• ETRI Journal
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• v.45 no.1
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• pp.171-179
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• 2023

We have developed an InAlAs/InGaAs metamorphic high electron mobility transistor device fabrication process where the gate length can be tuned within the range of 0.13㎛-0.16㎛ to suit the intended application. The core processes are a two-step electron-beam lithography process using a three-layer resist and gate recess etching process using citric acid. An electron-beam lithography process was developed to fabricate a T-shaped gate electrode with a fine gate foot and a relatively large gate head. This was realized through the use of three-layered resist and two-step electron beam exposure and development. Citric acid-based gate recess etching is a wet etching, so it is very important to secure etching uniformity and process reproducibility. The device layout was designed by considering the electrochemical reaction involved in recess etching, and a reproducible gate recess etching process was developed by finding optimized etching conditions. Using the developed gate electrode process technology, we were able to successfully manufacture various monolithic microwave integrated circuits, including low noise amplifiers that can be used in the 28 GHz to 94 GHz frequency range.

• Journal of the Korean Geotechnical Society
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• v.23 no.8
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• pp.117-127
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• 2007

Slope stability analysis is a geotechnical engineering problem characterized by many sources of uncertainty. Some of them are connected to the uncertainties of soil properties involved in the analysis. In this paper, a numerical procedure for integrating commercial finite difference method into probabilistic analysis of slope stability is presented. Since the limit-state function cannot be expressed in an explicit form, the ANN-based response surface method is adopted to approximate the limit-state function and the first-, second-order reliability method and the Monte Carlo simulation technique are used to calculate the probability of failure. Probabilistic stability assessments for a hypothetical two-layer slope and the Sugar Creek embankment were performed to verify the application potential to the slope stability problems. The examples show the successful implementation and the possibility of the extension of the proposed procedure to the variety of geotechnical engineering problems.

• Composites Research
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• v.22 no.6
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• pp.13-17
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• 2009

This paper decided the 3D shape of sandwich composite for the cradle of CT instrument, suggested the stacking sequence with satisfaction on structural criteria using the Finite Element Analysis, and introduced the manufacturing method to meet the X-ray transmission performance uniformly. The design of Cradle was considered the space between other parts, fixing method, and assembly condition with headrest part. It is decided the stacking sequence to meet the criteria that the deflection at the end point is less than 20 mm when it is applied to 135 kg load at the specific locations. In site of manufacturing method, at first, it is used the hand lay-up for carbon UD and carbon fabric/polyester resin, but it had the ununiform X-ray transmission performance due to the void and excess resin. For solving this problem, it was replaced with the infusion method for the first layer of face material and the application of carbon UD or fabric/epoxy resin prepreg for other layers. Therefor, the property of X-ray transmission was improved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.2
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• pp.165-171
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• 2022

The SiO₂/TiO₂ multilayer thin films used for narrow band pass filter were fabricated using E-beam evaporation method. The narrow band pass filter was used to enhance the resolution of spectroscopy and sensor applications with near infrared (NIR) light source. The narrow band pass filter with multilayer thin films were designed with Essential Macleod program. The multilayers of SiO₂/TiO₂ with 32 layers were deposited on the silicon encapsulation of IR with peak wavelength (λ_p) of 660 nm and NIR LEDs with λ_p of 830 nm, 880 nm, and 955 nm. After NIR light passed through the narrow band pass filter, the full width of half maximum of 33.4~48.6 nm became narrow to 20~24 nm owing to the absorption of photons with short or long wavelength of designed band of 20 nm. The SiO₂/TiO₂ band pass filter fabricated in this study can be used for sensor, optoelectronics, and NIR spectroscopy applications.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.5 no.3
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• pp.27-36
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• 2015

Electronic cultural atlases based on a variety of topics have been studied because of recently increased interest about them. Existing cultural atlases are difficult to analyze the correlation between the subjects and to make utilization based on the various points of view since they are implemented mostly by a single theme. To solve these problems, we propose a method that express a variety of themes by using layer functions of electronic cultural atlases. Using thematic overlay functions, also, application plans are suggested to analyze the relationship between subjects and to derive new knowledge through the association of various themes.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2256-2262
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• 2023

The electrochemical corrosion behaviors of SA106 Grade B (SA106B) carbon steel in H₂SO₄4-N₂H₄ and H₂SO₄-N₂H₄-CuSO₄ solutions at 95 ℃ have been investigated with the addition of commercial corrosion inhibitors (CI#30 and No. 570S), to determine the stability of SA106B in the hydrazine-based reductive metal ion decontamination (HyBRID) process. The potentiodynamic polarization experiment revealed that the corrosion inhibitors were capable of lowering the corrosion rate of SA106B in H₂SO₄-N₂H₄ solution. It was found that the corrosion inhibitors induced formation of fixed surface layer on the carbon steel upon the corrosion. This corrosion inhibition performance was reduced in the presence of CuSO₄ in the solution owing to the chemical reactions between organic compounds in the corrosion inhibitors and CuSO₄. CI#30 showed a better corrosion inhibition effect in the H₂SO₄-N₂H₄-CuSO₄ solution. Although the corrosion inhibitors can provide better stability to SA106B in the HyBRID solution, their application should be carefully considered because it may result in reduced decontamination performance and increased secondary waste generation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.6
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• pp.1530-1544
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• 2023

Data monitoring is an important foundation of modern science. In most cases, the monitoring data is time-series data, which has high application value. The deep learning algorithm has a strong nonlinear fitting capability, which enables the recognition of time series by capturing anomalous information in time series. At present, the research of time series recognition based on deep learning is especially important for data monitoring. Deep learning algorithms require a large amount of data for training. However, abnormal sample is a small sample in time series, which means the number of abnormal time series can seriously affect the accuracy of recognition algorithm because of class imbalance. In order to increase the number of abnormal sample, a data augmentation method called GANBATS (GAN-based Bi-LSTM and Attention for Time Series) is proposed. In GANBATS, Bi-LSTM is introduced to extract the timing features and then transfer features to the generator network of GANBATS.GANBATS also modifies the discriminator network by adding an attention mechanism to achieve global attention for time series. At the end of discriminator, GANBATS is adding averagepooling layer, which merges temporal features to boost the operational efficiency. In this paper, four time series datasets and five data augmentation algorithms are used for comparison experiments. The generated data are measured by PRD(Percent Root Mean Square Difference) and DTW(Dynamic Time Warping). The experimental results show that GANBATS reduces up to 26.22 in PRD metric and 9.45 in DTW metric. In addition, this paper uses different algorithms to reconstruct the datasets and compare them by classification accuracy. The classification accuracy is improved by 6.44%-12.96% on four time series datasets.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.11
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• pp.1672-1678
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• 2022

In this paper, the relay antenna was designed in consideration of the performance of the 28GHz band 5G mobile communication relay horn antenna, such as radiation pattern and return loss. A horn array for 5G mobile communication repeater was designed by arranging the antenna elements in phase, and the performance was analyzed. Unlike conventional WCDMA (3G) and LTE (4G), in millimeter wave band communication, high path loss occurs between transmission and reception. In the design of a 5G millimeter wave horn antenna, antenna performance such as isolation and gain between antenna elements as well as gain and bandwidth of the antenna must be additionally considered. The antenna gain of the single horn antenna (1×1) and the array horn antenna (2×4) in the 28GHz band is about 10.44d Bi and 19.58dBi, respectively, and the return loss is designed to be less than -18dB. It has proven its validity and has been shown to be suitable for application to 5G mobile communication relay system.

• Analytical Science and Technology
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• v.22 no.3
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• pp.247-253
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• 2009

Porous silicon films are electrochemically etched from crystalline silicon wafers in an aqueous solution of hydrofluoric acid(HF). Careful control of etching conditions (current density, etch time, HF concentration) provides films with precise, reproducible physical parameters (morphology, porosity and thickness). The etched pattern could be varied due to (1) current density controls pore size (2) etching time determines depth and (3) complex layered structures can be made using different current profiles (square wave, triangle, sinusoidal etc.). The optical interference spectrum from Fabry-Perot layer has been used for forensic applications, where changes in the optical reflectivity spectrum confirm the identity. We will explore a method of identifying the specific pattern code and can be used for identities of individual code with porous silicon based encoded nanosized smart particles.

• Membrane Journal
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• v.33 no.3
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• pp.127-136
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• 2023

In this study, the electrochemical performance of a 5-layer fuel cell stack using silica composite membranes as polymer electrolyte membranes was evaluated. It was observed that the flow rate of the fuel gases plays a crucial role in stack performance, particularly being mainly dependent on the flow rate of hydrogen. Increasing the flow rate of oxygen resulted in negligible changes in performance, whereas an increase in the flow rate of hydrogen demonstrated performance improvements. However, this led to an imbalance in the ratio of hydrogen to oxygen flow rates, causing significant degradation in stack performance and durability. A decline in stack performance was also observed over time due to the degradation of stack components. This phenomenon was consistently observed in individual unit cells. Based on these findings, it was emphasized that, in addition to optimizing the performance of each component during stack operation, it is important to optimize design and operating conditions for uniform flow rate control. Lastly, the developed silica composite membrane was assessed to have sufficient performance for application in actual fuel cell systems, exhibiting a performance of over 25 W based on maximum power.