• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1712-1713
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• 2011

Inkjet technology have many merits in plenty of industrial applications. However, deposited droplet has a very critical issue that is coffee ring effect, for the application to an industrial manufacturing process. To remove the coffee ring effect, the effect of thermal treatment conditions on shapes of inkjet printed silver patterns were investigated in various surface condition. The surface changes were characterized by the contact angle measurement. Droplets from a 50 ${\mu}m$ nozzle were printed on the substrate after optimizing the ejection of individual droplets. Ink with a high boiling point of main solvent results in coffee ring effect. This result implies that the dominant factor that determines the shape of droplet is the drying conditions of main solvent of silver nanoparticle colloidal ink. As a results, selecting a proper thermal treatment conditions is very crucial for better shapes of inkjet printed silver nanoparticle colloidal patterns.

• Carbon letters
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• v.11 no.3
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• pp.211-215
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• 2010

Multi-walled carbon nanotube (MWCNT)/poly(vinyl alcohol) (PVA) nanocomposite hydrogels were prepared by freezingthawing method for the electro-responsive transdermal drug delivery. MWCNTs were used as the functional ingredient to improve both mechanical and electrical properties of MWCNT/PVA nanocomposite hydrogels. The morphology of nanocomposites revealed the uniform distribution of MWCNTs and the good interfacial contact. The compression moduli of hydrogel matrices increased greatly from 40 to 1500 kPa by forming MWCNT/PVA nanocomposites. The swelling ratio of MWCNT/PVA nanocomposites decreased as the content of MWCNTs increased under no electric voltage applied. However, the swelling ratio of MWCNT/PVA nanocomposites increased as the content of MWCNTs increased under electric voltage applied and the applied electric voltage increased. The drug was released in the electro-responsive manner through the skin due to the electro-sensitive swelling characteristics of MWCNT/PVA nanocomposite hydrogels.

• Fire Science and Engineering
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• v.18 no.4
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• pp.72-77
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• 2004

In this paper, we studied on the short-circuit process, surface structure, and component variation of vinyl cords. In the results of high speed imaging system (HSIS) analysis, as soon as wire covering was damaged by heat, the conductor of wire came in contact with the other conduct of wire, and the short-circuit occurred. Stereomicroscope and SEM analysis indicated that the source part of wire showed V-type form. The molten beads of load part were bigger than those of source part. In the results of EDX analysis, Cu and O were detected in the source part, whereas covering material (Cl, Ca), Cu and O were detected in the load part. The results will help us to find out the cause of electrical fire.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.21-21
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• 2003

To increase the light-emission efficiency of LED, we increased the internal and external quantum efficiency by suppressing the defect formation in the quantum well and by increasing the light extraction efficiency in LED, respectively. First, the internal quantum efficiency was improved by investigating the effect of a low temperature (LT) grown p-GaN layer on the In$\sub$0.25/GaN/GaN MQW in green LED. The properties of p-GaN was optimized at a low growth temperature of 900oC. A green LED using the optimized LT p-type GaN clearly showed the elimination of blue-shift which is originated by the MQW damage due to the high temperature growth process. This result was attributed to the suppression of indium inter-diffusion in MQW layer as evidenced by XRD and HR-TEM analysis. Secondly, we improved the light-extraction efficiency of LED. In spite of high internal quantum efficiency of GaN-based LED, the external quantum efficiency is still low due to the total internal reflection of the light at the semiconductor-air interface. To improve the probability of escaping the photons outside from the LED structure, we fabricated nano-sized cavities on a p-GaN surface utilizing Pt self-assembled metal clusters as an etch mask. Electroluminescence measurement showed that the relative optical output power was increased up to 80% compared to that of LED without nano-sized cavities. I-V measurement also showed that the electrical performance was improved. The enhanced LED performance was attributed to the enhancement of light escaping probability and the decrease of resistance due to the increase in contact area.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.36-38
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• 2003

In this paper, the surface modificatioin of PDMS (polydimethyl-siloxane) which is a useful material of microfluidic devices is presented. PDMS-based devices can be fabricated by casting the polymer in a mold, but the porosity and the hydrophobicity of PDMS make difficult to use as bio-medical devices. To overcome these disadvantages, the PDMS surface is grafted with HEMA (2-Hydroxyethyle methacrylate) treatments and $O_2$ plasma process. The $O_2$ plasma process is performed for 20 sec after curing PDMS, and PDMS is put in the prepared HEMA without Monomethyle Ether Hydroquinone. Residual monomers and homopolymers of HEMA-treated PDMS surface are removed using soxhlet extractor. The PDMS surface modification using HEHA without Monomethyle Ether Hydroquinone is experimented, and compare to when additing $FeCl_2{\cdot}2H_2O$. A method with a soxhlet extractor compare to the existing rinse method. The hydrophilicity is confirmed by the measurement of a contact angle, and we observe whether the hydrophilicity is retained.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1349_1350
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• 2009

Thin films of pp(ST-Co-VA) were fabricated by plasma deposition polymerization (PVDPM) technique. Properties of the plasma polymerized pp(ST-Co-VA) thin films were investigated for application to semiconductor device as insulator. Thickness, dielectric property, composition of the pp(ST-Co-VA) thin films were investigated considering the relationship with preparation condition such as gas pressure and deposition time. In order to verify the possibility of application to organic thin film transistor, a pentacene thin film was deposited on the pp(ST-Co-VA) insulator by vacuum thermal evaporation technique. Crystalline property of the pentacene thin film was investigated by XRD and SEM, FT-IR. Surface properties at the pp(ST-Co-VA)/pentacene interface was investigated by contact angle measurement. The pp(ST-Co-VA) thin film showed a high-k (k=4.6) and good interface characteristic with pentacene semiconducting layer, which indicates that it would be a promising material for organic thin film transistor (OTFT) application.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1169_1170
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• 2009

This paper introduces insulator pollutant accumulate pattern in the tunnel of korea railroad. To accomplish this goal, effective sample collecting method was proposed for the first step. Dust at the surface was collected directly. Distilled water and brush was used while collecting. Through this method dust is easily and accurately collected. The second step is pollutant analysis. Several analyze item is selected such as quantity, conductivity, contact angle, Optical Microscope(OM), IR, Equivalent Salt Deposit Density(ESDD), and ICP-AES. The third step, best represent tunnel was selected considering location, length and natural surroundings. Also to consider the difference at inside the tunnel, several bracket insulators were selected along to the location. To make the result precise, above procedure was repeated several times at the same target. Finally relation among type of train, numbers of movement, surroundings, length will be considered in combination with the pollution. With this result pollute map for KORAIL could be accomplished and inspect period will be optimized case by case.

• Journal of KSNVE
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• v.5 no.4
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• pp.565-575
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• 1995

Gearboxes are often used in the petrochemical and electrical power plants to transmit mechanical power between two branches of a machinery train rotating at different speeds. When the gearboxes are connected with rotors supported by journal bearings, bearing loads vary in magnitude and direction with rotor speed and torque transmitted by the gearboxes. In this study, dynamic characteristics of the system which consists of gearboxes and a rotor supported by journal bearings are investigated analytically and experimentally by employing the polynomial transfer matrix method and modal analysis under different speeds and torque levels. Journal bearing loads due to the transmitted torque are claculated analytically and the stiffness and damping coefficient of the journal bearings are obtained using finite element method. Comparison of the analytical and experimental results shows that the cross coupled stiffness coefficients increase with increasing rotor speed, while the cross coupled damping coefficients decrease. This generates the oil whirl instability in the journal bearings. As the transmitted torque level goes up, the stiffness coefficients of the journal bearing and the first horizontal natural frequency increase. High levels of the transmitted torque produce high bearing stiffness since the contact loads of the mating gear teeth increase. The logarithmic decrement, which is a stability indicator, is shown to decrease with increasing speed and decreasing torque. Thus, at the low torque level, the system become unstable even at the low shaft speed.

• Tribology and Lubricants
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• v.34 no.4
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• pp.132-137
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• 2018

Ultrasonic waves are used in various applications in multiple devices, sensors, and high-power machinery, such as processing machines, welders, and cleaners, because the acoustic vibration frequencies are above the human audible frequency range. In ultrasonic machining, electrical energy at a high frequency of 20 kHz or more is converted into mechanical vibration by a vibrator and an amplifier. This technique allows instantaneous separation between a tool and a workpiece during machining, machining by pulse impulse force at the time of re-contact and minimizes the minute elastic deformations of the workpiece and machine tools due to the cutting effect. The Al7075 alloy used in this study is a typical aluminum alloy with superior strength that is mainly used in aircrafts, automobiles, and sporting goods. To investigate the optimal conditions for machining aluminum alloy using ultrasonic vibration, the present experiment utilized the Taguchi orthogonal array method, and the coefficient of friction was analyzed using the characteristics of the Taguchi technique. In ultrasonic friction and abrasion tests, the changes in the friction coefficient were measured in the absence of ultrasonic vibrations and at 28 kHz and 40 kHz. As a result, the most considerable influence on the friction coefficient was found to be the normal load, and the frequency of ultrasonic vibrations increases, the coefficient of friction increases. It was thus confirmed that the amount of wear increases when ultrasonic vibration is applied.

• Journal of Sensor Science and Technology
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• v.27 no.5
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• pp.340-344
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• 2018

Electrodes are an important part of electrocardiography (ECG); disposable electrodes have been extensively used. However, personal ECG monitoring devices for Internet of Things applications require reusable electrodes. As there have been no systematic studies on the characteristics of reusable electrodes to date, we conducted this study to assess the performance and feasibility of electrodes with different materials. We built reusable electrodes using twelve different metallic materials, including commonly used copper, silver, zinc, plating materials, chemically inert titanium, stainless steel, and aluminum. Each electrode was fabricated to a size of $5{\times}10mm$. Their characteristics such as offset, baseline drift, stabilization time, and chemical inertness were compared. A personal ECG monitoring system was used to test the manufactured electrodes. The performances of the Ag, Cu, and Zn electrodes were better than the performances of other electrodes. However, these materials may not be used owing to the chemical changes that occur when the electrodes are in contact with the skin, such as discoloration and corrosion, which deteriorate their electrical characteristics. Titanium, stainless steel, and aluminum are chemically stable. The titanium electrode showed the best performance among the three, and it is our recommendation as a material for manufacturing reusable electrodes.