Magnetic Pulse Research Articles

Mechanical properties and interface morphology of magnetic pulse-welded Al–Fe tubes with preset geometric features

A dissimilar metal tube joint fabricated by magnetic pulse welding (MPW) usually has uneven mechanical properties and an uneven morphology along the welding direction due to the small discontinuous matching range of the collision parameters. In this work, inclined, concave, and convex wall features were prefabricated on the target tube to improve the uniformity of the mechanical properties. The effects of the types of features and the prefabricated angle on the collision parameters, the axial distribution of the strength, and the interfacial morphology were investigated by simulations, shear tests, and microscopic observations, respectively. The results show that the collision parameters were increased with the increase of the prefabricated angle under the three types of features. Compared with the case without features, the increment of the collision parameters was found to be the greatest under the convex wall feature, and the smallest under the concave wall feature. With the increase of the prefabricated angle under the three types of features, the average shear strength tended to be reduced. When the prefabricated feature was the concave wall with a prefabricated angle of 5°, the quality of the joint was the best; it had an average shear strength of 46.46 MPa, an increase of 87%, and a low standard deviation of 4.96 MPa, a decrease of by 81%, as compared with that without geometric features. The transition layer was found to be the largest under the concave wall feature, and the maximum thickness decreased with the increase of the prefabricated angle.

Does the Motor Cortex Want the Full Story? The Influence of Sentence Context on Corticospinal Excitability in Action Language Processing

The reading of action verbs has been shown to activate motor areas, whereby sentence context may serve to either globally strengthen this activation or to selectively sharpen it. To investigate this issue, we manipulated the presence of manual actions and sentence context, assessing the level of corticospinal excitability by means of transcranial magnetic stimulation. We hypothesized that context would serve to sharpen the neural representation of the described actions in the motor cortex, reflected in context-specific modulation of corticospinal excitability.Participants silently read manual action verbs and non-manual verbs, preceded by a full sentence (rich context) or not (minimal context). Transcranial magnetic stimulation pulses were delivered at rest or shortly after verb presentation. The coil was positioned over the cortical representation of the right first dorsal interosseous (pointer finger).We observed a general increase of corticospinal excitability while reading both manual action and non-manual verbs in minimal context, whereas the modulation was action-specific in rich context: corticospinal excitability increased while reading manual verbs, but did not differ from baseline for non-manual verbs. These findings suggest that sentence context sharpens motor representations, activating the motor cortex when relevant and eliminating any residual motor activation when no action is present.

Effect of Magnetic Pulse Treatment on Hexagonal Scandium-Substituted Ferrites with Multiferroic Properties

Effect of Magnetic Pulse Treatment on Hexagonal Scandium-Substituted Ferrites with Multiferroic Properties

Topological optimization of magnetic pulse welding coils with a connectivity-constrained particle swarm optimization algorithm

A connectivity-constrained optimization methodology based on a discretized particle swarm optimization (PSO) algorithm is proposed for the continuum structural design of a magnetic pulse welding coil. To address the classical continuum topological challenges of conductors, such as simple connectivity and checkerboard phenomena in the optimal topology, the PSO algorithm is combined with connectivity constraints and filtration. The evolutionary history and parametric tests in an electromagnetic structure study are employed to demonstrate the efficiency and robustness of the novel algorithm. Physical tests show that the optimized coil can form a larger effective welding area between aluminum alloy (AA5052) and steel (HC420LA) sheets compared with the joint formed by the original coil. The maximum tensile load is also significantly improved by 19.88% with a discharge energy of 22 kJ.

Induction Heating during Magnetic Pulse Processing of Metals: Perspective Schemes and their Application

The paper, based on a review of modern literature, highlights the features of the processes of magnetic pulse processing of metals in traditional schemes of technological processes of modern industrial production. New directions of their development are noted, which provide for the transformation of the natural forces of repulsion of the metal of the processed object into the forces of magnetic-pulse attraction while reducing the operating frequencies of the existing fields. The physics of Lenz-Joule heat dissipation is described, the result of which is the induction heating of conductors by Foucault currents in an external electromagnetic field. Examples of the use of induction heating in modern industry are given. Schemes of practical realizationof preinduction heating are offered, which allow to use both autonomous devices for eddy current excitation and stationary connection for the same purpose of additional power source. The possibility of increasing efficiency by increasing the ductility of the metal when heated is noted, as well as its possible limitations associated with increasing the active resistance of metals during the growth of Lenz-Joule heat dissipation. It is offered to use the received results at a choice of design decisions for elements of new schemes of the equipment of magnetic pulse processing of metals.

Magnetic-field-synchronized wireless modulation of neural activity by magnetoelectric nanoparticles

The in vitro study demonstrates wirelessly controlled modulation of neural activity using magnetoelectric nanoparticles (MENPs), synchronized to magnetic field application with a sub-25-msec temporal response. Herein, MENPs are sub-30-nm CoFe2O4@BaTiO3 core-shell nanostructures. MENPs were added to E18 rat hippocampal cell cultures (0.5 μg of MENPs per 100,000 neurons) tagged with fluorescent Ca2+ sensitive indicator cal520. MENPs were shown to wirelessly induce calcium transients which were synchronized with application of 1200-Oe bipolar 25-msec magnetic pulses at a rate of 20 pulses/sec. The observed calcium transients were similar, in shape and magnitude, to those generated through the control electric field stimulation with a 50-μA current, and they were inhibited by the sodium channel blocker tetrodotoxin. The observed MENP-based magnetic excitation of neural activity is in agreement with the non-linear M − H hysteresis loop of the MENPs, wherein the MENPs’ coercivity value sets the threshold for the externally applied magnetic field.

Magnetic Field Magnitudes Needed for Skyrmion Generation in a General Perpendicularly Magnetized Film.

Due to its topological protection, the magnetic skyrmion has been intensively studied for both fundamental aspects and spintronics applications. However, despite recent advancements in skyrmion research, the deterministic creation of isolated skyrmions in a generic perpendicularly magnetized film is still one of the most essential and challenging techniques. Here, we present a method to create magnetic skyrmions in typical perpendicular magnetic anisotropy (PMA) films by applying a magnetic field pulse and a method to determine the magnitude of the required external magnetic fields. Furthermore, to demonstrate the usefulness of this result for future skyrmion research, we also experimentally study the PMA dependence on the minimum size of skyrmions. Although field-driven skyrmion generation is unsuitable for device application, this result can provide an easier approach for obtaining isolated skyrmions, making skyrmion-based research more accessible.

Comprehensive Weldability Criterion for Magnetic Pulse Welding of Dissimilar Materials

Despite its exceptional ability to join dissimilar materials and environmental friendliness, several challenges must be addressed in magnetic pulse welding (MPW). The conventional weldability criterion (i.e., minimum impact velocity) is analytically calculated as a function of material properties without considering the geometry of electromagnetic coil, electrical and physical parameters, making the minimum impact velocity a necessary but not sufficient condition for a sound MPW joint. A new weldability criterion, namely effective impact velocity, is proposed, which overcomes the conventional weldability criterion’s limitations. The effective impact velocity can be inversely modelled to identify shop-floor relevant process parameters and it eliminates the need to fabricate several coils in the process and product proving stages. The proposed approach is demonstrated by a case study on tubular welding of Aluminium and SS304. The weld’s soundness produced with computed process parameters was corroborated by experimental observations on lap shear tests, hardness measurements, optical and scanning electron microscopy, and surface energy dispersive spectroscopy mapping. This investigation is expected to pave the way for developing the process window for MPW of several material combinations, with high cost and time savings.

Properties of Compacts from Mixtures of Calcium Fluoride Micro- and Nanopowders

In this work, compacts from mechanical mixtures of CaF2 micron powder (MCP) with CaF2 nanopowder (NP) additives were produced, with mass ratios of the mixture components ranging from 10:0.125 to 10:1, respectively, using magnetic pulse (MP) and static pressing (SP) methods. The effects of pressure (Pp) and pressing temperature (Tp), concentration and phase composition of the additive on the density and color of compacts were studied, taking into account the properties of the initial components of the mixtures. The evolution of pulsed cathodoluminescence (PCL) spectra and photoluminescence (PL) of compacts from pure powders and their mixtures depending on Pp, Tp and characteristics of initial CaF2 NP was also studied. A new near-infrared (NIR) band associated with fluoride vacancies was discovered with a maximum at ~765 nm in PCL spectra of compacts produced by MP at a temperature of 425 °C. A blue band at 435 nm associated with impurity oxygen vacancies in the CaF2 lattice was found in PL spectra compacts of pure NP and powder mixtures. The density of compacts of pure NP and MCP reached 89% of the theoretical density, and the density of compacts of mixtures did not exceed 78%. The defective structure and phase composition of the CaF2 NP had a decisive effect on the luminescent properties of compacts from mixtures of micro- and nanopowders.

Photocatalytic and Antibacterial Activity of CoFe2O4 Nanoparticles from Hibiscus rosa-sinensis Plant Extract.

Biogenic CoFe2O4 nanoparticles were prepared by co-precipitation and Hibiscus rosa sinensis plant leaf was used as a bio-reductant of the nanoparticle productions. The biosynthesized CoFe2O4 nanoparticles were characterized by XRD, FTIR, UV, VSM, and SEM via EDX analysis. The cubic phase of biosynthesized CoFe2O4 nanoparticles and their crystallite size was determined by XRD. The Co-Fe-O bonding and cation displacement was confirmed by FTIR spectroscopy. The presence of spherically-shaped biosynthesized CoFe2O4 nanoparticles and their material were confirmed by SEM and TEM via EDX. The super-paramagnetic behaviour of the biosynthesized CoFe2O4 nanoparticles and magnetic pulse was established by VSM analysis. Organic and bacterial pollutants were eradicated using the biosynthesized CoFe2O4 nanoparticles. The spinel ferrite biosynthesized CoFe2O4 nanoparticles generate radical and superoxide ions, which degrade toxic organic and bacterial pollutants in the environment.

Magneto-optical Spectroscopy with RAMBO: A Table-Top 30 T Magnet

Optically probing materials in high magnetic fields can provide enlightening insight into field-modified electronic states and phases, while optically driving materials in high magnetic fields can induce novel nonequilibrium many-body dynamics of spin and charge carriers. While there are high-field magnets compatible with standard optical spectroscopy methods, they are generally bulky and have limited optical access, which prohibit performing state-of-the-art ultrafast and/or nonlinear optical experiments. The Rice Advanced Magnet with Broadband Optics (RAMBO), a unique 30-T pulsed mini-coil magnet system with direct optical access, has enabled previously challenging experiments using femtosecond optical pulses, including time-domain terahertz spectroscopy, in cutting-edge materials placed in strong magnetic fields. Here, we review recent experimental advances made possible by the first-generation RAMBO setup. After summarizing technological aspects of combining optical spectroscopic techniques with the mini-coil magnet, we describe results of magneto-optical studies of a wide variety of materials, providing new insight into the states and dynamics of four types of quasiparticles in solids - excitons, plasmons, magnons, and phonons - in high magnetic fields.

Magnetoelectric effects in a composite ferromagnet–piezoelectric heterostructure under pulsed excitation

Magnetoelectric (ME) effects in multiferroic ferromagnet–piezoelectric (PE) composite heterostructures result in a change in the electric polarization under the action of magnetic field or a change in the magnetization under the action of electric field and, therefore, are interesting from scientific point of view and for applications. In this work, the direct and converse ME effects are experimentally studied when a planar amorphous ferromagnet–PE lead zirconate–titanate structure is excited by magnetic and electrical field pulses with duration from microseconds to tens of milliseconds. Under the action of magnetic field pulses, the structure generates damped voltage oscillations with a frequency equal to the acoustic resonance frequency of the structure, as well as an exponentially decreasing dc voltage. By choosing the duration of magnetic pulses, it is possible selectively excite the linear ME effect in the structure or generate the second voltage harmonic at the resonance frequency. Electrical field pulses result in the excitation of damped magnetization oscillations at the resonance frequency of the heterostructure. The pulsed excitation method allows to estimate the ME conversion coefficients for both the direct and converse ME effects.

Dynamics of magnetic flux propagation in bulk, single grain superconducting rings during pulsed field magnetisation

When used as trapped field magnets (TFMs), single grain, bulk high-temperature superconducting (HTS) rings are promising candidates for the generation of strong, uniform magnetic fields for nuclear magnetic resonance. The pulsed field magnetisation (PFM) technique provides a low cost, compact and portable method to magnetise these samples as TFMs; however it has proven difficult to achieve high trapped fields in HTS rings using PFM. To date, a record field of only 0.60 T has been achieved for rings magnetised by single-pulse PFM—compared with over 4 T for disc-shaped HTS—and the reasons for this discrepancy are poorly understood. In this work, we use the finite element method to model the propagation of magnetic flux into HTS rings under quasi-static zero field cooled magnetisation and PFM, and validate the results analytically and experimentally. Magnetic flux is found to penetrate finite HTS rings from both the inner and outer surfaces, inducing a negative field at the inner face of the ring. This field is reversed as the applied field increases past the point of full penetration, locally dissipating magnetic energy and heating the sample. HTS rings are therefore more susceptible to local instabilities that severely limit their ability to trap a useful magnetic field. Consequently, thermomagnetic stability of HTS rings during single-pulse PFM can only be ensured by taking careful consideration of reducing flux movement through the bulk around the point at which the field is reversed. This may require more advanced PFM techniques like waveform control or multi-pulse stepwise-cooling to reduce local heating and increase the trapped field.

A magnetic pulse does not affect free-flight navigation behaviour of a medium-distance songbird migrant in spring.

Current evidence suggests that migratory animals extract map information from the geomagnetic field for true navigation. The sensory basis underlying this feat is elusive, but presumably involves magnetic particles. A common experimental manipulation procedure consists of pre-treating animals with a magnetic pulse, with the aim of re-magnetising particles to alter the internal representation of the external field prior to a navigation task. Although pulsing provoked deflected bearings in caged songbirds, analogous studies with free-flying songbirds yielded inconsistent results. Here, we pulsed European robins (Erithacus rubecula) at an offshore stopover site during spring migration and monitored their free-flight behaviour with a regional-scale network of radio-receiving stations. We found no pulse effect on departure probability, nocturnal departure timing departure direction or consistency of flight direction. This suggests either no use of the geomagnetic map by our birds, or that magnetic pulses do not affect the sensory system underlying geomagnetic map detection.

Generation of adiabatic pulses

A two-dimensional GaAs/AlGaAs quantum disk under the influence of a non-central potential resulting in azimuthal distortion, subjected to an external static electric field, is exposed to a linearly polarized laser pulse. Adiabatic magnetic pulses are found to be generated due to the introduction of distortion in the system. The magnitude of distortion is expected to serve as one of the crucial control parameters for the manipulation of the generated magnetic pulses. The production of desired magnetic pulses may prove beneficial in many bio-medical applications. • A distorted GaAs/AlGaAs quantum disk is exposed to sub-picosecond laser pulse. • Non-zero radial charge currents in addition to the azimuthal components are observed. • Optimized laser parameters are found to generate pure adiabatic magnetic pulses. • These photo-induced pulses are much prominent in case of finite azimuthal distortion. • Such magnetic pulses may prove beneficial for various bio-medical applications.

Commissioning Experiments at the Naval Postgraduate School Pulsed Power and EM Launch Laboratory

A new laboratory for pulsed power and electromagnetic (EM) launch research has been built and commissioned at the Naval Postgraduate School, Monterey, CA, USA. This facility is comprised of new, compact pulsed power modules that are 18 kJ each, as well as 1.1-MJ modules from the previous Electric Launch Facility at Kirkcudbright, Scotland. A total of 20 MJ of capacitive energy is stored to deliver pulsed, mega-ampere currents to loads, such as medium- and minor-caliber EM launchers, high-current test fixtures, and magnetic pulse generators. This equipment was recently commissioned with new instrumentation and data acquisition systems. A 5-m-long, medium caliber launcher was fired to commission the new facility, pulsed power, controls, and instrumentation. Circuit simulations compare favorably with experiments, exhibiting error on the order of 1%.

Prediction of response to repetitive transcranial magnetic stimulation for major depressive disorder using hybrid Convolutional recurrent neural networks and raw Electroencephalogram Signal.

Major Depressive Disorder (MDD) is a high prevalence disease that needs an effective and timely treatment to prevent its progress and additional costs. Repetitive Transcranial Magnetic Stimulation (rTMS) is an effective treatment option for MDD patients which uses strong magnetic pulses to stimulate specific regions of the brain. However, some patients do not respond to this treatment which causes the waste of multiple weeks as treatment time and clinical resources. Therefore developing an effective way for the prediction of response to the rTMS treatment of depression is necessary. In this work, we proposed a hybrid model created by pre-trained Convolutional Neural Networks (CNN) models and Bidirectional Long Short-Term Memory (BLSTM) cells to predict response to rTMS treatment from raw EEG signal. Three pre-trained CNN models named VGG16, InceptionResNetV2, and EffecientNetB0 were utilized as Transfer Learning (TL) models to construct hybrid TL-BLSTM models. Then an ensemble of these models was created using weighted majority voting which the weights were optimized by Differential Evolution (DE) optimization algorithm. Evaluation of these models shows the superior performance of the ensemble model by the accuracy of 98.51%, sensitivity of 98.64%, specificity of 98.36%, F1-score of 98.6%, and AUC of 98.5%. Therefore, the ensemble of the proposed hybrid convolutional recurrent networks can efficiently predict the treatment outcome of rTMS using raw EEG data.

Influence of impulse magnetic fields of extremely low frequencies on H2O2- and Fe2+-induced free radical lipid oxidation in liposomal suspensions

Background: For a long time, special attention in experimental biology and medicine is paid to free radical processes involving reactive oxygen species. In electromagnetic biology, the interest in free radical oxidation in biological membranes has increased significantly due to the discovery of spin mechanisms of magnetic fields on free radical processes. In the present day, these mechanisms are considered to be key in the processes of magnetoreception in living organisms. Liposomes, as the simplest models of biological membranes, are often used to study the primary mechanisms of action of different factors on the structural and functional properties of membranes. However, the influence of ecological significant extremely low-frequency magnetic fields on free radical oxidation in liposomal suspensions has not been studied enough. Objectives: The elucidation of the peculiarities of the influence of the extremely low frequency pulsed magnetic fields (ELF PMF) on H2O2- and Fe2+-induced peroxidation of natural phospholipids in liposomal suspensions. Materials and methods: The liposomal suspensions in phosphate buffer pH=7.4 were used. According to the literature and own results on light scattering the average diameter of liposomes was about 500Å. Ultra-weak chemiluminescence of liposomal suspensions was recorded using a device that operated in the mode of single photons counting. It consisted of a light-insulated cuvette unit where the test samples were placed, as well as a temperature sensor and a solenoid, which was used to create the PMF. Optical contact of the test samples with the photoelectron multiplier was carried out using a light guide. The recording system consisted of a broadband photomultiplier tube detector — FEU-130, which was at a temperature of –20°C. The pulse analyzer AI-256 was used to separate the useful signal that corresponded to the registration of single chemiluminescence light quanta. The voltage on the photomultiplier tube detector was applied in the range of current-voltage characteristics of this detector, in which a random voltage fluctuation had a minimal effect on the measurement of the useful signal. The number of light quanta that were recorded for defined time intervals characterized the overall intensity of the process of free radical oxidation of lipids in the experimental samples. The pulsed magnetic field was created using a solenoid coil located in the cuvette part. PMF was created using a serial generator G6-28. The magnetic field pulses were rectangular in shape with variable polarity for a period of oscillations. The induction of PMF was monitored using microteslameter G-79. The series of extremely low frequencies (5–80 Hz) and induction (5–500 μT) of PMF was chosen due to their environmental and physiological significance. Results: PMF of different frequencies with induction of 5 and 50 μT did not affect (p>0.05) H2O2- and Fe2+-induced lipid oxidation in liposomal suspensions. Statistically significant changes (p<0.05) were revealed only when liposomal suspensions were exposed to PMF with induction of 500 μT. It was found that the action of PMF with the frequency of 8 Hz 500 μT significantly inhibited H2O2-induced and enhanced Fe2+-induced chemiluminescence. This effect is associated with inhibition of the decomposition and with the accumulation of phospholipid hydroperoxides, which decompose and recombine in the presence of Fe2+ ions, which is accompanied by stronger chemiluminescence. The study of the dependence of the dynamics of the chemiluminescence intensity on the frequency of the PMF indicates the presence of a certain dependence of the effects in the range of up to 30 Hz. However, the inhibitory effect of PMF for the H2O2-induced oxidation phase is not always accompanied by a statistically significant increase in the amplitude of Fe2+-dependent light flash of chemiluminescence that indicates the general inhibitory effect of PMF at a certain frequency. Conclusions: PMF of extremely low frequencies statistically significantly affects the free radical oxidation in liposomal suspensions only at inductions exceeding several hundred microteslas. This indicates the effect of PMF on free radical processes for the conditions of the selected membrane model is realized mainly through spin interactions that determine the recombination of free radicals. The decrease of induction by one or two orders of magnitude, as well as increasing in frequency of the PMF above 50 Hz, leads to a decrease in the effectiveness of the influence of this physical factor on the intensity of lipid-free radical oxidation in liposomal suspensions. The most sensitive to the influence of ELF PMF is the phase of H2O2-induced free radical oxidation of lipids.

Characterization and evaluation of cold atmospheric plasma as seedborne fungal disinfectant and promoting mediator for physico-chemical characteristics of Moringa oleifera seedlings

Non-thermal atmospheric pressure plasmas are a powerful tool to impact seed germination and microbial decontamination. Air large volume atmospheric pressure glow discharge plasma was developed and investigated to improve the biological activities of Moringa oleifera seeds. Ninty ns magnetic pulse compression high voltage system was used to generate the plasma. The plasma discharges current increases with increasing applied voltage and it decreases with increasing discharge gap. There was a steady reduction in the count of seedborne fungi on the application of air cold plasma with complete elimination of fungi at ≥ 10.94 mJ per pulse. The low doses of plasma (2.46 and 4.35 mJ) induced an increase in the seed germination, a significant increase in chlorophyll content (chl a and chl b) and antioxidant activities of the seedlings emerged from soaked or wet seeds rather than dry seeds. At lower plasma doses (2.46 and 4.35 mJ) there was a significant increase in leaf area and chlorophyll content (chl a and chl b) of the seedlings that emerged from H2O2 soaked seeds rather than that of free from H2O2. The plasma was harmful when applied at higher doses (≥ 10.94 mJ) and more harmful to the wet seeds compared to the dry ones.

Simulation and experimental analysis of Al/Ti plate magnetic pulse welding based on multi-seams coil

Magnetic pulse welding is an effective way to achieve Al/Ti welding of light alloy materials via pulse electromagnetic forces. A new multi-seams structure coil applied to magnetic pulse welding technology was proposed to improve welding performance in this paper. The performance of the magnetic field, force filed, and displacement field applied by the new coil was also studied. Joining mechanism, mechanical properties and interface morphology of welded joints were studied by numerical simulation, tensile test and microscopic observation. The results show that the multi-seams coil has a larger welding area, and can improve the strength of welded joint by 28.8 % ~ 178.6 % under different standoff distance. The images from scanning electron microscopy showed that all welding interfaces were well connected without defects. And it was observed that the discharge energy would affect the welding interface morphology. This research can broaden the related applications of Al/Ti alloy welding.