Initial Relative Permeability Research Articles

RF electromagnetic wave absorbing properties of ferrite polymer composite materials

The frequency dispersion of complex initial (relative) permeability ( μ * = μ ′ - j μ ″ ) and the electromagnetic wave absorbing properties of composite materials based on NiZn sintered ferrite and a polyvinylchloride (PVC) polymer matrix have been studied in frequency range from 1 MHz to 1 GHz. The complex permeability of the composites was found to increase as the ferrite content increased, and was characterized by frequency dispersion localized above 50 MHz. The variation of return loss (RL) of single-layer RF absorbers using the prepared composite materials has been investigated as a function of frequency, ferrite content and the thickness of the absorbers.

Magnetic properties of Be or Cu-substituted NiZn ferrites

Polycrystalline NiZn ferrites with the chemical formula ( Ni 0.3 Zn 0.7 ) 1 - x Me x Fe 2 O 4 where Me is Be or Cu and x = 0.05 , 0.1 and 0.25 have been prepared by a ceramic method. Selected magnetic properties such as Curie temperature T c and saturation magnetization M s of the ferrites have been measured and discussed. Complex initial (relative) permeability μ ˜ = μ ′ - j μ ″ measurements have also been performed on the samples in the frequency range from 100 kHz to 100 MHz and the contribution of magnetization mechanisms is discussed.

Microwave sintering of high-permeability (Ni 0.20Zn 0.60Cu 0.20)Fe 1.98O 4 ferrite at low sintering temperatures

The (Ni 0.20Zn 0.60Cu 0.20)Fe 1.98O 4 ferrite was sintered using microwave sintering and conventional sintering technique, respectively. It was found that microwave sintering technique can effectively promote the forward diffusion of ions and thus accelerate the sintering process, resulting in the grain growth and the densification of matrix. At the low frequency of 100 kHz, the magnetizing contribution of domain wall motion is predominant, and compact and coarse matrixes are favorable for domain wall motion, giving rise to improvement of relative initial permeability and loss of ferrites. Using microwave sintering technique, for the (Ni 0.20Zn 0.60Cu 0.20)Fe 1.98O 4 ferrite, the relative initial permeability μ i of about 2000 and the relative loss factor tan δ/μ i of about 8.7×10 −6 at 100 kHz were achieved at only 980 °C sintering temperature. In addition, the sintering time of ferrites was reduced from 5 to 0.5 h by using microwave sintering technique.

Preparation and investigation of low firing temperature NiCuZn ferrites with high relative initial permeability

The effects of CuO and V 2O 5 additions and the particle sizes of precursor materials on the microstructure and relative initial permeability of low firing temperature NiCuZn ferrites were investigated. It was found that additions of CuO and V 2O 5 contribute to the grain growth and densification of matrix in the sintering process, which were favorable for increase in relative initial permeability. The relative initial permeability was also strongly affected by the average particle size of precursor materials. Through using precursor materials of 0.8 μm average particle size and adding 10 mol% CuO and 0.20 mol% V 2O 5, for the low firing temperature NiCuZn ferrite, very high relative initial permeability of 1417 can be achieved at the frequency of 1 MHz.

Nickel‐Iron Alloys with Special Soft Magnetic Properties for Specific Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

Investigating Uncertainties in Relative Permeability Measurements

In this article, relative permeability measurement methods for water-oil systems mimicking displacement processes in porous media when reservoir pressure is supported by an active aquifer or a water injection scheme are compared. The measurement methods are compared within the context of reservoir wettability. It is suggested that for reservoirs with predominant water-wetness, unsteady-state experiments could be run under the suggested Peters and Khataniar (1987) stability criteria. Steady-state experiments could also be run for comparative and in turn quality control purposes. In addition, a combination of unsteady-, steady-state and centrifugal experiments could be adopted to generate trustful results for reservoirs with intermediate wettability, but only if one has a reliable initial relative permeability to oil (k ro ) at a representative initial water saturation (S wi ). As such, it is recommended to use an unsteady-state technique for the initiation of the displacement experiments, a steady-state method for mid-range saturations, and the centrifuge for tail-end saturations. It should be noted that for the centrifugal method, comparable centrifugal and viscous forces are required to mimic displacement processes. Coyne's procedure could also be used for comparative and quality control purposes.

Depletion oil recovery for systems with widely varying initial composition

The principal depletion drive mechanism is the expansion of oil and gas initially in the reservoir—neglecting water influx. The main factors in depletion drive reservoir performance are total cumulative compressibility, determined mostly by initial composition (gas–oil ratio), saturation pressure, PVT properties, and relative permeability. In this paper, we systematically study the effect of initial composition on oil recovery, all other parameters held constant. We also evaluate other aspects of reservoir performance, but the main emphasis is surface oil recovery including condensate. To analyze the effect of initial composition, a series of fluid systems was selected by a recombination of separator samples at varying gas–oil ratios. The systems ranged from low-GOR oils to high-GOR gas condensates, with a continuous transition from gas to oil through a critical mixture. Black oil and compositional material balance calculations, 2D fine-grid, and 3D coarse-grid models have been used to investigate the effect of initial fluid composition on reservoir depletion performance. Systematic variation of relative permeabilities was also used to map the range of fluid systems, which were most sensitive to relative permeability. For reservoir oils, the depletion recovery of surface oil initially increases with increasing initial gas–oil ratio. Oil recovery reaches a maximum for moderate-GOR oil reservoirs, followed by decreasing oil recoveries with increasing initial solution GOR. A minimum oil recovery is reached at a near-critical oil. For gas reservoirs, depletion drive condensate recovery increases monotonically from a near-critical gas towards near 100% condensate recovery for very-high GOR systems. STO recovery from oil reservoirs depends increasingly on gas–oil relative permeabilities as initial solution GOR increases, up to a point. At higher initial solution GORs, oil recovery becomes less dependent on relative permeability and, as the fluid system transitions to a gas at the critical point, relative permeability dependence rapidly diminishes. Condensate recovery from gas condensate systems is more or less independent of gas–oil relative permeabilities, with only slight dependence for near-critical gases.

Nickel–iron alloys with special soft magnetic properties for specific applications

The magnetic properties of the initial permeability and the saturation induction characterize mainly the different available soft magnetic nickel–iron alloys. The nickel–iron alloys Magnifer 75, Magnifer 7904 and Magnifer 8105 with nickel contents between appr. 75 and 82% achieve a saturation induction of appr. 0.8 T. The initial permeability of these alloys can reach values up to a few 100,000 depending on thickness of the material and the frequency of the applied magnetic field. On the other hand, nickel–iron alloys are also available with a higher saturation up to appr. 1.6 T, but then in general with a lower initial permeability around 10,000. These are the alloys Magnifer 36 and Magnifer 50 with nickel contents of appr. 36% and 48%, respectively. In the case of Magnifer 50 different grades can be produced by different processing routes having the different grain and texture structures resulting in different magnetic behaviours. An exception is the alloy Magnifer 53 that combines both properties—high saturation induction and a relative high initial permeability—by applying a magnetic field annealing after the standard high-temperature heat treatment using tape wound cores processed from thin foil of the material. A description of the soft magnetic characteristics of nickel–iron alloys produced by ThyssenKrupp VDM GmbH and some of their applications will be presented.

The influence of Ge 4+ and Ti 4+ ions substitution on the magnetic properties of copper ferrite

Two mixed copper ferrite systems, Cu 1+ x Ge x Fe 2−2 x O 4 (system 1) and Cu 1+ x Ti x Fe 2−2 x O 4 (system 2) with x = 0, 0.1, 0.2, 0.3 and 0.4 were analogously investigated. The two systems were prepared using the standard ceramic method. X-ray analysis shows that both systems were formed in a single spinel phase except the sample with x = 0.4 for the two system. Some of the magnetic properties were measured, such as the initial permeability, magnetization and relative permeability. It was found that the Curie temperature ( T C) decreases from 714 to 542 K for the first system while it decreases from 714 to 570 K for the second system. The cation distribution of the two systems was proposed. The sample with x = 0 (CuFe 2O 4) shows the lowest magnetization value for both systems. The behaviour of relative permeability shows two regions for the first system and three for the second system.

Low-temperature synthesis of Mn0.2Ni0.2Zn0.6Fe2O4 ferrites by citrate precursor method and study of their properties

Mn0.2Ni0.2Zn0.6Fe2O4 ferrite nano-particles are processed at temperatures as low as 60 °C by the citrate precursor method. The lattice parameter is observed to increase from 8.415 to 8.438 Å with increase in calcination temperature from 60 °C to 500 °C. The increase in saturation magnetization from 19 to 43 emu/gm (A m2/kg) with increase in calcination temperature is attributed to a change in the cation distribution and random canting of particle surface spins in nanosize particles. For improved magnetic properties, samples are sintered at temperatures ranging from 1100–1400 °C. The substantial increase in initial relative permeability (from 150 to 700) with increase in sintering temperature is attributed to an increase in intra-granular domain walls. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic behaviour versus tensile deformation mechanisms in a non-oriented Fe–(3 wt.%)Si steel

This study presents an extended in situ magnetic characterisation of a non-oriented (NO) Fe–(3 wt.%)Si steel. An appropriate experimental device was created and magnetic measurements were performed under uniaxial tensile stresses approaching and exceeding the macroscopic elastic limit σ e and in the corresponding unloaded states. Both Barkhausen noise and B–H hysteresis loops were measured. The sensitivity to stress was found to be qualitatively similar to that of polycrystalline iron. The different stages of the tensile deformation (perfectly elastic stage, microplastic yielding stage, the two strain-hardening stages) were clearly identified by the magnetic parameters. In the plastic strain domain, the coercive field H c and the inverse of the initial relative permeability 1/ μ r i linearly increase, while the maximal relative permeability μ r max and the Barkhausen noise peak height BN max linearly decrease with the applied stress σ. The remnant induction B r keeps a low and constant value. Furthermore, a linear dependence of 1/ μ r i, H c, μ r max and BN max on the kinematic hardening X was found. By using measurements on prestrained specimens under reloaded elastic stresses, an accurate identification of the effect of dislocations acting as pinning sites and of the magnetoelastic effect of long-range internal stresses was proposed.

Effect of Manganese Impurity on the Conductivity, Dielectric Behavior and Magnetic Properties of Ni0.3MnxZn0.7-xFe2O4

Ni0.3MnxZn0.7-xFe2O4 samples, with x=0.1, 0.2, 0.3, 0.4, 0.5, have been prepared by the citrate precursor method and their dc resistivity, complex initial permeability, permittivity and saturation magnetization are studied. Initial increase followed by a decrease is observed in dc resistivity and saturation magnetization (maximum 57 emu/gm) with increase in x. Initial relative permeability is observed to decrease from 550 to 100 with increase in manganese content. A shift in dielectric relaxation peak towards higher frequencies is observed with increase in x. A slight variation of resistivity is observed with increasing applied field.

Influence of stoichiometry on the magnetic disaccommodation in barium M-type hexaferrites

The time decay of the relative initial magnetic permeability after sample demagnetization has been measured in the temperature range 80 K<T<420 K in series of samples with initial composition BaO⋅nFe2O3(n = 5.7, 6 and 6.3), i.e. the stoichiometric M-type barium ferrite and compositions with excess and defect of iron. These samples have been sintered under different conditions of temperature and partial oxygen pressure. The results have been represented by means of isochronal curves. We have observed that the behaviour changes drastically with the sintering atmosphere, and the results with less iron are qualitatively different from the others when sintering in air. The underlying mechanisms responsible for the relaxation phenomena observed are pointed out in terms of the formation of different hexagonal phases.

Magnetic properties of Mn-substituted Ni–Zn ferrites

Mn x Ni 0.5−x Zn 0.5 Fe 2 O 4 ferrites with x=0.05, 0.1, 0.2, 0.3, and 0.4, have been synthesized by the citrate precursor method and investigated for their magnetic properties. The initial relative permeability is observed to increase with increase in manganese concentration up to x=0.2 followed by a decrease, the maximum value being 632. An initial increase followed by a subsequent decrease of saturation magnetization with increase in x is observed. Curie temperature is observed to decrease continuously from 488 to 418 °C when x increases from 0.05 to 0.4. Frequency variation of complex initial permeability indicates that resonance peak due to domain wall oscillations is at a frequency above 13 MHz. Saturation magnetization is observed to increase by about 22% when the sintering temperature is increased from 1200 to 1400 °C. Initial permeability and B–H loops are observed to increase and constrict, respectively, with increase in sintering temperature.

The use of a modified Petrov-Galerkin method for gas-sold reaction modelling

A new numerical technique for simulating gas-solid reactions including diffusion through the reactant and product layers, reaction on the shrinking surface and internal reaction is presented Some transformations are introduced, and this model can be reduced to dimensionless form including a selfadjoint, singularly perturbed, two-point boundary-value problem and two initial-value problems. A combination of the Petrov-Galerkin finite element method and predictor-corrector method is applied to solve the problem. It is shown that the shrinking-core model including both surface reaction and product layer diffusion can arise for low initial relative permeability and the diffusion-controlled shrinking-core model occurs when the product layer diffusional resistance is large relative to the surface reaction. This method is simple and there is no limit on the range of the parameters. Computed results are numerically evaluated for comparison with results of previous authors.

Inductance of a coil on a thick ferromagnetic metal plate

We study the frequency-dependent inductance of a small air-cored coil of wire placed flat upon various ferromagnetic metal plates. The change in the complex inductance of the coil, measured with an HP 4193A impedance analyzer, is reported for frequencies between 1 kHz and 1 MHz. The metal plates consisted of commercially pure (99.7% and 99.9%) Ni, commercially pure (99.9%) Fe, and a suite of medium carbon steels. For the steel plates, inductance changes were consistent with a simple half-space model that treats the metal as a continuum defined by a conductivity /spl sigma/ and a relative initial-permeability /spl mu/ where these material parameters are isotropic, local, and uniform throughout the plate. The inductance changes for Ni and Fe could not be fit to the half-space model for any values of /spl sigma/ and /spl mu/, but were consistent with a model that assumes a thin (/spl sim/10 /spl mu/m) surface layer with a significantly reduced permeability-a dead layer. We tested the existence of the hypothetical dead layer in several ways. We found that the inductance increased when the surface was chemically etched (presumably eroding the dead layer) and decreased when the surface was mechanically polished (presumably increasing the dead layer). We also found that the inductance of the Fe and Ni samples decreased substantially over the course of days and months when exposed to air.

High-frequency permeability of soft-magnetic Fe–Hf–O films with high resistivity

A series of Fe–Hf–O films has been prepared by means of rf sputter deposition. The composition for optimal permeability was found to be Fe55Hf17O28. These films exhibit a combination of soft-magnetic properties (μ&amp;gt;103, Hc&amp;lt;50 A/m, μ0Ms⩾1.0 T) and a high resistivity (ρ&amp;gt;1 mΩ cm) after rapid thermal annealing in flowing argon at 400 °C in a dc magnetic field. The structure of the films consists of α-Fe nanocrystallites, randomly dispersed in an amorphous matrix. The amorphous phase is essential in achieving the advantageous combination of properties. In contrast to conventional soft-magnetic films, the properties of the Fe55Hf17O28 films do not show a strong thickness dependence for thicknesses up to 10 μm. Therefore, the roll-off frequency of the initial relative permeability for 10 μm thick films is high, but not as high as expected from only the resistivity. It is shown that, besides electromagnetic induction, ferromagnetic resonance is also essential in explaining the observed frequency dependence of the permeability.

Some aspects of the magnetomechanical coupling in the strengthening of nonoriented and grain-oriented 3% SiFe alloys

An investigation has been carried out on the effect of plastic strains on the magnetic properties of grain-oriented and nonoriented 3% by weight SiFe alloys. A drastic degradation of these properties with increasing deformations is observed for magnetic field amplitudes ranging between 0 and 2000 A/m. Empirical relationships between plastic strain and magnetic characteristics are obtained. Materials exhibit a Luders strain state under tensile loading in a low plastic deformation range. Meanwhile, the classical Ramberg-Osgood law is verified. The observation of the dislocation features at various plastic strain levels shows three typical configurations: hexagonal cells in the Luders strain state, small tangles and isolated screw dislocations at medium values of strain, and finally high-density tangles at higher deformations. In the same way, the densities of main and secondary magnetic domains follow an evolution in three stages with increasing strains. It is shown that the transverse domain patterns take place to counterbalance the increase of magnetoelastic energy due to the strengthening. The evolution of the coercivity and the initial relative permeability with the strains can be explained using potential model theories for the grain-oriented alloy in the range [2-8]%. Domain wall bowing theories could successfully be applied to both alloys at the ultimate stage of the strengthening. The relationship between the coercivity and the strengthening displays two linear stages for both 3% SiFe alloys instead of the three stages ordinarily reported in the case of polycrystalline high-purity iron.

Interpretation of Oil-Water Relative Permeabilities from Centrifuge Experiments

ABSTRACT Collection of production data from centrifuge displacement with a time resolution of seconds and volume resolution of 4 µl provides the precision for interpreting the transient data for the displaced phase relative permeability curve. Interpretation for the relative permeability requires a simulation model that includes all relevant phenomena that affects the displacement. This includes the variation of the centrifugal force within the sample and during the centrifuge start-up period. Capillary pressure is a significant factor in both the initiation and cessation of production and thus must also be included in the analysis. The finite mobility of the invading phase places limitations on the portion of the relative permeability curve that is in the region of the shock. In addition, the finite mobility of the invading phase reduces the sensitivity to the initial (end ppinf) relative permeability of the displaced phase. The design of experiments in mixed wet systems require a balance between the Brownell-Katz (or Bond) number criteria for displacement of a disconnected phase and retention due to a capillary end effect.

ナノ結晶Fe-Cu-Nb-Si-B合金の誘導磁気異方性と磁気特性

The induced magnetic anisotropy and magnetic properties of nanocrystalline Fe-Cu-Nb-Si-B alloys were investigated by changing the field annealing condition. The induced anisotropy increased with the field annealing time. A high relative initial permeability μr, a flat B-H loop. and low remanence were obtained by transverse field annealing for a short time. The maximum value of the relative initial permeability, over 130,000, occurred not at zero anisotropy but at a low value, Ku=2.5 J/m3, of the transverse anisotropy. Nanocrystalline Fe-Cu-Nb-Si-B alloys are used in several applications such as choke coils for noise filters, pulse transformers, and current transformers. We found a proportionality between the μr-1 value and the induced anisotropy Ku. However, the proportionality factor depended on the direction of Ku. The above types of behavior are similar to those of Co-based amorphous alloys.