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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Magnetics
Journal Basic Information
Journal DOI :
The Korean Magnetics Society
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Volume & Issues
Volume 20, Issue 4 - Dec 2015
Volume 20, Issue 3 - Sep 2015
Volume 20, Issue 2 - Jun 2015
Volume 20, Issue 1 - Mar 2015
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Recycling of Sintered Nd-Fe-B Magnets Doped with PrNd Nanoparticles
Zhang, Xuefeng ; Liu, Fei ; Liu, Yanli ; Ma, Qiang ; Li, Yongfeng ; Zhao, Qian ; Wang, Gaofeng ; Li, Zhubai ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 97~102
DOI : 10.4283/JMAG.2015.20.2.097
The waste of sintered Nd-Fe-B magnets was recycled using the method of dopingPrNd nanoparticles. The effect of PrNd nanoparticle doping on the magnetic properties of the regenerated magnets has been studied. As the content of the PrNd nanoparticles increases, the coercivity increases monotonically, whereas both the remanence and the maximum energy products reach the maximum values for 4 wt% PrNd doping. Microstructural observation reveals that the appropriate addition of PrNd nanoparticles improves the magnetic properties and refines the grain. Domain investigation shows that the self-pinning effect of the rare earth (Re)-rich phase is enhanced by PrNd nano-particle doping. Compared to the magnet with 4 wt% PrNd alloy prepared using the dual-alloy method, the regenerated magnet doped with the same number of PrNd nanoparticles exhibits better magnetic properties and a more homogeneous microstructure. Therefore, it is concluded that PrNd nanoparticle doping is an efficient method for recycling the leftover scraps of Nd-Fe-B magnets.
Performance Analysis of Low-level Radiation Shielding Sheet with Diamagnetic Nanoparticles
Cho, Jae-Hwan ; Kim, Myung-Sam ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 103~109
DOI : 10.4283/JMAG.2015.20.2.103
In this study, the authors attempted to produce a medical radiation shielding fiber that can be produced at a nanosize scale and that is, unlike lead, harmless to the human body. The performance of the proposed medical radiation shielding fiber was then evaluated. First, diamagnetic bismuth oxide, an element which, among elements that have a high atomic number and density, is harmless to the human body, was selected as the shielding material. Next, 10-100 nm sized nanoparticles in powder form were prepared by ball milling the bismuth oxide (
), the average particle size of which is
, for approximately 10 minutes. The manufactured bismuth oxide was formed into a colloidal solution, and the radiation shielding fabric was fabricated by curing after coating the solution on one side or both sides of the fabric. The thicknesses of the shielding sheets prepared with bismuth oxide were 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 1.0 mm. An experimental method was used to measure the absorbed dose and irradiation dose by using the lead equivalent test method of X-ray protection goods presented by Korean Industrial Standards; the resultant shielding rate was then calculated. From the results of this study, the X-ray shielding effect of the shielding sheet with 0.1 mm thickness was about 55.37% against 50 keV X-ray, and the X-ray shielding effect in the case of 1.0 mm thickness showed shielding characteristics of about 99.36% against 50 keV X-ray. In conclusion, it is considered that nanosized-bismuth radiation shielding fiber developed in this research will contribute to reducing the effects of primary X-ray and secondary X-ray such as when using a scattering beam at a low level exposure.
Tunable Slow Light with Large Bandwidth and Low-dispersion in Photonic Crystal Waveguide Infiltrated with Magnetic Fluids
Lei, Weizheng ; Pu, Shengli ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 110~113
DOI : 10.4283/JMAG.2015.20.2.110
Two kinds of magnetic fluids with different volume fractions are symmetrically filled into the W0.9 photonic crystal waveguide structure. The 2D plane-wave expansion method is used to investigate the slow light properties numerically. The constant group index criterion is employed to evaluate the slow light performance. The wavelength bandwidth
varies from 32.4 to 44.2 nm when the magnetic field factor
changes from 0 to 1. And the corresponding normalized delay bandwidth product can be tuned from 0.221 to 0.258. For comparison and optimization, two infiltration cases are investigated and the more advantageous infiltration scheme is found.
Study on Improvement of Blood Stagnation by Pulsed Magnetic Field
Son, Hee Jung ; Yoo, Jun Sang ; Lee, Myeung Hee ; Hwang, Do Gwen ; Lee, Hyun Sook ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 114~119
DOI : 10.4283/JMAG.2015.20.2.114
This study explored the effect of pulsed magnetic field (PMF) stimulus on the improvement of blood stagnation by means of photoplethysmography (PPG). Our stimulus system was designed to generate PMF with a maximum intensity variation of 0.20 T at a transition time of
, with pulse intervals of 1 Hz. In order to quantitatively estimate vascular condition, indices such as blood vessel tension (BVT), stress power (SP), differential pulse wave index (DPI) and remained blood volume (RBV) were calculated from the second derivative of the PPG signal and power density spectrum (PDS). Our results showed that non-invasive PMF stimulus was effective in improving blood stagnation. Therefore, it may be concluded that appropriate PMF stimulus affects the blood circulatory system.
Improvement of Beam-Quality Evaluation Method for Medical Linear Accelerator Using Magnetic Field
Kim, Jeongho ; Han, Manseok ; Yoo, Sejong ; Kim, Kijin ; Cho, Jae-Hwan ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 120~128
DOI : 10.4283/JMAG.2015.20.2.120
Beam-quality of medical linac evaluations vary by diverse factors. Because conventional beam-quality evaluation methods yield fragmentary results, a new beam-evaluation method is suggested, and its feasibility is evaluated. The PDDs (percentage depth doses) of 6 MV (Mega-voltage) and 10 MV photon, R (Range) of a 6 MeV (Mega Electron-voltage) and 9 MeV electron were measured and compared with the conventional evaluation methods, and the improved methods
as the magnetic field of the bending magnet was changed to +2% to -2%, and the results were compared. The comparison showed that the improved methods exhibit a higher discrimination than the conventional methods in each energy regime.
should be applied. These methods exhibit a higher discrimination in each energy regime than conventional beam-quality evaluation methods; therefore, they should be used for beam-quality evaluation according to the magnetic field variation.
The Effects of Repetitive Transcranial Magnetic Stimulation on the Gait of Acute Stroke Patients
Ji, Sang-Goo ; Kim, Myoung-Kwon ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 129~132
DOI : 10.4283/JMAG.2015.20.2.129
The aim of the present study was to examine whether repetitive transcranial magnetic stimulation (rTMS) can improve gait ability of acute stage stroke patients. This study was conducted with 39 subjects who were diagnosed as having a hemiparesis due to stroke. The experimental group included 20 subjects who underwent repetitive transcranial magnetic stimulation and the control group included 19 subjects who underwent sham therapy. The stroke patients in the experimental group underwent conventional rehabilitation therapy and rTMS was applied daily to the hotspot of the lesional hemisphere. The stroke patients in the control group underwent sham rTMS and conventional rehabilitation therapy. Participants in both groups received therapy five days per week for four weeks. Temporospatial gait characteristics, such as stance phase, swing phase, step length in affected side, velocity, and cadence, were assessed before and after the four week therapy period. A significant difference was observed in post-treatment gains for the step length in the affected side, velocity, and cadence between the experimental group and control group ( p < 0.05). However, no significant differences were observed between the two groups on stance phase and swing phase ( p > 0.05). We conclude that rTMS may be beneficial in improving the effects of acute stage stroke on gait ability.
The Effects of Repetitive Transcranial Magnetic Stimulation Integrated Mirror Therapy on the Gait of Chronic Stroke Patients
Cha, Hyun-Gyu ; Kim, Myoung-Kwon ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 133~137
DOI : 10.4283/JMAG.2015.20.2.133
This study was conducted to determine the effects of repetitive transcranial magnetic stimulation (rTMS) integrated mirror therapy on the gait of post-stroke patients. Thirty patients who were six months post-stroke were assigned to either the experimental group (n = 15) or the control group (n = 15). Stroke patients in the experimental group underwent rTMS and mirror therapy for the lower limbs, while those in the control group underwent rTMS and sham therapy. Participants in both groups received therapy five days per week for four weeks. A significant difference in post-training gains for the single support phase, step length, stride length and velocity was observed between the experimental group and the control group (p < 0.05). The experimental group showed a significant increment in the single support phase, step length, stride length, swing phase, velocity, cadence, double support phase and step width as compared to pre-intervention (p < 0.05). The control group showed a significant increment in step length, velocity, cadence and step width compared to preintervention (p < 0.05). Further investigation of the availability and feasibility of rTMS integrated mirror therapy for post-stroke patients as a therapeutic approach for gait rehabilitation is warranted.
Nano-scale Inter-lamellar Structure of Metal Powder Composites for High Performance Power Inductor and Motor Applications
Kim, Hakkwan ; An, Sung Yong ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 138~147
DOI : 10.4283/JMAG.2015.20.2.138
The unique nano-scale inter-lamellar microstructure and unparalleled heat treatment process give our developed metal powder composite its outstanding magnetic property for power inductor & motor applications. Compared to the conventional polycrystalline Fe or amorphous Fe-Cr-Si-B alloys, our unique designed inter-lamellar microstructure strongly decreases the intra-particle eddy current loss at high frequencies by blocking the mutual eddy currents. The combination of optimum permeability, magnetic flux and extremely low core loss makes this powder composite suitable for high frequency applications well above 10 MHz. Moreover, it can be also possible to SMC core for high speed motor applications in order to increase the motor efficiency by decreasing the core loss.
Core Loss Effects on Electrical Steel Sheet of Wound Rotor Synchronous Motor for Integrated Starter Generator
Lee, Choong-Sung ; Kim, Ji-Hyun ; Hong, Jung-Pyo ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 148~154
DOI : 10.4283/JMAG.2015.20.2.148
48-V ISG (Integrated Starter Generator) system has attracted attention to improve the fuel efficiency of ICE (Internal Combustion Engine) vehicle. One of the key components that significantly affects the cost and performance of the 48-V ISG system is the motor. In an ISG motor, the core and copper loss make the motor efficiency change because the motor has a broad driving operated range and more diverse driving modes compared with other motors. When designing an ISG motor, the selection of an electrical steel sheet is important, because the electrical steel sheet directly influences the efficiency of the motor. In this paper, the efficiency of the ISG motor, considering core loss and copper loss, is analyzed by testing different types of electrical steel sheets with respect to the driving speed range and mode. Using the results of a finite element method (FEM) analysis, a method to select the electrical steel sheet is proposed. This method considers the cost of the steel sheet and the efficiency according to driving mode frequency during the design process of the motor. A wound rotor synchronous machine (WRSM) was applied to the ISG motor in this study.
Efficiency Improvement of an Automotive Alternator by Heat Treatment
Kim, Ji-Hyun ; Hong, Jung-Pyo ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 155~160
DOI : 10.4283/JMAG.2015.20.2.155
emission standards and fuel efficiency legislation has been tightened globally. Therefore automotive alternator performance becomes increasingly important to meet the requirements. Many proposed methods have suggested adding magnets or regulation control to increase alternator efficiency and output. However, this creates a significant additional cost. During the stator lamination process, the magnetic property of the stator deteriorates mainly due to stamping and slinky process for an alternator. To maximize the alternator performance, heat treatment of the stator core was performed and magnetic properties were compared to find the optimal condition. Finally, alternator output and efficiency test were performed resulting in significant output and efficiency improvement up to 6.8% and 0.6% respectively.
Optimal ECO-Design of Permanent Magnet Brushless DC Motor Using Modified Tabu Search Optimizer and Finite Element Analysis
Yazdani-Asrami, Mohammad ; Alipour, Mohammad ; Gholamian, S. Asghar ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 161~165
DOI : 10.4283/JMAG.2015.20.2.161
The Permanent Magnet Brushless DC (PMBLDC) motors have been used in modern industrial factories, hazardous chemical process, modern medical devices, and especially in advanced military devices such as army drones. By considering their sensitive role in the industrial and military applications, their optimal design has a real concern. This paper proposes a method for optimal eco-design of a PMBLDC motor using improved tabu search optimization. The objective function is based on losses, volume and cost. Electrical and mechanical requirements and other limitations are combined into constraints of problem. Also, finite element analysis has been used for verifications in magnetic mode.
Design and Torque Ripple Analysis of Brush-less DC Motor According to Delta Winding Connection
Lee, Tae-Yong ; Seo, Myung-Ki ; Kim, Yong-Jae ; Jung, Sang-Yong ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 166~175
DOI : 10.4283/JMAG.2015.20.2.166
In this study, we describe the design method of a Brush-less DC (BLDC) motor with delta winding connection. After designing delta winding connection model with the
flat-top region of the Back Electro-Motive Force (BEMF), an ideal current source analysis and a voltage source analysis, with a 6-step control, were conducted primarily employing Finite Element Method. In addition, as a current controller, we considered the Current Regulator with PI controller using Simulink for the comparison of torque characteristics. When the input current is controlled, the switching regions and reference signals are determined by means of the phase BEMF zero-crossing point. In reality, the input current variation depends on the inductance as well as input voltage, and it causes a torque ripple after all. Therefore, each control method considered in this research showed different torque ripple results. Based on the comparison, the causes of the torque ripple have been verified in detail.
Cogging Torque Reduction in Permanent-Magnet Brushless Generators for Small Wind Turbines
Chung, Dae-Won ; You, Yong-Min ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 176~185
DOI : 10.4283/JMAG.2015.20.2.176
We present the design optimization of the magnetic pole and slot design options that minimize the cogging torque of permanent-magnet (PM) brushless generators for small wind turbine generators. Most small wind-turbines use direct-driven PM generators which have the characteristics of low speed and high efficiency. Small wind-turbines are usually self-starting and require very simple controls. The cogging torque is an inherent characteristic of PM generators, and is mainly caused by the generator's geometry. The inherent the cogging torque can cause problems during turbine start-up and cut-in in order to start softly and to run a power generator even when there is little wind power during turbine start-up. Thus, to improve the operation of small turbines, it is important to minimize the cogging torque. To determine the effects of the cogging torque reductions, we adjust the slot opening width, slot skewing, mounting method of magnets, magnet shape, and the opening and combinations of different numbers of slots per pole. Of these different methods, we combine the methods and optimized the design variables for the most significant design options affecting the cogging torque. Finally, we apply to the target design model and compare FEA simulation and measured results to validate the design optimization.
Analysis of Coaxial Magnetic Gear with Low Gear Ratios for Application in Counter Rotating Systems
Shin, H.M. ; Chang, J.H. ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 186~192
DOI : 10.4283/JMAG.2015.20.2.186
This paper describes the electromagnetic and mechanical characteristics of coaxial magnetic gear (CMG) with a low gear ratio. The analysis models are restricted to a CMG with a gear ratio of less than 2. The electromagnetic characteristics including transmitted torque and iron losses are presented according to the variation of the gear ratio. The pole pairs of high speed rotor are chosen as 6, 8 and 10 by considering the torque capability. As the gear ratio approaches 1, both iron losses on the ferromagnetic materials and eddy current losses on the rotor permanent magnets are increased. The radial and tangential forces on the modulating pieces are calculated using the Maxwell stress tensor. When the maximum force is exerted on the modulating pieces, the mechanical characteristics including stress and deformation are derived by structural analysis. In CMG models with a low gear ratio, the maximum radial force acting on modulating pieces is larger than that in CMG models with a high gear ratio, and the normal stress and normal deformation are increased in a CMG with a low gear ratio. Therefore, modulating pieces should be designed to withstand larger radial forces in CMG with a low gear ratio compared to CMG with a high gear ratio.
Shape Optimization to Minimize The Response Time of Direct-acting Solenoid Valve
Shin, Yujeong ; Lee, Seunghwan ; Choi, Changhwan ; Kim, Jinho ;
Journal of Magnetics, volume 20, issue 2, 2015, Pages 193~200
DOI : 10.4283/JMAG.2015.20.2.193
Direct-acting solenoid valves are used in the automotive industry due to their simple structure and quick response in controlling the flow of fluid. We performed an optimization study of response time in order to improve the dynamic performance of a direct-acting solenoid valve. For the optimal design process, we used the commercial optimization software PIAnO, which provides various tools for efficient optimization including design of experiments (DOE), approximation techniques, and a design optimization algorithm. 35 sampling points of computational experiments are performed to find the optimum values of the design variables. In all cases, ANSYS Maxwell electromagnetic analysis software was used to model the electromagnetic dynamics. An approximate model generated from the electromagnetic analysis was estimated and used for the optimization. The best optimization model was selected using the verified approximation model called the Kriging model, and an optimization algorithm called the progressive quadratic response surface method (PQRSM).