• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.448-448
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• 2010

Magnetic random access memory (MRAM) has made a prominent progress in memory performance and has brought a bright prospect for the next generation nonvolatile memory technologies due to its excellent advantages. Dry etching process of magnetic thin films is one of the important issues for the magnetic devices such as magnetic tunneling junctions (MTJs) based MRAM. CoFeB is a well-known soft ferromagnetic material, of particular interest for magnetic tunnel junctions (MTJs) and other devices based on tunneling magneto-resistance (TMR), such as spin-transfer-torque MRAM. One particular example is the CoFeB - MgO - CoFeB system, which has already been integrated in MRAM. In all of these applications, knowledge of control over the etching properties of CoFeB is crucial. Recently, transferring the pattern by using milling is a commonly used, although the redeposition of back-sputtered etch products on the sidewalls and the low etch rate of this method are main disadvantages. So the other method which has reported about much higher etch rates of >$50{\AA}/s$ for magnetic multi-layer structures using $Cl_2$/Ar plasmas is proposed. However, the chlorinated etch residues on the sidewalls of the etched features tend to severely corrode the magnetic material. Besides avoiding corrosion, during etching facets format the sidewalls of the mask due to physical sputtering of the mask material. Therefore, in this work, magnetic material such as CoFeB was etched in an ICP etching system using the gases which can be expected to form volatile metallo-organic compounds. As the gases, carbon monoxide (CO) and ammonia ($NH_3$) were used as etching gases to form carbonyl volatiles, and the etched features of CoFeB thin films under by Ta masking material were observed with electron microscopy to confirm etched resolution. And the etch conditions such as bias power, gas combination flow, process pressure, and source power were varied to find out and control the properties of magnetic layer during the process.

• Journal of the Earthquake Engineering Society of Korea
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• v.23 no.6
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• pp.321-327
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• 2019

We performed seismic noise level analysis to access the proper functioning of 11 newly established seismic stations in the southeastern region of Korea. One-hour long segments of seismograms were selected from the continuous data of the 3 elements for 61 days from March 1, 2019. For each segment of data, the power spectral density (PSD) was estimated from the continuous back ground noise data of the 3 elements for periods ranging from 0.02~100 s. The median noise levels (NLs) of the stations were compared with the new noise model (NNM) of USGS and NLs of station TJN installed in a tunnel on a granite basement. We observed that the NLs of the newly installed seismometers were between the upper and lower limit of the NNM. In a comparison with the noise level of station TJN, the new seismometers had their own noteworthy features. The NLs from accelerometers (Epi-sensors) were ~ 40 dB higher than the NLs from velocimeters (STS-sensors) for periods > 10 s, which is because the small and light Epi-sensors are sensitive to environmental changes. Daily and weekly variations in spectral noise level were observed clearly in short periods < 1 s, and these are considered to be related to human activities. The seismometers in boreholes showed ~20 dB weaker NLs in the cultural noise band. The NLs of accelerometers at a depth of 30 m were also much lower by 30 dB for long periods > 10 sec. Overall the functioning of the new velocimeter and accelerometer stations was reliable for periods ranging from 0.02~100 s and 0.02~10 s, respectively.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.18 no.4
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• pp.1-14
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• 2019

In order to minimize problems related to the performance and safety of automobiles, the "Age Limit for Vehicles System" which restricts the age of buses, taxis, and trucks, was implemented in 1973. This contributed to the reduction of accidents and increase of user's service satisfaction. However, the restriction system for trucks was abolished in August 1997 as it was deemed restrictive to economic growth. It is found that one of main causes of traffic accidents such as Changwon Tunnel accident occurred in recent years, is the aging of trucks. Thus, There is a growing need for the management of the age of trucks. In this study, the time when cargo vehicles need to be managed is suggested, by analyzing the safety of cargo vehicles using vehicles inspection data.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.418-425
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• 2019

A piezoelectric ceramic fiber composite (PCFC) was successfully fabricated using $0.69Pb(Zr_{0.47}Ti_{0.53})O_3-0.31[Pb(Zn_{0.4}Ni_{0.6})_{1/3}Nb_{2/3}]O_3$ (PZT-PZNN) for use in small-scale wind energy harvesters. The PCFC was formed using an epoxy matrix material and an array of Ag/Pd-coated PZT-PZNN piezo-ceramic fibers sandwiched by Cu interdigitated electrode patterned polyethylene terephthalate film. The energy harvesting performance was evaluated in a custom-made wind tunnel while varying the wind speed and resistive load with two types of flutter wind energy harvesters. One had a five-PCFC array vertically clamped with a supporting acrylic rod while the other used the same structure but with a five-PCFC cantilever array. Stainless steel (thickness: $50{\mu}m$) was attached onto one side of the PCFC to form the PZT-PZNN cantilever. The output power, in general, increased with an increase in the wind speed from 2 m/s to 10 m/s for both energy harvesters. The highest output power of $15.1{\mu}W$ at $14k{\Omega}$ was obtained at a wind speed of 10 m/s for the flutter wind energy harvester with the PZT-PZNN cantilever array. The results presented here reveal the strong potential for wind energy harvester applications to supply sustainable power to various IoT micro-devices.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.11
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• pp.944-951
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• 2018

Artificial icing test and wind tunnel test can be performed to reduce the development period when a rotorcraft is required operation under icing situations. Artificial icing test of the KUH(Korean Utility Helicopter) was performed in advance to verify anti-icing and de-icing performance before natural icing test. Although high-precision sensor, the CCP(Cloud Combination Probe) is used to measure icing test condition parameters such as LWC(Liquid Water Content) and MVD(Median Volume Diameter), the measured values need to be verified in various methods due to the possibility of uncertainties which are the test atmosphere environment, sensor errors, and etc. The calculated LWC from the ice thickness cumulated on the fuselage of the KUH is compared to the measured value by CCP, and the results show the effective indirect method to check the test conditions.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.591-602
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• 2020

Several alternative rock-cutting concepts, which are modified from the conventional ones, have been developed lately. Of the concepts, undercutting is one of the latest technologies. In this study, as a fundamental study on the undercutting technique, the rock-cutting mechanism and important parameters of the undercutting were introduced. This study built up cutting test system for evaluating the cutting performance of an actuated undercutting disc cutter (ADC), and carried out a series of cutting tests under different cutting parameters of ADC. The characteristics of cutter forces obtained from ADC rock-cutting tests were analyzed. The both average and peak values of the three directional cutter forces were linearly increased with the increases of linear velocity, penetration depth in vertical direction and eccentricity of ADC.

• Journal of Ocean Engineering and Technology
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• v.35 no.3
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• pp.173-182
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• 2021

The maneuvering performance of a ship on the actual sea is very different from that in calm water due to wave-induced motion. Enhancement of a ship's maneuverability in waves at the design stage is an important way to ensure that the ship navigates safely. This paper focuses on the maneuvering prediction of a Russian trawler in wind and irregular waves. First, a unified seakeeping and maneuvering analysis of a Russian trawler is proposed. The hydrodynamic forces acting on the hull in calm water were estimated using empirical formulas based on a database containing information on several fishing vessels. A simulation of the standard maneuvering of the Russian trawler was conducted in calm water, which was checked using the International Maritime Organization (IMO) standards for ship maneuvering. Second, a unified model of seakeeping and maneuvering that considers the effect of wind and waves is proposed. The wave forces were estimated by a three-dimensional (3D) panel program (ANSYS-AQWA) and used as a database when simulating the ship maneuvering in wind and irregular waves. The wind forces and moments acting on the Russian trawler are estimated using empirical formulas based on a database of wind-tunnel test results. Third, standard maneuvering of a Russian trawler was conducted in various directions under wind and irregular wave conditions. Finally, the influence of wind and wave directions on the drifting distance and drifting angle of the ship as it turns in a circle was found. North wind has a dominant influence on the turning trajectory of the trawler.

• Tunnel and Underground Space
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• v.32 no.6
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• pp.586-597
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• 2022

In this study, a model was developed for the estimating the locational thickness information of the upper clay layer to be used for the consolidation vulnerability evaluation in the Nakdong river estuary. To estimate ground layer thickness information, we developed four spatial estimation models using machine learning algorithms, which are RF (Random Forest), SVR (Support Vector Regression) and GPR (Gaussian Process Regression), and geostatistical technique such as Ordinary Kriging. Among the 4,712 borehole data in the study area collected for model development, 2,948 borehole data with an upper clay layer were used, and Pearson correlation coefficient and mean squared error were used to quantitatively evaluate the performance of the developed models. In addition, for qualitative evaluation, each model was used throughout the study area to estimate the information of the upper clay layer, and the thickness distribution characteristics of it were compared with each other.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.11-22
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• 2023

In this study, a structural concrete square beam was developed using the centrifugal molding technique. In order to secure the bending stiffness of the cross section, the hollow rate of the cross section was set to 10% or less. Instead of using the current poor mixture of concrete, a special formwork for producing a centrifugal square beam was manufactured, and a concrete mixing ratio with a high slump (150-200) and a design strength of 100 MPa or more was developed and applied. The produced centrifugally formed rectangular beams were subjected to performance tests according to the standard bending and shear test standards for centrifugally formed members. The static load test results for the four specimens exceeded both the nominal bending strength and nominal shear strength, which are design values through structural design, proving the structural reliability of the ultra-high-strength centrifugally formed square beam.

• Journal of Advanced Navigation Technology
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• v.27 no.2
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• pp.197-202
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• 2023

This paper presents the design method and electrical characteristics of a high-efficiency power amplifier for a 50 Watts class repeater applied to a 5G system and used in in-building, subway, and tunnel. GaN was used for the termination transistor of the power amplifier designed here, and intermodulation signals were removed using DPD to satisfy linearity. In addition, in order to handle various requirements such as amplifier gain control and alarm processing required in the 5G system, the microprocessor is designed to exist inside the power amplifier. The amplifier manufactured to confirm the electrical performance of the power amplifier satisfying these conditions satisfied 46.5 dBm and the overall efficiency of the amplifier was 37%, and it was confirmed that it satisfied various alarm conditions and electrical characteristics required by telecommunication companies.