Magnetic Parts Research Articles

Entropy change of martensitic transformation in ferromagnetic shape memory alloys

A consistent analysis of the entropy change that accompanies the martensitic transformation (MT) of ferromagnetic shape memory alloys has been carried out using the Landau theory of phase transitions. The interrelation between the values of entropy change and the widths of the temperature intervals of MTs, observed in experiments with different alloys, was described. General theoretical expressions for the non-magnetic and magnetic parts of the total entropy change were obtained and then applied to the Ni–Mn–Ga and Ni–Fe–Ga shape memory alloys. For Ni–Mn–Ga alloys the theoretical values of the magnetic parts of entropy changes appeared to be close to the measured total entropy changes. This fact demonstrated the crucial role of the interaction between the magnetic and elastic subsystems of these alloys in the thermodynamic characteristics of MTs. A theoretical estimation of the magnetic entropy change has been obtained from the experimental temperature dependence of magnetization of a Ni–Fe–Ga alloy.

Pressure dependence of magneto-structural properties of Co-doped off-stoichiometric Ni2MnGa alloys

A strong effect of pressure on magnetization and paramagnetic moment of the Co-doped Mn-rich Ni 50-x Co x Mn 25+y Ga 25-y (x = 5,7,9 and y = 5,6,7,8) Heusler alloys is presented and compared with very weak pressure sensitivity of magnetization of the stoichiometric Ni 2 MnGa alloy. The effects of both, the pressure and the magnetic field, on temperature of the structural martensitic transition in the alloys are discussed with a use of the Clausius-Clapeyron relations. An analysis of pressure and field effects provides a possibility to evaluate structural and magnetic parts of latent heat of the martensitic transitions in the studied alloys. The Curie temperature of martensite phase of the Co-rich alloys is not affected by pressure.

Design of an active hydromagnetic journal bearing

An active hydromagnetic journal bearing is designed and presented in this study, which is a new and innovative type of hybrid journal bearing. The proposed new mechatronic smart device has a common bearing shell that contains the two parts of the bearing, which is an attempt to combine the advantages of both types of bearings to overcome their drawbacks and give rise to new possibilities for instability control, increased load-carrying capacity, diagnostics of the rotor system, etc. The active hydromagnetic journal bearing should operate as either a hydrodynamic, active magnetic or hybrid journal bearing, depending on the needs of the rotating machinery. The hydrodynamic lubrication is developed in the inner bearing surface, and the electromagnets of the magnetic bearing are placed outside its outer surface. The active hydromagnetic journal bearing is designed with the appropriate clearance, so that both the hydrodynamic and magnetic bearings can operate. The suitable operational regions for the active hydromagnetic journal bearing are calculated and presented as a combination of the optimum ratio between the air gap and the clearance. Additionally, a simulation code using the two-dimensional finite element method (ANSYS) is developed to simulate the performance of the magnetic component of the active hydromagnetic journal bearing, and the ANSYS software is used to obtain a solution for the hydrodynamic pressure field. The dynamic characteristics of the hybrid journal bearing in terms of the stiffness and damping coefficients versus the Sommerfeld number are calculated and presented. In the hybrid bearing operation, the corresponding stiffness and damping coefficients are used to simulate the hydromagnetic bearing dynamic behaviour. Each hybrid coefficient consists of two parts; the hydrodynamic and the magnetic part. When the operation is purely hydrodynamic, the magnetic parts of the dynamic coefficients are zero and vice versa, whereas both parts are present in the hybrid operation mode.

Effects of standoff distance on porosity, phase distribution and mechanical properties of plasma sprayed Nd–Fe–B coatings

Fabrication of components that require magnetic parts such as in micro motors and micro generators demands an alternative to micro machining processes that are costly and time consuming. In this study, Nd–Fe–B coatings with an average thickness of 200μm were deposited onto stainless steel substrates by an atmospheric plasma spray technique using amorphous feedstock powder of spherical morphology. The microstructure of the coatings shifted from lamellar to spherical in nature as standoff distance (SOD) increased. The total porosity of the coatings exhibited a minima with respect to SOD and ranged from 1.8 to 8.2%. Two distinct phases; i.e., the Nd-rich and Fe-rich phases, were observed and imply phase separation during the plasma spray process. Occurrence of phase separation was argued to arise due to metastable phase formation and non-equilibrium solidification. The Fe-rich phase increased with increasing SOD due to longer in-flight time allowing non-equilibrium solidification to occur. The presence of two phases results in a bimodal Weibull distribution for Vickers hardness data. However, Weibull plots for Knoop hardness and elastic modulus show monomodal behaviour. The correlation between the degree of data scattering, as reflected by the Weibull modulus, with porosity and phase percentage was determined.

Invariants for tendex and vortex fields

Tendex and vortex fields, defined by the eigenvectors and eigenvalues of the electric and magnetic parts of the Weyl curvature tensor, form the basis of a recently developed approach to visualizing spacetime curvature. In analogy to electric and magnetic fields, these fields are coordinate-dependent. However, in a further analogy, we can form invariants from the tendex and vortex fields that are invariant under coordinate transformations, just as certain combinations of the electric and magnetic fields are invariant under coordinate transformations. We derive these invariants, and provide a simple, analytical demonstration for non-spherically symmetric slices of a Schwarzschild spacetime.

Analytical tendex and vortex fields for perturbative black hole initial data

Tendex and vortex fields, defined by the eigenvectors and eigenvalues of the electric and magnetic parts of the Weyl curvature tensor, form the basis of a recently developed approach to visualizing spacetime curvature. In particular, this method has been proposed as a tool for interpreting results from numerical binary black hole simulations, providing a deeper insight into the physical processes governing the merger of black holes and the emission of gravitational radiation. Here we apply this approach to approximate but analytical initial data for both single boosted and binary black holes. These perturbative data become exact in the limit of small boost or large binary separation. We hope that these calculations will provide additional insight into the properties of tendex and vortex fields and will form a useful test for future numerical calculations.

Minimization of cogging torque in permanent magnet machines using the topological gradient and adjoint sensitivity in multi-objective design

The paper presents an application of the topological derivative and continuum sensitivity analysis for the optimal design of the permanent magnet excited machines with the adjustable excitation. In our work we applied a topological optimization in order to find a general shape of rotor poles consisted of an iron and magnet part. An essential advantage of the proposed method is its numerical effectiveness. In order to verify results, three-dimensional models were developed and thoroughly analyzed. Aspresented in thecomparative analysis of 3D results, theapplied method lead to thesignificant reduction of both, the cogging torque and a level of higher harmonics in the voltage induced in the armature windings.

Orientation-controlled parallel assembly at the air–water interface

This paper presents an experimental and theoretical study with statistical analysis of a high-yield, orientation-specific fluidic self-assembly process on a preprogrammed template. We demonstrate self-assembly of thin (less than few hundred microns in thickness) parts, which is vital for many applications in miniaturized platforms but problematic for today's pick-and-place robots. The assembly proceeds row-by-row as the substrate is pulled up through an air–water interface. Experiments and analysis are presented with an emphasis on the combined effect of controlled surface waves and magnetic force. For various gap values between a magnet and Ni-patterned parts, magnetic force distributions are generated using Monte Carlo simulation and employed to predict assembly yield. An analysis of these distributions shows that a gradual decline in yield following the probability density function can be expected with degrading conditions. The experimentally determined critical magnetic force is in good agreement with a derived value from a model of competing forces acting on a part. A general set of design guidelines is also presented from the developed model and experimental data.

Characterization of the sand of Brahmaputra river of Bangladesh

The aim of this paper is to study on the mineralogy, morphology, magnetic property and composition of the sand of Brahmaputra River, Bangladesh. The sand has been collected from randomly selected seven places and separated by High Intensity Rolling Magnetic Separator into three fractions, viz. magnetic, para-magnetic and non-magnetic parts. The identifications of the valuable heavy minerals existing in these fractions have been performed. The valuable heavy minerals in the separated fractions have been counted under reflected and polarizing microscope and it is found that the magnetic fraction contains ilmenite, magnetite and garnet. The major grain size fraction of the magnetic fraction is 125 - 250 ?m (57.18%). Zircon, rutile, xenotime, monazite, sillimanite etc. have been counted in other two fractions. X-ray Diffraction (XRD), X-ray Fluorescence (XRF) and Isodynamic Separator have been applied for mineral assessment and to quantify the relative proportion of mineral species. DOI: http://dx.doi.org/10.3329/bjsir.v47i2.11448 Bangladesh J. Sci. Ind. Res. 47(2), 167-172, 2012

Tidal indicators in the spacetime of a rotating deformed mass

Tidal indicators are commonly associated with the electric and magnetic parts of the Riemann tensor (and its covariant derivatives) with respect to a given family of observers in a given spacetime. Recently, observer-dependent tidal effects have been extensively investigated with respect to a variety of special observers in the equatorial plane of the Kerr spacetime. This analysis is extended here by considering a more general background solution to include the case of matter which is also endowed with an arbitrary mass quadrupole moment. Relations with curvature invariants and Bel–Robinson tensor, i.e. observer-dependent super-energy density and super-Poynting vector, are also investigated.

Multiphysics Modeling of a Permanent Magnet Synchronous Machine by Using Lumped Models

This paper describes the modeling of a permanent magnet synchronous machine (PMSM) by using lumped models (LMs). Designing electrical machines necessarily involves several fields of physics, such as electromagnetics, thermics, mechanics, and acoustics. Magnetic, electrical, electronic, and thermal parts are represented by LMs, whereas vibro-acoustic and mechanical parts are represented by analytical models. The aim of this study is to build a design model of a PMSM for traction applications. Each model is parameterized to optimize the machine. The method of taking into account saturation and movement is described. These fast, LMs make it possible to couple the software used with optimization tools. Simulation results are presented and compared with the finite-element method and the experiments performed.

Theoretical Study of Twin Boundary Motion in Heusler Ni-Mn-Ga Alloys Using Monte Carlo Method

The twin boundary motion in Ni-Mn-Ga Heusler alloys has been investigated using Monte Carlo simulations. The Hamiltonian of system includes magnetic and elastic parts and two magnetoelastic terms. It is shown that the twin boundary shifts in a magnetic field at the constant temperature. The spin and strain volume fractions have been obtained at different temperatures.

Analysis and Application of a Hybrid Motor Structure Convenient to Modify the Magnet and Reluctance Torques on the Rotor

This paper presents a hybrid motor prototype convenient to modify the magnet and reluctance torques. The rotor of the prototype consists of magnet and reluctance parts, so the generated torque includes both magnet and reluctance torques. A considerable feature of the motor is that the ratio of the magnet and reluctance parts can be modified on the rotor and the rotor hybridization ratio can be varied. Another important point is the mechanical angle between the parts changed by means of the suitable construction of the parts on the rotor shaft. Finite element (FE) analysis was carried out for the proposed motor and static torque measurements were realized. The FE results were compared with the experimental results. Average torque and maximum torque values were obtained and three dimensional 3-D graphs were formed by using the experimental data. It is possible to make different combinations by changing the parts and the angle between the parts due to the proposed motor. So the magnet and reluctance torques are modified and different combinations give different torque behavior.

Origins of axial inhomogeneity of magnetic performance in hot deformed Nd-Fe-B ring magnets

Hot-deformed Nd-Fe-B ring magnets have wide potential applications. These ring magnets, however, exhibit axial inhomogeneity of magnetic performance. In this work, the effects of density, pressure, deformation temperature, deformation rate, and texture on axial magnetic performance were investigated over ring magnets prepared by backward extrusion method. It was demonstrated that the texture accounted for the variation of magnetic performance along axial direction. Microstructures of the ring magnets were examined with SEM, which further revealed two different origins of axial inhomogeneity of magnetic performance. The deformation degree of Nd-Fe-B grains plays a critical role in the performance difference between the top and middle part of ring magnet. But that between the middle and bottom part mainly results from different alignment orientations of platelet Nd-Fe-B grains. It was both deformation degree and alignment orientation that determined the axial texture and consequent magnetic performance of hot-deformed ring magnets.

Observer-dependent tidal indicators in the Kerr spacetime

The observer-dependent tidal effects associated with the electric and magnetic parts of the Riemann tensor with respect to an arbitrary family of observers are discussed in a general spacetime in terms of certain ‘tidal indicators’. The features of such indicators are then explored by specializing our considerations to the family of stationary circularly rotating observers in the equatorial plane of the Kerr spacetime. There exist a number of observer families which are special for several reasons and for each of them such indicators are evaluated. The transformation laws of tidal indicators when passing from one observer to another are also discussed, clarifying the interplay among them. Our analysis shows that no equatorial plane circularly rotating observer in the Kerr spacetime can ever measure a vanishing tidal electric indicator, whereas the family of Carter’s observers measures zero tidal magnetic indicator.

ディーゼルエンジン向けインジェクタ用電磁弁部品の開発

Hitachi Powdered Metals and Denso developed new magnetic parts which consists of a high performance powder base soft magnetic core and a composite armature, and have been installed as magnetic parts in injectors for common rail systems meeting the EURO V regulation. The new powder base soft magnetic core for the stator, had achieved both high magnetic properties and outstanding machinability as a result of various improvements of the insulation property of the iron powder itself, optimization of the resin content and addition method, and optimization of the heat treatment method. On the other hand, the composite armature had achieved combined properties of good wear resistance, wrought steel, and excellent magnetic properties, sintered magnetic core, in a single device by using the sinter diffusion bonding method. These properties are more excellent than conventional parts. As a result, the performance of the injector has improved drastically.

Simultaneous Design Optimization of Permanent Magnet, Coils, and Ferromagnetic Material in Actuators

This paper presents structural topology optimization of an electro/permanent magnet linear actuator. The optimization goal is to maximize the average magnetic force acting on a plunger that travels over a distance of 20 mm. To achieve this goal, the magnetic field sources (i.e., permanent magnet, positive and negative direction coils), and ferromagnetic material of the yoke are simultaneously co-designed using four design variables for each finite element. The magnetic force is calculated using the Maxwell stress tensor method coupled with finite-element analysis. The optimization sensitivity analysis is performed using the adjoint method, and the optimization problem is solved using a sequential linear programming method. To illustrate the utility of the proposed design approach, linear actuators are designed, and the optimal shapes and locations of the yoke permanent magnet, coils, and ferromagnetic part are provided. In addition, the effects of the PM magnetization direction and the current density strength on design results are described.

Magnetic, magnetocaloric, and lattice properties of the La(Fe x Si1 − x )13 ferromagnets

The magnetic and lattice properties of a sample of La(Fe0.86Si0.14)13 ferromagnet have been measured. The influence that neutron irradiation has on the physical properties of this ferromagnet is studied. It is shown that the irradiation of this sample by a fluence of 3 × 1019 n/cm2 increases the lattice constant a and the Curie temperature (TC) as the volume magnetostriction decreases. A model of ferromagnet is proposed which satisfactorily describes the dependence a(T) of the initial and irradiated samples and their magnetic properties. The temperature dependence of the change in entropy when switching the magnetic field on and off is calculated. It is established that the change in both the magnetic and lattice parts of the total entropy at the magnetic phase transition must be taken into account for La(FexSi1 − x)13 compounds.

Field-tuned Fermi liquid in quantum critical YFe2Al10

We present measurements of the magnetization $M$, ac susceptibility ${\ensuremath{\chi}}^{\ensuremath{'}}$, electrical resistivity $\ensuremath{\rho}$, and specific heat $C$ in single crystals of metallic YFe${}_{2}$Al${}_{10}$. The magnetic susceptibility follows a Curie-Weiss temperature dependence for $75\phantom{\rule{0.28em}{0ex}}\text{K}\ensuremath{\le}T\ensuremath{\le}750$ K, with a fluctuating Fe moment of 0.45${\ensuremath{\mu}}_{B}$/Fe, and the ac susceptibility ${\ensuremath{\chi}}^{\ensuremath{'}}$ diverges at lower temperatures ${\ensuremath{\chi}}^{\ensuremath{'}}\ensuremath{\sim}{T}^{\ensuremath{-}1.28\ifmmode\pm\else\textpm\fi{}0.04}$ when the ac field is in the basal plane. The field $B$ and temperature $T$ dependencies of the magnetization $M$ are well described by the scaling expression $M{T}^{\ensuremath{-}\ensuremath{\beta}}$ $=$ $\mathcal{F}$($B$/$T$${}^{\ensuremath{\beta}+\ensuremath{\gamma}}$) for $1.8\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4pt}{0ex}}\text{K}\ensuremath{\le}T\ensuremath{\le}30$ K and for fields larger than 0.1$T$. These results indicate that strong quasi-two-dimensional critical fluctuations are present that can be suppressed by magnetic fields. The magnetic and electronic parts of the specific heat $C$${}_{M}$ show a similar divergence for $0.4\phantom{\rule{0.28em}{0ex}}\text{K}\ensuremath{\le}T\ensuremath{\le}12$ K, where ${C}_{M}/T\ensuremath{\sim}{T}^{\ensuremath{-}0.47\ifmmode\pm\else\textpm\fi{}0.03}$. The divergences in ${\ensuremath{\chi}}^{\ensuremath{'}}$ and ${C}_{M}/T$ indicate that YFe${}_{2}$Al${}_{10}$ is located near a quantum critical point, and no magnetic order is observed above 0.09 K. We argue that our results are inconsistent with quantum impurity or disorder models, suggesting instead that YFe${}_{2}$Al${}_{10}$ is on the verge of bulk magnetic ordering, and that the critical fluctuations that are associated with this quantum critical point lead to the divergencies in ${C}_{M}/T$ and ${\ensuremath{\chi}}^{\ensuremath{'}}$.

In Situ Fabrication and Actuation of Polymer Magnetic Microstructures

We demonstrate a single-exposure in situ magnetic actuator fabrication technique using magnetic nanoparticles (MNs) containing UV curable polymer in a Polydimethylsiloxane (PDMS) channel. Microstructures with a 3-D anchored cantilever as well as free-floating components are fabricated in a single step at a single site without the use of a sacrificial layer. By controlling the location of high oxygen concentration area through PDMS substrate patterning, we can create partially bound and free-floating movement-restricted structures. This allows us to create complex magnetic actuators, such as a 3-D anchored cantilever, motor type, and rail-guided magnetic actuators. The actuating performance of UV photopatterned magnetic microstructures depends on the MN concentration in photopolymer resin and magnetic field intensity. The measured translational velocity of magnetic microactuators with a 1 : 10 MN concentration is 140 μm/s under 1400 G of magnetic field in poly(ethylene glycol) diacrylate resin. Also, we demonstrate selective magnetic actuation of heterogeneous structures composed of magnetic and nonmagnetic parts self-assembled in railed microfluidic channels. Only magnetic parts from the assembly selectively actuated due to the magnetic field without response to the flow. Therefore, we have developed a versatile magnetic microstructure fabrication method that is very simple and fast, enabling rapid in situ fabrication and actuation.