• Journal of Korean Neurosurgical Society
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• v.48 no.2
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• pp.109-114
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• 2010

Objective : To evaluate the clinical outcome of coil embolization for unruptured intracranial aneurysm (UIA) with oculomotor nerve palsy (ONP) compared with surgical clipping. Methods : A total of 19 patients presented with ONP caused by UIAs between Jan 2004 and June 2008. Ten patients underwent coil embolization and nine patients surgical clipping. The following parameters were retrospectively analyzed to evaluate the differences in clinical outcome observed in both coil embolization and surgical clipping : 1) gender, 2) age, 3) location of the aneurysm, 4) duration of the symptom, and 5) degree of ONP. Results : Following treatment, complete symptomatic recovery or partial relief from ONP was observed in 15 patients. Seven of the ten patients were treated by coil embolization, compared to eight of the nine patients treated by surgical clipping (p = 0.582). Patient's gender, age, location of the aneurysm, size of the aneurysm, duration of symptom, and degree of the ONP did not statistically correlate with recovery of symptoms between the two groups. No significant differences were observed in mean improvement time in either group (55 days in coil embolization and 60 days in surgical clipping). Conclusion : This study indicates that no significant differences were observed in the clinical outcome between coil embolization and surgical clipping techniques in the treatment of aneurysms causing ONP. Coil embolization seems to be more feasible and safe treatment modality for the relief and recovery of oculomotor nerve palsy.

• Journal of Biomedical Engineering Research
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• v.29 no.2
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• pp.99-106
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• 2008

To improve $B_1$ homogeneity in high field MRI, the RF power is applied to the transmit array coil elements sequentially in the time-multiplexed way. Since only a single coil element is activated in a time-multiplexing slot, the global standing wave formation in the human body is greatly suppressed. The time-multiplexing slot width is on the order of micro seconds, hence, high-order-harmonic slices can be placed far from the transmit coil and simultaneous multiple slice selection can be avoided. The $B_1$ homogeneities of a birdcage coil and an eight-channel transmit array coil have been compared through finite difference time domain simulations. The simulation results indicate that the proposed technique can reduce the peak-to-peak $B_1$ inhomogeneity down to one fourth of the transmission with a birdcage coil on the central plane of the human head model at 3 T. The mimicking experiments at 3 T, eight separate experiments with a single coil element activated and image reconstruction by combining the eight images, also show promising results. It is expected that the proposed technique has some advantages over other $B_1$ improving methods in real practice since simple RF switching circuitries are only necessary and electromagnetic coupling between the coil elements is out of concern in its realization.

• The Journal of the Korea Contents Association
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• v.18 no.10
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• pp.158-164
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• 2018

The purpose of this study is to statistically analyze the signal intensity pattern according distance from the surface coil center and to maintain optimal signal intensity under clinical circumstances where the surface coil centers are not correctly positioned due to various causes. The cylindrical fluid phantom was placed and moved from the coil center in vertical direction with 1 cm increments. The signal intensities were measured and compared. As a result, the signal intensity showed no significant difference within 4 cm and 1 cm from in T1 weighted images while in T2 weighted images the signal intensity was maintained up to 5 cm and lower 3 cm in the upper and lower direction from the coil center. In conclusion, to maintain the optimal signal intensity the target region should be located within the reference distances proposed in this study.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.3
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• pp.269-275
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• 2005

A flux lock-type SFCL consists of two coils which are wound in parallel each other through an iron core, and a HTSC thin film connects in series with coil 2. The operation of the flux-lock type SFCL can be divided into the subtractive polarity winding and the additive polarity winding operations according to the winding directions between coil 1, coil 2. When a fault occurs, the fault current in the HTS thin film exceeds the critical current so that resistance is generated in the HTS film, and thereby the fault current is limited by an instant rise in the impedance of the flux-lock type SFCL. We investigated he variances of initial fault current limiting instant according to the ratio of inductance of coil 1 and coil 2 in the flux-lock type SFCL. It was confirmed from experiments that the initial fault current limiting instant in the subtractive polarity and additive polarity windings were faster as the ratio of coil 2' inductance for coil 1's inductance increased. The 1st peak of fault current in case of the subtractive polarity winding was higher as the ratio of coil 2's inductance for coil 1's inductance increased. On the other hand, in case of the additive polarity winding, the 1st peak of fault current was lower.

• Journal of the Korean Magnetics Society
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• v.26 no.5
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• pp.154-158
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• 2016

A CRDM (Control Rod Drive Mechanism) is an electromagnetic device which drives a control rod assembly linearly to regulate the reactivity of a nuclear core. An RPIS (Rod Position Indication System) is used as a position indicator for a control rod assembly of a CRDM of SMART, and an RPIS consists of permanent magnets and reed switches. SMART is designed for the maximum coolant temperature of $350^{\circ}C$, and the permanent magnets are installed inside of the reactor. The reed switches and electrical circuit are installed outside of the reactor on the other hand. Test coil for a reed switch is test equipment for quality verification of a reed switch, and a test coil consists of a coil and core. In this study, magnetic property of test coil and permanent magnet on a reed switch is compared by using finite element electromagnetic simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.277-281
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• 2007

We investigated fault current limitation characteristics of the resistive superconducting fault current limiter (SFCL) which consisted of a Bi-2212 bulk coil and a shunt coil. The Bi-2212 bulk coil and the shunt coil were connected in parallel. The Bi-2212 bulk coil was placed inside the shunt coil to induce field-assisted quench. The fault test was conducted at an input voltage of $200V_{rms}$ and fault current of $12kA_{rms}\;and\;25kA_{rms}$. The fault conditions were asymmetric and symmetric, and the fault period was 5 cycles. The test results show that the SFCL successfully limited the fault current of $12kA_{rms}\;and\;25kA_{rms}$ to below $5.5{\sim}6.9kA_{peak}\;within\;0.64{\sim}2.17$ msec after the fault occurred. Limitation was faster under symmetric fault test condition due to the larger change rate of current. We concluded that the speed of fault current limitation was determined by the speed of current rise rather than the amplitude of a short circuit current. These results show that the Bi-2212 bulk coil is suitable for distribution-class SFCLS.

• Journal of Biomedical Engineering Research
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• v.16 no.4
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• pp.481-491
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• 1995

Endovaginal and endorectal receiver only surface coils were designed for MR imaging (MRI) and $^1H$ MR spectroscopy (MRS) for the uterine cervix and the prostate. The shape of endovaginal coil wire was rectangular with round corner. Size of the coil wire was empirically determined for 7cm and 4cm along the long and short axis, respectively. The coil wire loop was supported by acryl handle and bent about $150^{\circ}$ at one side of the loop considering the average angle of the cervix to the vagina. We called this as a "spoon-type endovaginal coil". The wire of the endorectal coil was made of the flexible materials so that the wire loop became long elliptic shape by pushing the acryl handle into the plastic tube for the comfort of patients when the coil was inserted into the cervix. Then, the shape was maintained to be circle by popping out handle. Conventional spin echo (SE) and fast spin echo (FSE) sequences were used as 71 and 72 weighted imaging sequences, respectively. Matrix size was 128~$256{\times}256$. FOVs for surface coil and body coil were 14cm and 24cm, respectively. 3D volume localized in vivo $^1H$ MR spectroscopy of the human cervix and prostate was performed using PRESS or STEAM localization method with the following parameters . TR=3 sec, TE=135 msec for PRESS or 30 msec for STEAM, NEX=2, NS=48, Sl=2048, and SW=2500 Hz. Using home-built endovaginal and endorectal coils, excellent T1- and T2-images were obtained to visualize early cervical and prostate tumors. 3D volume localized in vivo IH MRS was useful to differentiate the cancerous tissue from the normal tissue.

• Journal of Sensor Science and Technology
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• v.22 no.5
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• pp.333-337
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• 2013

This study proposes a simply fabricated micro stator for higher output power than previously reported micro stators. The stator has been fabricated by inserting enamel coil in silicon mold formed by micro etching process. The most merits of the proposed micro stator are the simple fabrication process and high output power. Previously reported micro stators have high resistance because the micro coil is fabricated by relatively thin-film-based deposition process such as sputtering and electroplating. In addition, the previously reported micro coil has many electrical contact points for forming the coil structure. These characteristics of the micro stator can lead to low performance in output power. However, the proposed micro stator adopts commercially available enamel coil without any contact point. Therefore, the enamel coil of the proposed micro stator has low junction resistance due to the good electrical quality compared with the deposited or electroplated metal coil. Power generation tests were performed and the fabricated stator can produce 5.4 mW in 4000 RPM, $1{\Omega}$ and 0.3 mm gap. The proposed micro stator can produce larger output power than the previously reported stator spite of low RPM and the larger gap between the permanent magnet and the stator.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.61-69
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• 2021

This paper presents the analysis and experiment results on the electrical and thermal characteristics of metal insulation (MI) REBCO racetrack coil, which was wound with stainless steel (SS) tape between turn-to-turn layers, under rotating magnetic field and conduction cooling system. Although the field windings of superconducting rotating machine are designed to operate on a direct current, they may be subjected to external magnetic field due to the unsynchronized armature windings during electrical or mechanical load fluctuations. The field windings show the voltage and magnetic field fluctuations and the critical current reduction when they are exposed to an external magnetic field. Moreover, the cryogenic cooling conditions are also identified as the factors that affect the electrical and thermal characteristics of the HTS coil because the characteristic resistance changes according to the cryogenic cooling conditions. Therefore, it is necessary to investigate the effect of external magnetic field on the electrical and thermal characteristics of MI-SS racetrack coil for further development reliable HTS field windings of superconducting rotating machine. First, the major components of the experiment test (i.e., HTS racetrack coil construction, armature winding of 75 kW class induction motor, and conduction cooling system) were fabricated and assembled. Then, the MI racetrack coil was performed under liquid nitrogen bath and conduction cooling conditions to estimate the key parameters (i.e., critical current, time constant, and characteristic resistance) for the test coil in the steady state operation. Further, the test coil was charged to the target value under conduction cooling of 35 K then exposed to the rotating magnetic field, which was generated by three phrase armature windings of 75 kW class induction motor, to investigate the electrical and thermal characteristics during the transient state.

• Transactions of Materials Processing
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• v.28 no.3
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• pp.135-144
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• 2019

Electromagnetic impulse welding (EMIW) is a type of solid state welding using the Lorentz force generated by interaction between the magnetic field of the coil and the current induced in the workpiece. Although many experimental studies have been investigated on the expansion and compression welding of tube using the EMIW process, studies on the EMIW process of lap joint between flat sheets are uncommon. Since the magnetic field enveloped inside the tube can be controlled with ease, the electromagnetic technique has been widely used for tube welding. Conversely, it is difficult to control the magnetic field in the flat sheet welding so as to obtain the required welding velocity. The current study analyzed the effects of coil shape on the impulse velocity for suitable flat one-turn coil for the EMIW of the flat sheets. The finite element (FE) multi-physics simulation involving magnetic and structural field of EMIW were conducted with the commercial software LS-DYNA to evaluate the several shape variables, viz., influence of various widths, thicknesses, gaps and standoff distances of the flat one-turn coil on the impulse velocity. To obtain maximum impulse velocity, the flat one-turn coil was designed based on the FE simulation results. The experiments were performed using an aluminum alloy 1050 sheets of 1.0mm thickness using the designed flat one-turn coil. Through the microscopic interfacial analysis of the welded specimens, the interfacial connectivity was observed to have no defects. In addition, the single lap joint tests were performed to evaluate the welding strength, and a fracture occurred in the base material. As a result, a flat one-turn coil was successfully designed to guarantee welding with bond strength equal to or greater than the base material strength.