• Progress in Superconductivity and Cryogenics
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• v.20 no.2
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• pp.1-5
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• 2018

Arsenic (As) is one of the elements having most harmful impact on the human health. Arsenic is a known carcinogen and arsenic contamination of drinking water is affecting on humans in many regions of the world. Adsorption has been proved most preferable technique for the removal of arsenic. Many researchers have studied various types of solid materials as arsenic adsorbent, and iron oxide and its modified forms are considered as the most effective adsorbent in terms of adsorption capacity, recovery, and economics. However, most of all iron oxides have small surface area in comparing with common adsorbents in environmental application such as activated carbon but the activated carbon has weak sorption affinity for arsenic. We have used an activated carbon as base adsorbent and iron oxide coating on the activated carbon as high affinity sorption sites and giving magnetic attraction ability. In this study, adsorption properties of arsenic and magnetic separation efficiency of the magnetized activated carbon (MAC) were evaluated with variable iron oxide content. As the iron oxide content of the MAC increased, adsorption capacity has also gradually increased up to a point where clogging by iron oxide in the pore of activated carbon compensate the increased sorption capacity. The increase of iron oxide content of the MAC also affected magnetic properties, which resulted in greater magnetic separation efficiency. Current results show that magnetically modified common adsorbent can be an efficiency improved adsorbent and a feasible environmental process if it is combined with the magnetic separation.

• Structural Monitoring and Maintenance
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• v.4 no.3
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• pp.237-253
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• 2017

Among various structural health monitoring technologies, impedance-based damage detection has been recognized as a promising tool for diagnosing critical members of civil structures. Since the piezoelectric transducers used in the impedance-based technique should be bonded to the surface of the structure using bonding layers (e.g., epoxy layer), it is hard to maintain the as-built condition of the bonding layers and to reconfigure the devices if needed. This study presents an experimental investigation by using magnetically attached PZT-interface for the impedance-based damage detection in bolted girder connections. Firstly, the principle of the impedance-based damage detection via the PZT-interface device is outlined. Secondly, a PZT-interface attachment method in which permanent magnets are used to replace the conventional bonding layers is proposed. Finally, the use of the magnetic attraction for the PZT-interface is experimentally evaluated via detecting the bolt-loosening events in a bolted girder connection. Also, the sensitivity of impedance signatures obtained from the PZT-interface is analyzed with regard to the interface's material.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.12
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• pp.592-600
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• 2005

In this paper, a low loss magnetic levitation(Maglev) system is suggested and tested. The suggested Maglev system includes four hybrid magnets which consist of permanent magnet and coil. In the steady state, the levitated module system can be supported by attraction force generated by permanent magnet. The coil current controls only dynamic loads due to external disturbances. The module systems are designed by using finite element method(FEM) software tools such as MAXWELL and ANSYS. Also, digital control systems are designed to keep the magnet airgap at a constant value. The control systems include a VME(versa module europa)-based CPU(central processing unit) board, AD(analog to digital) board, PWM(pulse width modulation) board, 4-quadrant chopper, and sensors. In order to estimate the vertical velocity of the magnet, we use second order state observer with acceleration and gap signals as input and output signals, respectively. The characteristics of the suggested low loss Maglev system are demonstrated by experimental results showing coil current of 0A in the steady state of 3m airgap and performance specifications are satisfied for reference gap and force disturbance.

• The Korean Journal of Rheology
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• v.11 no.2
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• pp.128-134
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• 1999

Rheological characterization was examined for two different types of magenetic particle (rod-like $\gamma$-$Fe_{2}O_{3}$, $CrO_2$ )suspension in this study. The measured suspension viscosity (viscosity vs. concentration or shear rate) is used to obtain the dependence of viscous energy dissipation on the microstructural states of magnetic particle dispersions as well as the microstructural shape effects which are related to magnetic particle orientation. The empirical formulas from mean field theory and the Mooney equation are used to relate suspension viscosity to particle concentration. Intrinsic viscosities of these two different types of rod-like magnetic particle suspensions are found to exceed the prediction of hydrodynamic theory for dilute suspensions and support the existence of flocs containing significant amounts of immobilized suspending medium due to native attraction forces among particles in the microstructures.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.2
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• pp.259-266
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• 2020

Magnetic gears have the same characteristics as mechanical gears, and each rotor does not come in contact, which is advantageous over mechanical gears in friction noise, heat generation, and maintenance. In addition, when the rotor using the coil-winding is applied, it is possible to control the output of the gear as well as to cut off its own drive in the emergency situation and to change its gear ratio. So the application of the magnetic gear is infinite. However, when the coil-winding rotor is used, cogging torque due to the attraction force between the permanent magnet and the iron core appears, which leads to an increase in the torque ripple component causing the rotor vibration. Therefore, in this paper, various shapes of the coil-winding rotor are analyzed to reduce the torque ripple of the rotor, and the optimum shape for reducing the torque ripple of the magnetic gear is presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.3
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• pp.162-173
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• 1996

Dry magnetic particle inspection(MPI) was performed to detect the surface defects of steel ingot cast billets. Magnetic properties of several materials were characterized by the measurement of the B-H hysteresis curve. The inspection results were evaluated in terms of the magnetizing current, temperature, and the amount of magnetic particles applied to billets. Magnetic flux leakage near the defect site of interest was measured and compared with the results of calculation by the finite element method in the case of direct magnetizing current. Direct and alternating magnetizing currents for materials were deduced by the comparison of the inspections. Results of the magnetic particle inspection by direct magnetizing current were compared with those of finite element method calculations, which were verified by measuring magnetic leakage flux above the surface and the surface defects of the material. For square rods, due to the geometrical effect, the magnetic flux density at the edges along the length of the rods was about 30% of that at the center of rod face for a sufficiently large direct magnetizing current, while it was about 70% for an alternating magnetizing current. Thus, an alternating magnetizing current generates rather uniform magnetic flux density over the rods, except for the region on the face across about 10 mm from the edge. The attraction of the magnetic particle by the magnetic leakage field was nearly independent of the surface temperature of the billets up to $150^{\circ}C$. However, the temperature should have been limited below $60^{\circ}C$ for an effective fixing of gathered magnetic particles to the billet surface using methylene chloride. We also found that the amount of applied magnetic particles tremendously affected the detection capability.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.2
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• pp.146-153
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• 2005

In a permanent magnet brushless dc motor, cogging torque is produced by the magnetic attraction between the rotor mounted permanent magnets and the stator teeth. This always produces a pulsating torque ripple resulting in vibration and acoustic noise, which is detrimental to the motor performance. This paper deals with the analytical prediction of cogging torque and the various cogging torque minimization techniques as applied to a permanent magnet brushless dc motor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.816-821
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• 2002

It is getting more important that energy efficiency and manufacturing cost of the electric motor in appliance. The SRM has been alternative choice. But acoustic noise and harshness in this motor was widely known. So this paper had been studied on the noise reduction of a SRM in air conditioner. This works include some parameters regarding to blown noise sources like a reluctance torque ripple, air gap eccentricity, Especially, it was focused on dynamic characteristics of the system based on mechanical viewpoint. It came to successful results. Besides, this gave us a validity of phase excitation in experimental measurements.

• Progress in Superconductivity
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• v.5 no.2
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• pp.141-143
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• 2004

For designing a flywheel system using superconductor, it is necessary to understand the basic characteristics of the classical superconductor bearing. It is difficult to expect the characteristics of superconductor bearings using models that have been introduced up to now. In the "Frozen image" concept, the farce between the permanent magnet and the superconductor can be divided into two forces between permanent magnet and two imaginary magnets in the superconductor; one represents attraction farce and the other represents a repulsion force. We calculated the characteristics of two superconductor bearings, such as an axial, the radial stiffness and the levitation force. This calculation method was very helpful to expect the characteristics of the superconductor bearings. Using this model, we established the optimum condition for the superconductor bearing.r bearing.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.312-316
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• 2014

This paper describes a turnout without movable parts for magnetically levitated vehicles with hybrid magnets, which have been studied by the authors in place of streetcars. Their low construction cost and low maintenance is key to their practical use. Magnetic levitation systems using forces of attraction can generate guidance force automatically, but the damping force against lateral motion is negligible. However, the lateral damping characteristic was improved by using divided iron type magnets and rails. Using this turnout without movable parts will facilitate smooth direction switching.