Initial Relative Permeability Research Articles

Pseudo-Core-Shell Permalloy (Supermalloy)@ZnFe2O4 Powders and Spark Plasma Sintered Compacts Based on Mechanically Alloyed Powders.

Soft magnetic composite cores were produced by spark plasma sintering (SPS) from Ni3Fe@ZnFe2O4 and NiFeMo@ZnFe2O4 pseudo-core-shell powders. In the Fe-Ni alloys@ZnFe2O4 pseudo-core-shell composite powders, the core is a large nanocrystalline Permalloy or Supermalloy particle obtained by mechanical alloying, and the shell is a pseudo continuous layer of Zn ferrite particles. The pseudo-core-shell powders have been compacted by SPS at temperatures between 500-700 °C, with a holding time of 0 min. Several techniques were used for the characterisation of the powders and sintered compacts: X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, magnetic hysteresis measurements (DC and AC), and electrical resistivity. The electrical resistivity is stabilised at values of about 7 × 10-3 Ω·m for sintering temperatures between 600-700 °C and this value is three orders of magnitude higher than the electrical resistivity of sintered Fe compacts. The best relative initial permeability was obtained for the Supermalloy/ZnFe2O4 composite compacts sintered at 600 °C, which decreases linearly for the entire frequency range studied, from around 95 to 50. At a frequency of 2000 Hz, the power losses are smaller than 1.5 W/kg. At a frequency of 10 kHz, the power losses are larger, but they remain at a reduced level. In the case of Supermalloy/ZnFe2O4 composite compact SPS-ed at 700 °C, the specific power losses are even lower than 5 W/kg. The power losses' decomposition proved that intra-particle losses are the main type of losses.

The effect of BaTiO3 on the magnetic behavior of MnZn ferrites at frequencies > 5 MHz

In this article an extensive study is presented on the effect of BaTiO3 on the high frequency performance of MnZn ferrite having a nominal composition Mn0.9Zn0.1Fe2.45O4. It is shown that BaTiO3 at an optimum concentration of 200 ppm wt. is a bulk dopant that dissolves in the spinel lattice leading to microstructures with smaller grain sizes, lower grain boundary resistivities and higher resonance frequencies. Despite an observed increase on the hysteresis losses, the main impact on the magnetic performance is the significant reduction of the high frequency resonance losses. In addition, no dependency has been observed on the particle size of BaTiO3 since nanoparticles produce the same effects as microparticles. Through exploitation of the beneficial effects of BaTiO3, MnZn ferrites with power losses of 195 kW m−3 (5 MHz, 10 mT, 100 °C) or 1125 kW m−3 (10 MHz, 10 mT 100 °C) and a relative initial permeability of 200 could be synthesized. These results belong to the best reported in literature and indicate that the application region of MnZn ferrites can be extended up to application frequencies traditionally dominated by other ferrite material families.

Multiscale fractal-power-law model for shale extraction with water reflux case

After the shale reservoir is hydraulically fractured, the shale gas is transported to the horizontal well through various media. Hydraulic fracturing produces hydraulic fractures and generates secondary fractures. The hydraulic fractures and fracture induction areas are filled with gas and water phases. In this work, using power-law fracture distribution and porous media fractal theory, as well as accounting for seepage mechanisms in both the water and gas phases, a shale multi-scale mining model is constructed. The results of the study demonstrated that: (1) The degree of hydraulic fracturing is determined by a number of factors. An appropriate degree of hydraulic fracturing is more conducive to improving gas production. There is a competitive relationship between shale gas seepage and water reflux. Either above or below the moderate interval may lead to excessive water reflux and affect gas production. (2) Various properties of the water phase also influence the production results and pore structure evolution. A moderate maximum relative permeability of water and non-wetting phase entry pressure can contribute to a good pore structure progression and a more desirable gas production. (3) The contribution of hydraulic fracturing porosity to pore structure evolution is greater than the initial relative permeability of water and non-wetting phase entry pressure.

Producing Soft Magnetic Composites by Spark Plasma Sintering of Pseudo Core-Shell Ni-Fe Alloy@Mn0.5Zn0.5Fe2O4 Powders.

Soft magnetic composite (SMC) cores have been obtained by Spark Plasma Sintering (SPS) using pseudo core-shell powders. Pseudo core-shell powders are formed by a core of soft magnetic particle (nanocrystalline permalloy or supermalloy) surrounded by a thin layer (shell) of nanosized soft ferrite (Mn0.5Zn0.5Fe2O4). Three compositions of pseudo core-shell powders were prepared, with 1, 2 and 3 wt.% of manganese-zinc mixt ferrite. The pseudo core-shell powders were compacted by SPS at temperatures between 500 and 700 °C, with a holding time ranging from 0 to 10 min. Several techniques have been used for characterization of the samples, both, powders and compacts X-ray diffraction (XRD, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), magnetic hysteresis measurements (DC and AC) and electrical resistivity. The electrical resistivity is in the order of 1 × 10-2 Ωm, 3-4 orders of magnitude higher than supermalloy electrical resistivity. The SPS at lower temperatures (500 °C) conserves the initial phases of the composite, but increasing the sintering temperature and/or sintering time produces a solid-state reaction between the alloy and ferrite phases, with negative consequence on the magnetic properties of the compacts. The initial relative permeability is around 40 and remains constant until to 2000 Hz. The power losses are lower than 2 W/kg until to 2000 Hz.

Impact of the Surface Irregularities of NiFeMo Compacted Powder Particles on Irreversible Magnetization Processes.

One specific group of materials with excellent application potential are powder-compacted soft magnetic materials. These materials have been intensively studied by materials scientists to improve their magnetic properties. This work describes the influence of mechanical smoothing applied to Ni80Fe15Mo5 (wt.%) alloy particle surfaces before the process of compaction. The soft magnetic properties of compacted powders prepared from smoothed and non-smoothed particles were investigated using the following measurements: coercive field, permeability, excess loss, and Barkhausen noise analysis. We found that compactions prepared with smoothed powder particles exhibit a lower value of coercivity (4.80 A/m), higher initial (10,850) and maximum relative permeability (27,700), and low-frequency core losses (1.54 J/m3) in comparison with compactions prepared with non-smoothed particles.

Soft magnetic composites based on Fe fibres and powders prepared by cold sintering process

The manuscript provides a new strategy for preparation of soft magnetic composites that involves the consolidation of the ferromagnetic phase (fibres or powders), which is first covered with an insulating layer, via the cold sintering process. The manuscript reports on the preparation and characterisation of cold sintered compacts based on Fe fibres and Fe powders coated with ZnO and sintered at the temperature of 200 °C for 60 min under the pressure of 600 MPa. The amount of ZnO used as dielectric phase was 10 and 20 wt%. The absence of any reaction between phases that compose the compacts (Fe fibres or powders and ZnO) during the cold sintering process was proved by X-ray diffraction (XRD). Electron microscopy and X-ray micro-analysis (SEM-EDX) were used for morphology and chemical analysis of the cold sintered compacts. The influence of the type of ferromagnetic phase (fibres or particles), as well as the influence of the amount of dielectric phase on the saturation induction (Bs), the coercive field (Hc), and the maximum relative permeability (µrmax) of the cold sintered magnetic cores, was investigated and discussed. The effect of the same factors on the total core power losses (P) and the initial relative permeability (µri) of the cold sintered compacts, upon increasing the frequency of the magnetising field up to 10 kHz, was analysed. The feasibility of applying a heat treatment at the temperature of 450 °C for 1 h was investigated, leading to the enhancement of both DC and AC magnetic properties of the cold sintered compacts.

Hydrothermal Deposition of ZnO Layer on Fe-Based Amorphous Fibres Used for the Preparation of Cold Sintered Fibre-Based Soft Magnetic Composites

This paper presents findings on the influence of hydrothermal deposition processing parameters (precursor concentration and deposition duration) on the characteristics of ZnO layers deposited on the surface of amorphous Fe-based fibres. The characteristics of the coated fibres, especially the deposited layer, were investigated from structural, morphological, chemical, thermal and magnetic points of view. It was found that the use of a zinc acetate-based solution of 0.05 M concentration and a deposition duration of 24 h leads to a continuous, thin and adherent layer of ZnO on the surface of the fibres. The thickness of the ZnO layer is 450–500 nm, as shown by TEM-EDX investigations. The ZnO coated fibres were used to prepare fibre-based soft magnetic composites via a cold sintering process. The composites obtained are the first reported soft magnetic composites based on amorphous fibres. The coercive field of the cold sintered composites is 3.5 to 8.6 times lower, and the maximum relative permeability is 2.4 times larger, than the best coercive field and the maximum relative permeability reported until now for a crystalline fibre-based soft magnetic composite. The initial relative permeability of cold sintered composites is constant up to the frequency of 1000 Hz.

Scale Effect of the Model Extent on Seepage Analysis of Circular Tunnels under Drained Conditions

Numerical simulations have been widely used to predict groundwater inflow into tunnels during excavations. An appropriate geometric size of a numerical model is crucial for reducing the simulation time and ensuring the accuracy of numerical results. However, to the best of our knowledge, no information concerning the scale effect of the model extent on the seepage characteristics of tunnels under drained conditions has been published. This study evaluates how the model extent affects the tunnel inflow, drawdown, and water pressure via the Signorini type variational inequality formulation. A series of two-dimensional finite element models are conducted with various combinations of tunnel parameters, including tunnel radius, initial groundwater level, lining thickness, and relative permeability. Subsequently, a comprehensive function to yield the optimum model extent within an allowable error is proposed. Interestingly, the optimum model extent for both tunnel inflow and water pressure decreases with an increase in the relative permeability, whereas that of the drawdown exhibits the opposite pattern. A model extent of no less than 200 times the tunnel radius is recommended to acquire accurate model results and is verified with existing analytical methods. This study therefore not only highlights the drainage effect of the tunnel but also provides universal suggestions for engineering practice.

Preparation and characterization of Fe-SiO2 soft magnetic composites prepared by classic and modified Stöber Method

In this study, gas atomized iron powder with the particle size of 10 - 100 μm was coated in two different ways. The coating was created by a chemical procedure, the powder was treated for different periods of time with the classical and modified Stöber process. Toroidal samples were then prepared using different pressures. These samples were heat treated in an argon shielding gas. The complex permeability spectra of the green and heat-treated samples were measured and the effect of pressure, chemical coating time and heat treatment was investigated. The formation of the coatings in each case was confirmed by scanning electron microscopic examinations. Samples with long-term chemical treatment and without heat treatment were appropriate in high-frequency applications (μstat = 50, fFMR = 5 − 15 MHz). After the heat treatment, the relative initial permeability has increased significantly (160-180) and the resonance frequency has decreased (400-4000Hz). Furthermore, it can be stated that a more coherent, thicker coating can be obtained with the modified Stöber method.

Parametric description of power loss in soft magnetic materials with unbiased, rate-independent hysteresis loops

This paper develops a parametric model describing power loss per unit volume, PV, on unbiased minor loops, in the low frequency limit, using the corresponding remanence Br, coercivity Hc, saturated field value BS and power loss per unit volume PVS, from the major loop. In the saturating regime where Hmax>Hc, PV scales as BSHc, and depends on BrHmax/(BSHc), with Hmax the maximum value H on the minor loop. In the intermediate regime where Hmax<Hc, PV scales as μ0μiHc2, and depends on Hmax/Hc. For composite magnetic materials, a major loop may be inaccessible, in which case an expression is obtained for the low field regime, where PV scales as Hmax2, and depends on the initial relative permeability μi. The models are in good agreement with published experimental data. Observed deviations are explained through experimental uncertainties and limitations of the model.

Evaluation of Insulating Magnetic Materials Composed of Epoxy Resin and Pure Iron Powder for Motor and Reactor Core Applications

Insulation and magnetic properties of epoxy composites filled with pure iron powders were studied as a function of iron powder volume fraction (R Fe ) in the range of 0-70 vol% to achieve a good balance between insulation and magnetic properties. Frequency-dependent impedance measurement revealed that the relative permittivity, e r ’ increased from 4.2 to 194.5 with increasing R Fe up to 50 vol%. The loss factor, e r increased from 100.2 to 959.3 and the electric conductivity, σ increased from 5.6×10−5 S/m to 5.3× 10−4 S/m with increasing R Fe up to 70 vol%. The dependence of the σ value on the R Fe value was explained by the equivalent serial CR connection model. The initial maximum relative permeability, μ r_max increased from 3.73 to 8.89 with increasing R Fe up to 70 vol%. These data were compared with those for sample Reference, which has been in practical use in industrial electric machine applications.

Prediction of Power Generation Performance of Wound Rotor Synchronous Generator Using Nonlinear Magnetic Equivalent Circuit Method

This paper presents a nonlinear magnetic equivalent circuit method and an electromagnetic characteristic analysis and verification of a wound rotor synchronous generator (WRSG). The reluctance generated by the stator, rotor, and air gap is subdivided to form a reluctance construction. A nonlinear magnetic equivalent circuit (MEC) for the WRSG is constructed and solved by an iteration method. Moreover, to calculate the inductance of the generator, the reluctance circuit of the d−qaxis is constructed, and the inductance of the generator is obtained using the initial relative permeability of the material. Using the electromagnetic parameters obtained via the MEC method, the power generation characteristics of the generator are predicted. The results of this MEC method are also verified by comparing them with the finite element analysis (FEA) results and experimental results.

Leaking pipes and the urban karst: a pipe scale numerical investigation on water leaks flow paths in the subsurface

Millions of cubic meters of water are lost every year from water utilities, with detrimental consequences on the environment and on society. However, this large amount of water is not necessarily lost. Although leaking water utilities have the potential to recharge urban aquifers, very little is known about the fate of leaked water and its interaction with subsurface anthropogenic features, such as the high permeability trenches surrounding utility pipelines. As these features are deemed to create preferential pathways, it is crucial to understand if these can reduce urban aquifers recharge by interception and diversion of water leaked. Through a series of transient 3D numerical simulations under a variety of conditions (i.e., different native soil properties, slopes of the utility trench, depths of the groundwater table, and leak rates), this study provides evidence that utility trenches can potentially alter the migration pathway of water leaked from utility pipelines located above the groundwater table. Therefore, the urban karst effect has the potential to occur directly at the utility trench. Indeed, from roughly 55% up to 73% of the water leaked is retained within the utility trench and does not reach the underlying aquifer in one third of the scenarios modeled. This occurs because of the combined effect of soil retention properties, initial effective water saturation, relative permeability, and intrinsic permeability. Although this analysis is still preliminary, these results potentially challenge the traditional concept of leaking pipes recharging groundwater.

Analysis of stress influence and plastic strain on magnetic properties during the forming process

The aim of this paper is to analyze the relation between magnetic and mechanical properties during and after forming processes. For this purpose, several tensile tests were carried out on sheet metal samples up to a defined plastic strain. The specimens were left in the clamping device in order to relieve the force in several steps until the specimen was completely relieved. As a consequence, the gradual relief leads to a reduction of internal stress states. During the forming process, the initial magnetic relative permeability and magnetic anisotropy of the sample were measured several times. Both properties are related to the mechanical states in the material through the effects of magnetic embrittlement and magneto-elasticity. The plastic strain of the specimens was determined by optical measurements and the stresses in the measurement range during the tensile test was determined with the help of a subsequent numerical simulation. This made it possible for the first time to measure the magnetic properties of samples with different plastic strain and different stress states. The evaluation shows that there is a strong correlation between permeability and plastic strain as well as anisotropy and stress. Based on these findings, it has been confirmed, that the determination of the plastic strain by a soft sensor is possible.

Thermal Hysteresis Control in Fe49Rh51 Alloy through Annealing Process

We report the results of studies of the magnetic and transport properties of Fe49Rh51 alloy prepared by different sequences of quenching and the annealing process. The temperature dependences of the relative initial magnetic permeability and resistivity are analyzed. An optimal regime consisting of annealing at 1300 K for 440 min and quenching from 1300 K to 275 K is found to observe the desired narrow antiferromagnetic–ferromagnetic transition in Fe49Rh51 alloy under cyclic conditions. This has the potential to increase the efficiency of cooling devices based on the magnetocaloric effect of magnetic materials with a first-order field-induced phase transition.

Correction for capillary pressure influence on relative permeability by combining modified black oil model and Genetic Algorithm

The substantial interference of the tight reservoir's capillary pressure on relative permeability measurement can significantly diminish the prediction accuracy of the oilfield production. This study established an innovative method to eliminate the capillary pressure effect on relative permeability calculation by combining the modified numerical simulation model and the Genetic Algorithm. Steady-state measurements were conducted on tight core sample (0.0321mD) to obtain the initial relative permeability curves using Darcy's law. A modified numerical simulation model that considers equivalent phase pressure for water and oil at outlet surface and directly simulates fixed injection-rate boundary conditions without using wells has been proposed. After analysis of water saturation distribution and pressure distribution along the core, absolute permeability, residual water saturation, and the two-phase relative permeability at corresponding saturation need to be optimized by the Genetic Algorithm based on the initial relative permeability curves to match the experimental results. The outcomes show that the optimized absolute permeability is 19.63% higher than the experimentally measured value, and the optimized residual water saturation is 17.46% lower than the experimental residual water saturation. For the other saturations, the differences between the optimized relative permeability and the experimental results range from 25.93% to 10.57%. The whole divergence of the experiment results and the simulation results about average water saturation and inlet pressure using optimized Kr curves is 1.57%, far less than 69.72% of the unoptimized Kr curves. This research is of great significance for accurately obtaining the relative permeability curves of the tight oil reservoir with intense capillary pressure. • A modified black-oil model is built for accurately simulating capillary end effect. • Lower water injection rate affects relative permeability curves more significantly. • The actual residual water saturation is 17.46% lower than the measured one.

Thermal instabilities of cobalt containing MnZn ferrite cores for medium (500 kHz) frequency applications

MnZn ferrites of the nominal composition (Mn0.81Zn0.19)Fe2.13O4, doped with cobalt, have been studied concerning the evolution of their medium (500 kHz) frequency power losses and initial magnetic permeabilities upon ageing at various temperatures for various times. Thermal ageing results to significant power loss reduction by about 50% at 400 kHz-50 mT (i.e. at 90 °C from initially 58–29 mW cm−3) and about 30% at 500 kHz–100 mT (i.e. at 90 °C from initially 690–480 mW cm−3), accompanied with a simultaneous decrease of the relative initial permeability from initially 1700–1200. The extent of power loss reduction depends on ageing time and temperature and can be described by a thermally activated process, during which Co2+ ions fall from a metastable high energy state to a stable lower energy state with an activation energy 0.33 eV/cation. Addition of TiO2 to an amount of 4000 ppm (wt.%) appears to retard the cobalt-induced ageing process by increasing the activation energy to 0.45 eV/cation, while equal amount additions of SnO2 did not seem to have any effect.

Quintuple AISI 1010 carbon steel core coil for highly focused transcranial magnetic stimulation in small animals

Transcranial magnetic stimulation (TMS) is a non-invasive neuromodulation technique used to regulate the synaptic activity of neurons in the brain, improving the functionality of connecting regions and bringing effective treatment to different neurological and psychiatric disorders. The TMS induced E-field needs to be focal enough to avoid unwanted side effects caused by stimulation of the regions adjacent to the target. Attempts at TMS in small animals like rodents are highly constrained, since most of these studies use commercial equipment intended for humans, with power and coil geometries not designed for small animals. Using finite element modeling in ANSYS Maxwell, the present work shows the design and evaluation of customized arrays of two and five dual-winding solenoids, including a ferromagnetic core, to restrict the stimulation to areas as small as 1 mm2. Each solenoid is made with 50 turns of a wire with thickness = 1 mm, height = 25.4 mm and elliptical top-view cross section. Ferromagnetic cores with V-shape tip sharpening were included, using AISI 1010 carbon steel of 2 T of saturation flux density (Bsat) at 4×104 A/m, and an initial relative permeability µr=667.75. Electric fields and magnetic flux densities were calculated around 4.00 mm below the coil (vertical distance from the top of the scalp to the cortical layer 5/6 in adult rats) with peak currents of 10kA, in a single non-repetitive pulse at 2.5kHz. The achieved 100V/m in a small area of 1 mm2 suggests the suitability of the coil for in vivo experimentation in rodents. Future works will seek to improve the duration of the pulses for repetitive TMS with pulse shaping techniques and validate the novel coil with in vivo experiments in rat models.

Influence of fibres diameter on the AC and DC magnetic characteristics of Fe/Fe3O4 fibres based soft magnetic composites

Fibres-based soft magnetic composites (FSMCs) have been prepared by using Fe fibres of different diameters (65, 125, 250 and 500 μm). The Fe fibres were coated with a 3 μm thick layer of Fe3O4 via the blackening process and subsequently compacted at 700 MPa. The X-ray diffraction analysis (XRD) was used to prove the formation of the Fe3O4 coating on the surface of the fibres. The thickness and the uniformity of the coating were analysed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The DC measurements performed on the composite cores revealed that the saturation induction increase from 1.36 to 1.68 T, the maximum relative permeability increase from 550 to 940, and the coercive field decrease from 796 to 454 A/m as the fibre's diameter increase from 65 to 500 μm. By using thinner fibres (65 and 125 μm), composites with low losses and stable initial relative permeability, in the frequency range 50 Hz–10 kHz, can be obtained. To distinguish between different types of losses dissipated by our compacts, and the influence of the fibre's diameter on the different components of the total losses, a numerical model for loss separation is proposed. The comparative evolution of the AC magnetic characteristics of the FSMCs and powder-based SMCs is presented. According to the presented results, this new type of composites can be successfully used to prepare magnetic cores designated to work in the medium to high-frequency range.

Waterflood Performance Analyses for the Bhagyam Viscous Oil Reservoir

Summary The Bhagyam field contains medium-gravity viscous crude oil. Notably, its waterflood performance has been substantially worse than projected in its initial field development plan (FDP) and poorer than in nearby analog fields and other viscous oil waterfloods from around the world. Early simulation models could not replicate Bhagyam waterflood performance without numerous major modifications. Poor performance was initially attributed to unforeseen severe heterogeneity. As data accumulated, conceptual simulations showed that an extreme level of heterogeneity was required to match observed performance, suggesting permeability heterogeneity alone could not explain results. Log data from later infill wells also showed that injected water was not confined to high-permeability streaks but was areally and vertically widespread. Two major changes drove significant improvements in waterflood simulation history matches. First, a new porosity/permeability model calibrated to pressure falloff (PFO) tests in the aquifer resulted in a higher degree of heterogeneity, which accelerated water production in updated simulation models. Second, a new oil/water relative permeability model that accounted for the hypothesized presence of a small, solid wax saturation reduced initial oil relative permeability and predicted oil rates, and further accelerated water production. Resulting simulation models showed excellent history matches and have continued to match performance during the past 2 years with only minor additional modifications.