• Journal of Welding and Joining
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• 제11권1호
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• pp.52-61
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• 1993

Laser welding of ASTM no. 1060 Al plate with a pulsed Nd: YAG laser of 200W average power was performed for end capping of KMRR nuclear fuel elements In this research, we performed basic welding experiments. Firstly, laser output parameters which affect laser welding parameters were studied by changing laser input parameters for effective welding of 1060 Al plates. We found that laser power density and pulse energy are important parameters for smooth bead shape. Secondly, welding parameters which affect weld width-to-depth ratio were studied by changing power density and pulse energy, shielding gas, and defocusing. We found that power density must be higher than 0.3 Mw/cm$^{2}$ pulse energy must be higer than 3 J. travel speed must not exceed 200mm/sec, laser focus must be existed beneath 2-3mm from plate surface and helium is proper shielding gas. Thirdly, we studied the weld defects of Al-1060 such as crack and porosity in lap-joint welding. We designed new welding geometry for crack free welding of Al-1060 plates, and obtained crack free weldment but with lack of fusion. However, with Ti, Zr grain refiner elements, we can weld Al plates without solidification hot crack. Finally, we studied the origin of porosity by changing shielding gas. And we found that porosity was resulted from entrapment of shielding gas by the collapsing keyhole.

• Journal of Power Electronics
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• 제2권2호
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• pp.112-123
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• 2002

This paper presents a novel prototype of the utility AC power interfaced soft-switching sinewave pulse modulated inverter using the high-frequency flyback for the small scale distributed renewable energy power conditioner. The proposed cricuit with a high-frequency isolation link has a funtion of electrical isolation, which is more cost-effective and reliable for the small-scale distributed renwal energy utilization system from a safety point of riew. The discontinuous conduction mode(DCM) operation of the high-frequency flyback transformer is adopted to establish a simple and low-cost circuit configuration and control scheme. For the simplicity, the circuit operating principle is described on the basis of the modified conventional full bridge inverter, whitch is the typical conventional high-frequency full-bridge inverter employing the high requency flyback transformer to eanble the effictive function of the electrical isolation. Than, the new circuit topology of the unility-interfaced soft-switching sinewave pulse modulated inverter using IGBTs is proposed. The proposed cricuit topology is additionally composed of the auxiliary power regenerating snubber cricuits, which are also mathematically analyzed for the parameter desigen settings. Finally, the performance of the propose inverter is evaluated on the basis of computer-aid simulation. It is noted that the sinewave pulse modulated output current of the inverter is synchronous to the AC main voltage.

• 전력전자학회논문지
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• 제6권5호
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• pp.377-385
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• 2001

물을 전기분해하여 얻은 일정 부피비를 갖는 수소와 산소 혼합가스를 수산화가스로 명명하며, 이를 역반응시켜서 열 에너지원으로 사용하고 있다. 수산화가스는 경제성, 안전성 및 환경친화적인 고유한 특성을 지니고 있어서 현재 가스용접기에 적용하고 있으며 여러 가지 응용분야에 적용할 수 있도록 연구 중에 있다. 본 논문에서는 수산화가스의 특성에 관하여 고찰하고 발생기용 전원에 대하여 소개하고 이 중에서 아직까지 적용되지 않은 펄스전원을 적용하여 여러 가지 운전주파수에서 비교분석 하였다.

• 한국광학회지
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• 제20권1호
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• pp.34-40
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• 2009

$MgF_2$, $SiO_2$ 및 ZnS 박막을 물리 증기 증착하는 동안 펄스 레이저(Nd-YAG, 제2고조파 532 nm)로 Annealing 하여 표면 거칠기 특성을 개선하였다. 펄스 반복율이 10 Hz, 펄스폭 5 ns, 파장 532 nm인 펄스레이저로 Annealing한 유리 기판에 증착된 $MgF_2$와 $SiO_2$ 시료들은 레이저 에너지가 $140\;mJ/cm^2$ 경우에 산란 총량 값이 최소가 되었지만, ZnS 박막의 경우에는 Annealing 레이저광 에너지가 $62\;mJ/cm^2$일 때 산란 총량이 최소값을 나타냈다. AFM을 사용하여 박막시료의 표면 거칠기에 대한 펄스 레이저 Annealing 효과를 측정 하였다. 그 결과는 TIS 측정치와 유사 하여 표면 거칠기는 Annealing 하기위해 조사된 레이저 에너지에 의존 하여 감소하였다.

• 한국정보통신학회논문지
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• 제13권6호
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• pp.1141-1149
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• 2009

Pulse 펄스형 Nd:YAG 레이저는 피부재생치료에 적합하고, 램프에 의해서 연속발진은 물론 정상발진, Q-스위치 및 모드동기 발진까지 다양한 발전 형태가 가능하며 미세수술 및 피부재생 촉진에 널리 사용되어지고 있다. 치료목적에 따라 에너지 밀도를 제어하는 것이 매우 중요하다. 에너지 밀도의 제어는 레이저 출력의 펄스반복률을 제어하는 방법이 주로 사용된다. 본 연구에서는 펄스형 Nd:YAG 레이저의 펄스반복률을 제어할 수 있는 제 2고조파 발생(second harmonic generation: SHG)로 각주파수인 광파의 에너지 일부가 비선형 결정안을 전파하면서 각주파수인 광파의 에너지로 변환되는 현상을 적용하여 2차 비선형성에 의한 제2고조파 발생을 통해 피부심부까지 치료 가능하다는 것은 간단히 관찰할 수 있었다.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.53-59
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• 2009

A chirped-pulse amplification Ti:sapphire laser system has been designed using a 10-Hz 100-TW Ti:sapphire laser to generate 0.1-Hz 0.5-PW laser pulses and optimize their temporal qualities such as temporal contrast and pulse duration. A high-energy booster amplifier to be added is expected to produce an energy above 30 J through the parasitic lasing suppression and the efficient amplification. To improve the temporal contrast of the laser pulses, a high-contrast 1-kHz amplifier system is used as a front-end. A grating stretcher which makes the laser pulse have 1-ns duration is used to prevent optical damages due to high pulse energy during amplification. A grating compressor has been designed with group delay analysis to obtain the recompressed pulse duration close to the transform-limited pulse duration. The final laser pulses are expected to have energy above 20 J and duration below 40 fs.

• KEPCO Journal on Electric Power and Energy
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• 제1권1호
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• pp.33-38
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• 2015

시간대별 효율적인 전력 운영과 전력품질 향상을 위해 ESS (Energy Storage System)의 보급이 세계적으로 활발하게 이루어지고 있다. 이러한 ESS용 전원소자로 리튬이차전지의 채용이 급격히 늘어남에 따라, 리튬이차전지의 수명 및 출력 열화 거동을 측정 및 예측하는 기술이 시급히 요구되고 있다. 특히, ESS 운영에 있어 핵심 특성인 리튬이차 전지 출력은 측정이 어려울 뿐만 아니라, 정확한 측정을 위해서는 많은 시간이 소요되는 문제점이 있다. 따라서, 본 연구에서는 ESS용 리튬이차전지 단전지를 전산 모델링 한 후, 펄스 측정법을 적용하여 충전상태에 따른 방전 및 충전시의 직류저항(DC-IR)과 출력을 예측한다. 또한, 두 가지 펄스 측정법인 HPPC (Hybrid Pulse Power Characteristics)와 J-Pulse (JEVS D 713, Japan Electric Vehicle Association Standards)의 결과를 비교 분석한다.

• Journal of Periodontal and Implant Science
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• 제41권5호
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• pp.234-241
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• 2011

Purpose: One of the most frequent complications related to dental implants is peri-implantitis, and the characteristics of implant surfaces are closely related to the progression and resolution of inflammation. Therefore, a technical modality that can effectively detoxify the implant surface without modification to the surface is needed. The purpose of this study was to evaluate the effect of erbium-doped: yttrium, aluminium and garnet (Er:YAG) laser irradiation on the microstructural changes in double acid-etched implant surfaces according to the laser energy and the application duration. Methods: The implant surface was irradiated using an Er:YAG laser with different application energy levels (100 mJ/pulse, 140 mJ/pulse, and 180 mJ/pulse) and time periods (1 minute, 1.5 minutes, and 2 minutes). We then examined the change in surface roughness value and microstructure. Results: In a scanning electron microscopy evaluation, the double acid-etched implant surface was not altered by Er:YAG laser irradiation under the condition of 100 mJ/pulse at 10 Hz for any of the irradiation times. However, we investigated the reduced sharpness of the specific ridge microstructure that resulted under the 140 mJ/pulse and 180 mJ/pulse conditions. The reduction in sharpness became more severe as laser energy and application duration increased. In the roughness measurement, the double acid-etched implants showed a low roughness value on the valley area before the laser irradiation. Under all experimental conditions, Er:YAG laser irradiation led to a minor decrease in surface roughness, which was not statistically significant. Conclusions: The recommended application settings for Er:YAG laser irradiation on double acid-etched implant surface is less than a 100 mJ/pulse at 10 Hz, and for less than two minutes in order to detoxify the implant surface without causing surface modification.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1994년도 춘계학술대회 논문집
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• pp.42-45
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• 1994

In this paper, we will report on the effect of the pointed end shape of an electrode, discharge energy, pulse width and discharge current on machining characteristics. The results obtained are as tollows: 1)As the discharge Energy increases, the diameter and the depth of the discharged crater becomes larger and deeper. 2) The discharge energy is not constant during discharge but varies depending on the pointed end shape of th8 electrode. 3) The shape of crater depends on the pulse width and discharge current.

• KIEE International Transactions on Electrophysics and Applications
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• 제11C권4호
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• pp.127-132
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• 2001

We describe the pulse forming of pulsed $CO_2$laser using multi-pulse superposition technique. A various pulse length, high duty cycle pulse forming network(PFN) is constructed by time sequence. That is, this study shows a technology that makes it possible to make various pulse shapes by turning on SCRs of three PFN modules consecutively at a desirable delay time with the aid of PIC one-chip microprocessor. The power supply for this experiment consists of three PFN modules. Each PFN module uses a capacitor, a pulse forming inductor, a SCR, a High voltage pulse transformer, and a bridge rectifier on each transformer secondary. The PFN modules operate at low voltage and drive the primary of HV pulse transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence. We investigated laser pulse shape and duration as various trigger time intervals of SCRs among three PFN modules. As a result, we can obtain laser beam with various pulse shapes and durations from about 250 $mutextrm{s}$ to 600 $mutextrm{s}$.