• Progress in Superconductivity
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• v.11 no.1
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• pp.1-7
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• 2009

HTS coated conductor was heat treated at high temperatures below the melting points of silver and YBCO at different oxygen partial pressures. Current carrying capacity and microstructure were varied depending on the presence of silver protection layer. Critical current of coated conductor without silver protection layer was not changed when heat treatment was performed at $850^{\circ}C$ for 2 hr in an oxygen atmosphere. However, coated conductor with silver protection layer revealed abrupt drop of $I_c$ from 140A to 8A when heat treatment was performed at $800^{\circ}C$ for 2 hr in an oxygen atmosphere. Coated conductor with silver protection layer retained $70{\sim}80$ percent of its original $I_c$ when heat treatment was performed at $800^{\circ}C$ for 2 hr in an argon atmosphere containing 1000ppm oxygen. SEM and XRD observations showed the presence of interaction between YBCO and silver depending on the atmosphere of heat treatment. The reaction between YBCO superconductor and silver was accelerated at high oxygen partial pressure and resulted in the change in microstructure and decrease of critical current density even by the heat treatment performed at temperature much lower than the melting points of silver and YBCO.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.4
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• pp.137-141
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• 2004

In this paper, a thermopneumatic PMDS (polydimethlysiloxane) micropump with nozzle/diffuser elements is presented. The micropump is composed of nozzle/diffuser elements as dynamic valves, an actuator consisting of a circular PDMS diaphragm and a Cr/Au heater on a glass substrate. Four PDMS layers are used for fabrication of an actuator chamber, actuator diaphragm by a spin coating process, spacer layer, and nozzle/diffuser by the SU-8 molding process. The radius and thickness of the actuator diaphragm is 2 mm and 30 ${\mu}{\textrm}{m}$, respectively. The length and the conical angle of the nozzle/diffuser elements are 3.5 mm and 20$^{\circ}$, respectively. The actuator diaphragm is driven by the air cavity pressure variation caused by ohmic heating and natural cooling. The flow rate of the micropump in the frequency domain is measured for various duty cycles of the square wave input voltage. When the square wave input voltage of 5 V DC is applied to the heater, the maximum flow rate of the micropump is 44.6 ${mu}ell$/min at 100 Hz with a duty ratio of 80% under the zero pressure difference.

• Transactions of the Korean hydrogen and new energy society
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• v.6 no.2
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• pp.65-73
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• 1995

Negative electrode was prepared by mixing $Ti_{0.7}Zr_{0.3}Cr_{0.3}Mn_{0.3}V_{0.6}Ni_{0.8}$ alloy powder with copper or nickel powder and pressing in the air. The cycled electrodes were analyzed with SEM, potentiostat and electrochemical impedance spectroscopy. It was found that the Cu-compacted electrode showed better low temperature dischargeability and higher rate capability than Ni-compacted electrode. From SEM analysis of the cycled electrode compacted with copper powder, it was observed that the surface of MH particles was covered with copper grains and whisker precipitated from electrolyte after dissolution during cell test. It is found that the improved electrode characteristics are attributed to the copper layer on MH particles deposited by dissolution and precipitation(DP) process.

• Transactions on Electrical and Electronic Materials
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• v.13 no.5
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• pp.215-220
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• 2012

Miniature ultrasonic and tactile sensors on Si substrate have been proposed, fabricated and characterized to detect objects for a dexterous robot. The ultrasonic sensor consists of piezoelectric PZT thin film on a Pt/Ti/$SiO_2$ and/or Si diaphragm fabricated using a micromachining technique; the ultrasonic sensor detects the piezoelectric voltage as an ultrasonic wave. The sensitivity has been enhanced by improving the device structure, and the resonant frequency in the array sensor has been equalized. Position detection has been carried out by using a sensor array with high sensitivity and uniform resonant frequency. The tactile sensor consists of four or three warped cantilevers which have NiCr or $Si:B^+$ piezoresistive layer for stress detection. Normal and shear stresses can be estimated by calculation using resistance changes of the piezoresitive layers on the cantilevers. Gripping state has been identified by using the tactile sensor which is installed on finger of a robot hand, and friction of objects has been measured by slipping the sensor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.11
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• pp.803-809
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• 2014

In this paper, we investigate physical layer security in a cooperative cognitive radio networks (CRN) with a relay selection in the presence of a primary user and an eavesdropper. To protect the CRN from wiretapping by the eavesdropper, we propose employing an opportunistic relay selection scheme and multiple antennas at the destination that work based on the availability of channel state information at the receivers. Under these configurations, we derive an exact closed-form expression for the secrecy outage probability of the CRN, and also derive an asymptotic probability. Numerical results will be presented to verify the analysis.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.292-300
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• 2001

The paper describes spectroscopic characteristics of plasma induces in the pulsed YAG laser welding of alloys containing a large amount of volatile elements. The authors have conducted the spectroscopic analyses of laser induced Al-Mg alloys plasma in the air and argon atmosphere. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg lines, as well as the intense molecular spectra of A10 and Mg0 formed by chemical reactions of evaporated Al and Mg atoms from the pool surface with oxygen in the air. In argon atmosphere, Mg0 and AI0 spectra vanished, but AIH spectrum was detected. The hydrogen source was presumably hydrogen dissolved in the base metals, water absorbed on the surface oxide layer, or $H_2$ and $H_2O$ in the shielding gas. The resonant 1ines of Al and Mg were strongly self-absorbed, in particular, self-absorption of the Mg 1ine was predominant. These results show that the laser induced plasma was made of metal1ic vapor with relatively low temperature and high density.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2322-2327
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• 2002

The corrosion degradation characteristics of the 12Cr alloy steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the backward radiated Rayleigh surface wave. In order to evaluate corrosion degradation characteristics, we constructed automated system for the backward radiation, and the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the specimens. The velocity of the surface wave decrease as the increase of the aging time in the backward radiation profile, which seems to result from the increase of the effective degrading layer thickness. And, amplitude of the surface wave increase as the aging time, which seems to result from the increase of the intergranular corrosion. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion degradation characteristics of the aged materials.

• Journal of Sensor Science and Technology
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• v.16 no.1
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• pp.62-67
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• 2007

This paper presents a novel MEMS condenser microphone with rigid backplate to enhance acoustic characteristics. The MEMS condenser microphone consists of membrane and backplate chips which are bonded together by gold-tin (Au/Sn) eutectic solder bonding. The membrane chip has 2.5 mm${\times}$2.5 mm, $0.5{\mu}m$ thick low stress silicon nitride membrane, 2 mm${\times}$2 mm Au/Ni/Cr membrane electrode, and $3{\mu}m$ thick Au/Sn layer. The backplate chip has 2 mm${\times}$2 mm, $150{\mu}m$ thick single crystal silicon rigid backplate, 1.8 mm${\times}$1.8 mm backplate electrode, and air gap, which is fabricated by bulk micromachining and silicon deep reactive ion etching. Slots and $50-60{\mu}m$ radius circular acoustic holes to reduce air damping are also formed in the backplate chip. The fabricated microphone sensitivity is $39.8{\mu}V/Pa$ (-88 dB re. 1 V/Pa) at 1 kHz and 28 V polarization voltage. The microphone shows flat frequency response within 1 dB between 20 Hz and 5 kHz.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.434-437
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• 2005

Chemical Mechanical Polishing (CMP) has become an essential step in the overall semiconductor wafer fabrication technology. In general, CMP is a surface planarization method in which a silicon wafer is rotated against a polishing pad in the presence of slurry under pressure. The polishing pad, generally a polyurethane-based material, consists of polymeric foam cell walls, which aid in removal of the reaction products at the wafer interface. It has been found that the material removal rate of any polishing pad decreases due to the so-called 'pad glazing' after several wafer lots have been processed. Therefore, the pad restoration and conditioning has become essential in CMP processes to keep the urethane polishing pad at the proper friction coefficient and to allow effective slurry transport to the wafer surface. Diamond pad conditioner employs a single layer of brazed bonded diamond crystals. Due to the corrosive nature of the polishing slurry required in low pH metal CMP such as copper, it is essential to minimize the possibility of chemical interaction between very low pH slurry (pH <2) and the bond alloy. In this paper, we report an exceptional protective coated conditioner for in-situ pad conditioning in low pH Cu CMP process. The protective Cr-coated conditioner has been tested in slurry with pH levels as low as 1.5 without bond degradation.

• Korean Journal of Materials Research
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• v.28 no.3
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• pp.135-141
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• 2018

Stainless steel is being used in various industries such as automobile and aerospace for its cheap manufacturing cost and excellent mechanical properties. However, stainless steel failed to stably protect a specimen with a $Cr_2O_3$ protective layer at temperatures above $1000^{\circ}C$. Thus, improving the high temperature flame resistance of the specimen through additional surface coating was needed. In this study, multilayer coatings of YSZ and $Al_2O_3$ were performed on SUS 304 specimens using pack cementation coatings and thermal plasma spray. The multilayer coated specimen showed enhanced thermal properties due to the coated layers. The microstructures and phase stability are discussed together with flame conditions at $1350^{\circ}C$.