Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.331-335
First-principle Study for AlxGa1-xP and Mn-doped AlGaP2 Electronic Properties
The ferromagnetic and electronic structure for the Al
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.336-341
Preparation and Magnetic Properties of MnBi Alloy and its Hybridization with NdFeB
MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.342-346
Nuclear Magnetic Resonance Study of 23Na Nucleus in NaBrO3 Single Crystal
The nuclear magnetic resonance of the 23Na nucleus in a NaBrO3 single crystal was investigated at the temperature range of 200 K~410 K. The tendencies of temperature dependence of the nuclear quadrupole coupling for the two magnetically inequivalent Na(I) and Na(II) centers are found to be opposite to each other. The nuclear spin-lattice relaxation mechanism of 23Na in the NaBrO3 crystal is investigated, and the result revealed that the Raman process is dominant in the temperature range investigated. The relaxation process of the 23Na nuclear spins was well described by a single exponential function in time. The T1 values of the 23Na nuclei in the NaBrO3 single crystal decreased with increasing temperature. The calculated activation energy for the 23Na is 0.032 ± 0.002 eV.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.347-352
Effect of Bias Magnetic Field on Magnetoelectric Characteristics in Magnetostrictive/Piezoelectric Laminate Composites
The magnetoelectric (ME) characteristics for Terfenol-D/PZT laminate composite dependence on bias magnetic field is investigated. At low frequency, ME response is determined by the piezomagnetic coefficient
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.353-359
Relaxor Behaviors in
Ms. Dung and Ms. Hoa contributed equally to this work.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.360-365
Magnetic Flux Density Distributions and Discharge Characteristics of a Newly Designed Magnetized Inductively Coupled Plasma
Spatial distributions of magnetic flux density in a newly designed magnetized inductively coupled plasma (M-ICP) etcher were investigated. Radial and axial magnetic flux densities as well as the magnetic flux density on the center of the substrate holder were controllable by placing multiple circular coils around the etcher properly. The plasma density non-uniformity in M-ICP (25 Gauss) can be reduced (1.4%) compared to that in ICP (16.7%) when the neutral gas pressure was 0.67 Pa and a right-hand circularly polarized wave (R-wave) can be propagated in to the etcher by making magnetic flux density increases both radially and axially from the center of the substrate holder.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.366-370
Newly Designed Ion Beam Etcher with High Etch Rate
New ion beam etcher (IBE) using a magnetized inductively coupled plasma (M-ICP) has been developed. The magnetic flux density distributions inside the upper chamber, where the plasma is generated by inductive coupling, were successfully optimized by arranging a pair of circular coils very carefully. More importantly, the proposed M-ICP IBE exhibits higher etch rate than ICP.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.371-376
Properties of Polyalphaolefin-Based Ferrofluids
Magnetite nanoparticles were synthesized by adding excess ammonium hydroxide to a solution of iron (II) and (III) chlorides. The surfactants of oleic acid and Span 80 were applied in sequence to the magnetic particles as a combined stabilizer, and poly-α-olefin (PAO) 30 or 60 was used as the liquid base with a low or high viscosity, respectively. The ferrofluids were prepared with the concentrations of 200, 300, 400, and 500 mg/mL, and characterized by density, dispersion, magnetization, and viscosity. The density of the fluids increased proportionally to the concentration from 0.98 to 1.27 g/mL and 1.01 to 1.30 g/mL with PAO 30 base and PAO 60 base, and the dispersion stability was 77-95 and 81-74% for the PAO-30 and PAO-60-based fluids, respectively. The observed saturation magnetization values of the PAO-30 and PAO-60-based ferrofluids were 16 to 42 mT and 17 to 41 mT with the concentration increase in the range 200-500 mg/mL, respectively, depending upon the content of magnetic particles in the fluid. The viscosity variation of the PAO-30 and PAO-60-based ferrofluids in the temperature range 20-80℃ was the least with the concentrations of 400 and 300 mg/mL, respectively.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.377-380
Pulsed Electromagnetic Fields to Influence Pain and Muscle Healing Following Muscle Injury in Rats
Muscle contusion has a negative effect on muscle function. Although several studies showed that pain control and muscle recovery is facilitated by pulsed electromagnetic fields (PEMF), there has not been much research regarding the specific effects of PEMF on them. The aim of the present study is to investigate effects of PEMF on pain and muscle recovery following extensor digitorum longus (EDL) contusion injury through measuring the expression of the c-fos proto-oncogene and nerve growth factor (NGF). Significantly reduced c-fos expression in the spinal cord was shown in PEMF groups compared with control (CON) groups. There was no significant difference between PEMF1 and CON1, but significantly increased NGF expression was shown in PEMF3 and PEMF5 compared with in CON groups, where the numbers in the group names are the days from contusion. In conclusion, PEMF could be used to not only reduce pain in muscle injuries by down-regulating c-fos expression in the spinal cord, but it could also influence muscle healing through increasing NGF expression in the injured muscle.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.381-386
Analysis of Image Distortion on Magnetic Resonance Diffusion Weighted Imaging
The purpose of this study is to improve diagnostic efficiency of clinical study by setting up guidelines for more precise examination with a comparative analysis of signal intensity and image distortion depending on the location of X axial of object when performing magnetic resonance diffusion weighted imaging (MR DWI) examination. We arranged the self-produced phantom with a 45 mm of interval from the core of 44 regent bottles that have a 16 mm of external diameter and 55 mm of height, and were placed in 4 rows and 11 columns in an acrylic box. We also filled up water and margarine to portrait the fat. We used 3T Skyra and 18 Channel Body array coil. We also obtained the coronal image with the direction of RL (right to left) by using scan slice thinkness 3 mm, slice gap: 0mm, field of view (FOV): 450 × 450 mm2, repetition time (TR): 5000 ms, echo time (TE): 73/118 ms, Matrix: 126 × 126, slice number: 15, scan time: 9 min 45sec, number of excitations (NEX): 3, phase encoding as a diffusion-weighted imaging parameter. In order to scan, we set b-value to 0 s/mm2, 400 s/mm2, and 1,400 s/mm2, and obtained T2 fat saturation image. Then we did a comparative analysis on the differences between image distortion and signal intensity depending on the location of X axial based on iso-center of patient’s table. We used “Image J” as a comparative analysis programme, and used SPSS v18.0 as a statistic programme. There was not much difference between image distortion and signal intensity on fat and water from T2 fat saturation image. But, the average value depends on the location of X axial was statistically significant (p < 0.05). From DWI image, when b-value was 0 and 400, there was no significant difference up to 2nd columns right to left from the core of patient’s table, however, there was a decline in signal intensity and image distortion from the 3rd columns and they started to decrease rapidly at the 4th columns. When b-value was 1,400, there was not much difference between the 1st row right to left from the core of patient’s table, however, image distortion started to appear from the 2nd columns with no change in signal intensity, the signal was getting decreased from the 3rd columns, and both signal intensity and image distortion started to get decreased rapidly. At this moment, the reagent bottles from outside out of 11 reagent bottles were not verified from the image, and only 9 reagent bottles were verified. However, it was not possible to verify anything from the 5th columns. But, the average value depends on the location of X axial was statistically significant. On T2 FS image, there was a significant decline in image distortion and signal intensity over 180mm from the core of patient’s table. On diffusion-weighted image, there was a significant decline in image distortion and signal intensity over 90 mm, and they became unverifiable over 180 mm. Therefore, we should make an image that has a diagnostic value from examinations that are hard to locate patient’s position.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.387-393
An Asymmetric Rotor Design of Interior Permanent Magnet Synchronous Motor for Improving Torque Performance
Torque ripple is necessarily generated in interior permanent magnet synchronous motors (IPMSMs) due to the non-sinusoidal distribution of flux density in the air gap and the magnetic reluctance by stator slots. This paper deals with an asymmetric rotor shape to reduce torque ripple which can make sinusoidal flux density distribution in the air gap. Meanwhile the average torque is relatively increased by the asymmetric rotor. Response surface method (RSM) is applied to find the optimum position of the permanent magnets for the IMPSM with improved torque performance. Consequently, an asymmetric structure is the result of RSM and the structure has disadvantage of a mechanical stiffness. Finally, the performance of suggested shape is verified by finite element analysis and structural analysis is conducted for the mechanical stiffness.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.394-399
Modeling of 3-stage Electromagnetic Induction Launcher
Electromagnetic Induction Launchers (EIL) have been receiving great attention due to their advantages of non-contact between the coils and a projectile. This paper describes the modeling and design of 3-stage EIL to accelerate a copper projectile of 50 kg with 290 mm diameter. Our EIL consists of three independent driving coils and pulsed power modules to generate separate driving currents. To find efficient acceleration conditions, the appropriate shape of the driving coils and the position of the projectile have been calculated by using a finite element analysis (FEA) method. The results showed that the projectile can be accelerated more effectively as the gap between the coils is smaller; a final velocity of 45 m/s was obtained. The acceleration efficiency was estimated to be 23.4% when a total electrical energy of 216 kJ was discharged.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.400-404
Reduction of Electromagnetic Force in AC Distributed Winding of Fault Current Limiter under Short-Circuit Condition
Various kinds of winding arrangements can be used to enable fault current limiters (FCL) to tolerate higher forces without resulting in a substantial increase in construction and fabrication costs. In this paper, a distributed winding arrangement is investigated in terms of its effects on the short-circuit forces in a three-phase FCL. The force magnitudes of the AC supplied windings are calculated by employing a finite element-based model in the time stepping procedure. The leakage flux and radial and axial force magnitudes obtained from the simulation are compared to those obtained from a conventional winding arrangement. The comparison shows that the distributed winding arrangement significantly reduces the radial and, especially, the axial force magnitudes.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.405-412
Dual-Halbach Array Permanent Magnet Tubular Generator for Free-Piston Generator
In this study, we describe the effects of changing the magnet shape of permanent magnets (PMs) in a rotor Halbach-array PM generator for reciprocating free piston generator applications. More specifically, the rectangular-shaped magnets were replaced by the trapezoidal-shaped magnets. The initial design, an analytical magnetic field solution of rectangular shaped magnets, is presented and air-gap magnetic flux density and thrust force were estimated. The results were compared to the finite element analysis (FEA) showing excellent agreement. Using FEA, the effect of the shape of the magnets on the flux density and thrust force waveforms is analyzed. Moreover, the proportion of the Halbach array in the machine was optimized by the means of a parametric search. The results obtained from the analytical calculations and FEA were validated by comparing to those of Radial-array PM generator.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.413-420
Design and Comparison of Multistage Axial Flux Permanent Magnet Machines for Potable Generating Application
In this study, we present a comparison of multistage axial flux permanent-magnet machines (AFPMs) with different topologies for use as 100 W-class portable generating systems. Three topologies were selected, and the maximum power density and high level of efficiency were achieved by following the response surface methodology (RSM) in the design. Three-dimensional finite element analysis (FEA) was used to conduct numerical experiments to obtain the optimum design using the RSM and suggest a proper configuration of the portable generating system.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.421-426
The Practical Method and Experimental Verification of Temperature Estimation in the Permanent Magnet of Electric Machine
This paper presents a practical method for estimation of average temperature in the permanent magnet (PM) of electric machine by using finite element analysis (FEA) and dynamo load experiment. First of all, the temperature effect of PM to the torque has been employed by FEA in order to evaluate the Temperature-Torque characteristic curve. The 1st order polynomial equation which is torque attenuation coefficient is derived by the FEA result of the Temperature-Torque curve. Next, torque saturation test with constant current condition is performed by dynamo load experiment. Then, the temperature trend can be estimated by adding the initial starting temperature using the torque attenuation coefficient and torque saturation curve. Lastly, estimated temperature is validated by infrared thermometer which measures temperature of PM surface. The comparison between the estimated result and experimental result gives a good agreement within a deviation of maximum 8 ℃.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.427-431
Effects of Repetitive Transcranial Magnetic Stimulation on Motor Recovery in Lower Extremities of Subacute Stage Incomplete Spinal Cord Injury Patients
The aim of this study was to investigate whether repetitive transcranial magnetic stimulation (rTMS) can improve motor recovery in the lower extremities of the patients with subacute stage spinal cord injury (SCI). This study was conducted with 19 subjects diagnosed with paraplegia because of SCI. The experimental group included 10 subjects who underwent active rTMS, and the control group included 9 subjects who underwent sham rTMS. The SCI patients in the experimental group underwent conventional rehabilitation therapy, and active rTMS was applied daily to the hotspot of the lesional hemisphere. The SCI patients in the control group underwent sham rTMS and conventional rehabilitation therapy. The participants in both the groups received therapy five days per week for six weeks. Latency, amplitude, and velocity were assessed before and after the six-week therapy period. A significant difference in post-treatment gains for the latency and velocity was observed between the experimental and control groups (p < 0.05). However, no significant differences in the amplitude were observed between the two groups (p > 0.05). The results of this study indicate that rTMS may be beneficial in improving motor recovery in the lower extremities of subacute stage SCI patients.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.432-438
Analytical and Experimental Study for Electromagnetic Performances of a Tubular Linear Machine with Axially Magnetized Single-sided Permanent Magnets
This paper presents an electromagnetic analysis of a tubular linear machine with axially magnetized permanent magnets using improved analytical techniques. Based on the magnetic vector potential and a two-dimensional polar-coordinate system, the magnetic field and armature reaction field can be derived. Using these, equivalent circuit parameters, such as the electromotive force and inductance, can be obtained analytically. Finally, the generating characteristics are derived with the equivalent circuit method. In this study, the finite element method was employed to provide a comparative evaluation, and experiments were conducted to validate the results of the analytical analysis.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.439-443
Study on Rod Position Indication System using Permanent Magnets with Shielding Plates for a Control Rod Drive Mechanism
A control rod drive mechanism (CRDM) is an electromechanical equipment that provides linear movement for the control rods to control the nuclear reactivity in a nuclear reactor. A rod position indication system (RPIS) detects the control rod’s position. To enhance the measurement accuracy of the system, a magnetostrictive type sensor with capability of generating operation limiting signals would be adapted instead of a conventional RPIS for a CRDM. An RPIS was modelled for a numerical analysis with the permanent magnets at the stationary limit positions and magnetic shielding plates with a moving permanent magnet. The performance analysis of the RPIS were conducted, and the results were discussed here.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.444-449
Design and Analysis for Loss Reduction of High-Speed Permanent Magnet Motor using a Soft Magnetic Composite
†S. H Lee and Y. J Kim contributed equally to this work.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.450-459
Analysis of Safety Distance and Maximum Permissible Power of Resonant Wireless Power Transfer Systems with Regard to Magnetic Field Exposure
In this paper, the safety distances and maximum permissible power (MPP) of resonant wireless power transfer systems are defined and derived with regard to human exposure to electromagnetic field (EMF). The definition is based on the calculated induced current density and electric field in the standard human model located between the transmitting and receiving coil. In order to avoid the adverse health effects such as stimulation of nerve tissues, the induced current and electric field must not exceed the basic restriction values specified in EMF safety guidelines. The different combinations of diameters of the coils and the distance between the two coils are investigated and their effects are analyzed. Two versions of EMF safety guidelines (ICNIRP 1998 and ICNIRP 2010) are used as bases for safety distance calculation and the difference between the two guidelines are discussed.
Journal of Magnetics, 31 Dec 2015, Vol.20 , No.4, pp.460-465
Exciting High Frequency Oscillations in a Coaxial Transmission Line with a Magnetized Ferrite
The paper presents methodologies and results concerning one- and two-dimensional numerical modeling of radio frequency oscillations in a coaxial transmission line fed with a short pulse of electric current. The line is partially filled with a ferrite material, magnetized longitudinally close to saturation. The 2D model has permitted analyzing, for the first time in the art, the spatial structure and dynamics of the wave field within the radially non-uniform cross-section planes of the non-linear and dispersive guiding structure. This opens ways for optimizing size parameters of the line and the extent to which it is filled with the ferromagnetic material, thus increasing the line’s electric strength and intensity of the r.f. oscillations.