Permeability Of Ferromagnetic Materials Research Articles

Application of a New Inversion Algorithm Based on Multi-Layer Model Hypothesis for Testing Stress-Depth Profiles by Multi-Frequency EC Method

Since the permeability of ferromagnetic materials is sensitive to the stress changes, it is feasible to acquire the stress level through detecting the change in permeability. In this study, to explore the distribution of stress or residual stress along the depth direction, a multi-layer model was established and a new inversion algorithm was proposed; and the hypothesis of uniformity of the material’s physical properties for each layer was introduced. Under laboratory conditions, the four-point bending experiment was then implemented with a sample of 45# steel. Global Fourier series fitting based on the least-squares method was used for signal process. The amplitude ratio of the induced voltage to the excitation current was extracted. The effective permeability and the associated hysteresis angle at the 0.25 mm deflection were calculated and presented good regular variations. Finally, under the 0.25 mm deflection, the effective permeability change along the depth was obtained, and the inversely fitted curve was consistent with the theoretical curve. It is verified that the sensor has good robustness by adding deviation of the detection depth. Thereby, it is feasible to test stress or residual stress as a function of depth by multi-frequency eddy current (EC) method.

Equivalent Strain and Stress Models for the Effect of Mechanical Loading on the Permeability of Ferromagnetic Materials

An equivalent strain/stress approach is proposed for modeling permeability change in ferromagnetic materials due to mechanical loadings. The model can be used for transforming complex multiaxial mechanical loadings into equivalent uniaxial loadings parallel to the magnetic field, such that the permeability can be predicted only based on uniaxial measurements. Contrary to earlier approaches, the new definition of the equivalent strain/stress also accounts for shear strain/stress with respect to the magnetic field. The results are shown to match well measurements under multiaxial stresses.

Effect of shear stress on electromagnetic behaviors in superconductor-ferromagnetic bilayer structure

In this paper, the electromagnetic response and shielding behaviour of superconductor-ferromagnetic bilayer structure are studied. The magnetomechanical coupling in ferromagnetic materials is also considered. Based on the linear piezomagnetic coupling model and anti-plane shear deformation, the current density and magnetic field in superconducting strip are obtained firstly. The effect of shear stress on the magnetization of strip is discussed. Then, we consider the magnetic cloak for superconductor-ferromagnetic bilayer structure. The magnetic permeability of ferromagnetic material is obtained for perfect cloaking in uniform magnetic field with magnetomechanical coupling in ferromagnet. The simulation results show that the electromagnetic response in superconductors will change by applying the stress only to the ferromagnetic material. In addition, the performance of invisibility of structure for non-uniform field will be affected by mechanical stress. It may provide a method to achieve tunability of superconducting properties with mechanical loadings.

Velocity effect analysis of dynamic magnetization in high speed magnetic flux leakage inspection

The investigation described in this paper focuses on the velocity effect of dynamic magnetization and magnetic hysteresis due to rapid relative motion between magnetizer and measured specimens in high-speed magnetic flux leakage (MFL) inspection. Magnetization intensity and permeability of ferromagnetic materials along with the duration of dynamic magnetization process were analyzed. Alteration of the intensity and distribution of magnetic field leakage caused by permeability of specimen were investigated via theoretical analysis and finite-element method (FEM) combined with the actual high-speed MFL test. Following this, a specially designed experimental platform, in which motion velocity is within the range of 5m/s–55m/s, was employed to verify the velocity effect and probability of a high-speed MFL test. Preliminary results indicate that the MFL technique can achieve effective defect inspection at high speeds with the maximum inspection speed of about 200km/h being verified under laboratory conditions.

Study on extraction of electrical runout in eddy current measurement using finite element method

Electrical runout is a bottleneck problem of eddy current sensor, which is caused by the maldistribution/variation of material electromagnetic properties of measurement target. However, extraction methods of electrical runout in eddy current displacement measurement remain ambiguous. Here, a 2D finite element model for the influence analysis of conductivity and permeability of ferromagnetic material on coil impedance of eddy current sensor is reported, which will be beneficial for detecting material properties and guiding manufacturing process. The relationships between the real and imaginary part of coil impedance with the varied material conductivity, relative permeability and the lift-off, which indicates the detecting distance, are investigated. When the conductivity, relative permeability of ferromagnetic material and the lift-off vary within a certain range, the relationships between the real and imaginary part of coil impedance are all nearly linear. This paper further shows that the character of distribution of resistance and reactance in diagram under different material properties and same measuring distance is linear. Furthermore, these lines under different measuring distances are parallel. Also the character under different measuring distances and same material property is linear, but these lines under different material properties are diffuse with same intercept. Altogether, the study shows that this method based on redesign of signal processing and its circuit is feasible and instructive in separating electrical runout from the output of eddy current sensor.

The Effect of Non-homogeneous Parts into Materials

This article deals with the verification of experimental results obtained by numerical simulation. We solved the effect of changes in the homogeneity of magnetic fields evoked by different samples from conductive and/or magnetic materials and the different types of inhomogeneity in the MR tomograph. Moreover, the paper will describe the suitable magnetic resonance techniques. 1. ANALYSIS OF THE TASK The numerical modelling was realized using the finite element method together with the Ansys system. As the boundary condition, there was set the scalar magnetic potential φm by solving Laplace’s equation ∆φm = divμ (−gradφm) = 0 (1) together with the Dirichlet boundary condition φm = konst. on the areas Γ1 a Γ2 (2) and the Neumann boundary condition un · gradφm = 0 on the areas Γ3 a Γ4. (3) The continuity of tangential elements of the magnetic field intensity on the interface of the sample region is formulated by the expression un × gradφm = 0 (4) The description of the quasi-stationary model MKP is based on the reduced Maxwell’s equations rotH = J (5) divB = 0 (6) where H is the magnetic field intensity vector, B is the magnetic field induction vector, J is the current density vector. For the case of the static magnetic irrotational field, the Equation (5) is reduced to the Expression (7). rotH = 0 (7) Material relations are represented by the equation B = μ0μrH (8) where μ0 is the permeability of vacuum, μr(B) is the relative permeability of ferromagnetic material. The closed area Ω, which will be applied for solving the Equations (6) and (7), is divided into the region of the sample Ω1 and the region of the medium Ω2. For these, there holds Ω = Ω1 ∪Ω2. For the magnetic field intensity H in area there holds the relation (7). The magnetic field distribution from the winding is expressed with the help of the Biot-Savart law, which is formulated as

Static and dynamic modeling of magnetoelastic dynamometers

Magnetoelastic transducers belong to the inductive transducers, in which the relative permeability of ferromagnetic materials changes on effect of mechanical loads. The change (of always anistropic character) of relative permeability results in a change of the impedance of the coil located in the transducer, or in a change of the transfer impedance in the case of several coils, too. The paper gives a newly developed description of the dynamic magnetoelastic interactions in dynamometers of magnetoelastic principle. The detailed description of calculation method of the electromagnetic field and impedance allows the design of the magnetoelastic dynamometers of anisotropic principle. The dynamic magnetomechanic interaction between the electric and mechanic variables means an additional information between the magnetostriction caused by ac current excitation and dynamic mechanic stress state inside of the ferromagnetic materials. According to the linearised mathematical model is ordered an equivalent electric circuit of the magnetomechanic interaction under the influence of the static mechanical load to be measured.

High Frequency Permeability of Ferromagnetic Materials

High Frequency Permeability of Ferromagnetic Materials

High Frequency Permeability of Ferromagnetic Materials

Methods are described for the measurement of resistive and inductive permeabilities over a range of frequencies from 150 to 10,000 Mc/s. The measurements of the resistive permeabilities were carried out by comparing the attenuation of a coaxial transmission line with the ferromagnetic as the inner conductor with that of a coaxial line having a non-ferromagnetic as inner conductor The inductive permeabilities were obtained from the wavelength in a coaxial line having the ferromagnetic as the inner conductor. The results show that at all frequencies the resistive permeability is greater than the inductive, and both decrease to unity at very high frequencies. The effective permeability, which is assumed to be complex, is deduced as a function of resistive and inductive permeabilities and plotted against frequency for a variety of materials. The experimental values are compared with theoretical values derived from two formal treatments.

Anomalous Magnetic Behaviour of Nickel–Iron at High Frequencies

IN the course of a series of experiments that is being carried out under the direction of Miss H. J. van Leeuwen in this Laboratory in order to determine the high-frequency magnetic permeability of ferromagnetic materials, a peculiar property of a nickel–iron alloy has been found.

High-Frequency Permeability of Ferromagnetic Materials

In view of the possibility of obtaining fuller information about the domain structure of ferromagnetics, by measurements of permeability at high frequencies, a method has been developed of measuring the effective reversible permeability of ferromagnetic materials in wire form over a fairly wide range of frequencies. A comprehensive review of earlier work has been given by Allanson1, and apart from the early work of Arkadiew2, who used a spark-gap source, no measurements of permeability have been recorded at frequencies higher than about 2,000 Mc./s.

The permeability of ferromagnetic materials at frequencies between 105and 1010c/s

The permeability of ferromagnetic materials at frequencies between 10⁵and 10¹⁰c/s

The permeability of ferromagnetic materials at frequencies between 105and 1010c/s

Methods of measuring the permeability of ferromagnetic materials in high-frequency fields are described, and the main results obtained by various investigators are collated and discussed. It appears that hysteresis effects cease between 105 and 107 c/s, and that the permeability decreases with increase of frequency until it reaches unity in the region of 1011 c/s. Various explanatory hypotheses are discussed. The most probable explanation is that the phenomena are due to eddy currents which delay the magnetization processes. These eddy currents are caused by the extensions or rotations of the magnetic domains, and act so as to slow down and finally prevent these changes. The theoretical data evaluated on the basis of this hypothesis are in general agreement with the practical observations.

The Inner, Initial, Magnetic Permeability of Iron and Nickel at Ultra-High Radiofrequencies

A new method for the measurement of the ultra-high frequency, initial, inner permeability of ferromagnetic materials has been developed which gives much greater accuracy and is much faster than the older methods. The probable error is under one percent at a frequency of 197 megacycles per second, as contrasted with previous methods in which the error is of the order of 10 to 20 percent. This improvement is due to three factors: (1) the use of a coaxial cable instead of Lecher wires, (2) the use of a fine central wire and (3) correction for the influence of the finite conductivity of the resonance system. The magnetic permeability of high purity, commercial iron wire was found to be 53.8\ifmmode\pm\else\textpm\fi{}0.3 at 1.97\ifmmode\times\else\texttimes\fi{}${10}^{8}$ cycles per second, and 25\ifmmode^\circ\else\textdegree\fi{}C. It was constant for all values of tension up to the breaking point of the wire at 980 grams force. It also remained constant for superimposed longitudinal magnetic fields up to 100 oersteds. The permeability of commercially pure nickel was found to be 3.61\ifmmode\pm\else\textpm\fi{}0.08 at the same frequency and temperature. As the temperature was raised the permeability increased to a value of 12.22 at 320\ifmmode^\circ\else\textdegree\fi{}C, beyond which it dropped rapidly to unity at 370\ifmmode^\circ\else\textdegree\fi{}C.

The Variation in the High-Frequency Resistance and Permeability of Ferromagnetic Materials due to a Superimposed Magnetic Field

The variation of the high-frequency resistance of ferromagnetic conductors as a function of a superimposed magnetic field is discussed. It is shown that very large changes in high-frequency resistance are obtainable in ferromagnetic conductors having high initial permeabilities. Some important applications of this effect are given. The application of high-frequency incremental permeability to remote tuning of radio circuits is briefly outlined.