Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.81-85
Effects of Nitrogen Defect on Magnetism of Cu-doped InN: First-principles Calculations
We investigate the electronic and magnetic properties in Cu-doped InN with the N vacancy (VN) from first principles calculations. There is the long-range ferromagnetic order between two Cu atoms, attributed to the hole-mediated double exchange through the strong p-d interaction between the Cu atom and neighboring N atom. The system of VN defect in Cu-doped InN has the lowest formation energy. Due to the hybridization between the Cu-3d and VN states, the spin-polarization on the Cu atoms in the InN lattice is reduced by VN defect. So, it shows a weak ferromagnetic behavior.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.86-89
Efficient Approach to Measure Crystallization Temperature in Amorphous Thin Film by Infrared Reflectivity
This paper shows a new effective approach to measure crystallization temperature of soft magnetic underlayer (SUL) for next generation of heat assisted perpendicular recording media. This approach uses temperature dependent reflectivity, which shows a clear jump when samples are crystallized. To achieve this measurement, an optical system is set up using hot plate and infrared laser. Reflectivity of SUL (Co70Fe30)92Ta3Zr5 shows a clear jump at its amorphous-crystalline transition temperature. Experiment results show this effect is clear in infrared region, and is weak for visible light.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.90-94
Projectile’s Velocity Effect for Voltage Induced at Sensing Coil for Applying to Air Bursting Munition
We designed a model composed of a ring type magnet, a yoke, and a sensing coil embedded in a projectile for simulating the muzzle velocity. The muzzle velocity was obtained from the master curve for the induced voltage at sensing coil and the velocity as the projectile pass through the magnetic field. The induced voltage and the projectile’s velocity are fitted by the 2nd order polynomial. The skin effect difference between projectiles which consist of aluminum-aluminum and aluminum-steel was small. The projectile will surely be burst at the pre-determined target area using the flight time and the projectile muzzle velocity calculated from the voltage induced at the sensing coil on the projectile.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.95-104
General Analytical Method for Magnetic Field Analysis of Halbach Magnet Arrays Based on Magnetic Scalar Potential
This paper presents a general analytical method for predicting the magnetic fields of different Halbach magnet arrays with or without back iron mounted on slotless permanent magnet (PM) linear machines. By using Fourier decomposition, the magnetization components of four typical Halbach magnet arrays are determined. By applying special synthetic boundary conditions on the PM surfaces, the expressions of their magnetic field distributions are derived based on the magnetic scalar potential (MSP), which are simpler than those based on the magnetic vector potential (MVP). The correctness of the method is validated by finite element analysis. The harmonics of airgap flux density waveforms of these Halbach magnet arrays with or without back iron are also compared and optimized.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.105-110
Estimation of Output Voltage and Magnetic Flux Density for a Wireless Charging System with Different Magnetic Core Properties
The design model and key parameters of the material design for the control of induced magnetic flux at the near-field and efficient power transfer in a modified wireless power transfer (WPT) system with a large air gap of wireless electric vehicles were investigated through analytical simulations for magnetic vector and timedomain transient analysis. Higher saturation magnetic core with low core loss induced a stronger vertical magnetic field by the W-type primary coil in the WPT system with a gap of 20 cm at 20 kHz, which is shown from the vector potentials of the magnetic induction. The transient analysis shows that the higher magnetic fluxes through the pick-up cores lead to a linear increment of the alternating voltage with a sinusoidal waveform in the non-contact energy transfer system.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.111-116
Characteristic Analysis of a Permanent Magnet Transverse Flux Linear Motor with Spiral Core
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.117-124
A Novel Cogging Torque Reduction Method for Single-Phase Brushless DC Motor
Single-phase, brushless DC (BLDC) motors have unequal air-gaps to eliminate the dead-point where the developed torque is zero. Unfortunately, these unequal air-gaps can deteriorate the motor characteristics in the cogging torque. This paper proposes a novel design for a single-phase BLDC motor with an asymmetric notch to solve this problem. In the design method, the asymmetric notches were placed on the stator pole face, which affects the change in permanent magnet shape or the residual flux density of the permanent magnet. Parametric analysis was performed to determine the optimal size and position of the asymmetric notch to reduce the cogging torque. Finite element analysis (FEA) was used to calculate the cogging torque. A more than 28% lower cogging torque compared to the initial model with no notch was achieved.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.125-129
Water-Cooled Direct Drive Permanent Magnet Motor Design in Consideration of its Efficiency and Structural Strength
This paper deals with a water-cooled direct drive permanent magnet (DD-PM) motor design for an injectionmolding application. In order to meet the requirements for the target application and consider the practical problems of the manufacturing industry, the DD-PM motor is designed in consideration of efficiency and structural strength with many constraints. The performances of the designed motor are estimated not only by magnetic field analysis, but also by thermal and structural analysis. The design and analysis results are presented with experiment results.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.130-134
Analysis of Symmetric and Periodic Open Boundary Problem by Coupling of FEM and Fourier Series
Most electrical machines like motor, generator and transformer are symmetric in terms of magnetic field distribution and mechanical structure. In order to analyze these problems effectively, many coupling techniques have been introduced. This paper deals with a coupling scheme for open boundary problem of symmetric and periodic structure. It couples an analytical solution of Fourier series expansion with the standard finite element method. The analytical solution is derived for the magnetic field in the outside of the boundary, and the finite element method is for the magnetic field in the inside with source current and magnetic materials. The main advantage of the proposed method is that it retains sparsity and symmetry of system matrix like the standard FEM and it can also be easily applied to symmetric and periodic problems. Also, unknowns of finite elements at the boundary are coupled with Fourier series coefficients. The boundary conditions are used to derive a coupled system equation expressed in matrix form. The proposed algorithm is validated using a test model of a bush bar for the power supply. And the each result is compared with analytical solution respectively.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.135-141
Efficient Fault Detection Method for a Degaussing Coil System Based on an Analytical Sensitivity Formula
This paper proposes an efficient fault detection method for onboard degaussing coils which are installed to minimize underwater magnetic fields due to the ferromagnetic hull. To achieve this, the method basically uses field signals measured at specific magnetic treatment facilities instead of time-consuming numerical field solutions in a three-dimensional analysis space. In addition, an analytical design sensitivity formula and the linear property of degaussing coil fields is being exploited for detecting fault coil positions and assessing individual degaussing coil currents. Such peculiar features make it possible to yield fast and accurate results on the fault detection of degaussing coils. For foreseeable fault conditions, the proposed method is tested with a model ship equipped with 20 degaussing coils.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.142-149
Clinical Application of MRI in an Animal Bone Graft Model
We aim to monitor vascularization of early bone perfusion following rabbit lumbar intertransverse bone graft fusion surgery using magnetic resonance imaging assessment. Correlation with graft survival status was evaluated by histological method. Experimental animals were randomly divided into three groups and the model was established by operating bilateral lumbar intertransverse bone graft with different types of bone graft substitute material. The lumbar intertransverse area of three groups of rabbits was scanned via MRI. In addition, histological examinations were performed at the 6th week after surgery and the quantitative analysis of the osteogenesis in different grafted area was carried out by an image analysis system. The MRI technique can be used for early postoperative evaluation of vascularized bone graft perfusion after transplantation of different bone materials, whereas histological examination allows direct visualization of the osteogenesis process.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.150-154
Control of Working Temperature of Isothermal Magnetic Entropy Change in La0.8Nd0.2(Fe0.88Si0.12)13 by Hydrogen Absorption for Magnetic Refrigerants
La1-
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.155-158
FeCoB Films with Large Saturation Magnetization and High Magnetic Anisotropy Field to Attain High Ferromagnetic Resonance Frequency
FeCoB films were being prepared on a Ru underlayer by using the oblique incidence of sputtered and backscattered particles which have a high in-plane magnetic anisotropy field
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.159-162
Optimization of Operation Frequency of Orthogonal Fluxgate Sensor Fabricated with Co Based Amorphous Wire
We present how to optimize the operation condition including frequency of the orthogonal fluxgate sensor in this paper. The orthogonal fluxgate sensor was fabricated with a Co-based amorphous wire with 10 mm long and 100 μm in the diameter and a 270-turn pickup coil wound on the amorphous wire. In order to investigate the frequency dependence of the sensitivity, output spectra of the sensor which was connected by using a coaxial cable with various lengths of 0.5-5 m were measured with a RF lock-in amplifier. The maximum sensitivities were obtained at different frequencies according to coaxial cable lengths. It was found that the optimal operation frequencies, at which maximum sensitivities were appeared, were almost identical to the frequencies of impedance resonance. The maximum sensitivity and optimal operation frequency were 1.1 V/Oe (≈ 11000 V/T) and 1.25 MHz respectively.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.163-167
Microfabrication of MEMS Cantilevers for Mechanically Detected High-Frequency ESR Measurement
We fabricated prototype cantilevers for mechanically detected high-frequency ESR measurement. Cantilevers are fabricated from silicon-on-insulator (SOI) wafers using standard MEMS techniques such as lithography, wet etching, and plasma etching. Using commercial SOI wafers, fabrication cost and the number of processes can be substantially reduced. In this study, three types of cantilevers, designed for capacitive and optical detection, are shown. Capacitive type with lateral dimensions of 3.5 × 1.6 mm2 is aimed for low spin concentration sample. On the other hand, optical detection type with lateral dimensions of 50 × 200 μm2 is developed for highsensitive detection of tiny samples such as newly synthesized microcrystals.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.168-172
Development of High-Field ESR System Using SQUID Magnetometer and its Application to Measurement under High Pressure
We have developed a high-field and high-frequency ESR system using a commercially available magnetometer equipped with the superconducting quantum interference device (SQUID). This is magnetization detection type ESR and ESR is observed as a change of the magnetization at the resonance condition under irradiation of the electromagnetic wave. The frequency range is from 70 to 315 GHz and the maximum magnetic field is 5 T. The sensitivity is estimated to be 1013 spins/G. The advantage of this system is that the high-field ESR measurements can be made very easily and quantitatively. Moreover, this high-field ESR can be applied to the measurements under pressure by using a widely used piston-cylinder pressure cell.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.173-177
Development of High-Sensitivity Cantilever-Detected ESR Measurement Using a Fiber-Optic Interferometer
Cantilever-detected high-frequency electron spin resonance (ESR) is a powerful method of sub-terahertz and terahertz ESR spectroscopy for a tiny magnetic sample at low temperature. In this technique, a small magnetization change associated with ESR transition is detected as deflection of a sample-mounted cantilever. So far, we have succeeded in ESR detection at 370 GHz using a commercial piezoresistive microcantilever. The spin sensitivity was estimated to ~1012 spins/gauss. In order to further increase the sensitivity, we adopt a fiber-opticbased detection system using a Fabry-Perot interferometer in place of piezoresistive system. Fabry-Perot cavity is formed between an optical-fiber end and microcantilever surface, and a change in the interference signal, corresponding to the cantilever deflection, is sensitively detected. This system is suitable for low-temperature and high-magnetic-field experiments because of its compact setup and less heat dissipation. In this study, performance of Fabry-Perot interferometer is evaluated, and its application to cantilever-detected ESR measurement is described.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.178-182
Development of a Wideband EPR Spectrometer with Microstrip and Loop Antennas
We have developed a new non-conventional electron paramagnetic resonance (EPR) spectrometer, in which no resonant cavity was used. We previously demonstrated a wide frequency range operation of an EPR spectrometer using two loop antennas, one for a microwave transmission and the other for signal detection
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.183-187
Analysis of Both Hands’ Two Pulse Waveforms using a Clip-type Pulsimeter Equipped with Magnetic Sensing Hall Device
Two concurrent signals of the pulse wave measured from both hands’ radial artery in un-pressurization condition using the prototype model of two clip-type pulsimeters with a permanent magnet and Hall device are investigated. The phase differences of two pulse waves from 22 subjects have some distinct points according to the handedness. Thus, the propagation of the pulse wave calculated from phase difference is both fast and slow to each other. It is confirmed that this phenomenon comes from the difference of blood vessel hardness between right- and left- hand of each subject rather than a quantity of muscle.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.188-191
The Magnetic Mobility of Biomolecule Sanals of the Lymphatic Primo Vascular System
The magnetic properties for sanal’s mobility inside of the lymphatic primo vascular system, the so-called Kyungrak (or meridian) system, are investigated under a low static magnetic field with the anatomy technology and optical microscope. One sanal with a size of 1 μm under microscope selected and separated from the primo vessels of the primo vascular system are observed in rabbits' lymphatic vessels around abdominal aorta and placed in PBS solution with petridish. The moving displacement of sanal versus the measuring time of 20 Oe below a magnetic field of 80 Oe is stronger in dominanting dependence according to the x-direction than y-direction.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.192-196
An Analytical Comparison in Electoencephalography and Electrocardiography under Pulsed Magnetic Field and Acupuncture Stimulus on Acupoint PC9
We have investigated the changes of electroencephalography (EEG) and electrocardiography (ECG) under pulsed magnetic field (PMF) and acupuncture stimulus on acupoint PC9. In order to compare quantitatively the effect of PMF and acupuncture stimulus, the difference of alpha activities are calculated from EEG spectra, and the spectrum curves of ECG were analyzed in the frequency domain of heart rate variability (HRV). The increase of alpha activities after both stimuli could be explained that the impulse of stimulus on PC9 might pass through sensory nerve following meridian and approach the cerebral cortex, causing the central nervous system (CNS) to be activated for pacifying emotion and calming the mind. The decrease in sympathovagal activity of HRV after both stimuli indicates that parasympathetic nerves were activated and the sympathetic nerves were in constrained condition. These findings suggest that PMF could be patient-friendly alternative non-invasive medical treatment for influencing human physiology, in comparison with acupuncture inserting the needle and inducing nervous and anxious state to subject.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.197-201
Methods for Determining the Quality of Magnetic Fluids
This paper presents the conversion parameter values of the magnetic properties of magnetic fluids. These values were determined for three magnetic fluid samples containing particles with diameters between 30 Å and 170 Å. The factors that may affect the value of this parameter (size of particle, magnetic properties, the presence of clusters and aggregates) are also studied. The determined values for the conversion parameter (γ) are between 0.25 and 0.76 and the determined limit value is 0.8. Because many applications require magnetic fluids with the saturation magnetization as high as possible and the viscosity as low as possible [1], it has been considered necessary to determine this parameter which describes the quality of magnetic fluids.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.202-206
Analysis and Depth Estimation of Complex Defects on the Underground Gas Pipelines
In this paper, the MFL (magnetic flux leakage) signals of complex defects on the underground gas pipeline are analyzed and their depths are estimated. Since closely-located defects (complex defects) affect each other, accelerate the progress of defection, and are finally combined to one (cluster), it’s meaningful to differentiate complex defects from single defects by analyzing their characteristics. Various types of complex defects are characterized and analyzed by defining the safety distance for interference. 26 artificial defects are carved on the pipeline simulation facility (PSF) to analyze the characteristics of complex defect and demonstrate the accuracy of the proposed complex defect estimation. The proposed method shows average length error of 5.8 mm, average width error of 15.55 mm, and average depth error of 8.59%, respectively.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.207-211
Effect of Stationary Pole Pieces with Bridges on Electromagnetic and Mechanical Performance of a Coaxial Magnetic Gear
In a coaxial magnetic gear, bridges connecting separate pole pieces are useful for fabrication and also improve mechanical reliability. However, they have a negative influence on electromagnetic performance parameters such as transmission torque and iron loss. This paper investigates the effect of stationary pole pieces connected by bridges on the electromechanical characteristics. The bridge type and thickness are the main parameters influencing the performance of a coaxial magnetic gear. The inner, center, and outer bridge types each show the best performance in terms of different characteristics. However, for any bridge type, an increase in the bridge thickness reduces the overall electromagnetic performance, except for the torque ripple, and improves the overall mechanical performance, including the deformation, von Mises stress, and natural frequency of the stationary part.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.212-215
Design Characteristics of Torque Harmonics Reduction of Induction Motors for Electric Vehicle Propulsion
This paper deals with torque harmonic characteristics and its reduction design of induction motors for electric vehicle (EV) propulsion. For calculating the stator harmonic flux of squirrel-cage induction motor, the numerical methods have been employed on the structural configuration design of stator and rotor teeth. In particular, torque ripples including spatial harmonics are obtained by Finite Element Method (FEM), and their individual harmonic components are identified with Fast Fourier Transform (FFT). In this paper, design modification on the teeth surface gives rise to the significant reduction of torque ripples including spatial torque harmonics, which have been obtained with FEM.
Journal of Magnetics, 30 Jun 2013, Vol.18 , No.2, pp.216-219
Numerical Analysis on Iron Loss and PM Loss of Permanent Magnet Synchronous Motor Considering the Carrier Harmonics
In this paper, the influence of inverter switching harmonics on iron loss and PM loss of Permanent Magnet Synchronous Motor (PMSM) is numerically investigated by Finite Element Method (FEM). In particular, nonlinear FEM is applied for a multi-layered PM Synchronous Motors (PMSMs), Interior buried PMSM (IPMSM) and PM assisted Synchronous Reluctance Motor (PMa-SynRM), which are adoptively designed and compared for Electric Vehicle (EV) propulsion. In particular, iron loss and PM eddy-current loss under the real current waveform including the carrier harmonics from inverter switching are numerically analyzed with nonlinear FEM by considering the skewed stator structure employed for minimizing spatial harmonics.