Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.303-307
Magnetic Properties of R-YIG (R = La, Nd, and Gd) Derived by a Sol-gel Method
Y3-xRxFe5O12 (R = La, Nd, and Gd) powder were fabricated using a sol-gel pyrolysis method. Their magnetic properties and crystalline structures were investigated using x-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and Mössbauer Spectrometer. The Mössbauer spectra for the powders were taken at various temperatures ranging from 12 K to Curie temperature (Tc). The isomer shifts indicated that the valence states of Fe ions for the 16(a) and 24(d) sites have a ferric character. The saturation magnetization (Ms) increases from 32 to 34 (emu/g) for the YIG, and Nd-YIG, respectively. However, Ms decreases to 27 (emu/g) at Gd-YIG.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.308-314
Crystallographic and Magnetic Properties of Co, Zn, Ni-Zn Substituted Nano-size Manganese Ferrites Synthesized by Sol-gel Method
Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, MnFe2O4, Mn0.8Co0.2Fe2O4, Mn0.8Zn0.2Fe2O4 and Mn0.8Ni0.1Zn0.1Fe2O4, were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The MnFe2O4 ferrite powder annealed at temperatures above 523 K exhibited a spinel structure, and the particle size increased as the annealing temperature increased. All ferrites annealed at 773 K showed a single spinel structure, and the lattice constants and particle size decreased with the substitution of Co, Zn, and Ni-Zn. The Mössbauer spectrum of the MnFe2O4 ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the Mössbauer spectra of the MnFe2O4, Mn0.8Co0.2Fe2O4, and Mn0.8Zn0.2Fe2O4 ferrite powders annealed at 773 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe3+ ions. However, the Mössbauer spectrum of the Mn0.8Ni0.1Zn0.1Fe2O4 ferrite powder annealed at 773 K consisted of two Zeeman sextets and one quadrupole doublet due to its ferrimagnetic and paramagnetic behavior. The area ratio of the Mössbauer spectra could be used to determine the cation distribution equation, and we also explained the variation in the Mössbauer parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure MnFe2O4, the saturation magnetizations and coercivities were larger in Mn0.8Co0.2Fe2O4 and smaller in Mn0.8Zn0.2Fe2O4, and Mn0.8Ni0.1Zn0.1Fe2O4. These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.315-321
M-Zn (M = Sb, V, and Nb) Substituted Strontium Hexaferrites with Enhanced Saturation Magnetization for Permanent Magnet Applications
M-Zn (M = Sb, V, Nb) substituted
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.322-329
Array Sensing Using Electromagnetic Method for Detection of Smelting in Submerged Arc Furnaces
In this paper, we propose an array sensing detection method for smelting of submerged arc furnaces (SAF) based on electromagnetic radiation. AC magnetic field generated by electrode currents and molten currents in the furnace is reflected outside of the furnace. According to the spatial distribution of electromagnetic field a radiation model of SAF is built. We design a 3D magnetic field sensing array system in order to collect the magnetic field information. Through the collected information, the current distribution characteristics of SAF are described and the key parameters of smelting are obtained. Theoretical simulation and field test show that the curves acquired by the sensing array can accurately reflect the information of the relative displacement when the relative displacement between the array and electrode is 10 cm. Compared with the detection method of 3D single point, the proposed array sensing method of magnetic field obtains better results in terms of real-time and accuracy, and has good practical value for industrial measurement.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.330-339
Design of the Magnetic Field Sensing System for Downlink Signal Reception and Interference Cancelling for Through-the-Earth Communication
A magnetic field sensing system with a single primary sensor and multiple reference sensors deployed locally and orthogonally, was proposed for downlink signal reception and interference cancelling for Through-the-Earth Communication (TEC). This paper mathematically analyzes a design optimization process for a search coil magnetometer (SCM), and applies that process to minimize the bandwidth of the primary SCM for TEC signal reception and the volume of reference SCMs for multiple distributions. The primary SCM achieves a 3-dB bandwidth of 7 Hz, a sensitivity threshold of 120 fT/√Hz, and a volume of 2.32 × 10−4 m3. The entire sensing system volume is as small as 10−2 m3. Experiments with interference from industrial frequency harmonics demonstrated an average of 36 dB and 18 dB improvements in signal-to-interference ratio and signal-to-interference plus noise ratio, respectively, using multichannel recursive-least-squares algorithm. Thus, the proposed sensing system can reduce the interference effectively and allows reliable downlink signal reception.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.340-347
Electromagnetic Actuator with Novel Electric Brake for Circuit Breaker
At the stroke end of an electromagnetic circuit breaker, the high speed of the mover makes a huge impact at the contact point, which induces the rebound problem of the mover that causes a breaker failure. Thus, a speed reduction equipment is required to address such problems. This study suggests to use an electric brake reduces the speed at the end of the stroke. The proposed circuit breaker which adopts the electric brake has a variable speed reduction function such that the continued rebound phenomenon ceases to occur. The electric brake is designed by the Finite Element Method (FEM) and the circuit and motion equations are solved using Time Difference Method (TDM). The comparisons between the simulation and experiments demonstrated the usefulness and validity of this study.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.348-355
Design of a Rectangular-Type Voice Coil Actuator for Frame Vibration Compensation
Precision motion stages used in the manufacturing process of flat-panel displays have inevitably low settling performance due to their huge mass and bulky structures. In order to improve the settling performance, several methods of frame vibration compensation have been developed so far. These methods are used to cancel the vibration by imposing a counter force or modifying the resonance mode of the frame of the stage. To compensate the frame vibration, high force actuators are required. In this paper, a mighty voice coil actuator is proposed to generate the counter force against the frame vibration. The proposed voice coil actuator has an axis-symmetric rectangular structure to achieve a large force with simple and low cost fabrication. Also, the voice coil actuator allows radial clearance up to ± 4 mm. Using an optimized design process and a magnetic circuit model, the power consumption is minimized while the required force is obtained. With a power of 322 W, the VCA has been designed to have a maximum force of 574 N with a force constant of 164 N/A. Experimental results verified the force constant of the fabricated voice coil actuator is well matched with the designed value.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.356-363
Modeling and Analysis of Drift Error in a MSSG with Double Spherical Envelope Surfaces
To improve the sensing accuracy of the newly developed magnetically suspended sensitive gyroscope (MSSG), it is necessary to analyze the causes of drift error. This paper build the models of disturbing torques generated by stator assembly errors based on the geometric construction of the MSSG with double spherical envelope surfaces, and further reveals the generation mechanism of the drift error. Then the drift error from a single stator magnetic pole is calculated quantitatively with the established model, and the key factors producing the drift error are further discussed. It is proposed that the main approaches in reducing the drift error are guaranteeing the rotor envelope surface to be an ideal spherical and improving the controlling precision of rotor displacement. The common problems associated in a gyroscope with a spherical rotor can be effectively resolved by the proposed method.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.364-373
The Creation of a Strong Magnetic Field by Means of Large Magnetic Blocks from NdFeB Magnets in Opposing Linear Halbach Arrays
The article presents the results and findings obtained through the assembly of opposing linear Halbach arrays from two magnet layers using large magnetic blocks from permanent NdFeB magnets, especially concerning the distribution of magnetic induction in an air gap. The use of these large blocks has led to a significant expansion of the area of magnetic field with a substantially higher value of magnetic induction in comparison with similar linear Halbach arrays composed of small magnets. The paper also discusses the determined dependences of magnetic induction on the parameters of the
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.374-378
A Study on the Transformer Design considering the Inrush Current Reduction in the Arc Welding Machine
The transformer used in an inverter type arc welding machine is designed to use high frequency in order to reduce its size and cost. Also, selecting core materials that fit frequency is important because core loss increases in a high frequency band. An inrush current can occur in the primary coil of transformer during arc welding and this inrush current can cause IGBT, the switching element, to burn out. The transformer design was carried out in
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.379-386
Analysis of Principle and Performance of a New 4DOF Hybrid Magnetic Bearing
To satisfy the requirement of magnetically suspended control moment gyroscope (MSCMG) that magnetic bearing can provide torque, a novel 4DOF hybrid magnetic bearing (HMB) with integrated structure was designed. Mathematical models of forces and torques are established by using equivalent magnetic circuit method. The current stiffness, displacement stiffness, tilting current stiffness and angular stiffness of the 4DOF hybrid magnetic bearing are derived by the mathematical models. Equivalent magnetic circuit method and finite element method (FEM) simulation results indicate that the force has a good linear relationship with both displacement and current, and the torque has a good linear relationship with angular displacement and current. The novel 4DOF HMB is capable of achieving control in both two radial translational degrees of freedom (DOF) and also two radial rotational DOFs. The 4DOF HMB is well adapted to MSCMG system, exhibiting advantages in the controllable DOF, light weight and easy to control.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.387-392
Circular Holes Punched in a Magnetic Circuit used in Microspeakers to Reduce Flux Leakage
Lower flux leakage designs have become important in the development of microspeakers used in thin and miniaturized mobile phones. We propose four methods to reduce the flux leakage of the magnetic circuit in a microspeaker. Optimization was performed based on the proposed approach by using the response surface method. Electromagnetic analyses were conducted using the finite element method. Experimental results are in good agreement with the simulated results obtained in one degree-of-freedom analysis from 100 to 5 kHz. Both the simulated and experimental results confirm that one of the proposed methods is much more effective in reducing flux leakage than the other methods. In the optimized method, compared with a default approach, the average radial flux density in the air gap decreased only by 5.5%, the maximum flux leakage was reduced by 28.6%, and the acoustic performance at primary resonance decreased by 0.45 dB, which gap is indiscernible to the human ear.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.393-398
Design and Analysis of a Novel 16/10 Segmented Rotor SRM for 60V Belt-Driven Starter Generator
This paper proposes a novel 16/10 segmented rotor switched reluctance motor (SSRM) for belt-driven starter generators (BSGs). Different from conventional SRMs, the stator of the proposed SSRM consists of two types of stator poles, i.e., exciting and auxiliary poles, and the rotor is constructed from a series of discrete segments. The topology and operation principle of this proposed SSRM are illustrated firstly, and then the design rules are listed. In addition, the finite element method (FEM) is employed to get the static and dynamic characteristics of the proposed SSRM. Finally, the simulation results are presented to show the validity of the proposed SSRM for BSGs.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.399-404
PM Assisted, Brushless Wound Rotor Synchronous Machine
This paper presents a new permanent magnet (PM) assisted topology for a recently introduced brushless wound rotor synchronous machine (BL-WRSM)
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.405-412
Design and Evaluation of a Multi-layer Interior PM Synchronous Motor for High-Speed Drive Applications
In general, surface mounted PM synchronous motors (SPMSMs) are mainly adopted as a driving motor for high-speed applications, because they have high efficiency and high power density. However, the SPMSMs have some weak points such as the increase of magnetic reluctance and additional losses as a consequence of using a non-magnetic sleeve. Especially, the magneto-motive force (MMF) in the air-gap of the SPMSMs is weakened due to the magnetically increased resistance. For that reason, a large amount of PM is consumed to meet the required MMF. Nevertheless, it cannot help using the sleeve in order to maintain the mechanical integrity of a rotor assembly in high-speed rotation. Thus, in this paper, a multi-layer interior PM synchronous motor (IPMSM) not using the sleeve is presented and designed as an alternative of a SPMSM. Both motors are evaluated by test results based on a variety of characteristics required for an air blower system of a fuel cell electric vehicle.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.413-420
Fault Diagnosis Method of Permanent Magnet Synchronous Motor for Electrical Vehicle
The permanent magnet synchronous motor has high efficiency driving performance and high power density output characteristics compared with other motors. In addition, it has good regenerative operation characteristics during braking and deceleration driving condition. For this reason, permanent magnet synchronous motor is generally applied as a power train motor for electrical vehicle. In permanent magnet synchronous motor, the most probable causes of fault are demagnetization of rotor’s permanent magnet and short of stator winding turn. Therefore, the demagnetization fault of permanent magnet and turn fault of stator winding should be detected quickly to reduce the risk of accident and to prevent the progress of breakdown of power train system. In this paper, the fault diagnosis method using high frequency low voltage injection was suggested to diagnose the demagnetization fault of rotor permanent magnet and the turn fault of stator winding. The proposed fault diagnosis method can be used to check the faults of permanent magnet synchronous motor during system check-up process at vehicle starting and idling stop mode. The feasibility and usefulness of the proposed method were verified by the finite element analysis.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.421-424
Effectiveness of a Turbo Direction Change for Reduction of Motion Artifact in Magnetic Resonance Enterography
The purpose of this study is to evaluate an effectiveness of switching turbo direction to improve motion artifacts of small bowels and aorta. From June to October 2015, 60 patients suspected of having Crohn’s disease were enrolled. The MR Enterography scans were performed using same protocol other than the turbo direction: with the Z phase encoding (group A) and with Y phase encoding (group B). Qualitative analysis of each group was performed to evaluate the effectiveness of switching turbo direction from Z to Y. As a result, the 5-point Likert scale for paired observers were 2.33±0.88 for group A and 3.80±0.85 for group B on dynamic contrast enhanced coronal images. In conclusion, group B is proved to be superior to group A and can lessen the motion artifacts derived from phase shifts.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.425-430
Analysis on Setup Variation According to Megavoltage Computed Tomography System
The aim of this study was to measure the setup variation for X (lateral), Y (longitude), and Z (vertical) by taking magnetic megavoltage computed tomography (MVCT) before treating the brain, oropharynx, lung, and prostate patients on helical tomotherapy. In this study, 30 patients were chosen for each of the treatment areas, and their skin was labeled with a mark on a treatment planning reference point when taking CT. We preceded MVCT prior to tomotherapy and then conducted an auto registration based on the bony landmarks; image registration was used for automatically matching the patient’s setup. Lastly, we confirmed and evaluated the translation coordinates of the images for 30 patients. The following shows the comparison result of the setup errors of each part: X (lateral) showed the highest setup errors with 3.44 ± 2.05 from Lung; Y (longitude) showed the highest setup errors showing 3.40 ± 2.87 mm from Prostate; and Z (vertical) showed the highest setup errors showing 6.62 ± 4.38 mm from Lung. This result verifies that the setup error can be prevented by taking MVCT before the treatment, and Planning Target Volume (PTV) margins can be reduced by referring to the resulting value of each treatment part. Ultimately, the dosage of the normal organs can be decreased as well as any side effects.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.431-436
An Efficient Model to Calculate Axial Natural Vibration Frequency of Power Transformer Winding
In the design of transformer winding, natural vibration frequency is an important parameter. This paper presents a 2D model to calculate axial vibration natural frequency of power transformer winding based on the elastic dynamics theory, and according to the elastic support equivalent principle of radial pressboards. The 3D model to calculate natural vibration frequency can be simplified as a 2D one as the support of pressboards on the winding is same. It is verified that results of the 2D model are consistent with those of 3D one, but the former can achieve much higher calculation efficiency. It shows that increasing the width and number of pressboards can improve axial natural frequency through formula analysis and simulation, and also the relations between the changes of axial pre-compression and axial natural vibration frequency on the windings are investigated. Finally, the proposed 2D model's effectiveness is proved when compared with tested ones.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.437-441
Dipole Model to Predict the Rectangular Defect on Ferromagnetic Pipe
Dipole model based analytical expression is proposed to estimate the length and depth of the rectangular defect on ferromagnetic pipe. Among the three leakage profiles of Magnetic Flux Leakage (MFL), radial and axial leakage profiles are considered in this work. Permeability variation of the specimen is ignored by considering the flux density as close to saturation level of the inspected specimen. Comparing the profile of both the components, radial leakage profile furnishes the better estimation of defect parameter. This is evident from the results of error percentage of length and depth of the defect. Normalized pattern of the proposed analytical model radial leakage profile is good agreement with the experimentally obtained profile support the performance of proposed expression.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.442-449
Numerical Method for Exposure Assessment of Wireless Power Transmission under Low-Frequency Band
In this paper, an effective numerical analysis method is proposed for calculating dosimetry of the wireless power transfer system operating low-frequency ranges. The finite-difference time-domain (FDTD) method is widely used to analyze bio-electromagnetic field problems, which require high resolution, such as a heterogeneous whole-body voxel human model. However, applying the standard method in the low-frequency band incurs an inordinate number of time steps. We overcome this problem by proposing a modified finite-difference time-domain method which utilizes a quasi-static approximation with the surface equivalence theorem. The analysis results of the simple model by using proposed method are in good agreement with those from a commercial electromagnetic simulator. A simulation of the induced electric fields in a human head voxel model exposed to a wireless power transmission system provides a realistic example of an application of the proposed method. The simulation results of the realistic human model with the proposed method are verified by comparing it with the conventional FDTD method.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.450-459
Wideband RF Radiation from a Nonlinear Transmission Line with a Pre-magnetized Ferromagnetic Core
Experimental results and data of numerical simulations are presented, concerning generation of wideband radio frequency (RF) oscillations in a nonlinear transmission line (NLTL) which contains a pre-magnetized core of ferrite material. Emphasis is made on the means for extracting the RF signal from the line, in order to radiate it into free space. Antennas of two types that can be used for the purpose are considered, both featuring a coaxial design. This permits availing of the principal advantages of coaxial systems, such as operation in the mode of a traveling TEM wave; wide range of the transmitted frequencies, and a reasonably simple design. The antennas studied, specifically a disc-cone dipole (DCD) and an impulse reflector antenna (‘Half-IRA’, or HIRA type) differ significantly in effective width of the radiated spectrum and in spatial characteristics of the radiated field in far region.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.460-467
Study of the Dependency of the Specific Power Absorption Rate on Several Characteristics of the Excitation Magnetic Signal when Irradiating a SPION-containing Ferrofluid
Magnetic hyperthermia mediated by superparamagnetic particles is mainly based in sinusoidal waveforms as excitation signals. Temperature changes are conventionally explained by rotation of the particles in the surrounding medium. This is a hypothesis quite questionable since habitual experimental setups only produce changes in the magnetic module, not in the field lines trajectories. Theoretical results were tested by changing the waveform of the exciting signal in order to compare non-sinusoidal signals against sinusoidal signals. Experiments were done at different frequencies: 200 KHz, 400 KHz, 600 KHz, 800 KHz and 1 MHz. Superparamagnetic Iron Oxide samples (SPION), made of magnetite (Fe3O4) and suspended in water (100 mg/ml), were used. Magnetic field strength varies from 0.1 ± 0.015 KA/m to 0.6 ± 0.015 KA/m. In this study was observed that the power loss depends on the applied frequency: for 1 to 2.5 RMS current the responses for each signal are part of the higher section of the exponential function, and for 3.5 to 8 RMS current the response is clearly the decrement exponential function’s tale (under 1 × 103 LER/gr).
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.468-475
Numerical Study of Entropy Generation with Nonlinear Thermal Radiation on Magnetohydrodynamics non-Newtonian Nanofluid Through a Porous Shrinking Sheet
In this article, entropy generation on MHD Williamson nanofluid over a porous shrinking sheet has been analyzed. Nonlinear thermal radiation and chemical reaction effects are also taken into account with the help of energy and concentration equation. The fluid is electrically conducting by an external applied magnetic field while the induced magnetic field is assumed to be negligible due to small magnetic Reynolds number. The governing equations are first converted into the dimensionless expression with the help of similarity transformation variables. The solution of the highly nonlinear coupled ordinary differential equation has been obtained with the combination of Successive linearization method (SLM) and Chebyshev spectral collocation method. Influence of all the emerging parameters on entropy profile, temperature profile and concentration profile are plotted and discussed. Nusselt number and Sherwood number are also computed and analyzed. It is observed that entropy profile increases for all the physical parameters. Moreover, it is found that when the fluid depicts non-Newtonian (Williamson fluid) behavior then it causes reduction in the velocity of fluid, however, non-Newtonian behavior enhances the temperature and nanoparticle concentration profile.
Journal of Magnetics, 31 Aug 2016, Vol.21 , No.3, pp.476-489
Squeezing Flow of Micropolar Nanofluid between Parallel Disks
In the present study, squeezing flow of micropolar nanofluid between parallel infinite disks in the presence of magnetic field perpendicular to plane of the disks is taken into account. The constitutive equations that govern the flow configuration are converted into nonlinear ordinary differential with the help of suitable similarity transforms. HAM package BVPh2.0 has been employed to solve the nonlinear system of ordinary differential equations. Effects of different emerging parameters like micropolar parameter