• Progress in Superconductivity and Cryogenics
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• v.6 no.3
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• pp.38-43
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• 2004

1MW class superconducting synchronous motor is designed considering several conditions such as superconducting wire length, machine efficiency and size. As the machine is larger and larger, the superconducting machine shows the advantages more and more over the conventional machines. Although the advantages at 1MW rating are not so great, the design approach to get an appropriate result would be very helpful for larger superconducting synchronous machine design. Major design concerns are focused on reducing expensive Bi-2223 HTS(High Temperature Superconducting) wire which is used for superconducting field coil carrying the rating current around 30K(-243$^{\circ}C$) while the machine efficiency is higher than conventional motors or generators with the same rating. Furthermore, some iron cored structure is considered to reduce the HTS wire requirement without bad effect on machine performances such as sinusoidal armature voltage waveform, synchronous reactance and so on.

• Journal of Sensor Science and Technology
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• v.27 no.2
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• pp.99-104
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• 2018

A micro electromagnetic actuator with high vibration efficiency is proposed for use in an implantable hearing device. The actuator, which can be implanted in the middle ear, consists of membranes based on the stainless steel 304 (SUS-304), and other components. In conventional actuators, in which a thick membrane and a silicone elastomer are used, the size reduction was difficult. In order to miniaturize the size of the actuator, it is necessary to reduce the size of the actuation potion that generates the driving force, resulting in reduction of the electromagnetic force. In this paper, the electromagnetic actuator is further miniaturized by the metal membrane and the vibration amplitude is also optimized. The actuator designed according to the simulation results was fabricated by using micro-electro-mechanical systems (MEMS) technology. In particular, a $20{\mu}m$ thick metal membrane was fabricated using the erosion process, which reduced the length of the actuator by more than $400{\mu}m$. In the experiments, the vibration displacement characteristics of the optimized actuator were above 400 nm within the range of 0.1 to 1 kHz when a current of $1mA_{rms}$ was applied to the coil.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.147-154
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• 2005

A precision hi-directional actuator for a high precision leveling system with $Z{\Theta}_x{\Theta}_y$ motions is proposed and designed in this paper. The actuator is composed of a force generation structure, a guide mechanism, and a symmetric structure. At first, its driving force is generated by a change of flux in air gaps by permanent and changeable flux. The permanent flux is generated by a permanent magnet. The changeable flux is created by variable current flowing through coil. The combination of permanent and changeable flux makes various flux densities in air gaps between moving part and fixed yokes. And then, the difference between flux densities in lower and upper gaps creates forces fur the $bi-direction({\pm}z)$ motion. The guide mechanism of this actuator is composed of two circular plates and one shaft. Reducing motions generated by forces except z-motion, these circular plates endow the actuator with high stiffness for fast settling time. And the function of the shaft is to transfer motion to an object. At last, total body has a symmetric structure to be stable on thermal error. The actuator is designed by MAXWELL 2D and ProMECHANICA. The designed actuator is evaluated by 8nm laser doppler vibrometer, dynamic signal analyzer, and simple PID controller.

• Progress in Superconductivity and Cryogenics
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• v.13 no.1
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• pp.12-16
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• 2011

In this paper, the prototype of the HTS motor with an on-board cryocooler, is fabricated and tested. The overall system is composed of the stator with conventional copper winding, the rotor with superconductor, and the rotating cryocooler designed from the on-board concept. The rotor is fabricated as the race-track coil with 2G, YBCO tape and contacts with the on-board cryocooler while being rotated together. An inline-type pulse tube refrigerator is used as the on-board cryocooler. The cryocooler is fabricated from optimal process to satisfy the structure and thermal stability of the on-board system. Each component is integrated according to carefully defined sequence. Specially, a combining method of torque tubes is an important part for sustaining stability of the rotor and the cryocooler. In the rotating test, the HTS motor is successfully operated with 240 rpm of rotating speed when 75 A current is supplied to the superconducting rotor. In this paper, potential problems of the HTS motor system using the on-board cryocooler are proposed and solved, and realistic possibility of this concept is also confirmed.

• Journal of Power Electronics
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• v.8 no.3
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• pp.217-227
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• 2008

The electric power subsystems (EPS) of most remote sensing satellites consist of a solar array as a source of energy, a storage battery, a power management and control (PMC) unit and a charge equalization unit (CEU) for the storage battery. The PMC and CEU use high frequency transformers in their power modules. This paper presents a design, implementation and testing results of a high frequency transformer for the EPS of satellite applications. Two approaches are used in the design process of the transformer based on the pre-determined transformer specifications. The transformer is designed based on an ETD 29 ferrite core. The implemented transformer consists of one center-tapped primary coil with eleven center-tapped secondary coils. The offline calculation results and measured values of R, L for transformer coils are convergence. A test circuit for measuring the transformer parameters like voltage, current and B-H hysteresis was implemented and applied. The test results confirm that the voltage waveforms of both primary and secondary coils were as desired. No overlapping occurred between the control signal and the transformer, which was not saturated during testing even during a short circuit test of the secondary channels. The dynamic B-H loop characteristics of the used transformer cores were measured. The sample test results are given in this paper.

• Journal of Korean Neurosurgical Society
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• v.56 no.5
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• pp.428-430
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• 2014

Isolated traumatic pseudoaneurysms of the basilar artery are extremely rare but often fatal resulting in a mortality rate as high as 50%. A 51-year-old man presented with craniofacial injury after blunt trauma. A brain computed tomography (CT) scan showed thick basal subarachnoid hemorrhage associated with multiple craniofacial fractures, while CT angiography revealed contrast extravasation at the distal basilar artery with pseudoaneurysm formation. After this primary survey, the condition of the patient suddenly deteriorated. Conventional angiography confirmed the contrast extravasation resulted from pseudoaneurysm formation, which was successfully treated with endovascular coil embolization. Decompressive craniectomy and coma therapy with propofol were also performed. However, the patient died on the 7th hospital day because of the poor initial clinical condition. The current case is the first report of acute pseudoaneurysm rupture arising from the basilar artery within the first day after trauma. Our findings suggest the possibility that pseudoaneurysm rupture should be considered if brain CT shows thick traumatic subarachnoid hemorrhage on the basal cistern with a basal skull fracture.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.932_933
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• 2009

A technology based on thyristors will be used to manufacture the super-conducting coil AC/DC converters because of the low ratio of cost over installed power compared to a design based on GTO or similar technology. But phase-controlled converter suffers from fundamental disadvantage. They inject current harmonics into the input ac mains due to their nonlinear characteristics, thereby distort the supply voltage waveform, and demand reactive power from the associated ac power system at retarded angles. To overcome this disadvantage, in the case of two series converters at the DC side, connected to the same step-down transformer, apply for the sequence control. It is the most simple and efficient way to reduce the reactive power consumption at low cost. Analytical sequence control algorithm is suggested, the validity of the proposed scheme has been verified by experimental results with the small-scaled International Thermonuclear Experimental Reactor (ITER) Power Supply to minimize reactive power consumption.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1334-1340
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• 2001

In this paper, the experimental modeling of the force between permanent magnet and iron-core solenoid is suggested for more accurate control of 3 D.O.F. motor using the electromagnetic force. In the case of iron-core solenoid, the general equation of solenoid cant be used simply because of its nonlinearity. Therefore, the magnetic flux density is estimated through the concept of equivalent permanent magnet. The force distribution between permanent magnet and iron-core solenoid is more dependent on the magnetization of iron core caused by the permanent magnet than any other parameters. Therefore, the equation of the force estimation between these magnetic systems can be modeled by the experimental function of the magnetization of iron core. Especially, if the distance between iron-core solenoid and permanent magnet is far enough, the force equation through experiment can be expressed from only the current of coil and the distance between iron-core solenoid and permanent magnet. It means that Coulombs law can be used for magnetic systems and it is validated through the experiment. Therefore, force calibration is performed by the concept of Coulombs law.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.3
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• pp.232-239
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• 2008

The position sensors used in a magnetic bearing system are desirable to provide some degree of fault-tolerance as the rotor position is necessary for the feedback control to overcome the open-loop instability. In this paper, we propose an inductive position sensor that can cope with a partial fault in the sensor. The sensor has multiple poles which can be combined to sense the in-plane motion of the rotor. When a high-frequency voltage signal drives each pole of the sensor, the resulting current in the sensor coil contains information regarding the rotor position. The signal processing circuit of the sensor extracts this position information. In this paper, we used the magnetic circuit model of the sensor that shows the analytical relationship between the sensor output and the rotor motion. The multi-polar structure of the sensor makes it possible to introduce redundancy which can be exploited for fault-tolerant operation. The proposed sensor is applied to a magnetically levitated turbo-molecular vacuum pump. Experimental results validate the fault-tolerance algorithm.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.1
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• pp.48-53
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• 2016

An EMAT can be used to reliably detect defects as it serves as a non-contact transducer with the ability to transmit ultrasonic waves into specimens without couplant. Moreover, an EMAT can easily generate desired waves by altering the design of the coil and magnet. This study proposes an SH-EMAT to evaluate the integrity of the TIG welding part. A stainless steel was welded using the TIG welding method. The welding current was varied to create artificial defects. Both the PA-UT and the RT were applied to verify the defect size. The experimental results generated by using the EMAT were compared with those methods. The amplitude was observed to decrease with an increase in the defect size. These results confirmed that the presence of defects can be reliably detected by attenuation of signal amplitude. The results demonstrated that the proposed method is suitable for evaluating the integrity of TIG welding.