• Carbon letters
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• v.15 no.3
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• pp.180-186
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• 2014

This study highlights a novel method and mechanism for the rapid and effective milling of carbon fibers (CFs) in silicon carbide (SiC) powder, and also the dispersion of CFs in SiC powder. The composite powders were prepared by chopping and exfoliation of CFs, and ball milling of CFs and SiC powder in isopropyl alcohol. A wide range of CFs loading, from 10 to 50 vol%, was studied. The milling of CFs and SiC powder was checked by measuring the average particle size of the composite powders. The dispersivity of CFs in SiC powder was checked through scanning electron microscope. The results show that the usage of exfoliated CF tows resulted in a rapid and effective milling of CFs and SiC powder. The results further show an excellent dispersion of CFs in SiC powder for all CFs loading without any dispersing agent.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.848-851
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• 2012

In this paper, circuit of reducing the offset voltage in Op-amp, effectively, is newly proposed by using dual capacitor. Capacitors and MOS switches are added in proposed circuit to make up for the weak points of previous circuits ofr reducing the offset voltage in auto-zeroing method. Also, it is designed to reduce the offset voltage in high frequency range by using chopping method, effectively. Circuit simulation and layout are executed by TSMC 1.8V, 0.18um process. From the simulation results, it is verified that magnitude of offset voltage is under 5mV and proposed circuit is good for compensation of offset voltage better than previous auto-zeroing method.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.23-31
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• 1994

The compartmentation model is represented by the characteristics and geometric information of the spaces defined by the structural members which are used for the boundary planes of the compartment. For the efficient compartment modeling a program performing the compartmentation design by the chopping and merging method was presented by authors. In this research, the development of an interactive ship compartmentation modeller is introduced. It is natural that the value of the program lessens if the input process is complicated and uneasy, even though the internal techniques for the compartmentation modeling are superior. In this paper, a method for the convenient input is proposed and implemented with the help of a graphical user interface technique. The modeling method introduced in this paper performs an efficient compartmentation modeling fast and conveniently by the solid modeling concept and the graphical user interface.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.525-528
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• 2000

This paper presents a circuit analysis and cotnrol example of favored configuration 6/4 SRM. SRM modeling and analysis are necessary for experiment. Thus this paper proposes a SRM modeling with PI controller (of driving converter) input voltage chopping and inductance profile when rotor position transformed. Through this simulation the designer can predict operating states of systems over a broad range of operating conditions.

• Proceedings of the KIPE Conference
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• 2009.11a
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• pp.188-190
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• 2009

본 연구에서는 독립운전 검출기법의 능동적 기법 중 AFDPF 기법을 IEEE Std 929-2000에 제시된 독립운전 시험 조건하에서 위상동기기법 영점검출방식(Zero Crossing PLL)을 적용하여 독립운전 시 chopping fraction에 따른 PCC(Point of Common Coupling)의 주파수 변동 특성을 PSIM을 통하여 분석하였다

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.9
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• pp.456-465
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• 2001

In this paper, breakdown voltages in $SF_6-N_2$ mixtures were experimentally investigated to understand characteristics of dielectric strength and physical phenomena in nonuniform field disturbed by a needle shape protrusion. The test voltages are the lightning impulse$(\pm1.2/44 \mus)$ and the damped oscillatory impulse$(\pm400 ns / 0.83 MHz)$ voltages which can be occurred by the operation of disconnecting switches in gas-insulated switchgears(GIS). The effects of the polarity and wave shape of the test voltages, and the gas pressure on the V-t characteristics were in detail examined. The V-t characteristic curves were measured in different two ways : (1) one is the method by taking the maximum voltage recorded at or prior to breakdown against the time to breakdown, that is, the Procedures recommended in IEC 60060-1, (2) the other is the method by taking the voltage at the instant of chopping against the time to breakdown. As a result, the V-t characteristics of $SF_6-N_2$ mixtures in nonuniform electric field were significantly affected by the polarity and wave shape of the applied voltages. The positive breakdown voltages resulted in lower breakdown voltages in the time ranges considered, and the V-t curves for the negative oscillatory impulse voltage were extended over the longer time range. For the lightning impulse voltages, the V-t curves obtained by IEC Pub. 60060-1 were nearly same with the V-t curves obtained by the voltage at the instant of chopping against the time to breakdown. It is clear that the actual breakdown voltages were much lower than the maximum voltages appearing at or prior to breakdown because of the displacement current produced as a result of the dV/dt during the oscillatory transient voltage app1ication. The scattering of the negative actual breakdown voltages was much larger than that of the positive.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.2
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• pp.109-116
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• 2016

Sensing module of standing and moving human body using shutter method was developed. The module consists of Fresnel lens, pyroelectric infrared (PIR) sensor, interface circuit of the PIR, micro control unit(MCU), and alarm light emitting diode(LED). The principle for standing human body is chopping the thermal of human body using camera shutter. The human sensing signal in MCU by algorithm of interrupt function is detected. By unifying an apparatus and print circuit board(PCB), the developed module can be replaced as commercial moving human body detector. Experiment results show that sensing distance is about 7.0m and sensing angles is about $110^{\circ}$ at room temperature. In these condition, sending ratio was 100% and the power dissipation of the module was 100mW.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.9
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• pp.97-104
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• 1999

Brake squeal noise has been a problem since the early days of motoring . It is important to obtain vibration mode shape for reduction of brake noise . Stroboscopic Electronic Speckle Pattern Interferometry is a very powerful measuring method for study of vibrating objects in static state compared with conventional methods because this method can give both resonance frequency and quantitative visualization of vibration mode shape at the same time. In this paper, we performed qualitative visualization and quantitative analysis of vibration mode shpae of disk brake by using stroboscopic ESPI and phase shifting method. The stroboscopic wavefronts are obtained by chopping continuous wave laser beam using acousto-optic modulator .Experiments were performed at the same constraint conditions as disk brake of the practical vehicle as far as possible. The experimental results of this paper show quantitative measurement of vibration mode shape and quantiative visualization of vibration amplitude of disk brake with 3D plotting.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.611_612
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• 2009

This paper deals with dynamic analysis of linear switched reluctance motor considering electromagnetic characteristics. First, inductance profile of linear switched reluctance motor calculate at align and unalign position and phase resistance using analytical method. Analytical method of this paper used space harmonics method, also, analysis result compares with data that is derived through an finite element method, and proved validity. In dynamic simulation of linear switched reluctance, we analyzed dynamic characteristic of linear switched reluctance motor according to single pulse waveform and hard chopping voltage PWM.

• Journal of Industrial Technology
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• v.24 no.A
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• pp.91-97
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• 2004

This paper describes the design of a 2-phase stepping motor driver using CPLD(Complex Programmable Logic Device). The driver IC such as L297(SGS-Thomson Microelectronics), which is mostly used has some difficulties in PWM control because of the switching noise of power MOSFETs. It causes current ripple and acoustic noise. To improve theses characteristics, we proposed a new current control method that the output PWM frequency is almost constant using a digital filter. Also we proposed constant current method for 1-2 phase(half step) excitation. The proposed method is implemented with CPLD(Xilinx, XC9572-PC44). Experimental results show the effectiveness of the proposed method.