Induced Magnetic Field Research Articles

A high bandwidth and high transmission STM bias line for ESR and quantum stochastic resonance measurements at 0.4 K.

We present a scanning tunneling microscope operating in a 3He cryostat at a base temperature of 0.4K, suitable for electron spin resonance (ESR) [S. Baumann, W. Paul, T. Choi, C. P. Lutz, A. Ardavan, and A. J. Heinrich, Science 350, 417 (2015)], quantum stochastic resonance (QSR) [M. Hänze, G. McMurtrie, S. Baumann, L. Malavolti, S. N. Coppersmith, and S. Loth, Sci. Adv. 7, eabg2616 (2021)], and electric pump-probe experiments. We achieve excellent signal transmission of -2 to -3 dB between 100kHz and 100MHz, -23 dB at 10GHz, -35 to -40 dB between 25 and 35GHz, and -45 dB at 40GHz, using a combination of normal conducting and superconducting semi-rigid, as well as flexible RF cables. SMK type 2.92mm and mini-SMP connectors are used to minimize reflections and losses over the entire frequency range. The ESR capability of our instrument is demonstrated on possibly hydrogenated titanium atoms adsorbed on two and three monolayers of MgO on Ag(100) at 0.4 and at 4.2K. We further show QSR measurements for Fe/MgO/Ag(100) and compare the driven relaxation time with the intrinsic energy relaxation time T1 reported for that system [W. Paul, K. Yang, S. Baumann, N. Romming, T. Choi, C. P. Lutz, and A. J. Heinrich, Nat. Phys. 13, 403 (2017)] as a function of magnetic field and tunnel current.

A microscopic theory for the calculation of magnetic field induction of nanowires

A microscopic theory for the calculation of magnetic field induction of nanowires

Geometry Driven Hall Effect Analysis for Development of a Sensitive Hall Effect Sensor

Hall voltage and Hall resistance manifest, as various metals and semiconductors are exposed to electric and magnetic fields in specific directions. In this work, we first generated the classical Hall effect and then attempted to generate the quantum Hall effect in various metallic thin films, to analyze the generated Hall resistance. This analysis provides the backbone for building the sensor. The Hall voltage developed depends on parameters like input current, magnetic field, input voltage, and distance of magnets from the specimen. Studies suggest that there is linearity between magnetic field and Hall voltage induced. Hall effect studies have importance in determining basic magnetic properties of metals and useful in metallurgical and mining industry. This implies that 0.5 mm thickness is not sufficient to induce the quantum Hall effect and the dimension of the sample must be reduced to much less than 0.5mm so that we can observe a staircase pattern as observed in Quantum Hall effect.

Magnetic imaging of Abrikosov vortices trapped near moats in the niobium thin film

Abstract Abrikosov vortices trapped in superconducting circuits can reduce their operation margin and, in some cases, even lead to failure. Moats have been introduced to reduce the impact of Abrikosov vortices by providing a favorable location for trapping them at a distance from the circuit. However, the distribution mechanism of vortices near moats driven by applied magnetic fields and currents remains unclear. In this study, we used multiple moats to construct square-shaped areas in the niobium (Nb) thin film and employed magnetic force microscopy to observe the distribution of vortices induced by applied magnetic fields and currents near these areas. The moats effectively prevented vortices from entering the square-shaped area, particularly when the spacing between two moats was <550 nm. Furthermore, we discovered that the edges of moats generated new vortices with polarities opposite to those entering from both the edges of the Nb film under applied current. These vortices attracted each other and annihilated in pairs. These findings provide more insights into designing the layouts of superconducting integrated circuits.

Lattice Boltzmann Formulation for Eight-Wave Magnetohydrodynamics

Magnetohydrodynamics couples the Navier–Stokes and Maxwell equations to describes flows in electrically conducting fluids. The divergence of the magnetic field must vanish, but numerical algorithms typically do not preserve this condition exactly. Artifacts can then arise in solutions, such as spurious forces parallel to the magnetic field. These artifacts can be alleviated by using extended sets of Maxwell’s equations that include magnetic charges and currents and hence are invariant under duality rotations that interchange the electric and magnetic fields. The eight-wave formulation supposes that the magnetic current arises from magnetic charges being advected by the fluid. The magnetohydrodynamic equations are then Galilean invariant even when the divergence of the magnetic field is nonzero. The evolution equation for the magnetic field then resembles Jeffery’s equation that describes the orientations of a suspension of axisymmetric particles. The ideal electric field is invariant under the extra terms proportional to the divergence of the magnetic field. This property leads to particularly simple lattice Boltzmann formulations for two of the three variants, with different treatments of the momentum equation, that are constructed and compared. The formulation that implements the Lorentz force directly, rather than via the Maxwell stress, proves more stable in numerical experiments.

Locomoting non-magnetic marbles through meniscus emerged on the water surface using a magnetically actuated ferrofluid marble under pulsating and steady magnetic fields.

Recent progress in digital microfluidics has revealed the distinct advantages of liquid marbles, such as minimal surface friction, reduced evaporation rates, and non-wettability compared to uncoated droplets. This study provides a comprehensive examination of an innovative technique for the precise, contamination-free manipulation of non-magnetic water liquid marbles (WLMs) carried by a ferrofluid liquid marble (FLM) under the control of direct current (DC) and pulse-width modulation (PWM) magnetic fields. The concept relies on the phenomenon in which an FLM and WLMs form a shared meniscus when placed together on a water surface, causing the WLMs to closely track the magnetically actuated FLM. The study also explores the dynamic behavior of the marbles by assessing several influencing parameters: magnetic coil current, the starting position of the marbles from the coil, the number of WLMs carried by the FLM, the volume ratio between the WLM and FLM, and the PWM magnetic field properties, including duty cycle and frequency. The results demonstrate that increasing the magnetic coil current or reducing the volume ratio decreases the travel time and enhances the velocity of the carrier FLM under both DC and PWM magnetic fields. Notably, the FLM exhibits significant capability to transport multiple WLMs, although its average and maximum velocity decrease with each additional WLM. Moreover, the travel time of the marbles varies proportionally with the PWM frequency while exhibiting an inverse relationship with the duty cycle.

A Charged Relativistic Engine Based on a Permanent Magnet

This paper aims to describe and analyze a relativistic engine that uses a permanent magnet and an electrically charged device. This is a novel device that was not described before. According to Newton’s third law, every action is met with an equal and opposite reaction, meaning the total force in a system unaffected by external forces is zero. However, relativity principles state that signals cannot travel faster than the speed of light, so actions and reactions cannot occur simultaneously. As a result, the total force cannot be zero at any given moment. This implies that the system gains mechanical momentum and energy over a finite period. The question then arises about how to uphold the law of momentum and energy conservation. It has been shown that momentum is balanced by an equal and opposite momentum in the field, while the energy gained by the engine is offset by a reduction in the field’s energy. Previous analyses assumed that the bodies involved were macroscopically neutral, meaning the number of electrons and ions was equal in every volume element. This paper relaxes that assumption and examines charged bodies interacting with magnetic currents from permanent magnetic materials, exploring the implications for a charged relativistic engine based on a permanent magnet.

Experimental study of magnetorheological fluids under large periodic deformations

Abstract Magnetorheological (MR) fluids are smart materials whose properties can be controlled by a magnetic field. They are used in a variety of applications with tailored operating parameters, facilitating broad and relatively straightforward implementation and control of the functional properties of these systems.

The aim of the study was to determine the variation in shear stress of MR fluids under varying shear deformation directions and different magnetic field induction levels. The experiments were carried out with the use of three commercially available fluids: MRF-122EG, MRF-132DG, and MRF-140CG, which primarily differ in the volumetric fraction of ferromagnetic particles. These fluids are designed for use in mechanical energy dissipation devices clutches, and brakes are characterized by high stability and a broad controllability range.

The experiments were performed using a rotational rheometer with a parallel plate measuring system to examine shear stress variability during both the deformation and rest phases. The study applied relatively large deformations, exceeding the linear viscoelastic range and the deformation corresponding to the yield point.

The test results revealed variations in the shear stress values across successive loading cycles, as well as fluctuations during the rest phase. It was also found that, depending on magnetic field induction level (i.e., the level of fluid magnetization), the rest period could result in either a decrease (relaxation) or an increase (hardening) in shear stress values. These findings have practical significance, particularly for MR fluid devices operating in shear mode.

Real-Time Computation of Brain E-Field for Enhanced Transcranial Magnetic Stimulation Neuronavigation and Optimization

Abstract Transcranial Magnetic Stimulation (TMS) coil placement and pulse waveform current are often chosen to achieve a specified E-field dose on targeted brain regions. TMS neuronavigation could be improved by including real-time accurate distributions of the E-field dose on the cortex. We introduce a method and develop software for computing brain E-field distributions in real-time enabling easy integration into neuronavigation and with the same accuracy as 1st-order finite element method (FEM) solvers. Initially, a spanning basis set (< 400) of E-fields generated by white noise magnetic currents on a surface separating the head and permissible coil placements are orthogonalized to generate the modes. Subsequently, Reciprocity and Huygens’ principles are utilized to compute fields induced by the modes on a surface separating the head and coil by FEM, which are used in conjunction with online (real-time) computed primary fields on the separating surface to evaluate the mode expansion. We conducted a comparative analysis of E-fields computed by FEM and in real-time for eight subjects, utilizing two head model types (SimNIBS’s ‘headreco’ and ‘mri2mesh’ pipeline), three coil types (circular, double-cone, and Figure-8), and 1000 coil placements (48,000 simulations). The real-time computation for any coil placement is within 4 milliseconds (ms), for 400 modes, and requires less than 4 GB of memory on a GPU. Our solver is capable of computing E-fields within 4 ms, making it a practical approach for integrating E-field information into the neuronavigation systems without imposing a significant overhead on frame generation. The software is available at https://github.com/NahianHasan/Real-Time-TMS.

Reversibly Switchable Magnetically Controlled Solid‐Liquid Triboelectric Nanogenerator Using Hierarchical Ecoflex/NdFeB Magnetic Polymer Surface

AbstractDroplet‐driven triboelectric nanogenerator (TENG) with reversible switching capability has been widespread concerned; particularly magnetically controlled solid‐liquid TENG, due to its fast and highly reversible responses. Herein, a hierarchical composite structured magnetic polymer surface (HCSMPS) is developed using template method and magnetic field induction, and construct a HCSMPS‐based TENG (HCSMPS‐TENG). The HCSMPS‐TENG shows different states—fallen, upright, and no magnetic field—when applying different magnetic fields. The wetting properties of HCSMPS under three states vary significantly. The current output of the HCSMPS‐TENG driven by deionized water and potassium chloride (KCl) solution varies across these states due to changes in the droplet contact area. As KCl concentration increases, the current signals of the HCSMPS‐TENG initially rise due to the increased free charges but subsequently decrease due to a screening effect caused by ion adsorption. For practical application, a real‐time monitoring system is developed for KCl concentration based on the HCSMPS‐TENG, integrating a convolutional neural network. This system, equipped with a compact current collection circuit capable of remote data transmission and a user‐friendly interface developed with LabVIEW, achieves 98.64% recognition accuracy. The HCSMPS‐TENG is applied to intravenous potassium supplementation, demonstrating its potential for medical KCl concentration and infusion flow rate monitoring.

Barkhausen Noise‐ and Eddy Current‐Based Measurements for Online Detection of Deformation‐Induced Martensite During Flow Forming of Metastable Austenitic Steel AISI 304L

ABSTRACTThis paper deals with micromagnetic measurements for online detection of strain‐induced α′‐martensite during plastic deformation of metastable austenitic steel AISI 304L. The operating principles of the sensors are magnetic Barkhausen noise (MBN) and eddy currents (EC), which are suitable for detection of microstructure evolution due to formation of ferromagnetic phases. The focus of this study was put on the qualification of different micromagnetic techniques and different measurement systems under conditions similar to the real ones during production, which is crucial for implementation of a property‐controlled flow forming process. The investigation was carried out on tubular specimens produced by flow forming, which have different content of α′‐martensite. To characterize the sensitivity of the sensors, different contact conditions between sensors and workpieces were reproduced. MBN sensors are suitable for detecting amount of α′‐martensite, but the measurements are affected by the surface roughness. This entails that the calibration models for MBN sensors must take account of these effects. EC sensors show a closer match with the amount of α′‐martensite without having major affectation by other effects.

Evaluation of MRI Safety of Ru-106 Eye Applicators

Introduction: Ruthenium-106 brachytherapy is a primary treatment for uveal melanoma (UM), the most common intra-ocular malignancy in adults. This study evaluated the safety of Ru-106 applicators at 3 Tesla (T) MRI and their impact on image quality. Methods: Magnetic attraction and eddy currents were tested on a 20-mm-diameter Ru-106 applicator using a nylon string and a porcine eye. Safety criteria were defined by ocular oncologists, comparing magnetic field interactions to the forces exerted on the eye during surgery. Five UM patients were scanned at 3T MRI with the applicator in situ using both conventional anatomical sequences and scans optimised to reduce metal artefacts. Results: Minimal magnetic interactions were observed. Eddy currents caused slight lagging during fast movements and temporary detachment of the applicator of the porcine eye in conditions that were considered unrealistic for clinical scans. Significant susceptibility artefacts compromised image quality of the affected eye. Conclusion: Patients with Ru-106 applicators can be safely used in 3T MRI with some simple precautions. MR image quality of the eye was poor due to major susceptibility artefacts; however, imaging of extra-ocular anatomy is feasible.

Sol-gel synthesis, structure and magnetic properties of barium aluminoferrite for use in magnetorheological fluids

A promising area of application of micro- and nanosized magnetic particles is the creation of magnetorheological materials in which such particles are a component of a complex dispersed phase. Of greatest importance is the high shear stress in suspensions based on magnetic particles when a magnetic field is applied, as well as low value of the coercive force. The aim of the work was to study the structure, morphology, and magnetic properties of barium aluminoferrite powders, and to evaluate their effectiveness in magnetic fields by the rheological properties of magnetorheological fluids fabricated using them. Barium aluminoferrite BaAl2Fe10O19 of hexagonal structure was synthesized by the citrate sol-gel method. Using the methods of X-ray phase analysis, scanning electron microscopy, IR spectroscopy, magnetometry, its structural and microstructural features, and magnetic properties were studied. The powder had a maximum specific magnetization M = 20.4 A × m2/kg and a coercive force Hc = 4.8 kOe (at 300 K). The high shear stress (3.5 kPa) at a relatively low magnetic field induction (625 mT) makes it possible to consider the resulting material as promising for use as an additional functional filler for magnetorheological fluids.

A wideband circularly polarized filtering dielectric resonator antenna array based on magneto-electric currents combination

ABSTRACT A circularly polarized (CP) filtering dielectric resonator antenna (DRA) array is proposed based on the magneto-electric currents combination (MECC) method in this paper. The array consists of four rectangular DRAs, four hook-shaped electric dipoles (HSED), and two layers of substrate integrated waveguide (SIW) cavities. The electric current (EC) on the HSED is excited by the slot aperture of the SIW cavity, and the equivalent magnetic current (MC) is simultaneously generated with HSED in the DRA. Based on the surface current regulation, the EC and MC are adjusted to achieve appropriate amplitudes and phases, thereby realizing wideband CP radiation. The filtering function is realized with the high-pass characteristics of the SIW and the effective suppression of the higher-order modes in the resonance cavity. Due to the presence of an air gap between the DRAs and HSED, the higher modes of the DRA are designed for bandwidth enhancement. The prototype of the DRA array has been fabricated and measured, exhibiting a relative bandwidth of 26.1% and an axial ratio bandwidth of 17.77%, with radiation nulls present at either side of the passband. With the advantages of wide bandwidth and high gain, the proposed DRA array can be applied to satellite communications.

Magnetization-current-induced E1 transition in the d+t→α+n+γ reaction

The d−t collisions have a minor reaction branch, of the order of 10−5, involving γ emission from the incident state with the spin of 3/2+ to the final 3/2− and 1/2− states of the α−n system. Standard E1 treatment of such a transition results in zero cross sections because of the spin conservation rule. For this reason, the first theoretical work on d+t→α+n+γ [], described the E1 transition as coming from the high-energy d-wave spin-1/2 state of the α−n partition of He5, coupled to the d−t component by tensor interaction. However, the exact E1 operator contains a contribution from the usually neglected magnetization current, represented by the nucleon spin operators, which can allow the E1 d+t→α+n+γ transition to occur without passing via the d-wave spin-1/2 α−n channel. The present paper studies the magnetization-current-induced E1 transition using several potential models of the d−t interaction. It was found that the strength of this transition depends strongly on the choice of the d−t interaction model. With the optical folding potential, correctly capturing the deuteron extended structure, this contribution is suppressed by three orders of magnitude, thus validating its neglect in the previous work. Published by the American Physical Society 2024

Optical reflection signature of an axion dielectric with magnetic current

Optical reflection signature of an axion dielectric with magnetic current

Performance evaluation of a racetrack high temperature superconductor winding in an HTS levitation platform

Abstract High temperature superconducting (HTS) is a key technology for next generation high-speed railway systems, which guarantees high current and highly efficient traction power supplies. HTS devices can reduce system weight and thus improve loads of vehicles. In high-speed maglev trains, HTS windings wound by second-generation HTS tapes play an important role in suspension and traction. However, in complex ferromagnetic environments, the performance of windings is notably influenced by the varying magnetic fields. In this paper, a new maglev platform is designed and comprised of a winding of six racetrack HTS coils, an E-shaped iron core and a magnetic guide rail. The air core structure of the winding is modeled and tested and the electromagnetic characteristics are analyzed for three dimensional finite element analysis of the platform. An A formulation is used to calculate magnetic vectors A and infer magnetic flux densities and current densities for the structures. After the winding is installed on the iron core and the magnetic guide rail is suspended above the iron core, the air gap between the iron core and the rail is varied from 0 mm to 20 mm in models and experiments. The magnetic fields, critical currents and losses of the winding in the cases of the air core and the iron core conditions are used for analysis. The comparison between the air core and the iron core conditions confirms the reliability of the proposed models. This study provides a means for the analysis of complex superconducting maglev systems.

Changes in the functional connections of the brain in patients with hypersomnia in acute ischemic stroke

BACKGROUND: The Disorders of cerebral circulation and sleep are inextricably related, since sleep disorders, including hypersomnia, are closely intertwined with cardiovascular diseases and increase the risk of stroke. Research works on visualization of functional brain changes in patients with sleep disorders and acute ischemic stroke are very few and need more study. AIM: to determine the functional connections of the brain in hypersomnia in patients with acute ischemic stroke by performing functional magnetic resonance imaging at rest. A study of 40 patients with acute ischemic stroke and sleep disorders was performed on the basis of the Federal State Budgetary Institution Almazov Research Center of the Ministry of Health of the Russian Federation. All patients underwent neurological examination, assessment of sleepiness, worry and depression, magnetic resonance imaging was performed on tomographs with a magnetic field induction force of 1.5T, using a standard protocol and special pulse sequences of T-gradient echo 3D MPRAGE and BOLD. Functional magnetic resonance imaging of the brain at rest was used to assess functional connections. Postprocessing was performed using specialized CONN-TOOLBOX software with an appropriate graphical representation of quantitative results based on the selection of areas of interest. RESULTS: Among the examined patients, 23 had hypersomnolence; of these, 8 patients were diagnosed with secondary hypersomnia associated with sleep apnea syndrome. Thus, in the examined sample, post-stroke hypersomnolence was detected in 15 patients (34%). Patients with an unspecified subtype of stroke and right-sided lesions showed a high degree of drowsiness (p 0.05). With the help of functional magnetic resonance imaging of the brain at rest, changes in functional connections between the main nodes of the default mode network with the left temporal pole, cerebellum, central cerebral cortex on the left, angular gyrus on the left, with the dorsal attention network on the right are determined (p 0.05). CONCLUSION: The use of complex magnetic resonance imaging, which includes structural and functional magnetic resonance imaging in patients with acute ischemic stroke and sleep disorders, allows us to identify structural changes and changes in functional connectivity and identify neuroimaging markers of this pathology. Hypersomnolence is typical for patients with an unspecified subtype of ischemic stroke and damage to the right hemisphere of the brain.

Functional study of the brain based on magnetic resonance imaging in patients with insomnia disorders

BACKGROUND: Insomnia has a significant impact on the quality of life of patients. Despite the progress in understanding the pathophysiological mechanisms of insomnia, the possibilities of its objective diagnosis remain insufficiently studied. This study can contribute to understanding the neural mechanisms of insomnia, contribute to the development of new diagnostic and treatment methods, and personalize therapeutic approaches to improve the quality of life of patients with insomnia disorders. AIM: to evaluate changes in the brain connectome in patients with psychophysiological and paradoxical insomnia by performing functional magnetic resonance imaging. MATERIALS AND METHODS: A total of 31 patients were examined who applied for a somnologist appointment at the Federal State Budgetary Institution Almazov National Medical Research Centre of the Ministry of Health of the Russian Federation with diagnosed chronic insomnia. All patients underwent polysomnographic examination using Embla N 7000 (Natus, USA) and SOMNO HD (SOMNOmedics, Germany) for one night with an assessment of the main characteristics of sleep according to the rules of AASM 2.5. Also, all study participants underwent magnetic resonance imaging of the brain on tomographs with a magnetic field induction force of 3.0 Tl at two time points. Statistical analysis of MRI data was performed using MathLab 2023a, CONN v22.a packages. Descriptive statistics, the Kolmogorov–Smirnov criterion were used for processing materials, depending on the characteristics of the data, the Mann–Whitney U-criterion and Pearson Chi-squared were used to analyze demographic data. DISCUSSION: The study demonstrates the possibilities of functional magnetic resonance imaging in obtaining data on the functional connections of the brain in insomnia. The detected changes in the activity of various brain regions indirectly or directly involved in the regulation of sleep and wakefulness are consistent with the most common pathogenetic models of insomnia, in particular with the theory of hyperactivation and the model of sleep reactivity to stress. CONCLUSION: The results of the study emphasize the relevance of studying functional changes in the brain in insomnia, opening up new opportunities for more accurate diagnosis and the development of personalized treatment methods.

Improvement of superconducting, morphological, and flux pinning ability of YBa2Cu3O7−y matrix with oxygen and Mn2O3 impurity

Abstract In the current work, the influence of oxygen and Mn2O3 impurity levels intervals 0.00 ≤ x ≤ 0.30 on various key properties such as electrical resistivity, superconducting, flux pinning ability, stabilization of ceramic system, and morphological properties of YBa2Cu3O7-y (Y-123) superconductor were examined by electrical resistivity, critical current density, and scanning electron microscopy (SEM), electron dispersive x-ray (EDX) measurements. The EDX test results indicated that all the Y-123 ceramics produced possessed different composition distributions on the sample surface. SEM photomicrographs also confirmed the improvement in the appearance of surface morphology and crystallinity quality of the YBa2Cu3O7-y system. Moreover, the development in the interaction quality between grains, pinning ability and strength quality of 2D coupled vortices was obtained with the oxygen ambient and optimum manganese impurity addition highly dispersing throughout the intra grain and inter-grain boundary couplings due to the increase in the artificial flux pinning nucleation sites in the Y-123 system. Thus, the best sample with the highest Jc value of 98 A/cm2 showed the most resistance to the applied magnetic field and current. Similarly, the same sample exhibited the greatest superconductive offset (98.320 K) and onset (100.504 K) temperatures values based on the development of the Cu-O coordination and stability of the crystal structure. In conclusion, this comprehensive study based on the analysis of oxygen and Mn2O3 impurity addition mechanism through the YBa2Cu3O7-y ceramic matrix may open a new and applicable field for advanced engineering, heavy industry technology and large-scale applications.