High Magnetic Permeability Research Articles

Soft magnetic composites based on hybrid coated Fe-Si nanocrystalline powders

The preparation and characterisation of soft magnetic composite compacts based on hybrid coated nanocrystalline Fe-Si powder are presented. The Fe-Si powder was prepared by mechanical milling of Fe-Si electrical steels sheets up to 20h. The hybrid coating consists in an electrically insulating phosphate and a polymer layer that covers the Fe-Si particles. The influence of phosphating duration on the particles surface was investigated by SEM, EDX, XRD, and FTIR investigations. The saturation magnetisation of the powders phosphated for 60s decreases with 17% as compared to the uncoated powder. The influence of the compaction pressure, as well as the phosphating duration, on initial relative permeability and power losses of the compacts was investigated. It was found that increasing the compaction pressure leads to the increase of the compact's permeability and a decrease of the hysteresis losses. A shorter phosphating duration leads to a partial coating with phosphate of the Fe-Si particles and to compacts with higher density characterised by high magnetic permeability.

Magnetic induction of hyperthermia by a modified self-learning fuzzy temperature controller.

The aim of this study involved developing a temperature controller for magnetic induction hyperthermia (MIH). A closed-loop controller was applied to track a reference model to guarantee a desired temperature response. The MIH system generated an alternating magnetic field to heat a high magnetic permeability material. This wireless induction heating had few side effects when it was extensively applied to cancer treatment. The effects of hyperthermia strongly depend on the precise control of temperature. However, during the treatment process, the control performance is degraded due to severe perturbations and parameter variations. In this study, a modified self-learning fuzzy logic controller (SLFLC) with a gain tuning mechanism was implemented to obtain high control performance in a wide range of treatment situations. This implementation was performed by appropriately altering the output scaling factor of a fuzzy inverse model to adjust the control rules. In this study, the proposed SLFLC was compared to the classical self-tuning fuzzy logic controller and fuzzy model reference learning control. Additionally, the proposed SLFLC was verified by conducting in vitro experiments with porcine liver. The experimental results indicated that the proposed controller showed greater robustness and excellent adaptability with respect to the temperature control of the MIH system.

Ionic liquid ferrofluid interface deformation and spray onset under electric and magnetic stresses

An experimental and computational study is presented on the interfacial dynamics of a colloidal fluid having both high electric conductivity and high magnetic permeability in the presence of simultaneous electric and magnetic stresses on the fluid/air interface. A transient computational model is developed that simultaneously solves the Navier-Stokes equation and Maxwells’ static equations to predict the transient geometry of the fluid subject to electric and magnetic stresses. This model is first applied to predict the onset of spray emission from a capillary needle electrospray source subjected to a magnetic field. The experimentally determined onset of emissions at each magnetic field agreed well with those predicted by the simulation tool. The predictive modeling tool was then applied to analyze the interfacial profile of a sessile droplet subjected to both electric and magnetic fields. The model captured the geometric evolution of the droplet for voltages up to approximately 85% of the critical onset voltage; near the onset, the model slightly overpredicted the droplet deformation. Using the interfacial stress obtained from the modeling tool, a quantitative discussion is made regarding the roles and magnitudes of the electric and magnetic stress components on the lead-up to the emission instability.

Magnetic flux biasing of magnetostrictive sensors

The performance of magnetostrictive materials, especially those with high initial magnetic permeability and associated low magnetic reluctance, is sensitive to not just the amount of magnetic bias but also how the bias is applied. Terfenol-D and Galfenol have been characterized under constant magnetic field and constant magnetomotive force, which require active control. The application of a magnetic flux bias utilizing permanent magnets allows for robust magnetostrictive systems that require no active control. However, this biasing configuration has not been thoroughly investigated. This study presents flux density versus stress major loops of Terfenol-D and Galfenol at various magnetic flux biases. A new piezomagnetic coefficient is defined as the locally-averaged slope of flux density versus stress. Considering the materials alone, the maximum is 18.42 T GPa−1 and 19.53 T GPa−1 for Terfenol-D and Galfenol, respectively. Compared with the peak piezomagnetic coefficient measured under controlled magnetic fields, the piezomagnetic coefficient is 26% and 74% smaller for Terfenol-D and Galfenol, respectively. This study shows that adding parallel magnetic flux paths to low-reluctance magnetostrictive components can partially compensate for the performance loss. With a low carbon steel flux path in parallel to the Galfenol specimen, the maximum increased to 28.33 T GPa−1 corresponding to a 45% improvement compared with the case without a flux path. Due to its low magnetic permeability, Terfenol-D does not benefit from the addition of a parallel flux path.

Ferromagnetic track-etched membrane for high-gradient magnetic separation

High-gradient magnetic field formed near pores of a ferromagnetic track-etched membrane retains on the membrane surface particles having a higher magnetic permeability than the surrounding medium. The feasibility of capturing particles of aqueous magnetite slurry on the ferromagnetic track-etched membrane has been experimentally shown. Calculation of the field strength near the membrane confirms the experimental results.

High-frequency current sensor based on lead-free multiferroic BiFeO 3 -BaTiO 3 -based ceramics

Abstract This paper presents the study of a high-frequency current sensor fabricated using BiFeO3-BaTiO3-based multiferroic ceramics. The frequency response of the sensor is ranged from 1 kHz to 1 MHz. The sensitivity of the current sensor is 4.5 mV/A in a flat response zone from 1 kHz to 20 kHz with an error of 5%. Besides, the sensor exhibits superior temperature stability with a wide operational temperature range (room temperature to ∼353 K). The sensor is also assembled with a high magnetic permeability material that is capable of shielding the DC biased magnetic field up to 2026 Oe. The environmental friendly sensing material and stable output characteristics make the proposed current sensor preferable for the high-frequency current measurement. Besides the performance evaluation, the non-linear frequency response of the current senor is also investigated quantitatively from the aspects of impedance and conductivity.

AC induction heating of ferromagnetic slabs saturated with a DC field

PurposeThis study aims to investigate the feasibility of saturated AC heating of magnetic metals. In AC heating of magnetic steel below the Curie temperature, because of the high magnetic permeability, the penetration depth is in the order of 1-6 mm at 50 Hz. Surface heating is then obtained, in practice, if large slabs are processed. The necessity to provide the required surface-to-core temperature uniformity (about 25°C) at the end of the heating process, avoiding excessive thermal stresses which can lead to cracks, thus implies a long heating time.Design/methodology/approachThe penetration depth can be increased if the material is brought to saturation by applying an external DC magnetic field, and a faster in-depth heating can be obtained. The DC saturating field can be produced with no losses over large volumes by means of superconducting (SC) coils.FindingsThe feasibility of in-depth induction heating of a 200 × 1,000 × 5,000 mm magnetic steel slab with an applied 2 T DC saturating field is numerically investigated. The results show that the use of a DC saturating field leads to shorter processes which fulfil the heating objectives.Practical implicationsA DC saturating field cannot be produced by means of copper coils because of the large amount of material and the unaffordable power required. However, this field can effectively be produced by means of SC magnets based on state-of-the-art materials.Originality/valueSuperconductivity may be the enabling technology for fast and efficient induction heating of magnetic steel slabs if the increase in productivity can balance the additional costs due to the SC magnet.

Reduction of eddy current losses in inductive transmission systems with ferrite sheets

BackgroundImprovements in eddy current suppression are necessary to meet the demand for increasing miniaturization of inductively driven transmission systems in industrial and biomedical applications. The high magnetic permeability and the simultaneously low electrical conductivity of ferrite materials make them ideal candidates for shielding metallic surfaces. For systems like cochlear implants the transmission of data as well as energy over an inductive link is conducted within a well-defined parameter set. For these systems, the shielding can be of particular importance if the properties of the link can be preserved.ResultsIn this work, we investigate the effect of single and double-layered substrates consisting of ferrite and/or copper on the inductance and coupling of planar spiral coils. The examined link systems represent realistic configurations for active implantable systems such as cochlear implants. Experimental measurements are complemented with analytical calculations and finite element simulations, which are in good agreement for all measured parameters. The results are then used to study the transfer efficiency of an inductive link in a series–parallel resonant topology as a function of substrate size, the number of coil turns and coil separation.ConclusionsWe find that ferrite sheets can be used to shield the system from unwanted metallic surfaces and to retain the inductive link parameters of the unperturbed system, particularly its transfer efficiency. The required size of the ferrite plates is comparable to the size of the coils, which makes the setup suitable for practical implementations. Since the sizes and geometries chosen for the studied inductive links are comparable to those of cochlear implants, our conclusions apply in particular to these systems.

Low-field switchable dynamic anisotropy in FeCoN thin film with weak stripe domain

In this work, the static and dynamic magnetic properties of FeCoN films with various thickness have been studied. By controlling the deposition conditions, two-fold static anisotropies, namely a perpendicular anisotropy and an in-plane anisotropy, are introduced into the films, forming weak stripe domain. It is found that, for the films with the thickness between 130 nm and 240 nm, the anisotropy of FMR response is switchable. More importantly, the switching field of the dynamic anisotropy is only about 40-50 Oe, which is far below the value required to switch traditional rotatable anisotropy. Combined with high magnetic permeability and low-field switchable anisotropy, these films are promising for practical applications in the microwave devices.

Exfoliated BN shell-based high-frequency magnetic core-shell materials.

The miniaturization of electric machines demands high frequency magnetic materials with large magnetic-flux density and low energy loss to achieve a decreased dimension of high rotational speed motors. Herein, we report a solution-processed high frequency magnetic composite (containing a nanometal FeCo core and a boron nitride (BN) shell) that simultaneously exhibits high electrical resistivity and magnetic permeability. The frequency dependent complex initial permeability and the mechanical robustness of nanocomposites are intensely dependent on the content of BN insulating phase. The results shown here suggest that insulating magnetic nanocomposites have potential for application in next-generation high-frequency electric machines with large electrical resistivity and permeability.

Damping of VFTO in Gas-Insulated Switchgear by a New Coating Material

Several methods of attenuation of very-fast transient overvoltages (VFTOs) in gas-insulated switchgear (GIS) are under development. An approach that is currently gaining high attention among researchers is based on the application of magnetic cores dissipating the energy associated with VFTO due to eddy current losses and magnetic hysteresis losses. This paper presents an advancement in this approach by introducing a new material type (denoted in this paper as “nanoflakes”). This new material comprises macro pieces of nanocrystalline ribbons (with the size ranging in square millimeters), acquired from crumbled nanocrystalline cores of a standard design. The material is characterized by relatively high magnetic permeability, poor electrical conductivity, and high saturation flux level. The material is suitable for application as a coating layer applied to the surfaces of an inner and/or an outer GIS conductor, as a fill-in material in the GIS shielding elements, or as a standard shaped core. This paper presents the material major features, outlines its development process, and reports on validation of the material effectiveness in real VFTO conditions. The validation is based on the measurement of VFTO attenuation in a full-scale 550 kV GIS test setup.

Signal sensitivity of alternating current potential drop measurement for crack detection of conductive substrate with tunable coating materials through finite element modeling

We adopt a finite element numerical modeling approach to investigate the electromagnetic coupling effect of two parallel electric conductors with tunable electric conductivity σ and magnetic permeability μ. For two parallel conductors C and S (μC ⋅ σC ≤ μS ⋅ σS), we find that the shape of current density profile of conductor S is dependent on the product of μC ⋅ σC, while the magnitude is determined by the AC current frequency f. On the other hand, the frequency f affects not only the shape but also the magnitude of the current density profile of conductor C. We further adopt a coplanar model to investigate the signal sensitivity of alternating current potential drop (ACPD) measurement for both surface crack and inner crack detection. We find that with modified coating materials (lower electric conductivity and higher magnetic permeability, compared with the substrate material properties), the crack detection signal sensitivity can be greatly enhanced for both the cracks within the coating and at the coating/substrate interface, where cracks are most commonly encountered in real situations.

Magnetic Mesoporous Photonic Cellulose Films.

Novel hybrid materials of cellulose and magnetic nanoparticles (NPs) were synthesized and characterized. The materials combine the chiral nematic structural features of mesoporous photonic cellulose (MPC) with the magnetic properties of cobalt ferrite (CoFe2O4). The photonic, magnetic, and dielectric properties of the hybrid materials were investigated during the dynamic swelling and deswelling of the MPC films. It was observed that the dielectric properties of the generated MPC films increased tremendously following swelling in water, endorsing efficient swelling ability of the generated mesoporous films. The high magnetic permeability of the developed MPC films in conjunction with their superior dielectric properties, predominantly in the swollen state, makes them interesting for electromagnetic interference shielding applications.

Fast and simple method for Goss texture evaluation by neutron diffraction

Requirement of low power losses is one of the crucial demands laid on properties of electric steel sheets used in construction of various magnetic circuits. For cold-rolled grain- oriented (CRGO) Fe-3%Si sheets used in majority of power distribution transformers, the Goss texture {110}<001> is known to provide the best utility properties (low power loses, high magnetic permeability). Due to the coarse grain size of CRGO steel, neutron diffraction (ND) is dominantly used to characterize the sheets' texture in order to achieve statistically significant data. In this paper, we present a fast and simple method for characterization of Goss texture perfection level in CRGO steel sheets based on monochromatic ND. The method is tested on 8 samples differing in fabrication technology and magnetic properties. Satisfactory performance of the method and its suitability for a detail texture analyses is tested by juxtaposition of the obtained textural and the magnetic characteristics measured by Barkhausen method.

Particle capture efficiency of elliptic cylinder matrices for high-gradient magnetic separation

ABSTRACTHigh-gradient magnetic separation (HGMS) is an effective method to recover fine weakly magnetic minerals or remove ferromagnetic and paramagnetic particles from aqueous solution. The most commonly used matrices are circular cylinders of high magnetic permeability. However, special cross-section matrices may present better magnetic characteristics and improve the separation efficiency. In this paper, the magnetic field and flow field characteristics of elliptic cross-section matrix were studied in the elliptic coordinate system. The particle capture of the elliptic matrix in the longitudinal configuration of HGMS was modelled and the motion equations of the magnetic particles were derived. The particle capture radius and efficiency were calculated and were compared with those of the circular matrix. Two circumstances were considered to investigate the particle capture of elliptic matrix: the short axis of the elliptic matrix is equal to the diameter of the circular matrix and the cross-section area of the elliptic matrix is equal to that of the circular matrix. The influence of λ (ratio of long axis to short axis) of the elliptic matrix on the capture efficiency of micron-sized paramagnetic particles in the two circumstances was also studied. The results showed that for all the conditions considered, there exists an optimum λ at which the particle capture efficiency reaches the maximum. With the matrices of the optimum λ and suitable d values, the capture efficiency of the 10 μm and 2 μm haematite particles can be improved by 6 ~ 22% and 1 ~ 3% compared with the circular matrices, respectively. Both approaches can be adopted to utilize elliptic matrices in HGMS to improve the particle capture efficiency. The results reveal the higher particle capture efficiency of the elliptic matrix and its application possibility in HGMS.

Investigation of the particle capture of elliptic cross-sectional matrix for high gradient magnetic separation

High gradient magnetic separation (HGMS) is an effective method to recover fine weakly magnetic particles from a suspension. Magnetic matrices are the crucial components of the HGMS system. The most commonly used matrices in HGMS are cylinder matrices of high magnetic permeability. Special cross-section shape matrix may have better magnetic characteristics and show better performance than circular cross-section matrix in HGMS. The particle capture of elliptic cross-section matrix in the three configurations of HGMS are modeled and investigated, aiming at revealing the application possibility of elliptic cross-section matrix in HGMS and providing a research clue for the development of novel high efficiency magnetic matrix for scientific researchers. The magnetic field and the flow field around the elliptic matrix are analytically calculated. The particle motion equations in the three configurations of HGMS are derived. The particle motion trajectories around the elliptic matrices are plotted. The particle capture radius and efficiency of the elliptic matrix are calculated and compared with those of the circular matrix, providing that the diameter of the circular matrix is equal to the short axis of the elliptic matrix. In the three configurations, the elliptic matrix can present higher particle efficiency than the circular matrix under some circumstances. The results indicate the promising application prospect of elliptic cross-section matrix in HGMS. The particle capture efficiency is influenced by many factors. In the development of novel high efficiency magnetic matrix, the magnetic characteristics, the flow characteristics and the arrangement of the matrix should all be taken into consideration.

Magnetne lastnosti in mikrostruktura masivne amorfne zlitine Fe61Co10Ti3Y6B20 v obliki palic in cevi

In this paper, studies are presented that characterize a bulk amorphous Fe61Co10Ti3Y6B20 alloy. Samples were fabricated in two forms: as a rod of 1 mm in diameter and as a tube of 1 mm in the outer diameter. The investigated material was obtained using the injection method, whereby the liquid alloy was injected into a copper mould. Using an X-ray diffractometer, a scanning electron microscope and computer tomography, the microstructures of these rapidly cooled samples were studied. Based on the obtained results, it was found that both the rod and the tube were fully amorphous. The cross-sections of the broken rod and tube were characterized by a mixed rupture consisting of smooth chevron and river patterns. This shows that there are regions of different ductility distributed throughout the volume of a sample. Three-dimensional images of the investigated materials, obtained with computer tomography, allowed the determination of the contribution of the pores (and their size) to the total volumes of the samples. The investigated alloy is a ferromagnetic material exhibiting good soft-magnetic properties such as a high saturation magnetization, a high magnetic permeability and a low value of the coercive field. The technique of injecting the liquid alloy into a copper mould, combined with the suction-casting method, can be used to produce toroidal cores that exhibit highly promising properties for a successful application in the construction of electric motors.

Absorption Properties of Composite Materials for the Encapsulation of Nano- Ferroferric Oxide in Mesoporous Materials

Nano-ferroferric oxide (Nano-Fe3O4) can be used as a ferrite absorbing material when exposed to microwave absorption due to its high magnetic permeability. However, a single nanometer-sized material has a narrow frequency range for its reflection absorption wave during the secondary polymerization process used for preparing nanomaterials. In this study, mesoporous materials and nano-Fe3O4 were used to prepare a nano-Fe3O4 mesoporous composite, which employs the complex permeability of the material to improve the absorption performance of the composites. The materials were characterized and the influence of absorption performance from chemical coprecipitation and encapsulation of suspension polymerization were investigated. The experimental results indicate that suspension polymerization produces materials with enhanced microwave absorption compared to chemical coprecipitation. In addition, results show that “microscopic structure trigger loss of resonance” is critical for the absorbance of composite materials. Furthermore, the eigen frequency of nano-Fe3O4was calculated. Keywords: Mesoporous materials, nano-Fe3O4, composite materials, microwave absorption.

Low loss and narrow-band THz filter based on magnetic photonic crystals

As a key point to applying and studying magnetic photonic crystal technology, communication devices such as the magnetic photonic crystal filters with high performance and easy integration are developed. We investigate the feasibility of ferrite magnetism materials that can be used to make photonic crystal filters. The optical properties of the magnetic materials may be tuned by adjusting the magnetic field or temperature. The band gap of the magnetic photonic crystal can thus be transferred by changing the external magnetic field. This kind of magnetic photonic crystal has a great application prospect. A low insertion loss and narrow-band filter is designed based on a magnetic field-controlled ferrite defect in a photonic crystal for a terahertz (THz) wave. Ferrite is a ferromagnetic metal oxide with high dielectric constant, low saturation magnetization intensity, and high magnetic permeability at high frequencies. According to the crystal structure it can be divided into three categories: spinel, garnet and magnetic rock types. The garnet ferrite crystal can be used to realize THz band transmission, and its absorption coefficient is low (0.05-0.3) in uniform polarization. In this paper, a novel magnetic THz photonic crystal filter is proposed, in which point defects are produced by the introduction of garnet ferrite magnetic materials. Based on the coupling characteristics between the linear defect wave guide and the point defects, THz wave with a certain wave length can be well coupled by changing the radius and arrangement of the resonant cavity, so as to achieve high efficiency filter function. The permeability properties of ferrite magnetic materials are changed with the variation of the intensity of the external magnetic field, and the tuning of the frequency of the resonance mode. The optical properties of the filter are analyzed in detail by using plane waves method(PWM) in finite difference time domain(FDTD). Simulation results show that by changing the point defect structure and the radius of a certain dielectric cylinder, the insertion loss and 3 dB bandwidth of the filter are 0.0997 dB and 8.22 GHz, respectively.

The Study of the Electrical Steel and Amorphous Ferromagnets Magnetic Properties

Materials with special magnetic characteristics are applied in various fields of industry. For instance, magnetic materials having the rectangular hysteresis loop are used in logics and computer science elements. In recent years, owing to obtained by the controlled crystallization from amorphous state nanomaterials properties studying, the soft magnetic materials with improved magnetic properties compared to the traditional amorphous alloys ones were obtained. The alloys possess the low coercive force and high magnetic permeability, besides, the above-mentioned materials have low magnetic reversal losses that provides their wide application as the transformer cores, pulse power supply sources. Magnetic materials along with semiconductors and dielectrics are important for electronic industry, therefore they require to be specially considered. Until recently such magnetic materials as crystal metal alloys, intermetallics and oxides (ferrites, etc.) were investigated. However, amorphous metals and alloys magnetism is intensively studied currently and some areas of amorphous magnets practical application are obviously observed. Nowadays, soft magnetic tape amorphous ferro- and ferrimagnetic materials representing the alloys of transitional metals and metalloids are widely used. The scientific problem of such materials obtaining by fast cooling from the liquid state is now becoming an important applied branch of engineering. One could confirm that the crystal magnetic materials era will be followed by the new magnetic metal materials era i.e. amorphous alloys. The object of the paper is the ferromagnetic materials magnetic characteristics studying through the digital method by the LabView software package applying. The description of normal magnetization curve control and measurement traditional methods (the magnetic induction dependence on the magnetic field intensity) is presented in the paper. The W-shaped core made of electrical steel and the ring-shaped one representing an amorphous alloy were used as the samples. The scheme of the experiment and its conducting description is offered. The hardware and software measuring complex was developed and the software allowing to obtain normal magnetization curve numerical values and to define the losses at magnetic reversal was implemented.