Values Of Magnetic Permeability Research Articles

The metallic sphere in a uniform ac magnetic field: A simple and precise experiment for exploring eddy currents and non-destructive testing

We describe a very simple experiment that utilizes standard laboratory equipment to measure the electromagnetic response of a metallic sphere exposed to a uniform ac magnetic field. Measurements were made for a variety of non-magnetic and magnetic metals, and in all cases the results fit very well with theory over the four orders of frequency (25 Hz to 102 kHz) explored here. Precise values of magnetic permeability and electrical conductivity can be extracted from fits to the data given the sphere radius only. The same apparatus is also used to explore the effects of geometry on eddy current generation as well as to demonstrate non-destructive testing through measurements on coins of different composition.

Effect of Inhibitors on the Crystallization and Magnetic Properties of Nanocrystalline Alloys

In the paper, the crystallization process of nanocrystaline alloys Fe73.5Cu1M3Si13.5B9 where M = Nb, W, Mo, V, Cr and the physical origin of different efficiency of impact that inhibitors exert on the structure and magnetic properties has been investigated. It is shown that the structure formed at the peak temperature of the crystallization process is close to the optimal one and ensures high values of magnetic permeability. The efficiency is directly related to the solubility of inhibitory elements in αFe, which in turn affects the diffusivity of atoms. Upon slow migration of grain boundaries, the inhibitory atoms with lower diffusivity, being concentrated near the front of moving boundary, provide stronger drag.

Static and high-frequency magnetic properties of nanocrystalline Fe-Zr-N films

The phase and structural states of nanocrystalline Fe-based films alloyed with Zr and N, which were prepared by reactive magnetron sputtering under different conditions, magnetic-structure parameters of the films and their static and high-frequency magnetic properties have been studied. The interrelation of static magnetic properties and magnetic-structure parameters with the value of real effective magnetic permeability μ’ and frequency range, for which the value is unchanged, has been studied.

Correlating elastic and plastic deformation with magnetic permeability values

This paper investigates the utilization of magnetic permeability method in determining elastic and plastic deformation state of ferromagnetic steels. The results have shown a strong degradation of the magnetic values on plastically region due to the irreversible movements of the magnetic domain walls.

AC magnetic and magnetoimpedance properties of CoFe(NbMnNi)BSi amorphous ribbons

We report magnetic and magnetoimpedance (MI) properties of cobalt-rich amorphous alloys to investigate the role of small quantities of 3d or 4d transition-metal elements in Co-rich alloys. The microstructure, thermal stability, AC soft magnetic properties and magnetoimpedance of the ribbons are investigated by substituting Nb in place of Ni and Mn. Present study shows an improvement in glass forming ability and reduction in electrical conductivity of the ribbon with Nb substitution. Higher Nb containing alloy shows minimum core loss compared to other compositions over a range of frequencies. Ribbon with higher core loss exhibited higher MI ratio (∼100% at 3 MHz), but decreased rapidly at higher frequencies due to its larger electrical conductivity. The ribbon with lower electrical conductivity showed a steady MI ratio and field sensitivity with frequency. These results indicate that MI and core losses at medium range of frequencies can be tuned by adding Nb that provides most favourable electrical conductivity and magnetic permeability values, which result in optimum skin depth and MI. The effect of electrical conductivity on MI is also validated through numerical simulations using standard electrodynamics models.

AC and DC-shielding properties for the Ni80Fe20/Cu film structures

Multilayered Ni80Fe20/Cu film shields were obtained via electrochemistry method with different thickness and number of partial magnetic layers. Magnetic properties and shielding characteristics were investigated as well as function of thickness and number of layers. Difference in magnetic properties for Ni80Fe20 films with different thickness is due to formation of defect layers on the top and bottom film surfaces during electrodeposition processes. These layers can be characterized as layers with high density defects (as a result poor iron content). Main deviation in magnetic properties is typical for thinner films. It was measured DC and AC shielding and results discussed. Maximal value of DC-shielding effectiveness was observed for multilayered samples with small number magnetic layers with large thickness (80–400μm). The minimal value of DC-shielding effectiveness was observed for the multilayered sample with the minimum thickness of the magnetic layer (5μm) and maximal number of the layers (80 layers). It is in good agreement with shunting mechanism. In low frequency range maximal values of AC-shielding effectiveness were observed like in case of DC-shielding for samples with small number magnetic layers with large thickness. With frequency increasing the situation was radically changed and AC-shielding effectiveness was higher for samples with maximal number of layers. In the frequency range above 40kHz AC-shielding effectiveness was sharply decreased due to sharply decreasing of permeability value. As a result it leads to decrease of absorption loses (SEabs.). It was discussed the main shielding mechanisms for multilayered Ni80Fe20/Cu film samples under different external influences. Main contribution in electromagnetic shielding in the range 300Hz–20kHz is absorption and reflection processes. In the range 20kHz–50kHz main shielding mechanisms are reflection and re-reflection. For 300Hz–50kHz frequency range most appropriate to use multilayered structures with large number of thin layers with cardinally different values of magnetic permeability and electrical conductivity.

Dependence of Magnetic Permeability on Residual Stresses in Welded Steels

The aim of this paper was to further broaden current knowledge of magnetic properties’ dependence on welded steels’ stress state. For this reason, commercial micro-alloyed steel was welded using tungsten inert gas as the welding technique. Magnetic stress calibration curve (MASC) was a useful laboratory tool for evaluating the material’s residual stress distribution with the aid of magnetic permeability values. X-ray and neutron diffraction techniques were used for determining surface and bulk residual stress values, respectively. The overall measurement results have shown that the residual stress determined by the magnetic method was in good agreement with the diffraction results. In order to investigate the potential utilization of the magnetic method in evaluating residual stresses, the magnetic calibration curves of various ferromagnetic steels’ grade were examined. The normalization of these curves revealed the existence of a unique curve, which suggested the existence of a universal relationship between the intrinsic magnetic properties and the internal elastic mechanical characteristics of steels. Further experimental investigations are required to validate the preliminary results and to verify the presence of a unique normalized magnetic stress calibration curve.

Study of structural, magnetic and microwave absorption properties of Dy-Mn substituted nanosized material in X-band frequency range

The main theme of present work was to synthesize the Dy-Mn substituted nanosized magnetic material and to study the effect of additives on structural, optical, magnetic and microwave absorption properties of the material. For this purpose, the sol gel method was adopted to prepare a series of rare earth element Dy3+ and divalent Mn2+ substituted Ba2-xDyxZn2Fe28-y MnyO46 (x = 0, 0.02, 0.06, 0.1 y = 0, 0.1, 0.3, 0.5) X-type hexagonal ferrites. The XRD patterns reveal the single phase for all the prepared material. FTIR spectrum also confirms the single phase for the material. The material was well crystallized in hexagonal phase and the particle size was varied in the range of 10–20 nm as observed from TEM and HRTEM analysis. These nano particles agglutinated to make relatively big platelet like structure grains and the grain size varied in the range of 0.412–0.239 μm for all concentrations. The low value of coercivity, high magnetic properties and high value of magnetic permeability with additives makes this material suitable for microwave absorption properties. The microwave absorption properties were calculated over the frequency range of 7–13 GHz. The material exhibits the minimum reflection loss (microwave absorption) of −55 dB at 11.62 GHz frequency. The microwave absorption properties make this material useful for super high frequency devices (SHF).

Investigation of electromagnetic properties of a high absorptive, weakly reflective metamaterial—substrate system with compensated chirality

In the present paper, a theoretical and experimental study of a highly absorptive, weakly reflective coating designed and fabricated on the basis of 3D THz resonant elements is reported. Transmission and reflection of electromagnetic waves from the metamaterial-substrate structure involving a highly absorptive, weakly reflective array of artificial bi-anisotropic elements were analyzed. The samples contained paired right-handed and left-handed helices, due to the fact that the chirality was compensated. The parameters of helices were optimized to achieve roughly identical values of dielectric permittivity and magnetic permeability. As a result, the metamaterial exhibited weak reflectivity in the vicinity of resonance frequency. On the other hand, effective resonance properties of the helices were tuned to ensure substantial absorption of THz radiation. Analytical expressions for the coefficients of radiation reflection and transmission in the samples were derived by solving a boundary-value problem for the propagation of electromagnetic waves in the metamaterial-substrate system. Simulated properties of fabricated structures were compared with experimental data.

Calculation of equivalent magnetic permeability of ferromagnetic materials for modeling of three-dimensional eddy current fields

The paper presents a method of calculating a constant value of magnetic permeability of ferromagnetic materials, equivalent to the basic magnetization curve by the criterion of real power. The proposed method makes it possible to use linear differential equations of the electromagnetic field in the analysis of three-dimensional fields of eddy currents in ferromagnetic materials, thus significantly reducing the calculation time. We propose a method of calculating the power of inductors using two-dimensional axisymmetric models. The scope of the proposed methods is limited to the case of placement of the inductor inside the ferromagnetic body.

Thermomagnetic analysis of soft magnetic nanocrystalline alloys

Abstract In the paper, the crystallization process of Fe 95.5− x − y (Co, Ni) x Cu 1 Nb 2 Mo 1.5 (Si, B) y alloys has been investigated using a thermomagnetic analysis. In the course of heating, continuous measurements of temperature and initial magnetic permeability were performed. Additionally, the structure and magnetic properties of the alloys were investigated at different stages of the crystallization process. It is shown that the structure formed at the peak temperature of the crystallization process is close to the optimal one and ensures high values of magnetic permeability. On the permeability-versus-time curve, a peak is found which lags behind the temperature peak. The decrease in the permeability, after its peak value is reached, can be attributed to the transition of the atomic and magnetic structure of alloy after crystallization into its stabilized state after crystallization.

Microwave absorption properties of FSS-impacted composites as a broadband microwave absorber

The development of a cost-effective microwave absorber with wide bandwidth corresponding to reflection loss (RL) ≤ −10 dB is still a very challenging task. A sugarcane bagasse-based agricultural waste composite has been analyzed for its elemental contents. The combination of elements is suitable for its possible usage as a cost-effective microwave absorbing material. Therefore, this composite has been subjected to morphological and electromagnetic studies to analyze its microwave absorbing behavior. The frequency dependent complex dielectric permittivity and complex magnetic permeability values were obtained using a transmission/reflection waveguide approach in the X-band. Furthermore, the effect of the Minkowski loop frequency selective surface (FSS) was studied over the absorption capability of the composite. It was found that the application of FSS leads to a reduction in thickness up to 2.9 mm and an enhancement in absorption bandwidth up to 3.6 GHz. The FSS patterned composite shows a remarkable performance with peak RL of −28.4 dB at 10.7 GHz and absorption bandwidth of 3.6 GHz.

Rewriting magnetic phase change memory by laser heating

Magnetic phase change memory (MAG PCM) consists of bits with different magnetic permeability values. The bits are read by measuring their effect on a magnetic probe field. Previously low permeability crystalline bits had been written in high permeability amorphous films of Metglas via laser heating. Here data is presented showing that by applying short laser pulses with the appropriate power to previously crystallized regions they can first be vitrified and then again crystallized. Thus, MAG PCM is rewriteable. Technical issues in processing the bits are discussed and results on thermal modeling are presented.

A STUDY OF COMPOSITE SUBSTRATES FOR VHF AND UHF ARTIFICIAL MAGNETIC CONDUCTORS AND THEIR APPLICATION TO A SATCOM ANTENNA

The bandwidth of Artificial Magnetic Conductor (AMC) structures based on the square patch geometry has been significantly increased by using composite ferrite particles. These magnetic composites are non-conducting materials which achieve extraordinarily high values of magnetic permeability in the VHF and UHF range. Two AMC designs are presented for two different bands: the lower VHF and the VHF/UHF bands. To realize the ultra-high bandwidth for those ranges two particular materials were considered; nickel zinc and bismuth strontium titanate based ferrites. The AMCs were designed and modeled via numerical simulations using real material parameters as reported in literature. A cross-dipole radiator was integrated with the AMC to create a wideband directive antenna for SATCOM applications.

Fractal Frequency-Selective Surface Embedded Thin Broadband Microwave Absorber Coatings Using Heterogeneous Composites

The development of thin microwave absorber coatings that operates for a wide range of frequencies is still a challenging task. This work presents a technique of blending a fractal frequency selective surface (FSS) with single- and double-layer coatings. These coatings are comprised of well-optimized micrometer-sized (80–90 $\mu{\hbox{m}}$ ) and nano-sized (20–30 nm) Ti particles based ${\hbox{Fe}}_{3} {\hbox{O}}_{4}$ (80–100 nm) composites. The main objective of this study is to achieve good absorption with wide bandwidth corresponding to ${\hbox{reflection loss (RL)}}~ \le 10~{\hbox{dB}}$ for less coating thickness ( $\le {\hbox{1.5 mm}}$ ). Waveguide measurements are carried out to obtain the effective complex dielectric permittivity ( $\varepsilon_{ r} =\varepsilon_{ r}^{\prime}-{ j}\varepsilon_{ r}^{\prime \prime}$ ) and effective complex magnetic permeability ( $\mu _{ r} =\mu_{ r}^{\prime}-{ j} \mu_{ r}^{\prime \prime}$ ) values of ${\hbox{Fe}}_{3} {\hbox{O}}_{4}$ -Ti based heterogeneous composites. The measured $\varepsilon_{ r}^{\prime}$ , $\varepsilon_{ r}^{\prime \prime}$ , $\mu_{ r}^{\prime}$ , and $\mu_{ r}^{\prime \prime}$ values are used for the designing of double-layer composite absorbers, where the suitable composite selection, layer preferences, as well as thickness of layers are optimized using a genetic algorithm. The fractal geometry based FSSs have been designed using an iterated function system, which are embedded with single- and double-layer composite absorbers to examine their effect on absorption. A double-layer composite coating with a Sierpinski gasket fractal FSS shows a strong RL of 35.57 dB at 9.5 GHz with broad bandwidth of 4.2 GHz in the range from 8.2 to 12.4 GHz. The total coating thickness is only 1.4 mm. Findings provide an effective and feasible way to develop thin and broadband absorber coatings for various practical applications.

RESEARCH OPPORTUNITIES FERRITE 2000NM THE SHORT PROCESS FLOW

The possibility of obtaining Mn—Zn-ferrite 2000 NM on the short process flow, which differs from the usual lack of diffusion operations roasting and grinding. It is shown that the use of the basic composition in sintering processes develop secondary recrystallization and zonal isolation, leading to the formation of highly inhomogeneous microstructure obtained with low values of the magnetic permeability. A homogeneous microstructure characteristic recrystallization, managed by doping copper oxide and zinc. By doping CuO permeability far from the desired value, but its temperature coefficient is small. By doping ZnO reached the desired value of magnetic permeability, but dramatically increases its temperature coefficient.The optimum combination of the magnetic parameters obtained in complex copper oxides doped ferrite and zinc.

Cylindrical radial superlattice conductors for low loss microwave components

Theory and experimental demonstration of a cylindrical radial superlattice (CRS) conductor composed of alternating nanoscopic non-ferromagnetic/ferromagnetic metal layers are presented with focus on low conductor loss in a K-band microwave spectrum. The dynamic frequency response of the ferromagnetic thin films has been extracted using the Landau-Lifshitz-Gilbert equation which shows a negative magnetic permeability value in the frequencies above its ferromagnetic resonance. The reduction of the conductor loss results from the eddy current canceling (ECC) effect in the CRS conductors, where the negative-permeability ferromagnetic and positive-permeability non-ferromagnetic metal layers produce a zero effective permeability, resulting in virtually infinite skin depth at the targeted frequency. The closed and uniform boundary conditions inherent in the radial shape conductors preclude discontinuity effects occurring at the edges of the planar superlattice conductor and end up with a more effective ECC effect in practice. The design aspects with regards to the CRS materials and structural configuration are discussed. Simulations using a full-wave finite element method high frequency structure simulator are performed to show the ECC effect inside the CRS conductors. An air-lifted inductor made of the CRS conductor has been implemented to prove the effectiveness of the conductor loss reduction with the CRS conductor. The inductor shows an inductance value of 1–2 nH and a Q-factor of 45 at 18 GHz, which is the highest value reported at the frequency by now.

Dependence of Granular Matrix Demagnetizing Factor on the Matrix Relative Size

We note that for a wide range of porous, especially granular, ferromagnetics used as matrices of magnetic filter-separators, there is still an issue of defining their demagnetizing factor N which has a dramatic effect on the values of average magnetic permeability of these operating units of filter-separators. The work aims at filling the existent gaps in the issue, we supply N values depending on the relative size of such magnets as well as a respective generalizing phenomenological dependence which is characterized by an exponential realtion between the demagnetizing factor and relative size radical. The established relation allows obtaining real values of magnetic permeability of a short filter matrix thus providing an unbiased comparative estimate of its technological workability.

Optimum reduction of the dynamo threshold by a ferromagnetic layer located in the flow.

We consider a fluid dynamo model generated by the flow on both sides of a moving layer. The magnetic permeability of the layer is larger than that of the flow. We show that there exists an optimum value of magnetic permeability for which the critical magnetic Reynolds number for dynamo onset is smaller than for a nonmagnetic material and also smaller than for a layer of infinite magnetic permeability. We present a mechanism that provides an explanation for recent experimental results. A similar effect occurs when the electrical conductivity of the layer is large.

A Working of Eddy Current Transducers under Control of Ferromagnetic Pipes in Condition of Insufficient Magnetic Saturation

The numerical method of calculation of electromagnetic field in a control sample at a time of work of encircling eddy current transducer is offered. The method is based on a numerical solution of the two Maxwell equations, which connect a change of electrical and magnetic fields. It allows to make calculations taking into account the actual value of magnetic inductivity of metal and to get results in any form, convenient for further interpretations. For the calculation of the encircling eddy current transducer the equivalent circuit of defect as step junction is offered. The numerical calculation shows, that the greatest sensitivity of the transducer is achieved when the value of magnetic permeability of the object of control is approximately 10-30. Therefore, it is not necessary to lead the material of the object of control up to satiety, as it considered before.