• Proceedings of the KWS Conference
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• 2002.10a
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• pp.600-605
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• 2002

The keyhole formed by high energy density laser-material interaction periodically collapses due to surface tension of the molten metal in partial penetration welds. The collapse sometimes traps a void at the bottom of the keyhole, and it remains as welding defects. This phenomenon is seen as one cause of the instability of the keyhole during laser beam welding. Thus, it seems likely that improving the stability of the keyhole can reduce voids and uniform the penetration depth. The goal of this work is to develop techniques for controlling laser weld keyhole dynamics to reduce weld defects such as voids and inconsistent penetration. Statistical analysis of the penetration depth signals in glycerin determined that keyhole dynamics are chaotic. The chaotic nature of keyhole fluctuations and the ability of laser power modulation to control them have been demonstrated by high-speed video images of laser welds in glycerin. Additionally, an incident leading beam angle is applied to enhance the stability of the keyhole. The quasi-sinusoidal laser beam power of 400Hz frequency and 15$^{\circ}$ incident leading beam angle were determined to be the optimum parameters for the reduction of voids. Finally, chaos analyses of uncontrolled signals and controlled signals were done to show the effectiveness of modulation on the keyhole dynamics. Three-dimensional phase plots for uncontrolled system and controlled system are produced to demonstrate that the chaotic keyhole dynamics is converted to regular periodic behavior by control methods: power modulation and incident leading beam angle.

• Journal of KSNVE
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• v.9 no.6
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• pp.1180-1186
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• 1999

The aim of this study is to investigate the sound insulation performance of windows according to the sound source in the field test. For this purpose, an experiment was performed by KSF 2235(method for field measurements of sound insulation of windows and doors). Based on this code, the sound insulation performance fo the windows was measured for different incident angles of the sound and the effect of incident angle was obtained and discussed. Finally, it was found that the sound insulation performance of the windows was affected by the incident angle of sound source, and the sound insulation rating scale was different for the same window. The main factor changing insulation rating scale is considered to be the sound transmission through the carck of the folding part between the two pieces of wndows. Therefore, when evaluating the sound insulation performance of the windows for the field test, first of all the place of the sound source should be identified and generalized.

• Journal of the Optical Society of Korea
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• v.20 no.6
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• pp.799-806
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• 2016

We present a polarization-dependent prism array film for controlling the viewing angle distribution of liquid crystal (LC) display panels without loss of light efficiency. On a directional backlight unit, our polarization-dependent prism array film, made into a stacked bilayer with a well-aligned liquid crystalline reactive mesogen (RM) layer on the UV-imprinted prism structure, can continuously control the light refraction function of the prism array by electrically switching incident polarization states of a polarization-controlling layer prepared by a twisted nematic LC mode. The viewing angle control properties of the polarization-dependent prism array film are analyzed under different prism angle and refractive index conditions of the RM layer. A simple analytic model is also presented to describe the intermediate viewing angle distributions with continuously varying applied voltages and incident polarization states.

• Journal of the Korean Solar Energy Society
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• v.24 no.3
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• pp.19-25
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• 2004

The measured solar radiation incident on tilted surfaces by all directions has been widely used as important solar radiation data in installing photovoltaic modules. To maximize the incident beam radiation, the slope, which is the angle between the plane of the surface in question and the horizontal, an4 the solar azimuth angles are needed for these solar photovoltaic systems. This is because the performance of the solar photovoltaic systems is much affected by angle and direction of incident rays. Recognizing those factors mentioned above are of importance, actual experiment has been performed in this research to obtain the an91e of inclination with which the maximum incident rays can be absorbed. The results obtained in this research could be used in installing optimal photovoltaic modules.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4022-4029
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• 2022

We investigated the possibility of using graphene for control of hydrogen isotopes by exploring adsorption, reflection, and penetration of hydrogen isotopes on graphene using molecular dynamics. Reflection is the dominant interaction when hydrogen isotopes have low incident energy. Adsorption rates increase with increasing incident energy until 5 eV is reached. After 5 eV, adsorption rates decrease as incident energy increases. At incident energies greater than 5 eV, adsorption rates increase with the number of graphene layers. At low incident energies (<1 eV), no isotopic effects on interactions are observed since the predominant interaction is derived from the force of π electrons. Between 1 eV and 50 eV, heavier isotopes exhibit higher adsorption rates and lower reflection rates than lighter isotopes, due to the greater momentum of heavier isotopes. Adsorption rates are consistently higher when the incident angle of the impacting atoms is smaller between 0.5 eV and 5 eV. At higher energies (>5 eV), larger incident angles lead to higher reflection and lower penetration rates. At high incident energies (>5 eV), crumpled graphene has higher adsorption and lower penetration rates than wrinkled or unwrinkled graphene. The results obtained in this research study will be used to develop novel nanomaterials that can be employed for tritium control.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.200-206
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• 1996

When a Gaussian beam is incident to a planar dielectric interface at an angle other than Brewster angle or the critical angle of total reflection, we derive the six nonspecular effects of rotation, lateral shift, focal shift, Rayleigh length change, magnitude and phase changes in the complex amplitude of the reflected beam simultaneously by taking account of the boundary condition. In the derivation we assume a Gaussian beam of fundamental mode to emerge from the interface and then match at the interface the constant, linear, and quadratic variations of the amplitude and phase of the reflected beam with those of the incident beam multiplied by the reflection coefficient. Our calculation shows that the six nonspecular effects can result from a linear variation of the natural logarithm of the reflection coefficient at the interface.

• Applied Science and Convergence Technology
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• v.27 no.1
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• pp.19-22
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• 2018

The ion energy and angle distributions (IEADs) in the DC magnetron sputtering systems are investigated for the variation of gas pressure using particle-in-cell simulation. Even for the condition of collisionless ion sheath at low pressure, it is possible to change the IEAD significantly with the change of gas pressure. The bombarding ions to the target with low energy and large incident angle are observed at low pressure when the sheath voltage drop is low. It is because the electron transport is hindered by the magnetic field at low pressure because of few collisions per electron gyromotion while the ions are not magnetized. Therefore, the space charge effect is the most dominant factor for the determination of IEADs in low-pressure magnetron sputtering discharges.

• Transactions of the Korean hydrogen and new energy society
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• v.11 no.3
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• pp.127-136
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• 2000

Molecular dynamics simulations have been carried out to investigate the scattering and penetration properties of hydrogen ions with the normal incident angle to Ni (100) surface. The initial kinetic energies of hydrogen ions range from 100 to 1,600 eV. The simulation results are used to assess the applicabilities of theoretical predictions based on the binary collision approximation, and, in the high kinetic regime, theoretical results for scattering energies were shown to he a good agreement with molecular simulations. The angle dependencies on both scattering and penetration distributions were found in the longitudinal direction, but not in the azimuthal direction except for the high kinetic energy of 1,600 eV.

• Applied Science and Convergence Technology
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• v.27 no.2
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• pp.26-29
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• 2018

The ion energy and angle distributions (IEADs) in the DC magnetron sputtering systems are investigated for the variation of gas pressure using particle-in-cell simulation. Even for the condition of collisionless ion sheath at low pressure, it is possible to change the IEAD significantly with the change of gas pressure. The bombarding ions to the target with low energy and large incident angle are observed at low pressure when the sheath voltage drop is low. It is because the electron transport is hindered by the magnetic field at low pressure because of few collisions per electron gyromotion while the ions are not magnetized. Therefore, the space charge effect is the most dominant factor for the determination of IEADs in low-pressure magnetron sputtering discharges.

• Journal of the Semiconductor & Display Technology
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• v.9 no.4
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• pp.31-37
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• 2010

In this paper, optical deflection of laser scattering has been investigated based on Rayleigh criterion for crystalline silicon wafer in solar cell. A laser scattering mechanism is newly designed using light scattering properties in silicon wafer. Intensity distributions of laser scattering are different, depending on the incident angle of laser computed from Rayleigh criterion. In case of the incident angle satisfied with the criterion, they are asymmetric. Also, their specular reflection angle is shifted to unpredicted ones. These phenomena are in accordance with previous theories of laser scattering. The optical deflection of laser scattering is experimentally identified with the designed laser scattering mechanism. Its mathematical model is presented from the geometric relationship of laser scattering. It is shown that the optical deflection of laser scattering agree with the presented model, exclusive of grazing angles which is satisfied with Rayleigh criterion.