• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.1
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• pp.97-103
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• 2013

A new precision positioning mechanism for stage was been developed by Displacement Magnification Device(DMD) in this paper. The DMD was composed of the beam and multilayer piezoelectric actuators. The theoretical and experimental analysis of DMD to enlarge displacement more then 50times were discussed. And the 2-axis stage by using displacement amplification apparatus was added in the new DMD, and it was able to do it through finite element analysis and experiment. As the results, the magnification of DMD can be obtained about $100{mu}m$ displacement to the 10V input voltage($1.5{mu}m$). And the about 50nm of linearity error in the $30{mu}m$ measurement range and 20times of the amplification in displacement can be measured. In addition, the experimental results are confirmed the possibility of millimeter displacement characteristics and correspond to finite element analysis results.

• ETRI Journal
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• v.26 no.1
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• pp.7-13
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• 2004

To improve the characteristics of breakdown voltage and specific on-resistance, we propose a new structure for a LDMOSFET for a PDP scan driver IC based on silicon-on-insulator with a trench under the gate in the drift region. The trench reduces the electric field at the silicon surface under the gate edge in the drift region when the concentration of the drift region is high, and thereby increases the breakdown voltage and reduces the specific on-resistance. The breakdown voltage and the specific on-resistance of the fabricated device is 352 V and $18.8 m{\Omega}{\cdot}cm^2$ with a threshold voltage of 1.0 V. The breakdown voltage of the device in the on-state is over 200 V and the saturation current at $V_{gs}=5V$ and $V_{ds}$=20V is 16 mA with a gate width of $150{\mu}m$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.65-69
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• 2004

The small form factor optical data storage devices are developing rapidly nowadays. Since it is designed for portable and compatibility with flash memory, its components such as disk, head, focusing actuator, and spindle motor should be assembled within 5 m thickness. The thickness of focusing actuator is within 2 mm and the total working range is $+/-100{\mu}m$, with the resolution of less than $1{\mu}m$. Since the thickness is limited tightly, it is hard to place the yoke that closes the magnetic circuit and hard to make strong flux density without yoke. Therefore, Halbach array is adopted to increase the magnetic flux of one side without yoke. The proposed Halbach array type focusing actuator has the advantage of thin actuation structure with sacrificing less flux density than conventional magnetic array. The optical head unit is moved on the swing arm type tracking actuator. Focusing coil is attached to swing arm, and Halbach magnet array is positioned at the bottom of deck along the tracking line, and focusing actuator exerts force by the Fleming's left hand rule. The working range and resolution of focusing actuator are analyzed with FEM and experiment.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.940-943
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• 2003

We report the fabrication and the characterization of white organic light-emitting devices consisting of a red-emitting layer of a new DCM derivative doped into 4,4'bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (${\alpha}-NPD$) and a blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi). The device structure is ITO/PEDOT:PSS/${\alpha}-NPD$ (50 nm)/${\alpha}-NPD$:DCM (5 nm, 0.2 %)/DPVBi (x)/Alq3 (40 nm)/LiF (0.5 nm)/Al. The electroluminescence (EL) spectra consist of two broad peaks around 470 nm and 580 nm with the spectral emission depending on the thickness of DPVBi. The device with the DPVBi thickness of about 20 nm show a white light-emission with the Commission Internationale d'Eclairage(CIE) chromaticity coordinates of (0.33, 0.36). The external quantum efficiency is 2.6% and luminous efficiency is 2.0 lm/W at a luminance of 100 $cd/m^{2}$. The maximum luminance is about 30,270 $cd/m^{2}$ at 13.9 V.

• Journal of the Korean Society of Radiology
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• v.10 no.2
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• pp.109-115
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• 2016

Despite of increasing the use of the digital imaging device in the radiology area, the setting on the optimal irradiation conditions are insufficient. In this study, the exposure dose and image quality by exposure condition of digital radiography device were compared. The exposure doses were obtained by adjusting the exposure condition as 5 steps respectively based on the exposure conditions that are currently used of CR and DR radiography devices. The acquired image has been assessed by 20 medical image professors using the assessment method of the Japanese Society for Tuberculosis Prevent. As a result, in the case of the CR system, the better image quality was obtained in the condition of 120 kVp and 1.5 mAs~2.4 mAs (quality score 91~95.5 points) than standard exposure condition(110 kVp, 3.2 mAs, 86 points). And exposure dose was evaluated as low with $61.3{\sim}98.4{\mu}Gy$ than standard condition($105.11{\mu}Gy$). In DR system, however, the image quality score was higher as 97~98.6 points in the lower tube voltage range (112 kVp, 2.4~3.2 mAs) condition than the standard exposure condition (125 kVp, 3.2 mAs, 91 points). In addition, the exposure dose was $61.5-77.2{\mu}Gy$ lower than standard condition($93{\mu}Gy$). In addition, the exposure dose was low as $61.5-77.2{\mu}Gy$ than standard condition($93{\mu}Gy$). With the results of this study, we confirmed that it is possible to reduce the patient exposure dose with the same image quality by adjusting the optimal exposure condition of digital device.

• Journal of Environmental Health Sciences
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• v.35 no.5
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• pp.355-361
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• 2009

This study evaluated the bacterial concentrations and affecting factors at the laboratories of a university in Seoul, Korea. Thirty-three samples of total airborne bacteria (TAB) and eighteen samples of gram negative bacteria (GNB) were collected from both microbiology laboratories (7) and chemistry laboratories (6). GM (GSD) of TAB and GNB concentrations were 194 (2.52) $cfu/m^3$, 24 (4.1) $cfu/m^3$, respectively. TAB concentrations in the chemical laboratories (GM (GSD): 193 (2.0) $cfu/m^3$) were not significantly different from those in microbial laboratories (GM (GSD): 202 (2.7) $cfu/m^3$, (p>0.05)). GM (GSD) of TAB concentrationsat the top of sink, the center of laboratory, and the front of ventilation ventilation device within laboratories, 182 (3.2) $cfu/m^3$, 217 (2.2) $cfu/m^3$, 176 (2.4) $cfu/m^3$, respectively, were not significantly different (p=0.48). Related factors were measured such as temperature, relative humidity, floor of laboratory, number of persons and laboratory area. TAB concentrations were significantly related to temperature (r=0.36, p<0.05), and the floor of laboratory and temperature were also significantly related (r=0.49, p<0.001). However, other factors such as relative humidity, number of persons and laboratory area did not show any significant relationship with TAB concentrations (p>0.05). TAB concentrations were affected significantly by cleaning frequency (p<0.001) and floor of laboratory (p<0.05). There was also a significant difference (p<0.01) between TAB indoor concentrations and TAB outdoor concentrations. However, other factors such as general ventilation did not affect TAB concentrations (p>0.05) in this study.

• Journal of Biosystems Engineering
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• v.28 no.2
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• pp.89-96
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• 2003

This study was aimed to identify how the main body vibration of power tiller will be transmitted to the trailer, and to find out the basic information for demage reducing method of agricultural products during transportation. The vertical vibration acceleration level was measured at 6 positions, i.e. engine, hitch, seal and three parts of trailer (front middle, and rear) for the not driving but at the engine speeds of 1,000rpm and driving at 0.35m/s. The results of this research could be summarized as follows; 1. For not driving, the accumulated acceleration level up to 120Hz was 50% of total accelerations at engine part and those were 28~41% at other parts. Those up to 40Hz were 20~30% at engine and hitch part and 2~8% at trailer part. And those up to 20Hz were 13~20% at engine and hitch part and 1~4% at trailer part 2. For the driving with 0.35m/s at paved road, the average vertical accelerations were in the range of 0.005~0.058m/s$^2$. The lowest value of 0.005m/s$^2$ was showed at engine part and the value of 0.031-0.058m/s$^2$ was showed at trailer part. 3. For the driving with 0.35m/s, the accumulated value of average vertical accelerations showed the lowest value at engine parts md showed 5 times value of engine part at trailer part especially highest value at middle part of trailer. 4. For the driving with 0.35m/s, the accumulated acceleration level up to 120Hz was 75% of total accelerations at engine part and those were 20~42% at other parts. Ant those up to 20Hz and 40Hz were 24~26% at engine part and 0.1~0.6% at trailer part.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.7
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• pp.747-752
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• 2014

This paper relates 10% shrink from $0.13{\mu}m$ design for logic devices as well as input and output (I/O) circuits, different from the previous shrink methodologies which shrink only core device. Thin gate oxide was changed to decoupled plasma nitridation(DPN) oxide as a thin gate oxide (1.2V) to reduce the flicker noise, resulting in three to five times lower flicker noise than pre-shrink process. Unavoidable issue by shrink is capacitor for this normally metal insulator metal (MIM). To solve this issue, 20% higher unit MIM capacitor ($1.2fF/{\mu}m^2$) was developed and its performance were evaluated.

• Smart Structures and Systems
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• v.32 no.6
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• pp.383-391
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• 2023

Energy harvesting in trams may become a prevalent source of passive energy generation due to the high density of vibrational energy, and this may help power structural health monitoring systems for the trams. This paper presents a broadband vibrational energy harvesting device design that utilizes a varied frequency from a tram vehicle using a 2 DOF vibrational system combined with electromagnetic energy conversion. This paper will demonstrate stepwise optimization processes to determine mechanical parameters for frequency tuning to adjust to the trams' operational conditions, and electromagnetic parameters for the whole system design to maximize power output. The initial optimization will determine 5 important design parameters in a 2 DOF vibrational system, namely the masses (m₁, m₂ (and spring constants (k₁, k₂, k₃). The second step will use these parameters as initial guesses for the second optimization which will maintain the ratios of these parameters and present electrical parameters to maximize the power output from this system. The obtained values indicated a successful demonstration of design optimization as the average power generated increased from 1.475 mW to 17.44 mW (around 12 times).

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.273-273
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• 2014

Quantum-dot sensitized solar cells (QDSCs) are an emerging class of solar cells owing to their easy fabrication, low cost and material diversity. Despite of the fact that the maximum conversion efficiency of QDSCs is still far less than that of Dye-Sensitized Solar Cells (>12 %), their unique characteristics like Multiple Exciton Generation (MEG), energy band tune-ability and tendency to incorporate multiple co-sensitizers concurrently has made QDs a suitable alternative to expensive dyes for solar cell application. Lead Sulfide (PbS) Quantum dot sensitized solar cells are theoretically proficient enough to have a photo-current density ($J_{sc}$) of $36mA/cm^2$, but practically there are very few reports on photocurrent enhancement in PbS QDSCs. Recently, $Hg^{2+}$ incorporated PbS quantumdots and Cadmium Sulfide (CdS) co-sensitized PbS solarcells are reported to show an improvement in photo-current density ($J_{sc}$). In this study, we explored the efficacy of $In_2S_3$ as an interfacial layer deposited through SILAR process for PbS QDSCs. $In_2S_3$ was chosen as the interfacial layer in order to avoid the usage of hazardous CdS or Mercury (Hg). Herein, the deposition of $In_2S_3$ interfacial layer on $TiO_2$ prior to PbS QDs exhibited a direct enhancement in the photo-current (Isc). Improved photo-absorption as well as interfacial recombination barrier caused by $In_2S_3$ deposition increased the photo-current density ($J_{sc}$) from $13mA/cm^2$ to $15.5mA/cm^2$ for single cycle of $In_2S_3$ deposition. Increase in the number of cycles of $In_2S_3$ deposition was found to deteriorate the photocurrent, however it increased $V_{oc}$ of the device which reached to an optimum value of 2.25% Photo-conversion Efficiency (PCE) for 2 cycles of $In_2S_3$ deposition. Effect of Heat Treatment, Normalized Current Stability, Open Circuit Voltage Decay and Dark IV Characteristics were further measured to reveal the characteristics of device.