Effects Of Magnetic Permeability Research Articles

INVESTIGATION ON THE EFFECT OF OSCILLATING MAGNETIC FIELDS ON FLUID FLOW AND FORCED-CONVECTION HEAT TRANSFER AROUND A SPHERE

In this article, the heat transfer of magnetic nanofluids over a sphere has been considered in the presence of an external oscillating uniform magnetic field for a wide range of Reynolds number values (Re). This study incorporates the effect of magnetic permeability and purposes the optimal operating condition for the first time. The significant difference between the magnetic property of the nanofluid and the heated sphere makes a non-uniform magnetic field around the sphere resulting in a significant alteration in the distribution of velocity and temperature around sphere. The variations of average Nusselt number (Nu<sub>avg</sub>) and drag coefficient (C<sub>d</sub>) have been studied to demonstrate the influence of magnetic field frequency and intensity, Re, and the relative magnetic permeability of the sphere. It has been found that the magnetic field causes the vortices to appear or grow behind the sphere. This leads to fluid separation even for low Re values in the presence of magnetic field. Local Nu value is minimum at the separation point. This point moves towards the front of sphere as the magnetic field intensity increases. These vortices lead to boundary layer distortion, thereby increasing heat-transfer rate and drag force. In addition, the obtained results clearly indicate that there is an optimal frequency at which Nu<sub>avg</sub> and C<sub>d</sub> can be maximized. The dimensionless optimal frequency (Ωτ) is about 0.6 regardless of Re value or magnetic field intensity. Moreover, the influence of the applied magnetic field is more noticeable for low Re values and/or frequencies near the optimum value. For instance, Nu<sub>avg</sub> and C<sub>d</sub> increase by 150% and 50%, respectively, for Re value of 30 while they are three times smaller for Re value of 200. Increase in the magnetic permeability of sphere enhances the Nu<sub>avg</sub> up to 170% (at Re = 50) close to the optimal frequency, whereas its effect is almost negligible for frequencies far away from the optimal one. Furthermore, the obtained results clearly demonstrate that the heat-transfer increase is much larger than the penalty due to the drag force increase for frequencies close to the optimal value.

Effect of magnetic permeability, shearing length, and shear gap on magnetic flux density of the magnetorheological damper through finite element analysis

The performance of the magnetorheological (MR) damper is determined based on the damping force of the damper which is used to reduce the unwanted vibrations in the automobile suspension system. In this study, an axisymmetric magnetorheological damper model is analyzed using ANSYS finite element (FE) analysis to simulate a distribution of magnetic field in the fluid flow region. Firstly, the materials used for the fabrication of MR damper such as SA1018 and Aluminium are used for the permeability analysis for applied current in shear mode operation. It is evident from the result that, a material with higher magnetic permeability (SA1018) gives higher magnetic flux density in the fluid flow gap. By using SA1018 material for further study the effect of increase in shear gap and shearing length of the MR damper, there is a exponential decay in the magnetic flux density in the flow gap. And finally, by using the response surface methodology optimum values are obtained for maximum magnetic flux density.

Improved reflection technique for the permittivity measurement of ferrites using slotted coaxial samples

This paper presents the effect of magnetic permeability on the permittivity measurement using coaxial line reflection technique. It discusses in detail about the design aspects, analysis and simulation of the slotted co-axial sample and fixture for dielectric characterization of the ferrites and garnets possessing both dielectric and magnetic properties. This technique makes use of improved coaxial fixture and APC 07 compatible slotted coaxial sample geometry to measure the complex permittivity of the ferrite material. Permittivity is calculated from the impedance of sample loaded fixture, which is independent of magnetic permeability, because of air slot cut in the coaxial hollow cylindrical sample along the length. Characterization data of dielectrics and ferrites is used in design of ferrite circulators, and pulse magnets for particle accelerator applications. This is also used in many other RF applications including design of dielectric resonator for spin wave line width measurement of ferrites. Design work is aimed at accurate measurement of complex permittivity; using reflection measurement in coaxial fixture over a wide frequency range of 20 kHz to 1 GHz. Reflection measurement technique is further explored for accurate measurement of complex permittivity.

Analysis of anomalous electrical conductivity and magnetic permeability effects using a frequency domain controlled-source electromagnetic method

Analysis of anomalous electrical conductivity and magnetic permeability effects using a frequency domain controlled-source electromagnetic method

Electric tuning of magnetization dynamics and electric field-induced negative magnetic permeability in nanoscale composite multiferroics.

Steering magnetism by electric fields upon interfacing ferromagnetic (FM) and ferroelectric (FE) materials to achieve an emergent multiferroic response bears a great potential for nano-scale devices with novel functionalities. FM/FE heterostructures allow, for instance, the electrical manipulation of magnetic anisotropy via interfacial magnetoelectric (ME) couplings. A charge-mediated ME effect is believed to be generally weak and active in only a few angstroms. Here we present an experimental evidence uncovering a new magnon-driven, strong ME effect acting on the nanometer range. For Co92Zr8 (20 nm) film deposited on ferroelectric PMN-PT we show via ferromagnetic resonance (FMR) that this type of linear ME allows for electrical control of simultaneously the magnetization precession and its damping, both of which are key elements for magnetic switching and spintronics. The experiments unravel further an electric-field-induced negative magnetic permeability effect.

Electric Tuning of Magnetization Dynamics and Negative Magnetic Permeability in Nanoscale Composite Multiferroics

Steering magnetism by electric fields upon interfacing ferromagnetic (FM) and ferroelectric (FE) materials to achieve an emergent multiferroic response bears a great potential for nano-scale devices with qualitatively new functionalities. FM/FE heterostructures allow, for instance, the electrical manipulation of magnetic anisotropy via interfacial magnetoelectric (ME) couplings. Here we present a magnon-driven, strong interfacial ME effect acting within the spin-diffusion length of the order of nanometers. This type of linear ME interaction allows for electrical control of simultaneously the magnetization precession and its damping, both of which are key elements for magnetic switching and spintronics. The ferromagnetic resonance unravels further an electric-field-induced negative magnetic permeability effect, pointing so to a new class of optical negative-index metamaterials based on composite multiferroics.

Geomagnetic field variations induced by internal and surface waves in the four-layer model of the marine environment

The layered model of the marine environment, including the atmosphere, two seawater layers with different conductivity and density, and the bottom rock layer, has been considered. The geomagnetic field variations, generated by internal and surface waves with different frequency and propagation direction, have been found in the scope of this model. The effect of magnetic permeability and electric conductivity of bottom rocks on induced magnetic field has been taken into account. The transfer functions and spectral densities of these variations have been analytically determined and numerically estimated.

Principal Component Analysis of Pulsed Eddy Current Response From Corrosion in Mild Steel

The effect of corrosion under coatings on carbon steel is a complex mix of many factors, including electrical conductivity, magnetic permeability, surface roughness, and coating thickness variations, which all have to be taken into account when analysing the pulsed eddy current (PEC) response from corrosion. In this paper, the PEC nondestructive evaluation method has been applied to a set of mild steel plates with varying levels of corrosion and various surface preparations. The panels are exposed outdoors for the same time-period and then the surfaces prepared in different ways, resulting in four different corrosion grades in accordance with the surface preparation standards of the society for protective coatings. Using principal component analysis (PCA) on nonnormalized and normalized PEC response waveforms, the most dominant features are extracted and used to classify and characterize the samples. Normalization has been done in an attempt to mitigate the effects of magnetic permeability and lift-off variations across the samples. The distribution of the first principal component coefficients are then compared against other time-domain features of the PEC waveform to provide a physical explanation, and relate the changes to differences in the corrosion grade and other properties of the samples. Despite the complex nature of the samples, the results show that with the application of normalization and PCA, it is able to classify the samples into different corrosion grades.

Optimization of soft magnetic properties and crystallization in FeAgNbSiB, FeAgNbB and FeAgCoNbB amorphous alloys

In the present paper the influence of 1-h annealing (temperature range from 300 to 800 K) on magnetic, plastic and electrical properties of the Fe 75.75Ag 0.25Nb 2Si 13B 9, Fe 75.75Ag 0.25Nb 2B 22, Fe 74.75Ag 0.25Co 5Nb 2B 18 amorphous alloys were carefully examined. For all the tested alloys the enhancement of magnetic permeability effect was observed—i.e. initial magnetic permeability measured at room temperature for annealed samples shows a sharp maximum. A possible mechanism explaining this effect is discussed in detail. Moreover it was found that at room temperature plastic deformation of the annealed samples depends on the progress of structural relaxation (free volume content). Activation energies and preexponential factors of the first stage of crystallization process were determined from the isochronal resistivity curves measured with different heating rates (Kissinger method). The Curie temperatures from the magnetization curves versus temperature were also determined.

SH surface acoustic wave propagation in a cylindrically layered piezomagnetic/piezoelectric structure

SH surface acoustic wave (SH–SAW) propagation in a cylindrically layered magneto-electro-elastic structure is investigated analytically, where a piezomagnetic (or piezoelectric) material layer is bonded to a piezoelectric (or piezomagnetic) substrate. By means of transformation, the governing equations of the coupled waves are reduced to Bessel equation and Laplace equation. The boundary conditions imply that the displacements, shear stresses, electric potential, and electric displacements are continuous across the interface between the layer and the substrate together with the traction free at the surface of the layer. The magneto-electrically open and shorted conditions at cylindrical surface are taken to solve the problem. The phase velocity is numerically calculated for different thickness of the layer and wavenumber for piezomagnetic ceramics CoFe 2O 4 and piezoelectric ceramics BaTiO 3. The effects of magnetic permeability on propagation properties of SH–SAW are discussed in detail. The distributions of displacement, magnetic potential and magneto-electromechanical coupling factor are also figured and discussed.

Theoretical analysis for superprisming effect of photonic crystals composed of magnetic material

In this work, we analyze theoretically the frequency-dependent phase index np(ω) of a guided mode in photonic crystals from the photonic band structures. The np(ω) reveals a promising possibility for fabricating a chromatic prism using photonic crystals. We then investigate the superprisming effect of a photonic-crystal prism for both guided continuous-wave TM and TE modes. In addition to dielectric intuition, the effects of magnetic permeability of a magnetic photonic crystal on the photonic band structure, the phase index, and the superprisming effect are examined. It was found that magnetic intuition could enhance the resolution of a photonic-crystal prism for dividing TE modes of various wavelengths, but reduce the resolution for dividing TM modes.

Fast approximate EM induction modeling of metallic and UXO targets using a permeable prism

The time-domain EM induction response of non-magnetic and magnetic targets can be approximated using a conductive permeable prism composed of six faces of conductive plates, each face being composed of a set of conductive ribbons. The effect of magnetic permeability is included by the use of two “apparent flux gathering” coefficients, and two “effective magnetic permeability” coefficients, in the axial and transverse directions. These four magnetic property coefficients are a function of physical properties and geometry of the target, but are independent of prism orientation relative to a transmitter. The approximation algorithm is computationally fast, allowing inversions for target parameters to be achieved in seconds. The model is tested on profiles acquired with a Geonics EM63 time-domain EM metal detector over a non-magnetic copper pipe target, and a steel artillery shell in horizontal and vertical orientations. Results show that this approximation to a permeable prism has a capability of fitting geometric, conductivity and magnetic parameters at both early and late sample times. The magnetic parameters show strong change from early to late times on the EMI decay curve, indicating that the magnetic properties of the target have non-linear characteristics. It is proposed that these magnetic parameters and the nature of their non-linearity may carry additional discrimination information for distinguishing between intact munitions and scrap in UXO studies.

EMI Shielding Effectiveness of Copper/Epoxy Composites

Samples of shaped and treated copper (Cu) fibre/brittle matrix composites have been fabricated with a variety of fibre shapes, treatments, diameters, and powder inclusions and tested for shielding effectiveness (SE) using the ASTM standard D4935-99 method over the frequency range 200 to 1500 MHz. A small amount of nickel (Ni) powder was included in some specimens to evaluate the effect of magnetic permeability on SE. Most tests were conducted at constant (15 vol%, “v%”) fibre volume fraction. Results show that a smaller fibre diameter results in significant SE improvements. SE was also substantially improved by relatively minor fibre shaping (which changes along the fibre length) or by fine-scale roughening via chemical treatment. Addition of small amounts of Cu powder leads to major improvements in SE. Most of the improvements are presumably due to the establishment of conductive networks, although fibre shaping or treatment allows greater scattering and thus more internal reflections with attendant absorption. The smaller diameter fibres consistently gave better SE. When a continuous fibre mesh was used, high SE resulted, showing the dominance of fibre connectivity for such materials; the surface condition of the mesh is relatively unimportant. The improvements in SE can be achieved with essentially identical mechanical properties, leading to an effective multifunctional material, although most of the SE values achieved so far are modest. Ni powder results in overall improvement in SE as well as a cyclic dependence of SE on frequency, which indicates phase interference at a scale of particle size not previously seen.

Analysis and interpretation of anomalous conductivity and magnetic permeability effects in time domain electromagnetic data: Part I: Numerical modeling

Time domain electromagnetic (TDEM) response is usually associated with eddy currents in conductive bodies, since this is the dominant effect. However, other effects, such as displacement currents from dielectric processes and magnetic fields associated with rock magnetization, can contribute to TDEM response. In this paper we analyze the effect of magnetization on TDEM data. We use a 3-D code based on finite-difference method, developed by Wang and Hohmann [Geophysics 58 (1993) 797], to study transient electromagnetic field propagation through a medium containing bodies with both anomalous conductivity and anomalous magnetic permeability. The remarkable result is that the combination of anomalous conductivity and permeability within the same body could increase significantly the anomalous TDEM response in comparison with purely conductive or purely magnetic anomalies. This effect has to be taken into account in interpretation of TDEM data over electrical inhomogeneous structures with potentially anomalous magnetic permeability.

Analysis and interpretation of anomalous conductivity and magnetic permeability effects in time domain electromagnetic data: Part II: Sμ-inversion

In the paper by Pavlov and Zhdanov [J. Appl. Geophys. (2001)], we demonstrated that anomalous magnetic permeability of an ore body could result in measurable anomalous effects in TDEM data, which can be used in geophysical exploration. In the current paper, we develop a new method of TDEM data interpretation, which allows simultaneous reconstruction of both electrical and magnetic properties of the rocks. The method is based on a generalization of the S-inversion technique [66th Ann. Int. Mtg., Soc. Expl. Geophys., Expanded Abstr. (1996) 1306; 68th Ann. Int. Mtg., Soc. Expl. Geophys., Expanded Abstr. (1998) 473; J. Appl. Geophys. (1999)] for models containing thin sheets with anomalous conductivity and anomalous magnetic permeability. We call this method Sμ-inversion. Numerical 3-D modeling results demonstrate that Sμ-inversion provides useful information about both subsurface conductivity and magnetic permeability distributions. It can be used as a new tool for imaging TDEM data in mineral exploration.

Effects of magnetic permeability and resistivity on magneto-impedance in Fe - Cu - Nb - Si - B alloy ribbons

The giant magneto-impedance (MI) effect and magnetic permeability of alloy ribbons were measured as a function of the annealing temperature. When the ribbons had been annealed at the optimum temperature () they exhibited both a large MI and excellent soft magnetic properties. The MI was also calculated on the basis of classical electromagnetic theory. It was found that a large change in the effective magnetic permeability, caused by the application of an external magnetic field in an excellent soft magnetic sample, was crucial for the MI effect. Furthermore, the effect of the resistivity on the MI was also investigated. When the resistivity decreases, the eddy current losses increase and the frequency at which the variation in the complex impedance exhibits its maximum moves to a low value; thus the sample exhibts a large MI effect.

Superconducting X-ray lithography 180 degrees bending dipole magnetics analysis methodology

The Superconducting X-ray Lithography Source (SXLS) being built at Brookhaven National Laboratory requires two superconducting bending magnets. The authors describe the magnetic analyses completed to support and direct the design of magnets capable of successfully meeting the system requirements. Because of the diversity of the effects investigated a number of analytical techniques were necessary. Each of the effects and the analytical approach chosen are outlined. The magnetic field calculation approach and verification are presented. To verify the satisfaction of requirements, field calculations to seven significant digits were necessary. The effects of magnetic permeability of magnet materials, eddy currents, superconductor magnetization, current leads, splices, structural deflection, and manufacturing tolerances were calculated in addition to the current density field calculations. >

Cryogenic Fatigue Properties of 304L and 316L Stainless Steels Compared to Mechanical Strength and Increasing Magnetic Permeability

Abstract For superconducting magnet applications, the 4 K fatigue life curves of the cryogenic structural materials 304L and 316L stainless steel were obtained using axial-strain control conditions. These curves were compared with others at 77 and 300 K and with data for other 300-series stainless steels in the literature. Increasing magnetic permeability with monotonic tensile and cyclic straining, due to strain-induced martensitic transformation, was also investigated, since 304L and 316L are metastable austenitic stainless steels. 4 K fatigue life curves relating magnetic permeability effects were obtained. Fatigue tests relating magnetic permeability at 77 and 300 K were also conducted for comparison. Finally, a cryogenic fatigue design criterion for preventing mechanical failure and increasing magnetic permeability was considered.

コア形状を考慮した広帯域ＦｅＡｌＳｉ積層薄膜ヘッド

Miniaturization of the magnetic head core was sought aiming for wide band recording. To achieve this, core size effect and magnetic permeability effect on reproducing efficiency of the film core head was studied by both computer simulation and experiment. The main results are as follows: Minimum core width can be reduced to around 160μm without apparent decreasing of core efficiency; and core efficiency depends strongly on the permeability of the film core. Finally, the frequency characteristic of the FeAlSi film laminated core head constructed by these concepts was measured. The core loss ratio of 3.8 dB was gained between the frequencies of 2 MHz. and 18 MHz.

Influence of permeability on wave-tilt of EM waves

Theoretical studies on the influence of magnetic permeability on the amplitude and phase of electric and magnetic wave-tilt have been carried out in the frequency range 102–106 Hz over a homogeneous half-space Earth model. Computational results show a pronounced effect of magnetic permeability on the amplitude of wave-tilt measurements.