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Results for “MAGNETIC CORES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Fabrication of magnetic core PEI-silica shell particles

Highlights: • PEI-silica shell fabrication was developed for iron-carbonyl core material. • Magnetic separation of core-free by-product of the fabrication proved successful. • Varying fabrication method/concentration successfully tuned shell characteristics. • Sonication methods produced smooth coatings with a trend towards multicore particles. • Raspberry-like coatings were made by the slow addition, one- and two-pot methods. - Abstract: Magnetic core-silica shell particles combine the physico-chemical properties of the silica shell with the magnetic properties of the core. Seven possible particle coating methods utilizing the biomimetic polyamine polyethyleneimine (PEI) as the silication catalyst, have been identified and the objective of this study was to link the properties of the final PEI-silica coating with the methodology. The PEI-silica coated carbonyl iron particles were characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transfer infrared spectroscopy. Varying the fabrication method and silane concentration successfully tuned the shell characteristics. Methods using sonication produced smooth more evenly distributed coatings with a tendency towards multicore particles. In contrast, raspberry-like coatings were produced via the slow addition, one- and two-pot methods. The magnetic separation process after synthesis achieved a degree of purification that makes these core–shell particles useful for potential applications that require specific surface interactions and the ease of magnetic separation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Magnetic-Core/Gold-Shell Nanoparticles for the Detection of Hydrophobic Chemical Contaminants

Magnetic-core/gold-shell nanoparticles (MAuNPs) are of interest for enabling rapid and portable detection of trace adulterants in complex media. Gold coating provides biocompatibility and facile functionalization, and a magnetic core affords analyte concentration and controlled deposition onto substrates for surface-enhanced Raman spectroscopy. Iron oxide cores were synthesized and coated with gold by reduction of HAuCl4 by NH2OH. MAuNPs were grafted with polyethylene glycol (PEG) and/or functionalized with 4-mercaptobenzoic acid (4-MBA) and examined using a variety of microscopic, spectroscopic, magnetometric, and scattering techniques. For MAuNPs grafted with both PEG and 4-MBA, the order in which they were grafted impacted not only the graft density of the individual ligands, but also the overall graft density. Significant Raman signal enhancement of the model analyte, 4-MBA, was observed. This enhancement demonstrates the functionality of MAuNPs in direct detection of trace contaminants. The magnetic deposition rate of MAuNPs in chloroform and water was explored. The presence of 4-MBA slowed the mass deposition rate, and it was postulated that the rate disparity originated from differing NP-substrate surface interactions. These findings emphasize the importance of ligand choice in reference to the medium, target analyte, and substrate material, as well as functionalization procedure in the design of similar sensing platforms.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Low-Loss, High-Flux Saturation Magnetic Cores for Power Converters

As new and alternative energy sources are added to the energy grid, efficient and low-loss power converters are essential to the storage of energy from these intermittent power sources. Higher operating frequency can reduce the size and weight of transformers. However, current magnetic cores limit the operating frequency because core losses increase with frequency. Therefore, new magnetic core materials are needed with higher resistivity (lower eddy-current losses), lower coercivity (lower hysteresis losses), and higher permeability and flux density (higher power density). These new materials must be integrated into isolated power converters designed to optimize efficiency based on the transformer performance. To address this need, Mainstream pursued a two-pronged approach in Phase I to develop novel magnetic materials and model a planar transformer design. We irradiated silicon steel with a high-energy electron beam in an attempt to induce nanocrystalline grain formation. The nanocrystalline grains were expected to increase resistivity to reduce eddy-current losses and decrease coercivity to reduce hysteresis losses. We also modeled the transformer performance through Simulation Program with Integrated Circuit Emphasis (SPICE) and analytical models to establish the effect of magnetic properties of the core on the performance of the transformer. There still are hurdles to be overcome in Phase II. The electron beam processing was successful in increasing the resistivity and the flux saturation density. However, the resistivity is still too low for high-frequency magnetic cores, because the eddy-current losses would be prohibitively high. Additionally, the coercivity increased for the processed samples leading to higher hysteresis losses. In comparing our SPICE and analytical models to the planar transformer measured values and impedance plots, good agreement was seen for primary and secondary short-circuit impedance measurements and for primary-to-secondary capacitance measurements. The SPICE model deviated from measured values, though, when measuring the transformer open-circuit impedance, indicating that we might need to add more model complexity to the transformer model. Phase II research will continue to build on the transformer model and integrating novel magnetic materials into high-frequency transformers.

15 GEOTHERMAL ENERGY↗
DOE OSTI2025

A Mössbauer Spectroscopy Investigation of Nickel‐Zinc Ferrites Synthesized by a Self‐Combustion Method for Soft Magnetic Core Applications

Soft ferrites are materials of interest for magnetic cores, as used for wireless charging transformers. Their low permeabilities, high resistivity, and magnetic polarization make them interesting for high-power electric vehicle charging and drive systems. The nickel-zinc-doped ferrites are of particular interest; however, the compositional space is quite large with respect to dopant concentrations, stoichiometric ratios and synthesis technique. Nickel-zinc spinel ferrites with varying nickel-zinc ratios prepared by a self-combustion reaction followed by heat treatment exhibit good crystallinity, and their low-temperature Mössbauer spectra show local magnetism and site occupation in agreement with materials prepared by solid-state reaction. Thus, the combustion synthesis method offers a facile tunability of compositions, which, combined with the possibility of rapid characterization of atomic-scale magnetism by Mössbauer spectroscopy, enables advances in the compositional and processing space at a fast pace. Low-temperature Mössbauer spectroscopy data for samples with increasing nickel content reveals a systematic increase in average hyperfine field (2.8 T/Ni) and decrease in average isomer shift (−0.036 mm/s/Ni) that can determine the nickel/zinc content, even in the absence of applied magnetic field data. Furthermore, a gradual evolution of color is also observed with increasing nickel content, albeit trends in color depend on sintering conditions.

Mössbauer spectroscopy↗
DOE OSTI2024

Fast ion confinement in the presence of core magnetic islands in Wendelstein 7-X

The effect of magnetic islands in the core region of Wendelstein 7-X (W7-X) on fast ion confinement is explored through simulations with the BEAMS3D code. A magnetic configuration where the n/m = 5/5 island chain is shifted to r/a ~ 0.7 allows the exploration of core island physics in W7-X. The control coil system on W7-X allows the tuning of the island size either increasing the island width or decreasing it. A coupling of the BEAMS3D code to the FIELDLINES code provides a versatile mechanism for incorporating magnetic islands and stochastic regions into the BEAMS3D code. Collisionless simulations suggest that the presence of core islands degrade the confinement of passing particles in the region of the island chain. Full neutral beam simulations of W7-X show a similar behavior with confinement decreasing as the island width is increased. Comparisons between a vacuum magnetic field and low beta HINT2 simulation are made showing similar fast ion behavior. Measurements of lost fast ions in W7-X confirm this trend with the control coil suppressed island configuration showing lower losses than that with no control coils applied. Simulations of fast ion wall loads are performed suggesting no drastic change in loss pattern and a slight reduction in losses with minimized islands.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

A TOpographic Mapping (ATOM) Method to Design Magnetic Cores

Wireless power transfer offers safe, convenient, and efficient way of charging electric vehicles. Ongoing research is targeting wireless charging pad design optimization; designing the magnetic component is the most important part of the coupler design because the magnetic part determines the coupling factor and efficiency. Optimizing the coil layout and geometry as well as ferrite design requires finite elements analysis based modeling and simulation for minimized core losses, maximized magnetic coupling, and minimized material use for cost-effectiveness. Although parametric finite element analysis or emerging artificial intelligence methods can generate very accurate results, simulation times are extremely long. To address this issue, this study proposes a simple, effective core design called A TOpographic Mapping (ATOM). The proposed design is based on the design of magnetic core by using the magnetic flux distribution. The thickness of the core increases with increasing magnetic flux density, forming a variable thickness core design with less material and minimized core losses compared to conventional designs. A superimposing method is used to create an optimal design for a rotational magnetic field-based system. According to simulation results, the ATOM design reduces the required material volume by 13.19% and yields the lowest core loss and highest mutual inductance compared to other designs. In addition, misalignment, electromagnetic interference, and thermal performance were evaluated for the proposed design.

Aydin, Emrullah [Oak Ridge National Laboratory (OR↗
DOE OSTI2015

DYNAMICS OF MULTI-CORED MAGNETIC STRUCTURES IN THE QUIET SUN

We report on the dynamical interaction of quiet-Sun magnetic fields and granular convection in the solar photosphere as seen by Sunrise. We use high spatial resolution (0.″15–0.″18) and temporal cadence (33 s) spectropolarimetric Imaging Magnetograph eXperiment data, together with simultaneous CN and Ca ii H filtergrams from Sunrise Filter Imager. We apply the SIR inversion code to the polarimetric data in order to infer the line of sight velocity and vector magnetic field in the photosphere. The analysis reveals bundles of individual flux tubes evolving as a single entity during the entire 23 minute data set. The group shares a common canopy in the upper photospheric layers, while the individual tubes continually intensify, fragment and merge in the same way that chains of bright points in photometric observations have been reported to do. The evolution of the tube cores are driven by the local granular convection flows. They intensify when they are “compressed” by surrounding granules and split when they are “squeezed” between two moving granules. The resulting fragments are usually later regrouped in intergranular lanes by the granular flows. The continual intensification, fragmentation and coalescence of flux results in magnetic field oscillations of the global entity. From the observations we conclude that the magnetic field oscillations first reported by Martínez González et al. correspond to the forcing by granular motions and not to characteristic oscillatory modes of thin flux tubes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

On the Geometry of the Near-core Magnetic Field in Massive Stars

It is well-known that the cores of massive stars sustain a stellar dynamo with a complex magnetic field configuration. However, the same cannot be said for the field's strength and geometry at the convective–radiative boundary, which are crucial when performing asteroseismic inference. In this Letter, we present 3D magnetohydrodynamic (MHD) simulations of a 7 M ⊙ mid-main-sequence star, with particular attention given to the convective–radiative boundary in the near-core region. Our simulations reveal that the toroidal magnetic field is significantly stronger than the poloidal field in this region, contrary to recent assumptions. Moreover, the rotational shear layer, also important for asteroseismic inference, is specifically confined within the extent of the Brunt–Väisälä frequency peak. These results, which are based on the inferred properties of HD 43317, have widespread implications for asteroseismic studies of rotation, mixing, and magnetism in stars. While we expect our results to be broadly applicable across stars with similar Brunt–Väisälä frequency profiles and stellar masses, we also expect the MHD parameters (e.g., Re m ) and the initial stellar rotation rate to impact the geometry of the field and differential rotation at the convective–radiative interface.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Anisotropic formation of magnetized cores in turbulent clouds

In giant molecular clouds (GMCs), shocks driven by converging turbulent flows create high-density, strongly magnetized regions that are locally sheetlike. In previous work, we showed that within these layers, dense filaments and embedded self-gravitating cores form by gathering material along the magnetic field lines. Here, we extend the parameter space of our three-dimensional, turbulent MHD core formation simulations. We confirm the anisotropic core formation model we previously proposed and quantify the dependence of median core properties on the pre-shock inflow velocity and upstream magnetic field strength. Our results suggest that bound core properties are set by the total dynamic pressure (dominated by large-scale turbulence) and thermal sound speed c{sub s} in GMCs, independent of magnetic field strength. For models with a Mach number between 5 and 20, the median core masses and radii are comparable to the critical Bonnor–Ebert mass and radius defined using the dynamic pressure for P{sub ext}. Our results correspond to M{sub core}=1.2c{sub s}{sup 4}(G{sup 3}ρ{sub 0}v{sub 0}{sup 2}){sup −1/2} and R{sub core}=0.34c{sub s}{sup 2}(Gρ{sub 0}v{sub 0}{sup 2}){sup −1/2} for ρ{sub 0} and v{sub 0}, the large-scale mean density and velocity. For our parameter range, the median M{sub core}∼0.1−1M{sub ⊙}, but a very high pressure cloud could have lower characteristic core mass. We find cores and filaments form simultaneously, and filament column densities are a factor of ∼2 greater than the surrounding cloud when cores first collapse. We also show that cores identified in our simulations have physical properties comparable to those observed in the Perseus cloud. Superthermal cores in our models are generally also magnetically supercritical, suggesting that the same may be true in observed clouds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Magnetic cores with high reluctance differences in flux paths

Embodiment of the present invention includes a magnetic structure and a magnetic structure used in a direct current (DC) to DC energy converter. The magnetic structure has an E-core and a plate, with the plate positioned in contact or in near contact with the post surfaces of the E-core. The E-core has a base, a no-winding leg, a transformer leg, and an inductor leg. The no-winding leg, the transformer leg, and the inductor leg are perpendicular and magnetically in contact with the base. The plate is a flat slab with lateral dimensions generally larger than its thickness. The plate has a plate nose that overlaps a top no-winding leg surface of the no-winding leg with a no-winding gap area to form a no-winding gap with a no-winding gap reluctance. The plate also has a plate end that overlaps a top inductor leg surface of the inductor leg with an inductor gap area to form an inductor gap with an inductor gap reluctance. In some embodiments, e.g., where the duty cycle is less than 50 percent, the inductor gap reluctance will be designed to be less than the no-winding gap reluctance. In these cases, the majority of the magnetic flux that passes through the transformer leg will return through the inductor leg, instead of through the no-winding leg. The inductor and no-winding gap reluctances can he adjusted, so that the electromotive force applied to a charge passing through the inductor will partially cancel the electromotive force applied by the transformer secondary. The gap reluctance ratio can be defined, so that the difference in secondary and inductor electromotive forces is equal to the output voltage defined by an optimal no-ripple duty cycle. In this way no changing current is required through the inductor to create a dI/dt inductive voltage drop across the output inductor. Zero output current ripple is achieved.Various embodiments of the plate, plate shape, and no-winding leg are disclosed. These embodiments allow achieving a high ratio of no-winding gap reluctance to inductor gap reluctance, for practical, affordable magnetic material structures and aspect ratios. A high gap reluctance ratio enables zero output current ripple for the high transformer turns ratios that are needed to achieve high input to output voltage ratios. The embodiments therefore allow achieving low output current ripple for 48 V or higher input voltages, 1 V or lower output voltages, and high output currents.

Yao, Yuan↗
DOE OSTI2021

Spin-lattice dynamics of surface vs core magnetization in Fe nanoparticles

Magnetization of clusters is often simulated using atomistic spin dynamics for a fixed lattice. Coupled spinlattice dynamics simulations of the magnetization of nanoparticles have up to now neglected the change in the size of the atomic magnetic moments near surfaces. We show that the introduction of variable magnetic moments leads to a better description of experimental data for the magnetization of small Fe nanoparticles. To this end we divide atoms into a surface-near shell and a core with bulk properties. Here, it is demonstrated that both the magnitude of the shell magnetic moment and the exchange interactions need to be modified to obtain a fair representation of the experimental data. This allows for a reasonable description of the average magnetic moment versus cluster size, and also the cluster magnetization versus temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Modeling and Measuring the Stress Distribution in Soft Magnetic Cores due to Epoxy Impregnation and Curing

Understanding the effects of viscoelastic relaxation of stresses is critical in electric motor and inductor applications, where the magnetic material is fully or partially comprised of an amorphous phase and impregnated in an epoxy. Magnetic Amorphous Nanocomposites (MANCs) are a class of recently developed high-frequency magnetic materials that exhibit low magnetic hysteresis, high saturation flux density and very low AC magnetic losses. MANCs are formed as long, thin ribbons, a shape factor that minimizes eddy current-induced self-heating. This feature, in addition to their 1 GPa strength, and makes them attractive candidates for high-speed, high-power density, electric motors. MANCs are used in the form of tape-wound cores (TWCs). During the manufacturing process, the cores are impregnated with liquid epoxy between each layer of ribbon. Validated knowledge of the stresses imposed by the manufacturing process and during operation is necessary to understand motor performance limitations with respect to strength. Magnetostriction, the strain imposed by reversal of the magnetic field, also affects performance. When the epoxy cures, it contracts volumetrically by 8%, imposing radial and circumferential stresses that vary along the radial direction. To date, these stresses have received little attention in the literature. Here, we model the stress distribution throughout a TWC due to epoxy curing. Strain gauge measurements reported here indicate substantially lower tangential strain than model values, which is beneficial and which we attribute to viscoelastic relaxation of the epoxy layers. We will incorporate a constitutive model of this viscoelastic relaxation, and conduct more detailed strain measurements to understand how this takes

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Extending Magnetic Core Shell Nanoparticle Extraction Technology to Cesium and Antimony Removal from Geothermal Brines in New Zealand

Our industrial client (Geo40) has developed and deployed a process to remove silica from geothermal fluids and produce a high-margin specialty colloidal silica product comparable to those of market leaders. Geo40 now wishes to explore opportunities to extend their mineral extraction operations to other elements that are present in these brines. Geo40 has identified cesium (Cs) that is present in Ohaaki brines (pH ~8–8.5) at parts per million levels and could be sold to customers if it could be produced at an attractive price. With support from the Department of Energy’s (DOE’s) Geothermal Technologies Office, a simple and highly cost-effective magnetic nanofluid method for extraction of rare earth elements (REEs) from geothermal brine solutions has been developed and demonstrated at the laboratory bench scale at Pacific Northwest National Laboratory (PNNL). Core shell sorbent particles are produced using an iron oxide core particle, which is used to anchor and grow a surrounding adsorbent shell functionalized with a chelating ligand that selectively binds REEs. We extended PNNL’s work by exploring new sorbent shells that are highly selective for Cs. Uptake of Cs was measured as a function of exposure time by analyzing solution samples extracted from batch sorption tests.

15 GEOTHERMAL ENERGY↗