Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.315-322
Concurrent Modeling of Magnetic Field Parameters, Crystalline Structures, and Ferromagnetic Dynamic Critical Behavior Relationships: Mean-Field and Artificial Neural Network Projections
In this work, Artificial Neural Network (ANN) was used to model the dynamic behavior of ferromagnetic hysteresis derived from performing the mean-field analysis on the Ising model. The effect of field parameters and system structure (via coordination number) on dynamic critical points was elucidated. The Ising magnetization equation was drawn from mean-field picture where the steady hysteresis loops were extracted, and series of the dynamic critical points for constructing dynamic phase-diagram were depicted. From the dynamic critical points, the field parameters and the coordination number were treated as inputs whereas the dynamic critical temperature was considered as the output of the ANN. The input-output datasets were divided into training, validating and testing datasets. The number of neurons in hidden layer was varied in structuring ANN network with highest accuracy. The network was then used to predict dynamic critical points of the untrained input. The predicted and the targeted outputs were found to match well over an extensive range even for systems with different structures and field parameters. This therefore confirms the ANN capabilities and indicates the ANN ability in modeling the ferromagnetic dynamic hysteresis behavior for establishing the dynamic-phase-diagram.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.323-326
Preparation and Physical Characterizations of Superparamagnetic Maghemite Nanoparticles
Superparamagnetic maghemite nanoparticles were prepared by chemical co-precipitation, followed by a temperate oxidation stage, and investigated using FE-SEM, XRD, TGA, VSM, and Mössbauer spectroscopy. Through SEM image and XRD analysis, its average particle size was found to be 13.9 nm. While VSM magnetic measurement showed typical superparamagnetic behavior at room temperature, Mössbauer spectroscopic investigation revealed that non-vanishing magnetic hyperfine structure were retained. Cation distribution estimated from Mössbauer spectroscopy confirmed the formation of maghemite nanophase in the sample.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.327-332
Microstructural Change and Magnetic Properties of Nanocrystalline Fe-Si-B-Nb-Cu Based Alloys Containing Minor Elements
The effect of minor element additions (Ca, Al) on microstructural change and magnetic properties of Fe-Nb-Cu-Si-B alloy has been investigated, in this paper. The Fe-Si-B-Nb-Cu(-Ca-Al) alloys were prepared by arc melting in argon gas atmosphere. The alloy ribbons were fabricated by melt-spinning, and heat-treated under a nitrogen atmosphere at 520-570℃ for 1 h. The soft magnetic properties of the ribbon core were analyzed using the AC B-H meter. A differential scanning calorimetry (DSC) was used to examine the crystallization behavior of the amorphous alloy ribbon. The microstructure was observed by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The addition of Ca increased the electrical resistivity to reduce the eddy current loss. And the addition of Al decreased the intrinsic magnetocrystalline anisotropy K1 resulting in the increased permeability. The reduction in the size of the α-Fe precipitates was observed in the alloys containing of Ca and Al. Based on the results, it can be concluded that the additions of Ca and Al notably improved the soft magnetic properties such as permeability, coercivity and core loss in the Fe-Nb-Cu-Si-B base nanocrystalline alloys.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.333-339
Growth of Oriented Thick Films of BaFe12O19 by Reactive Diffusion
Single crystal growth of BaFe12O19 by the solid state crystal growth method was attempted. Seed crystals of α-Fe2O3 were pressed into pellets of BaFe12O19 + 2 wt% BaCO3 and heat-treated at temperatures between 1150℃ and 1250℃ for up to 100 hours. Instead of single crystal growth taking place on the seed crystal, BaO diffused into the seed crystal and reacted with it to form a polycrystalline reaction layer of BaFe12O19. The microstructure, chemical composition and structure of the reaction layer were studied using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), x-ray Diffraction (XRD) and micro-Raman scattering and confirmed to be that of BaFe12O19. XRD showed that the reaction layer shows a strong degree of orientation in the (
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.340-344
Study on the Magnetic Characteristics of Anisotropic SmCo7-type Alloys Synthesized by High-energy Surfactant-assisted Ball Milling
An effective process was employed for synthesizing anisotropic magnetic SmCo7-type alloy flakes with high coercivity, which is highly desirable for many applications. The highest coercivity of 16.3 kOe corresponds to a typical flake thickness of 200 nm for the 3-h ball-milled sample. The anisotropy field was calculated by measuring the parallel and perpendicular directions to the easy magnetization direction of the powders. The anisotropy field decreased with the increase of the ball milling time, thus indicating that the decrease of coercivity was mainly caused by the reduction of the anisotropy field. Microstructure analysis indicated that the morphology, grain size, and anisotropy field of these samples have a great influence on the magnetic properties.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.345-348
Magnetic-field-tuned Insulator to Conductor Transition in Magnetorheological Suspension
Magnetorheological suspensions (MRSs) are smart materials that have the potential to revolutionize several industrial sectors because of their special rheological behaviors. In this paper, MRS, based on carbonyl iron (CI) microparticles that were dispersed in silicone oil with oleic acid, were prepared. We showed that the electroconductibility of MRS was significantly influenced by the intensity of the external magnetic field that was applied. The resistance value can vary from infinite to below 300 Ω after applying an external magnetic field. The results indicated that this MRS had the property of magnetic-field-tuned insulator to conductor transition. This system has potential applications in controllable MRS electrical devices.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.349-352
Magnetic Shielding Effect on Halbach Cylinder used in Magnetic Refrigerators
The system for producing magnetic field constitutes an important component of magnetic refrigerator. Many researchers have directed significant effort to increase the magnetic field intensity, because the magnetocaloric effect at the Curie temperature increases with the power of 2/3 of the magnetic field. In this study, we report the simulation of the magnetic field intensity at polar axis of a Halbach cylinder (HC) by i) changing the length and thickness of the HC, ii) having with or without gap of the HC, and iii) surrounding the HC with a soft magnet shell, acting as a shielding. We simulated the field distribution of a HC with a finite size. Furthermore, the detailed numerical results of the magnetic field distribution and its dependence on shielding are presented in this study.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.353-356
Effects of Mental Practice in Conjunction with Repetitive Transcranial Magnetic Stimulation on the Upper Limbs of Sub-acute Stroke Patients
The aim of the present study was to examine whether mental practice (MP) in conjunction with repetitive transcranial magnetic stimulation (rTMS) can improve the upper limb function of sub-acute stroke patients. This study was conducted with 32 subjects who were diagnosed with hemiparesis by stroke. The experimental group consisted of 16 members upon each of whom was performed MP in conjunction with rTMS, whreas the control group consisted of 16 members upon each of whom was performed MP and sham rTMS. Both groups received traditional physical therapy for 30 minutes a day, 5 days a week, for 6 weeks; additionally, they received mental practice for 15 minutes a day. The experimental group was instructed to perform rTMS, and the control group was instructed to apply sham rTMS for 15 minutes. A motor cortex excitability analysis was performed by motor evoked potentials (MEPs), and upper limb function was evaluated by Fugl-Meyer Assessment (FMA) and the Box and Block test (BBT). Results showed that the amplitude, latency, FMA, and BBT of the experimental group and the latency, FMA, and BBT of the control group were significantly improved after the experiment (p<0.05). Significant differences were found between the groups in amplitude and latency after the experiment (p<0.05). The results showed that MP in conjunction with rTMS is more effective in improving upper limb function than MP alone.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.357-364
Changes in Poly ADP Ribose Polymerase Immune Response Cells of Cerebral Ischaemia Induced Rat by Transcranial Magnetic Stimulation of Alternating Current Approach
This study examined effect of a transcranial magnetic stimulation device with a commercial-frequency approach on the neuronal cell death caused ischemia. For a simple transcranial magnetic stimulation device, the experiment was conducted on an ischemia induced rat by transcranial magnetic stimulation of a commercialfrequency approach, controlling the firing angle using a Triac power device. The transcranial magnetic stimulation device was controlled at a voltage of 220 V 60 Hz and the trigger of the Triac gate was varied from 45° up to 135°. Cerebral ischemia was caused by ligating the common carotid artery of male SD rats and reperfusion was performed again to blood after 5 minutes. Protein Expression was examined by Western blotting and the immune response cells reacting to the antibodies of Poly ADP ribose polymerase in the cerebral nerve cells. As a result, for the immune response cells of Poly ADP ribose polymerase related to necrosis, the transcranial magnetic stimulation device suppressed necrosis and had a protective effect on nerve cells. The effect was greatest within 12 hours after ischemia. Therefore, it is believed that in the case of brain damage caused by ischemia, the function of brain cells can be restored and the impairment can be improved by the application of transcranial magnetic stimulation.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.365-371
The Utility Evaluation of Reconstructed 3-D Images by Maximum Intensity Projection in Magnetic Resonance Mammography and Cholangiopancreatography
The aim of this study was to evaluate the utility of 3-D images by comparing and analyzing reconstructed 3-D images from fast spin echo images of MRI cholangiopancreatography (MRCP) images using maximum intensity projection (MIP) with the subtraction images derived from dynamic tests of magnetic resonance mammography. The study targeted 20 patients histologically diagnosed with pancreaticobiliary duct disease and 20 patients showing pancreaticobiliary duct diseases, where dynamic breast MR (magnetic resonance) images, fast spin echo imaged of pancreaticobiliary duct, and 3-D reconstitution images using a 1.5T MR scanner and 3.0T MR scanner were taken. As a result of the study, the signal-to-noise ratio in the subtracted breast image before and after administering the contrast agent and in the reconstructed 3-D breast image showed a high ratio in the reconstructed image of lesional tissue, relevant tissue, and fat tissue. However, no statistically meaningful differences were found in the contrast-to-noise ratio of the two images. In the case of the MRCP image, no differences were found in the ratios of the fast spin echo image and reconstructed 3-D image.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.372-377
How Computed Tomography Contrast Media and Magnetic Resonance Imaging Contrast Media Affect the Changes of Uptake Counts of 201Tl
The purpose of the study is to investigate how uptake counts of 201Tl of radioisotopes in the human body could change, when taking computed tomography and magnetic resonance imaging right after injecting contrast media. 201Tl radioisotope substances of iodine contrast medium, which is a computed tomography contrast medium, and paramagnetic contrast medium, which is an magnetic resonance imaging contrast medium, were used as study materials. First, 201Tl was put into 4 cc of normal saline in test tube, and then a computed tomography contrast medium of Iopamidol® or Dotarem®, was put into 2 cc of normal saline in test tube. An magnetic resonance imaging contrast medium of Primovist® or Gadovist® was also put into 2 cc of normal saline in test tube. Each contrast medium was distributed to make 201Tl as 3 mCi, with a total of 4 cc. Gamma camera, low energy high resolution collimator, and pinhole collimator were used to obtain images. The uptake count of 201Tl was measured with 1000 frames of images, and obtained after 10 times of repetition. This study revealed that the use of Gadovist®, which is an magnetic resonance imaging contrast medium, showed the smallest number of uptake count, after measuring 201Tl uptake count by low energy high resolution collimator. On the other hand, the use of Iopamidol®, which is a computed tomography contrast medium, showed the biggest difference in uptake count, when measuring 99mTc uptake count by Pinhole collimator. When examining with gamma camera, using contrast medium and 201Tl, identifying the changes of uptake count is very important for improving the value of diagnosis.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.378-384
An Approximate Calculation Model for Electromagnetic Devices Based on a User-Defined Interpolating Function
Optimization design and robust design are significant measures for improving the performance and reliability of electromagnetic devices (EMDs, specifically refer to relays, contactors in this paper). However, the implementation of the above-mentioned design requires substantial calculation; consequently, on the premise of guaranteeing precision, how to improve the calculation speed is a problem that needs to be solved. This paper proposes a new method for establishing an approximate model for the EMD. It builds a relationship between the input and output of the EMD with different coil voltages and air gaps, by using a user-defined interpolating function. The coefficient of the fitting function is determined based on a quantum particle swarm optimization (QPSO) method. The effectiveness of the method proposed in this paper is verified by the electromagnetic force calculation results of an electromagnetic relay with permanent magnet.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.385-392
A Robust Optimization Method Utilizing the Variance Decomposition Method for Electromagnetic Devices
Uncertainties in loads, materials and manufacturing quality must be considered during electromagnetic devices design. This paper presents an effective methodology for robust optimization design based on the variance decomposition in order to keep higher accuracy of the robustness prediction. Sobol’ theory is employed to estimate the response variance under some specific tolerance in design variables. Then, an optimal design is obtained by adding a criterion of response variance upon typical optimization problems as a constraint of the optimization. The main contribution of this paper is that the proposed method applies the variance decomposition to obtain a more accurate variance of the response, as well save the computational cost. The performance and robustness of the proposed algorithms are investigated through a numerical experiment with both an analytic function and the TEAM 22 problem.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.393-398
Design of Coaxial Magnetic Gear for Improvement of Torque Characteristics
This paper proposes new types of models that have coaxial magnetic gear (CMG) configurations to increase torque transmission capability. They have flux concentrating structures at the outer low speed rotor, and permanent magnets (PMs) are embedded in the space between stationary pole pieces. The torque performances of the proposed models are compared with those of a basic CMG model. The harmonic torque components due to air gap field harmonics are also analyzed to investigate the torque contribution of each harmonic by using finite element analysis (FEA) and the Maxwell stress tensor. The proposed CMG model is optimized to have high torque density with low torque ripples by response surface methodology (RSM). Compared to the basic CMG model, the proposed model has a huge increase in transmitted torque density, and is very advantageous in term of PM use.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.399-403
Magnetic Parameters for Ultra-high Frequency (UHF) Ferrite Circulator Design
We designed an ultra-high frequency (UHF: 300MHz to 3 GHz) ferrite circulator to investigate magnetic parameters, which are suitable for a self-biased GHz circulator design. The size of the ferrite disk was 1.58 mm in thickness and 13.5 mm in diameter. The saturation magnetization (4π
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.404-410
Design and Analysis of Interior Permanent Magnet Synchronous Motor Considering Saturated Rotor Bridge using Equivalent Magnetic Circuit
This paper considers the design and performance evaluation of interior permanent magnet synchronous motors (IPMSMs). The initial design such as the sizing and shape design of the stator and rotor is performed for a given load condition. In particular, the equivalent magnetic circuit (EMC) is employed both to design the mechanical parameters of the rotor while considering nonlinear magnetic saturation effect and to analyze the magnetic characteristics of the air-gap of the motor. The designed motor is manufactured and tested to confirm the validity of the design processes and simulated results.
Journal of Magnetics, 31 Dec 2014, Vol.19 , No.4, pp.411-417
Analysis and Design of a Novel-Shape Permanent Magnet Synchronous Motor for Minimization of Torque Ripple and Iron Loss
This paper presents the shape optimization of a permanent magnet synchronous motor to reduce the torque ripple and iron loss. Specifically, the harmonics of the electromotive force and cogging torque are decreased by adjusting the permanent magnet arrangement and non-uniform air gap length. In addition, an additional flux path along the