• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.314-317
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• 1991

The waveforms of high voltage and current pulse were measured using laser measuring systems. Existing potential transformer and current transformer have low measuring precision because of resonance phenomena and waveform distortion due to the magnetic saturation. But using laser measurement, it is possible to obtain clear waveforms which have no effect of distortion and harmonic resonances. And electromagnetic interferences (EMI) in the measuring of high voltage and current pulse, but the optical measuring systems are not subjet to the influence of EMI. Using laser measuring systems based upon Pockels effect and Faraday effect is not free from any errors yet, but it could replace existing measuring systems by routine experiments and error corrections. And it needs that more research and development of optical crystals and equipments would be taken.

• Journal of radiological science and technology
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• v.28 no.1
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• pp.25-32
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• 2005

Purpose : To evaluate the degree of the artifact which is caused by the mascara and the eye shadow when acquiring MR images and compare the difference of the image distortion according to the change of various pulse sequence. Material and Method : The popular domestic mascara and eye shadow products were selected from three different companies respectively and divided into two groups mascara (M1, M2, M3 ), eye shadow (E1, E2, E3). Self-designed quadrature type saddle coil which has 4 cm inside diameter, 8 cm length and which is for both Tx and Rx was used. MR image was acquired respectively after applying the mascara to the tape from study 1, the eye shadow to the tape from study 2 and adding the eye shadow to the mascara from study 3. The FSE(fast spin echo), the SE(spin echo), the GE(gradient echo) were used as pulse sequences. The degree of the image distortion which was measured from each sequence was analyzed in quality and quantity. Result : The mascara and the eye shadow caused the artifacts to the MR images partially and induced the image distortion. There was a little difference in terms of the degree of artifact according to the change of pulse sequence. From the study 3 in which the eye shadow was applied to the mascara, on the axial plane image, the width of artifact was 16.73 mm in the GE pulse sequence, 6.64 mm in the SE pulse sequence, and 6.19 mm in the FSE pulse sequence. The degree of the artifact appeared highly in order of the GE, the SE and the FSE. On the sagittal plane image, the length of artifact was 22.84 mm in the GE, 17.81 mm in the SE and it appeared highly with the SE and the FSE technique order. Conclusion : When examining the eyeball and the brain of a woman with the mascara and the eye shadow, we have to consider that the artifact caused by them can have an effect on the image diagnosis. We concluded that it is more suitable for a brain and a eyeball T2 emphasizing image to use the FSE technique than the GE technique.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.307-312
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• 1994

In this investigation the PFM(Pulse Frequency Modulation} will be used for optimizing PWM inverter pulse pattern. In traditional the pulse frequency of PWM is kept const. But modulated PWM's frequency in this study, the sinusoidal inverter's performance should be improved. The PWM pulsepatterns are definitely controlled so that the time-integral function of the voltage vectors in the space vector notation may show a circular locus. Further, performance index will be minimized because of minimizing distortion of output current. Finally, we will implement itusingsingle-chip microprocessor.

• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.235-242
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• 2008

In this paper, a 24-pulse AC-DC converter is designed, modeled, simulated, and developed to feed non-isolated varying loads. The proposed AC-DC converter configuration consists of an auto-transformer based on zigzag connection to overcome current harmonic problems in AC mains. It improves power quality at AC mains and it meets IEEE-519 standard requirements at varying loads. A set of power quality indices on input AC mains and on DC buses for a load fed from 6-pulse and 12-pulse AC-DC converters is also given to compare their performance. It is observed that input current total harmonic distortion(THD) of less than 8% is possible with the proposed topology of AC-DC converter at varying loads.

• Journal of information and communication convergence engineering
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• v.1 no.4
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• pp.228-232
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• 2003

The previous design work for very large final amplifier pumped by electron beam module was described from the point of view of energy characteristics. In this work, the design problems for phase front distortion, ASE, and gain control in large aperture amplifier are presented in detail.

• Journal of the Optical Society of Korea
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• v.1 no.1
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• pp.41-43
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• 1997

We report the operation of a self-adaptive vector phase conjugate laser (VPCL) oscillator which compensates intracavity polarization distortion and wavefront aberration simultaneously. The VPCL in Nd:YAG gain media produce an output with energy of 125mJ in a 20ns single-longitudinal-mode pulse at 10Hz, which is unaffected by intracavity polarization distortion.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1995.10a
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• pp.80-84
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• 1995

ABSTRACT - This paper presents a software based 3 phase 5 level pulse-width modulation(PWM) inverter to reduce total harmonic distortion. The proposed modulation technique can reduce total harmonic distortion and significantly improve the performance of the inverter. In the modulation mode where the frequency ratio is 36 and modulation index is 1.2∼2.0, harmonic components have been mostly eliminated and the magnitude of fundamental component have been maximized by the 3 phase 5 level PWM inverter.

• Journal of Power Electronics
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• v.19 no.3
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• pp.702-713
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• 2019

Multilevel Inverters (MLIs) are widely used in medium voltage applications due to their various advantages. In addition, there are numerous types of MLIs for such applications. However, the diode-less 3-level (3L) T-type Neutral Point Clamped (NPC) MLI is the most advantageous due to its low conduction losses and high potential efficiency. The power circuit of a 3L T-type NPC is derived by the conventional two level inverter by a slight modification. In order to explore the MLI performance for various Pulse Width Modulation (PWM) schemes, this paper examines the operation of a 3L (five level line to line) T-type NPC MLI for various types of Multi-Carriers Pulse Width Modulation (MCPWM) schemes. These PWM schemes are compared in terms of their voltage profile, total harmonic distortion (THD) and conduction losses. In addition, a 3L T-type NPC MLI is also compared with the conventional NPC in terms of number of switches, clamping diodes, main diodes and capacitors. Moreover, the capacitor-balancing problem is also investigated using the Neutral Point Fluctuation (NPF) method with all of the MCPWM schemes. A 1kW 3L T-type NPC MLI is simulated in MATLAB/Simulink and implemented experimentally and its performance is tested with a 1HP induction motor. The results indicate that the 3L T-type NPC MLI has better performance than conventional NPC MLIs.

• Investigative Magnetic Resonance Imaging
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• v.4 no.1
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• pp.7-13
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• 2000

Purpose : To assess the distortion of MRI with the Leksell stereotactic radiosurgery system in variable pulse sequence and imaging plane through phantom study, to find most adequate imaging plane and pulse sequence for stereotactic radiosurgery system. Materials and methods : We made the phantoms for MRI and get images in variable conditions and analyzed the image distortion using image analysis program, and statistically using paired student t-test. Results : The transeverse plane images had acceptable error ranges bless than 1.5mm) in all pulse sequence in both the analysis of fiducial marker in stereotactic G-frame and the phantom study. The coronal plane images had unacceptable large errors (more than 1.7mm) in the analysis of fiducial marker in the stereotactic G-frame, but had corrected small errors (less than 1.5mm) in the phantom study. Conclusion : We find from the phantom study that the present MR machines are adequate for stereotactic surgery system in frequently used pulse sequences, and imaging planes.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4350-4356
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• 2023

Radiation detection systems working at high count rates suffer from the overlapping of their output electric pulses, known as pulse pile-up phenomenon, resulting in spectrum distortion and degradation of the energy resolution. Pulse tail extrapolation is a pile-up correction method which tries to restore the shifted baseline of a piled-up pulse by extrapolating the overlapped part of its preceding pulse. This needs a mathematical model which is almost always nonlinear, fitted usually by a nonlinear least squares (NLS) technique. NLS is an iterative, potentially time-consuming method. The main idea of the present study is to replace the NLS technique by an integration-based non-iterative method (NIM) for pulse tail extrapolation by an exponential model. The idea of linear extrapolation, as another non-iterative method, is also investigated. Analysis of experimental data of a NaI(Tl) radiation detector shows that the proposed non-iterative method is able to provide a corrected spectrum quite similar with the NLS method, with a dramatically reduced computation time and complexity of the algorithm. The linear extrapolation approach suffers from a poor energy resolution and throughput rate in comparison with NIM and NLS techniques, but provides the shortest computation time.