• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.215-217
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• 2001

This paper describes an all solid-state switch pulse generator for various applications where square pulse voltage is required. The pulse generator produces various voltage pulses: voltage $5{\sim}100kV$. current $10{\sim}200A$, pulse width $1{\sim}10{\mu}sec$, repetition rate up to 500Hz. The output power is the combination of these parameters up to 10kW. It consists of a DC-DC converter and several pulse generating modules which are connected in series to obtain higher pulse voltage. Each module contains semiconductor switches (IGBT's), energy storage capacitors and control units to trigger switches. The structure and operational principle are described and the protection circuit for reliable operation is suggested. Experimental results show that the pulse generator can be used for applications with nonlinear loads.

• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1378-1389
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• 2005

This work provides the fundamental knowledge of energy transport characteristics during very short-pulse laser heating of semiconductors from a microscopic viewpoint. Based on the self-consistent hydrodynamic equations, in-situ interactions between carriers, optical phonons, and acoustic phonons are simulated to figure out energy transport mechanism during ultrafast pulse laser heating of a silicon substrate through the detailed information on the time and spatial evolutions of each temperature for carriers, longitudinal optical (LO) phonons, acoustic phonons. It is found that nonequilibrium between LO phonons and acoustic phonons should be considered for ultrafast pulse laser heating problem, two-peak structures become apparently present for the subpicosecond pulses because of the Auger heating. A substantial increase in carrier temperature is observed for lasers with a few picosecond pulse duration, whereas the temperature rise of acoustic and phonon temperatures is relatively small with decreasing laser pulse widths. A slight lagging behavior is observed due to the differences in relaxation times and heat capacities between two different phonons. Moreover, the laser fluence has a significant effect on the decaying rate of the Auger recombination.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.74-77
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• 2000

A pulsed Nd:YAG laser has been used in a wide variety of fields : measuring, material processing and so on. In a material processing, it is very important to control the laser energy density. A pulse repetition rate and a pulse width are regarded as the most dominant factors to control the energy density of laser beam. In this study, pulsed Nd:YAG laser system was designed and manufactured to control the laser output usefully and easily. This system adopted the sequential charge and discharge circuit is controlled by 80196 micro- processor. As a result, it is found that laser output is controlled minutely by changing laser input and pulse repetition rate, and usefully by using 80196 microprocessor.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.419-426
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• 2008

As pulse detonation engine(PDE) does not need compression mechanisms such as compressors because self-sustained detonation waves are able to compress propellant gases by their incident shock waves, the PDE can have a simple straight-tube structure. In this study, we propose an autonomous driving valve system of the PDE, which fill premixed gases into the PDE tubes at high frequency with high mass flow rate. The proposed valve is composed of only three parts: a piston, a cylinder, and a spring. This valve system can produce intermittent flow at high mass flow rate, and also can keep stable reciprocal motion by using the propellant-gas enthalpy. When the cylinder content product is assumed to be constant, experimental results of the mass flow rate were approximately equal to the calculation model. We confirmed the autonomous driving valve performance by experiments, and concluded that this extremely simple valve with no electrical power and controller can be used as the PDE propellant supply system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.898-906
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• 2002

In this paper, we investigated the improvement degree of transmission distance of the various initial frequency chirped optical pulse with 5 dBm initial power dependence on the various bit rate and fiber dispersion coefficient, when MSSI(Mid-Span Spectral Inversion) with the optimal pump power condition is adopted for the compensation method for optical pulse distortion. And we analyzed the influence of mutual relation of optical pulse frequency chirp and Kerr effect on the MSSI methods for the long-haul optical transmission through the computer simulation. We found that the compensation degree of distorted optical pulse varies as a consequence of the variation of combined phase modulation of self phase modulation(Kerr effect) and initial frequency chirp parameter dependence on the fiber dispersion coefficient. And we found that, if the transmission bit rate is increased k times, the dispersion coefficient value of dispersion shift fiber is decreased $2^k$ times so as to be almost the same performance of the transmission system with k times lower bit rate.

• Journal of Biomedical Engineering Research
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• v.34 no.3
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• pp.105-110
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• 2013

Respiratory signal is one of the important physiological information indicating the status and function of the body. Recent studies have provided the possibility of being able to estimate the respiratory signal by using a change of PWV(pulse width variability), PRV(pulse rate variability) and PAV(pulse amplitude variability) in the PPG (photoplethysmography) signal during daily life. But, it is not clear whether the respiratory monitoring is possible even during sleep. Therefore, in this paper, we estimated the respiration from PWV, PRV and PAV of PPG signals during sleep. In addition, respiration rates of the estimated respiration signal were calculated through a time-frequency analysis, and errors between respiration rates calculated from each parameter and from reference signal were evaluated in terms of 1 sec, 10 sec and 1 min. As a result, it showed the errors in PWV(1s: $36.38{\pm}37.69$ mHz, 10s: $36.53{\pm}38.16$ mHz, 60s: $30.35{\pm}38.72$ mHz), in PRV(1s: $1.45{\pm}1.38$ mHz, 10s: $1.44{\pm}1.37$ mHz, 60s: $0.45{\pm}0.56$ mHz), and in PAV(1s: $1.05{\pm}0.81$ mHz, 10s: $1.05{\pm}0.79$ mHz, 60s: $0.56{\pm}0.93$ mHz). The errors in PRV and PAV are lower than that of PWV. Finally, we concluded that PRV and PAV are more effective than PWV in monitoring the respiration in daily life as well as during sleep.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1072-1074
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• 1999

In this study, it is the purpose to develope a cheap and compact pulsed $CO_2$ laser with pulse repetition rate range of 1 kHz. We used a IGBT switched power supply as a power supply, which is cheap and simple comparing to others. PIC one-chip microprocessor was used for precise control of a laser power supply on the control part. And the laser cavity was fabricated as an axial and water cooled type. The laser performance characteristics as various parameters, such as pulse repetition rate gas pressure, and gas mixture rate have been investigated. The experiment was done under the condition of total pressure of $CO_2:N_2$:He = 1.3:10, 1:1.5:5 1:9:15 from 6 Torr to 15 Torr and pulse repetition rate from 100 Hz to 900 Hz. As a result, the maximum average output was about 20.5 W at the total pressure of 15 Torr, the gas mixture $CO_2:N_2$:He = 1:9:15 and the pulse repetition rate of 700 Hz.

• Women's Health Nursing
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• v.6 no.4
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• pp.579-593
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• 2000

The purpose of this study was to examine the effects of foot massage on anxiety response in preoperative patients undergoing total hysterectomy. Among the fifty patients, twenty-five were the experimental group receiving foot massage for 10-minutes and twenty-five were the control group. Subjects were admitted to a hospital in Inchon city for total hysterectomy. This study was carried out from July 10th, to September 18th, 2000. The levels of anxiety were measured by the Visual Aanalogue Scale(VAS). State Anxiety Scale, blood pressure, pulse rate and respiration rate. Data were analyzed using $x^2$-test, t-test, paired t-test, unpaired t-test and ANCOVA with SPSS/pc program. The results were summarized as followings: 1. After foot massage, VAS anxiety level, state anxiety level, systolic blood pressure, pulse rate and respiration rate of the experimental group were decreased significantly than those measurements before the foot massage. 2. After foot massage, significant differences in the VAS anxiety level, state anxiety level, systolic blood pressure, pulse and respiration rate between the experimental and control groups were found. In conclusion, foot massage for 10 minutes is a useful nursing intervention that decreases anxiety in preoperative patients undergoing total hysterectomy.

• Laser Solutions
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• v.16 no.2
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• pp.1-6
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• 2013

Picosecond lasers are a very effective tool for micromachining metals, especially when high accuracy, high surface roughness and no heat affected zone are required. However, low productivity has been a limit to broadening the spectrum of their industrial applications. Recently it was reported that in the micromachining of copper with a 1064nm picosecond laser, there exist the optimal pulse energy and repetition rate to achieve the maximum volume ablation rate. In this paper, we used a 515nm picosecond laser, which is more efficient for micromachining copper in terms of laser energy absorption, to obtain its optimal pulse energy and repetition rate. Theoretical analysis based on the experimental data on copper ablation showed that using a 515nm picosecond laser instead of a 1064nm picosecond laser is more favorable in that the calculated threshold fluence is 75% lower and optical penetration depth is 50% deeper.

• Journal of the Semiconductor & Display Technology
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• v.6 no.1 s.18
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• pp.11-15
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• 2007

Low-k wafer engraving process has been investigated by using UV pico-second laser with high repetition rate. Wavelength and repetition rate of laser used in this study are 355 nm and 80 MHz, respectively. Main parameters of low-k wafer engraving processes are laser power, work speed, assist gas flow, and protective coating to eliminate debris. Results show that engraving qualities of low-k layer by using a laser with UV pico-second pulse width and high repetition rate had better kerf edge and higher work speed, compared to one by conventional laser with nano-second pulse width and low repletion rate in the range of kHz. Assist gas and protective coating to eliminate debris gave effects on the quality of engraving edge. Total engraving width and depth are obtained less than $20\;{\mu}m$ and $10\;{\mu}m$ at more than 500 mm/sec work speed, respectively. We believe that engraving method by using UV pico-second laser with high repetition rate is useful one to give high work speed in laser material process.