant roles. Finally, these results are compared with functional fits of a compilation of Galileo flyby data obtained in the vicinity of Ganymede's orbit, suggesting Juno experienced somewhat similar conditions, despite a systematic overestimation in magnetic field intensity in the near‐Ganymede space.

Improving surface integrity of GH4169 alloy through magnetic-assisted cutting

GH4169 alloy presents superior properties such as high strength and resistance to high temperature, but possesses poor machinability. To ameliorate the problem and improve the machined surface integrity of GH4169 alloy, this paper focused on the application of magnetic-assisted cutting (MAC) for GH4169 alloy. In the MAC process, a permanent magnetic field (the magnetic field intensity is 0.25 T) was applied to the workpiece material during cutting, and its impact on chip morphology, tool damage and surface integrity was investigated. By comparing to traditional cutting (TC), the introduction of a magnetic field results in a reduction in the chip thickness and minimizes chip serration, leading to smoother cutting process and reduced fluctuations in cutting forces. Meanwhile, the introduction of magnetic field resulted in a substantial decrease in the notch wear and abrasion of cutting tool, and mitigated the excessive growth of built-up edge (BUE), which improved the tool life and machined surface integrity. By analyzing the machined surface at the end of TC and MAC, it was found that the surface roughness at the end of MAC was reduced by 22.4 %. Meanwhile, the cavity, side flow and debris of BUE, which tend to occur in the machined surface during the TC process, are effectively suppressed after MAC. Furthermore, Microstructural analysis of the machined surface indicated an enhancement in the dislocation density on the machined surface layer, suggesting the magnetoplastic effect of the magnetic field on GH4169 alloy.

Correct Criterion of Crustal Failure Driven by Intense Magnetic Stress in Neutron Stars

Magnetar outbursts are powered by an intense magnetic field. The phenomenon has recently drawn significant attention because of a connection to some fast radio bursts that has been reported. Understanding magnetar outbursts may provide the key to mysterious transient events. The elastic deformation of the solid crust due to magnetic field evolution accumulates over a secular timescale. Eventually, the crust fractures or responds plastically beyond a particular threshold. Determination of the critical limit is required to obtain the shear strain tensor in response to magnetic stress. In some studies, the tensor was substituted with an approximate expression determined algebraically from the magnetic stress. This study evaluated the validity of the approximation by comparing it with the strain tensor obtained through appropriate calculations. The differential equations for the elastic deformation driven by the magnetic field were solved. The results indicated that the approximation did not represent the correct strain tensor value, in both magnitude and spatial profile. Previous evolutionary calculations based on spurious criteria are likely to overestimate the magnitude of the strain tensor, and crustal failure occurs on a shorter timescale. Therefore, revisiting evolutionary calculations using the correct approach is necessary. This study is essential for developing the dynamics of crustal fractures and the magnetic field evolution in a magnetar.

Effect of the Magnetic Field, Electric Field, and Light Intensity on the Parameters of Recombination Waves in Silicon

Effect of the Magnetic Field, Electric Field, and Light Intensity on the Parameters of Recombination Waves in Silicon

Morphology-dependent magnetic hyperthermia characteristics of Fe3O4 nanoparticles

Magnetic hyperthermia therapy (MHT) represents an innovative approach to cancer treatment, harnessing the therapeutic capabilities of magnetic nanoparticles. Fe3O4 nanoparticles are often considered ideal candidates for MHT because of their biocompatibility. However, the clinical application of Fe3O4 nanoparticles is hindered by their low heating efficiency and concerns regarding potential toxicity linked to the high concentrations required to achieve therapeutic effects. In this study, two unique structures, hollow spherical and nanoflower Fe3O4, were successfully synthesized to enhance their magnetothermal conversion efficiency. The results indicate that Fe3O4 nanoflowers exhibit an intrinsic loss power (ILP) value of 6.52, which is 1.83 times greater than the ILP of hollow spherical Fe3O4 (3.55), indicating its enhanced potential for MHT applications. The COMSOL simulation demonstrated that higher magnetic field frequencies and intensities elevate tissue temperature and damage in tumor cells, particularly at 100 kHz and 400 kHz, with tumor tissue damage scores rising to 0.28 and 0.93, respectively. Shorter heating durations, such as 6 min, minimize harm to healthy tissue and are ideal for treatments requiring multiple sessions. After 12 min, tumor scores rose to 0.85, while normal tissue scores were 0.34, suggesting that longer durations improve therapeutic effects on tumors but also heighten the risk to healthy cells. This research provides a scientific foundation for selecting materials in the context of MHT for cancer treatment, potentially paving the way for more effective and safer therapeutic strategies.