• 대한기계학회논문집B
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• 제30권5호
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• pp.413-421
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• 2006

The bubble dynamics induced by direct laser heating is experimentally analyzed as a first step to assess the technical feasibility of laser-based ink-jet technology. To understand the interaction between laser light and ink, the absorption spectrum is measured for various ink colors and concentrations. The hydrodynamics of laser-generated bubbles is examined by the laser-flash photography. When an Ar ion laser pulse (wavelength 488 nm) with an output power up to 600 mW is incident on the ink solution through a transparent window, a hemispherical bubble with a diameter up to ${\sim}100{\mu}m$ can be formed with a lifetime in a few tens of microsecond depending on the laser power and the focal-spot size. Parametric study has been performed to reveal the effect of laser pulse width, output power, ink concentration, and color on the bubble dynamics. The results show that the bubble generated by a laser pulse is largely similar to that produced by a thin-film heater. Consequently, the present work demonstrates the feasibility of developing a laser-actuated droplet generation mechanism for applications in ink-jet print heads. Furthermore, the results of this work indicate that the droplet generation frequency is likely to be further increased by optimizing the process parameters.

• Journal of Advanced Marine Engineering and Technology
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• 제36권7호
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• pp.935-941
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• 2012

This paper describes a study of conventional electrical rig and simulated application of Flywheel Energy Storage system on the power system of the offshore plants with dynamic positioning system with the following aims: improve fuel consumption on engines, prevent blackout and mitigate voltage sags due to pulsed load and fault. Fuel consumption has been analyzed for the generators of the typical drilling rigs compared with the power plant with Flywheel Storage Unit which has an important aid in avoiding power interruption during DP (Dynamic Positioning) operation. The FES (Fly wheel Energy storage System) releases energy very quickly and efficiently to ensure continuity of the power supply to essential consumers such as auxiliary machinery and thrusters upon main power failure. It will run until the standby diesel generator can start and supply the electric power to the facilities to keep the vessel in correct position under DP operation. The proposed backup method to utilize the quick and large energy storage Flywheel system can be optimized in any power system design on offshore plant.

• 한국레이저가공학회지
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• 제7권1호
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• pp.37-47
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• 2004

Laser-assisted selective infiltration is a new method of building metal layers to make metal parts layer by layer, in which superheated microscopic metal droplets are infiltrated into a laser-preheated layer of microscopic metal powders. In this work, the selective infiltration of a low melting-point metal, Sn-37Pb wt%, was conducted to investigate the effects of such dominant parameters as superheating temperature, Nd:YAG laser power for preheating, substrate temperature, etc. The optimal conditions for successful selective infiltration of a single layer of microscopic metal powder were experimentally obtained

• 한국정보통신학회논문지
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• 제18권5호
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• pp.1243-1248
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• 2014

일반적으로 저피탐(Low Probability of Intercept, LPI) 레이더는 펄스레이더에 비해 매우 낮은 송신출력, 높은 안테나 이득 등으로 인해 상대방의 전자전 장비(Electronic Warfare Support, ES)에 탐지될 확률이 낮다. LPI 레이더는 RCS 감소 설계와 같이 전자파에 대한 스텔스 기법의 한 종류로, 궁극적인 목적은 상대방에게 탐지되는 거리를 줄이는 것이며 RCS 값, LPI 성능 중 한 가지라도 성능이 미흡하면 적보다 먼저 탐지되게 된다. 본 논문에서는 LPI 탑재 플랫폼의 피탐 확률 감소를 위해 고려해야할 사항을 제시하였다.

• Journal of Welding and Joining
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• 제17권1호
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• pp.82-87
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• 1999

The basic remote sleeve repair-welding technology by the pulsed Nd:YAG laser for increasing the lifetime of the steam generator tube in a nuclear power plant has been developed. The relationship between the connection width and welding parameters have been investigated for the fundamental research to apply the sleeve-repair-welding technique to the nuclear industry. The Inconel 600 tube and Inconel 690 sleeve used for high temperature and high pressure service were welded as round lap welding by Nd:YAG laser. It was observed that the tensile shear strength, 340MPa of the welded specimen is equivalent to about 60% of that of the base metal (Inconel 600), 550MPa. The difference between the hardness of the base metal and that of the laser welds was about 10%. Ductile fracture was partly occurred in the weld but the cracking has not been observed. In spite of absence of the crack, the strength of welds was not sufficient in terms of the tensile shear strength.

• 한국세라믹학회지
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• 제44권6호
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• pp.303-307
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• 2007

Transparent In-doped zinc oxide (IZO) thin films are deposited with variation of pulsed DC power at Ar atmosphere on coming 7059 glass substrate by pulsed DC magnetron sputtering. A c-axis oriented IZO thin films were grown in perpendicular to the substrate. The optical transmittance spectra showed high transmittance of over 80% in the UV-visible region and exhibited the absorption edge of about 350 nm. Also, the IZO films exhibited the resistivity of ${\sim}10^{-3}{\Omega}\;cm$ and the mobility of ${\sim}6cm/V\;s$. Organic Light-emitting diodes (OLEDs) with IZO/N,N'-diphenyl-N, N'-bis(3-methylphenl)-1, 1'-biphenyl-4,4'-diamine (TPD)/tris (8-hydroxyquinoline) aluminum ($Alq_3$)/LiF/Al configuration were fabricated. LiF layer inserted is used as an interfacial layer to increase the electron injection. Under a current density of $100\;mA/cm^2$, the OLEDs show an excellent efficiency (9.4 V turn-on voltage) and a good brightness ($12000\;cd/m^2$) of the emission light from the devices. These results indicate that IZO films hold promise for anode electrodes in the OLEDs application.

• 한국군사과학기술학회지
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• 제25권2호
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• pp.169-176
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• 2022

Laser ablation propulsion(LAP) is the method to create impulse by laser ablation. It can be used to deorbit the space debris(SD), as its long-range property and versatility on any material. In this paper, we find out several requirements of the LAP system(LAPS) to deorbit the SD by simple numerical calculations of the SD orbit and laser beam flux. As a result, minimum operable altitude angle turned out to be a crucial variable to the LAPS. Moreover, if minimum operable altitude angle is 10°, and if the minimum distance between the LAPS and the SD is below 450 km, 1 m/s² is sufficient to deorbit the SD by once. With 18 kJ/3 ns pulsed laser and cube shaped 100 kg SD, 1 m/s² acceleration can be achieved by increasing the pulse repetition rate over 34~53 Hz, depending on the size of the SD. This capability could compare with the conceptual design of the Japan Establishment for a Power-laser Community Harvest(J-EPoCH) facility, which include 8 kJ, 5 PW@100 Hz laser.

• Journal of Electrical Engineering and Technology
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• 제1권1호
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• pp.110-113
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• 2006

A high rate deposition sputtering process of magnesium oxide thin film in oxide mode has been developed using a 20 kW unipolar pulsed power supply. The power supply was operated at a maximum constant voltage of 500 V and a constant current of 40 A. The pulse repetition rate and the duty were changed in the ranges of $10\sim50$ kHz and $10\sim60%$, respectively. The deposition rate increased with rising incident power to the target. Maximum incident power to the magnesium target was obtained by the control of frequency, duty and current. The deposition rate of a moving state was 9 nm m/min at the average power of 1.5 kW. This result shows higher deposition rate than any other previous work involving reactive sputtering in oxide mode. The thickness uniformities over the entire substrate area of $982mm{\times}563mm$ were observed at the processing pressure of $2.8\sim9.5$ mTorr. The thickness distribution was improved at lower pressure. This technique is proposed for application to a high through-put sputtering system for plasma display panels.

• 한국결정성장학회지
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• 제13권2호
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• pp.79-82
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• 2003

ArF(193nm) 엑시머 레이저를 이용한 펄스레이저증착법(PLD)에 의해 GaN 소결체를 타겟 재료로 하여 $SiO_2$기판위에 GaN nanoparticles를 합성하였다. PLD 공정 중에는 100Pa, 50Pa, 10Pa및 1 Pa의 Ar gas 압력과 100mJ 및 200mJ의 레이저 에너지를 가하였다. 합성된 GaN nanoparticles는 XRD, SEM, TEM, XPS 및 optical absorption spectra 등에 의해 분석되었다. 합성된 GaN nanoparticles는 대체적으로 20~30nm의 입경을 갖는 균일한 분포를 하고 있었다. 또한, Ar 기체 압력이 낮아짐에 따라 합성된 GaN nanoparticles의 stoichiometry가 향상되고 optical band edge가 blueshift 경향을 나타내었다.

• Journal of Magnetics
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• 제18권3호
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• pp.342-347
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• 2013

Local wall thinning in pipelines affects the structural integrity of industries, such as nuclear power plants (NPPs). In the present study, a development of pulsed eddy current (PEC) technology that detects the wall thinning of pipelines covered with insulation is reviewed. The methods and experimental results, which have two kinds of probe with a single and double core, were compared. For this purpose, the single and double core probes having one and two excitation coils have been devised, and the differential probe with two Hall sensors has been fabricated to measure the wall thinning in insulated pipelines. The test sample is a stainless steel having different thickness, laminated by plastic insulation to simulate the pipelines in NPPs. The excitation coils in the probe is driven by a rectangular current pulse, the difference of two Hall sensors has been measured as a resultant PEC signal. The peak value of the detected signal is used to describe the wall thinning. The double core probe has better performance to detect the wall thinning covered with insulation; the single core probe can detect the wall thinning up to an insulation thickness of 18 mm, whereas the double probe can detect up to 25 mm. The results show that the double core PEC probe has the potential to detect the wall thinning in an insulated pipeline of the NPPs.