• Journal of Korean Ophthalmic Optics Society
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• v.8 no.2
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• pp.91-97
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• 2003

The behaviors of diamond deposition using microwave plasma chemical vapor deposition method have been studied by varying the concentration of methane in the methane - hydrogen gas mixture. The carbonization is checked from peak intensities of D($sp^3$) and G($sp^2$) peaks in Raman spectra. The hydronization and C-H bonding status in films can also be determined from FTIR results. Both the bonding strength of C-H and the ratio of $sp^3$ to $sp^2$ in bonding are found to be slightly dependent of partial pressure of $CH_4$ Judging from above results, we can conclude that the best value for partial pressure of $CH_4$ in growing process of thick films is about 13.8%.

• Current Optics and Photonics
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• v.6 no.6
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• pp.619-626
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• 2022

In this study, we develop a three-dimensional (3D) terahertz time-of-flight (THz-TOF) imaging technique with a large depth range, based on asynchronous optical sampling (ASOPS) methods. THz-TOF imaging with the ASOPS technique enables rapid scanning with a time-delay span of 10 ns. This means that a depth range of 1.5 m is possible in principle, whereas in practice it is limited by the focus depth determined by the optical geometry, such as the focal length of the scan lens. We characterize the spatial resolution of objects at different vertical positions with a focal length of 5 cm. The lateral resolution varies from 0.8-1.8 mm within the vertical range of 50 mm. We obtain THz-TOF images for samples with multiple reflection layers; the horizontal and vertical locations of the objects are successfully determined from the 2D cross-sectional images, or from reconstructed 3D images. For instance, we can identify metallic objects embedded in insulating enclosures having a vertical depth range greater than 30 mm. For feasible practical use, we employ the proposed technique to locate a metallic object within a thick chocolate bar, which is not accessible via conventional transmission geometry.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.2
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• pp.40-47
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• 1993

Composites composed of a precipitation harden 2124 alloy matrix reinforced by SiC whiskers, which are fabricated by powder metallugy, are suscepttible to fatigue damage due to the pile-up of moving dislocation and the microcrack initiation along SiC-Al interfaces, especially at the external surfaces of a body. The initial process, such as pile-up of dislocation or microcrack, that corresponds to the stage I during fatigue failure process are too small to be detected and characterized by conventional ultrasonic technique. This paper describes the applicability of an acoustic microscope with Line-Focus-Beam(LFB) lens of 225MHz to evaluate fatigue damage of SiC whiskers reinforced Al alloy. The specimens which were 6.6mm thick, 13mm wide, and 105mm long in the gage section were fatigued in tension-tension under load control. The velocity of leaky surface and leaky pseudosurface acoustic waves are obtained by FFT analysis technique from V(z) curve which is a record of output of piezoelectric transducer. These results are discussed with the change of number of fatigue cycles. The result obtained by acoustic microscope is compared with that by ultrasonic technique generated at 5MHz with conventional surface wave transducers.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.663-668
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• 2003

We studied a localized hologram recording method that can be used in a disk-shaped medium. In this method, the reference beam is focused by use of a cylindrical lens to get a thin spot in the medium, and then a hologram is recorded in that spot by illuminating the signal beam. Many localized holograms are multiplexed by shifting the medium by a distance more than the thin spot size of the reference beam. This method does not need recording-time scheduling for uniform diffraction efficiencies. We show that a minimal required thickness of the recording medium exists for a given spot size of the signal beam. We performed experiments for data storage and retrieval, and obtained a storage density of 20 bits/${\mu}{\textrm}{m}$$^2$ and a raw-bit error rate (RBER) of 2.5${\times}$10$^{-3}$ , when a 2 mm-thick Fe-doped LiNbO$_3$ crystal was used.

• Journal of the Korean Society of Radiology
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• v.15 no.2
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• pp.101-108
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• 2021

The CT can accurately present the anatomical structure of an organ in the human body, and the resolution of the image is excellent. On Brain CT examination, the radiation sensitivity of the orbit is high and it is subject to many exposure effects. To reduce exposure dose of lens, this study compares change of exposure dose and shielding rate about non-shielding and shielding in a way of using two shielding materials, bismuth and tungsten. In this study, we used bismuth and tungsten filament as shielding materials made by 3D printing to measure the exposure dose according to the materials thickness and each of slices. To compare each shielding rate, 1 mm to 5 mm of two materials was measured with the head phantom fixed and the Magicmax universal dosimeter placed on the eye when the shielding material is not placed, and the shielding material is placed on it. In the 1 mm thick filament, the bismuth filament showed 26.8% and the tungsten filament showed 43.1% shielding rate. Therefore, tungsten presents much greater shielding effect than bismuth.

• Korean Journal of Agricultural and Forest Meteorology
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• v.1 no.2
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• pp.127-134
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• 1999

This study was performed to obtain the basic data to present rational silvicultural tending plan. It makes these widely distributed pine-oak mixed stand and each of pure stand in middle province on object of this study and do comparative analysis of light condition about stand parameter and natural regeneration according to each slope(north, west and south) conditions of location in central part of South Korea. Sample plots for pine-oak mixed stand and pine and oak pure stand were established on each of southern, northern and western slopes based upon site and growth conditions of the slope. Sample plot was a circle of 0.05ha with a diameter of 25.24 m. A sample plot has between 30 and 40 tree in it. Total 23 sample plots were established; 9 pure pine stands, 8 pine-oak mixed stands. and 6 pure oak stands across lower, middle, upper parts of slopes. Relative light intensity within a stand was' measured by crown- photo(fish-eye lens; 180$^{\circ}$) system through fish-eye lens and by comparing each plot with the denuded through PAR-sensor. The crown closure ratio of pure pine stand (75%) shows much lower than that of mixed stand (90.9%) and pure oak stand (93%). The relative light intensity within a stand showed an opposite result. The crown closure of mixed stands tended to become gradually low as the slope moves from the north to the south, but the relative light Intensity within the stand tended to rise. By analyzing the relationship between the relative light intensity within a stand and stand parameter, light intensity within a stand tended to decrease as the diameter and N/ha increase. Number of oak seedlings and light intensity within a stand is in a straight-line regression relation. In particular, the number of oak seedlings was the highest in mixed stands on the southern slope. But no single pine seedling was found. The unfavorable conditions of l0cm thick litter layer and low relative light intensity in a stand (ranging between 4% and 8%) is considered to prevent pine seeds from germinating.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.430-430
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• 2008

Using multi plasma enhanced chemical vapor deposition system (Multi-PECVD), p-a-Si:H deposition layer as a $p^+$ region which was annealed by laser (Q-switched fiber laser, $\lambda$ = 1064 nm) on an n-type single crystalline Si (100) plane circle wafer was prepared as new doping method for single crystalline interdigitated back contact (IBC) solar cells. As lots of earlier studies implemented, most cases dealt with the excimer (excited dimer) laserannealing or crystallization of boron with the ultraviolet wavelength range and $10^{-9}$ sec pulse duration. In this study, the Q-switched fiber laser which has higher power, longer wavelength of infrared range ($\lambda$ = 1064 nm) and longer pulse duration of $10^{-8}$ sec than excimer laser was introduced for uniformly deposited p-a-Si:H layer to be annealed and to make sheet resistance expectable as an important process for IBC solar cell $p^+$ layer on a polished n-type Si circle wafer. A $525{\mu}m$ thick n-type Si semiconductor circle wafer of (100) plane which was dipped in a buffered hydrofluoric acid solution for 30 seconds was mounted on the Multi-PECVD system for p-a-Si:H deposition layer with the ratio of $SiH_4:H_2:B_2H_6$ = 30:120:30, at $200^{\circ}C$, 50 W power, 0.2 Torr pressure for 20 minutes. 15 mm $\times$ 15 mm size laser cut samples were annealed by fiber laser with different sets of power levels and frequencies. By comparing the results of lifetime measurement and sheet resistance relation, the laser condition set of 50 mm/s of mark speed, 160 kHz of period, 21 % of power level with continuous wave mode of scanner lens showed the features of small difference of lifetime and lowering sheet resistance than before the fiber laser treatment with not much surface damages. Diode level device was made to confirm these experimental results by measuring C-V, I-V characteristics. Uniform and expectable boron doped layer can play an important role to predict the efficiency during the fabricating process of IBC solar cells.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.372-377
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• 2016

Communication flow is changing rapidly. Recently, a range of wearable devices such as wearable glasses and wearable watch, have been launched. These kinds of wearable devices help people to live a more comfortable life. Wearable devices most have an antenna for wireless communication. This paper reports a transparent antenna that is made of an optically transparent material for wearable glasses. Transparent antenna can be applied to smart windows and will not disturb the view of user. IZTO/Ag/IZTO multilayer electrode has higher electrical and optical properties. This antenna is available because of its good electrical properties. This study measured the performance of the proposed transparent antenna, which is made of a multilayer electrode, applied to a lens. The proposed antenna was simulated with several substrates. The antenna impedance was matched with length and width of the antenna. The antenna's conductivity and transparency was measured using a HMS-3000 and UV-spectrometer. A 40nm thick Ag single layer antenna was fabricated on a flexible polyimide substrate for comparing the antenna performances. The fabricated antenna is useable at a frequency of 2.4-2.5GHz, which is suitable for Wifi communications and has peak gain of 2.89dBi and an efficiency of 34%.

• Progress in Medical Physics
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• v.13 no.3
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• pp.114-119
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• 2002

A immobilizing device that is essential for correct lung and lens shielding with homogenous dose distribution in fractionated total body irradiation was developed and it's efficiency was evaluated. The main frame was made of stainless steel bar (5 cm in diameter) to withstand up to 230 cm in height and 100 kg in weight to prevent any injury even in unconsciousness condition. The saddle was designed to adjust the body weight and hight of standing patients. Chest and back supporter were made of 1 cm acryl which could fix the lung block and cassette holder. Leather and sponge pedding were used for head rest to keep patients comfortable. The device was strongly fixed by specially designed bolts on the bottom panel which was made of 1 cm stainless steel and 10 cm thick wooden board. Precise manipulation ($\pm$2 mm) was possible by upper two pulleys and side handles. Average four minutes twenty five seconds were needed for exact setting in fractionated TBI. No significant difference of lung block location on repeated verification films was confirmed and relatively homogeneous dose distribution was measured in rando phantom experiments and patient treatments ($\pm$5%). This immobilizing device was very efficient to keep correct position of patients, which is essential for better result and less complication in fractionated TBI.