Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.221-224
Temperature Dependence of Mn2+ Paramagnetic Ion in a Stoichiometric LiNbO3 Single Crystal
Electron paramagnetic resonance (EPR) spectra of Mn2+ impurity ion in Stoichiometric LiNbO3 single crystal (SLN) was investigated with an X-band EPR spectrometer in the temperature range of 3 K~296 K. The intensity of EPR spectrum of Mn2+ ion was increased to 20 K and decreased again below 20 K as the temperature decreases. The zero-field splitting parameter D decreased as the temperature increases. It was suggested that Mn2+ ion substitute for Nb5+ ion instead of Li+ ion. No changes for hyperfine interaction of Mn2+ ion was obtained in the temperature range of 3 K~296 K.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.225-229
Anomalous Nernst Effects of [CoSiB/Pt] Multilayer Films
We report a measurement for the anomalous Nernst effects induced by a temperature gradient in [CoSiB/Pt] multilayer films with perpendicular magnetic anisotropy. The Nernst voltage shows a characteristic hysteresis which reflects the magnetization of the film as in the case of the anomalous Hall effects. With a local heating geometry, we also measure the dependence of the anomalous Nernst voltage on the distance
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.230-234
Effects of Solution Concentration on the Structural and Magnetic Properties of Ni0.5Zn0.5Fe2O4 Ferrite Nanoparticles Prepared by Sol-gel
The Ni0.5Zn0.5Fe2O4 nanoparticles about 30 nm were prepared using sol-gel method with metal nitrates dissolved in 2-methoxyathanol. The concentrations of the metal nitrates are adjusted from 0.1 to 0.75 M in order to study the influence on the structural and magnetic properties. The structure and morphology characterization revealed that the crystallinity was improved and the nanoparticle size was increased with the nutrition solution concentrations up to 0.5 M. Degraded crystallinity together with decreased nanoparticle size were observed for concentration of 0.75 M. The saturation magnetization at room temperature reached maximum at 0.5 M, which can be explained by considering the crystallinity and size effect.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.235-239
The Origin of Coercivity Enhancement of Sintered NdFeB Magnets Prepared by Dy Addition
The effect of Dy addition on the microstructure and magnetic properties of the sintered NdFeB magnets was investigated. The results of the microstructure analysis showed that Dy-free and Dy-doped samples are composed of Nd2Fe14B (
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.240-244
Magnetic Microstructures and Corrosion Behaviors of Nd-Fe-B-Ti-C Alloy by Ga Doping
The influences of Gallium doping on the magnetic microstructures and corrosion behaviors of Nd-Fe-B-Ti-C alloys are investigated. The cooling rate for obtaining fully amorphous structure is raised, and the glassforming ability is improved by the Ga addition. The High Resolution Transmission Electron Microscopy image shows that the α-Fe and Fe3B soft magnetic phases become granular surrounded by the Nd2Fe14B hard magnetic phase. The rms and (Δφ)rms value of Nd-Fe-B-Ti-C nanocomposite alloy thick ribbons in the typical topographic and magnetic force images detected by Magnetic Force Microscopy(MFM) decreases with 0.5 at% Ga addition. The corrosion resistances of Nd9Fe73B12.6C1.4Ti4-xGax (x = 0, 0.5, 1) alloys are enhanced by the Ga addition. It can be attributed to the formation of more amorphous phases in the Ga doped samples.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.245-249
Effect of α-Fe Content on the Magnetic Properties of MnBi/α-Fe Nanocomposite Permanent Magnets by Micro-magnetic Calculation
A finite element model was built for MnBi/α-Fe nanocomposite permanent magnets, and the demagnetization curves of the magnets were simulated by micro-magnetic calculation. The microstructure of the cubic model is composed of 64 irregular grains with an average grain size of 20 nm. With the volume fraction of soft magnetic phase (
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.250-254
Analysis and Experiments of the Linear Electrical Generator in Wave Energy Farm utilizing Resonance Power Buoy System
In this research, the linear electrical generator in wave energy farm utilizing resonance power buoy system is studied. The mechanical resonance characteristics of the buoy and the wave are analyzed to maximize the kinetic energy in a relatively small wave energy area where WRPS is operated. In this research, we chose an analog model of the linear electrical generator of which size is one-hundredth of an actual size of it in WPRS (Wave energy farm utilizing Resonance Power buoy System) prior to verifying the characteristics of actual model of linear electrical generator in WRPS. In addition, the finite element analysis is conducted using commercial electromagnetic analysis software named MAXWELL to examine the electric characteristic of linear generator. Finally, for the verification of dynamic and electric characteristics of linear generator, the prototype was manufactured and the experiments to measure the displacement and the output electric power were performed.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.255-259
Numerical Analysis for Characterization of Single Phase Induction Motors by using Circuit Equations Coupled with Magnetic Field Distribution
In this paper a new coupling method for efficient and simple analysis of single phase induction motor is presented. The circuit representation of both the stator winding and each conducting rotor loop (composed of rotor bar and end ring segment) is used in conjunction with the distribution of magnetic flux linkage instead of inductance matrix. The flux linkage is calculated using air-gap flux density distributions driven by unit currents in the stator windings and rotor bars. The field distribution of one turn of a coil is calculated by FEM and the result is used to calculate total flux linkage by employing a coordinate transformation. The numerical results give good agreement with prior literature. The method is particularly effective in analyzing the effect of the number of rotor bars.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.260-267
Analytical Investigation on Fundamental Electrical Characteristics of Large Air-gap Superconducting Synchronous Machine
In this paper a general 2-D model of a large air-gap synchronous machine either with non-magnetic or magnetic core rotor is investigated and electrical characteristics of the machine are analytically calculated. Considering the general model, analytical equations for magnetic field density in different regions of the large air-gap machine are calculated. In addition, self and mutual inductances in the proposed model of the machine have been developed, which are the most important parameters in the electromagnetic design and transient analysis of synchronous machines. Finite element simulation has also been performed to verify the obtained results from the equations. Analytical results show good agreement with FEM results.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.268-275
Investigation on Performance Characteristics of IPM for Electric Vehicles Considering Driving Conditions and Pole-Slot Combinations
This paper shows the characteristics of performance for interior permanent magnet machine (IPM) considering driving conditions such as maximum torque per ampere (MTPA) and flux-weakening control especially in terms of harmonic loss. In particular, based on finite element analysis (FEA), permanent magnet (PM) eddycurrent loss and the harmonic iron loss have been computed where the models have been intentionally designed to identify the effects of pole-slot combinations on the loss while maintaining the required power for electric vehicle. From the analysis results, it was shown that the rotor iron loss and PM eddy-current loss of machine employing fractional slot winding are extremely large at load condition. Furthermore, it was revealed that the harmonic iron loss at high-speed operation is mainly distributed over stator teeth and rotor surface, which may aggravate cooling system of the rotor structure in the vehicle.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.276-282
Analysis and Case Study of Permanent Magnet Arrays for Eddy Current Brake Systems with a New Performance Index
In this paper, magnetic flux distributions of several permanent magnet arrays, including Halbach array, are analyzed and compared. Also, braking force characteristics on a moving solid conductor in the eddy current brake systems with such magnet arrays are analyzed. Then, a new performance index taking into account the maximum braking force and the volume of the magnet is introduced for the comparison and case study of permanent magnet arrays. By changing the lengths, magnetization directions and the height of the permanent magnet arrays, a higher braking force per volume of the magnet can be achieved.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.283-288
Topology Design Optimization of Electromagnetic Vibration Energy Harvester to Maximize Output Power
This paper presents structural topology optimization that is being applied for the design of electromagnetic vibration energy harvester. The design goal is to maximize the root-mean-square value of output voltage generated by external vibration leading structures. To calculate the output voltage, the magnetic field analysis is performed by using the finite element method, and the obtained magnetic flux linkage is interpolated by using Lagrange polynomials. To achieve the design goal, permanent magnet is designed by using topology optimization. The analytical design sensitivity is derived from the adjoint variable method, and the formulated optimization problem is solved through the method of moving asymptotes (MMA). As optimization results, the optimal location and shape of the permanent magnet are provided when the magnetization direction is fixed. In addition, the optimization results including the design of magnetization direction are provided.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.289-296
The Effects of Rotating Magnetic Field on Growth Rate, Cell Metabolic Activity and Biofilm Formation by Staphylococcus Aureus and Escherichia Coli
This work presents results of the study which concerns the influence of the rotating magnetic field (RMF) on the growth rate, cell metabolic activity and ability to form biofilms by
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.297-301
A Study on the Iron Loss and Demagnetization Characteristics of an Inset-type Flux-Reversal Machine
Flux-reversal machine (FRM) is cost effective and suitable for mass production due to its simple structure. However, there is a notable permanent magnet flux leakage which deteriorates the performance. To compensate this drawback with a design method, an Inset-Permanent-Magnet-Type FRM (ITFRM) has been proposed. The ITFRM has permanent magnets perpendicular to the stator teeth surface, and thus, is much more difficult to demagnetize. In this paper, we deal with the iron losses and irreversible permanent magnet demagnetization characteristics of the ITFRM according to various design variables and driving conditions. To analyze the characteristics, a two-dimensional finite-element method (2D-FEM) considering nonlinear analysis of permanent magnets is used. As a result, we propose the design variables that have the largest effects on the iron losses and irreversible magnet demagnetization.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.302-307
Thrust Hybrid Magnetic Bearing using Axially Magnetized Ring Magnet
Hybrid-type magnetic bearings using both permanent magnets and electromagnets have been used for rotating machinery. In the case of conventional thrust hybrid magnetic bearings supporting axial loads, radially magnetized permanent ring magnets, which have several demerits such as difficult magnetization and assembly, have been used to generate bias flux. In this study, a novel thrust hybrid magnetic bearing using an axially magnetized permanent ring magnet is presented. Because it is easy to magnetize a ring magnet in the axial direction, the segmentation of the ring magnet for magnetization is not required and the assembly process can be simplified. For verifying the performance of the proposed method, a test rig that consists of a proposed thrust magnetic bearing and variable loads is constructed. This paper presents the detailed design procedures and the obtained experimental results. The results show that the developed thrust magnetic bearing has the potential to replace conventional thrust magnetic bearings.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.308-310
Field-Induced Translation of Single Ferromagnetic and Ferrimagnetic Grain as Observed in the Chamber-type μG System
Translation induced by the field-gradient force is being observed for a single ferromagnetic iron grain and a ferrimagnetic grain of a ferrite sample (CuFe2O4). From measurements on the translation, precise saturated magnetization of
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.311-316
Application of Image Processing to Determine Size Distribution of Magnetic Nanoparticles
Digital image processing has increasingly been implemented in nanostructural analysis and would be an ideal tool to characterize the morphology and position of self-assembled magnetic nanoparticles for high density recording. In this work, magnetic nanoparticles were synthesized by the modified polyol process using Fe(acac)3 and Pt(acac)2 as starting materials. Transmission electron microscope (TEM) images of as-synthesized products were inspected using an image processing procedure. Grayscale images (800 × 800 pixels, 72 dot per inch) were converted to binary images by using Otsu’s thresholding. Each particle was then detected by using the closing algorithm with disk structuring elements of 2 pixels, the Canny edge detection, and edge linking algorithm. Their centroid, diameter and area were subsequently evaluated. The degree of polydispersity of magnetic nanoparticles can then be compared using the size distribution from this image processing procedure.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.317-320
Polarization State of Scattered Light in Apertureless Reflection-mode Scanning Near-Field Optical Microscopy
We studied the polarization state in an apertureless scanning near-field microscopy (a-SNOM) operating in reflection mode by using three-dimensional Finite-difference Time-domain (FDTD) method. As a result, the electric field around tip apex in the near-field region enhanced four times stronger than the incident light for ppolarization when the tip-sample separation was 10 nm. We find that the p- and s-polarization state is maintained for the scattered light when the probe is perpendicular to the sample. When the probe is not perpendicular to the sample, the polarization state of scattered light will rotate an angle that equals to the inclination angle of probe with p-polarization illumination. On the other hand, the polarization state will not rotate with s-polarization illumination.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.321-325
Effect of a Magnetic Field on Mixed Convection of a Nanofluid in a Square Cavity
The problem of mixed convection in a differentially heated lid-driven square cavity filled with Cu-water nanofluid under effect of a magnetic field is investigated numerically. The left and right walls of the cavity are kept at temperatures of Th and Tc respectively while the horizontal walls are adiabatic. The top wall of the cavity moves in own plane from left to right. The effects of some pertinent parameters such as Richardson number (ranging from 0.1 to 10), the volume fraction of the nanoparticles (ranging 0 to 0.1) and the Hartmann number (ranging from 0 to 60) on the fluid flow and temperature fields and the rate of heat transfer in the cavity are investigated. It must be noted that in all calculations the Prandtl number of water as the pure fluid is kept at 6.8, while the Grashof number is considered fixed at 104. The obtained results show that the rate of heat transfer increases with an increase of the Reynolds number, while but it decreases with increase in the Hartmann number. Moreover it is found that based the Richardson and Hartmann numbers by increase in volume fraction of the nanoparticles the rate of heat transfer can be enhanced or deteriorated compared to the based fluid.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.326-330
Efficiency of Exponential Deperm Protocol
Magnetic treatment of surface vessels and submarines (Deperm) is required to camouflage them against magnetic detection from enemy marine force. So far, deperm has been accomplished by applying an alternating magnetic field of which amplitude decreases linearly. However, the reduction of the residual flux density in the direction of magnetic field is not linear in the case of the linear protocol, since the ferromagnetic material used to construct a surface vessel, mainly Fe-C, shows a nonlinear behavior in an alternating magnetic field. This is one of main reasons to make an ordinary deperm protocol inefficient. In this paper, we propose the exponential deperming protocol and compare the exponential protocol to conventional linear protocol within the framework of deperm performance. We found out that step number could be reduced in the exponential protocol compare with in the linear protocol, because the larger numbers of deperm steps are dedicated in the irreversible domain process region on the magnetic hysteresis.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.331-338
Recent Developments in Magnetic Measurements: from Technical Method to Physical Knowledge
We present a few significant advances in methods and concepts of magnetic measurements, aimed both at providing novel routes in the characterization of hard and soft magnetic materials and at improving our basic knowledge of the magnetization process. We discuss, in particular, investigation methods and experimental arrangements that have been developed in recent times for: 1) Hysteresis loop determination in extra-hard magnets by means of Pulsed Field Magnetometry; 2) Broadband observation of domain wall dynamics by highspeed stroboscopical Kerr techniques; 3) Entropy measurements in magnetocaloric materials by calorimetry in magnetic field. While pertaining to somewhat independent fields of investigation, all these measuring techniques have in common a solid approach to the underlying physical phenomenology and have a potential for further developments.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.339-341
So, You Need Reliable Magnetic Measurements You Can Use With Confidence? How the Magnetic Measurement Capabilities at NPL Can Help
The magnetic field standards, facilities and capabilities available at NPL for the calibration of magnetometers and gradiometers and the measurement of the magnetic properties of materials will be introduced. The details of the low magnetic field facility will be explained and the capabilities this facility enables for the characterisation and calibration of ultra-sensitive room temperature magnetic sensors will be presented. Building on core material capabilities that are compliant with the IEC 60404 series of written standards, the example of a standard permeameter that has been modified for the measurement of strips for real world conditions is discussed. This was incorporated into a stress machine to measure the DC properties of the soft magnetic materials used by the partners of a collaborative industry led R&D project at stress levels of up to 700 MPa. The results for three materials are presented and the changes in the properties with applied stress compared to establish which material exhibits favourable properties.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.342-347
Review paper: Application of the Pulsed Eddy Current Technique to Inspect Pipelines of Nuclear Plants
Local wall thinning in pipelines affects the structural integrity of industries, such as nuclear power plants (NPPs). In the present study, a development of pulsed eddy current (PEC) technology that detects the wall thinning of pipelines covered with insulation is reviewed. The methods and experimental results, which have two kinds of probe with a single and double core, were compared. For this purpose, the single and double core probes having one and two excitation coils have been devised, and the differential probe with two Hall sensors has been fabricated to measure the wall thinning in insulated pipelines. The test sample is a stainless steel having different thickness, laminated by plastic insulation to simulate the pipelines in NPPs. The excitation coils in the probe is driven by a rectangular current pulse, the difference of two Hall sensors has been measured as a resultant PEC signal. The peak value of the detected signal is used to describe the wall thinning. The double core probe has better performance to detect the wall thinning covered with insulation; the single core probe can detect the wall thinning up to an insulation thickness of 18 mm, whereas the double probe can detect up to 25 mm. The results show that the double core PEC probe has the potential to detect the wall thinning in an insulated pipeline of the NPPs
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.348-351
Magnetic NDE for Sensitization of Inconel 600 Alloy
Inconel 600 alloy, Ni base alloy, is widely used for steam generator tubings where sensitization occurs at grain boundaries and sensitization will induce tubing failures. This alloy has usually paramagnetic property, however, it transforms into ferromagnetic property along grain boundaries when sensitization occurs: this means NDE using magnetism for sensitization is possible. Therefore, in this study, Inconel 600 alloys were heat treated at 873 K from 0 to 400 hours so as to generate sensitization and their magnetic properties were investigated in detail. The saturation and the residual magnetization increase with increasing heat treatment time and take a maximum. On the other hand, the coercive force decreases with the increase in time of heat treatment. We confirmed that characteristics at only grain boundaries change into ferromagnetic phase by a MFM observation. As a trial for industrial application, heat treated Inconel 600 alloy was scanned by a magnetic field sensor, and the variations in magnetization were obtained nondestructively. The results indicate a feasibility of magnetic NDE for sensitization of Inconel 600 alloy.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.352-356
Design of Auxiliary Teeth on the Edge of Stationary Discontinuous Armature PM-LSM with Concentrated Winding
Recently, the stationary discontinuous armature, Permanent Magnet Linear Synchronous Motor (PM-LSM), was suggested as a driving source for long-distance transportation system. However, as these motors arrange armatures discontinuously, an edge occurs thereby leading to a cogging force. This works as a factor that hinders the acceleration and deceleration that takes place when movers enter into and eject from armatures. Therefore, in this study, the installation of auxiliary teeth on the edge of the armature of PM-LSM is suggested in order to reduce the cogging force caused by the edge when the armature is placed in a discontinuous arrangement. Auxiliary teeth are optimally designed by a 2-D numerical analysis using the finite element method was performed to generate the optimum design of the auxiliary teeth. The validity of the study was confirmed through the comparison of the cogging force induced at the edge in respect to the design parameter using the basic model.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.357-360
Implementation of a Modified SQI for the Preprocessing of Magnetic Flux Leakage Signal
A modified SQI method using magnetic leakage flux (MFL) signal for underground gas pipelines’ defect detection and characterization is presented in this paper. Raw signals gathered using MFL signals include many unexpected noises and high frequency signals, uneven background signals, signals caused by real defects, etc. The MFL signals of defect free pipelines primarily consist of two kinds of signals, uneven low frequency signals and uncertain high frequency noises. Leakage flux signals caused by defects are added to the case of pipelines having defects. Even though the SQI (Self Quotient Image) is a useful tool to gradually remove the varying backgrounds as well as to characterize the defects, it uses the division and floating point operations. A modified SQI having low computational complexity without time-consuming division operations is presented in this paper. By using defects carved in real pipelines in the pipeline simulation facility (PSF) and real MFL data, the performance of the proposed method is compared with that of the original SQI
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.361-364
Design Techniques for Reducing Cogging Torque in Permanent Magnet Flux Switching Machine
Permanent magnet flux switching motor (PMFSM) is a novel double salient machine which employs PMs instead of field winding for excitation. PMFSM contains only one set of armature winding, thereby features simple control strategy, low cost power inverter and substantial high efficiency. Due to the unique double salient structure and operation principle, the generated cogging torque in PMFSM is critical and quite different compared to the traditional PM machines. This paper presents and investigates various design techniques for reducing cogging torque in PMFSM. Firstly, an analytical model is proposed to study the influence of different methods on cogging torque. Then the optimal design parameters for minimizing cogging torque are determined by the analytical model, which significantly reduces the computational efforts. At last, the cogging torque with different design approaches are simulated by FEA along with the average output electromagnetic torque, which validates the analysis above.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.365-369
Content and Distribution of Transition Metals and Rare Earth Elements in Magnetically and Mechanically Separated Brown Coal Ash
Coal ash is known to contain a noticeable amount of valuable elements, including transition metals and lanthanides. Therefore it is quite actual problem to extract them for metallurgy and other applications. This paper presents the results of high gradient magnetic and mechanical separation, microscopy, element analyses and optical spectroscopy of brown coal ash taken from the combustion camera and chimney-stalk of Angren thermal power station. The separated magnetic fraction was 3.4 wt.%, where the content of Fe in ferrospheres increased to 58 wt.%. The highest contents of Fe and rare earth elements were found in the fine fractions of 50- 100 μm. Optical absorption spectroscopy of water solutions of the magnetic fractions revealed Fe2+ and Fe3+ ions in the ratio of ~1:1. The separated coal ash could be used for cleaning of technological liquid waste by means of the high gradient magnetic field.
Journal of Magnetics, 30 Sep 2013, Vol.18 , No.3, pp.370-374
Study of a Hybrid Magnet Array for an Electrodynamic Maglev Control
This paper introduces an innovative hybrid array consisting of both permanent and electro magnets. It will enable us to develop an active control mechanism for underdamped electro-dynamic suspension (EDS) Maglev systems. The proposed scheme is based on the Halbach array configuration which takes the major technical advantage from the original Halbach characteristics: a strongly concentrated magnetic field on one side of the array and a cancelled field on the opposite side. In addition, the unique feature of the proposed concept only differs from the Halbach array with permanent magnets. The total magnetic field of the array can be actively controlled through the current of the electro-magnet’s coils. As a result, the magnetic force produced by the proposed hybrid array can also be controlled actively. This study focuses on the magnetic characteristics and capability of the proposed array as compared to the basic Halbach concept. The results show that the proposed array is capable of producing not only an equivalent suspension force of the basic Halbach permanent magnet array but also a controlled mode. Consequently, the effectiveness of the proposed array confirms that this study can be used as a technical framework to develop an active control mechanism for an EDS Maglev system.