• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.2
• /
• pp.101-108
• /
• 2007

This paper presents an efficient meshless method for analyzing cracked piezoelectric structures subjected to mechanical and electrical loading. The method employs an element free Galerkin (EFG) formulation and an enriched basic function as well as special shape functions that contain discontinuous derivatives. Based on the moving least squares (MLS) interpolation approach, The EFG method is one of the promising methods for dealing with problems involving progressive crack growth. Since the method is meshless and no element connectivity data are needed, the burdensome remeshing procedure required in the conventional finite element method (FEM) is avoided. The numerical results show that the proposed method yields an accurate near-tip stress field in an infinite piezoelectric plate containing an interior hole. Another example is to study a ceramic multilayer actuator. The proposed model was found to be accurate in the simulation of stress and electric field concentrations due to the abrupt end of an internal electrode.

• Journal of Sensor Science and Technology
• /
• v.15 no.5
• /
• pp.334-340
• /
• 2006

A compact biosignal monitoring device was developed. Electrodes for electrocardiogram (ECG) and a LED and silicon detector for photoplethysmogram (PPG) were used. A lead II type was arranged for ECG measurement and reflected light was measured at the finger tip for PPG. A single chip microprocessor (model ADuC812, Analog Device) controlled a measurement protocol and processed measured signals. PPG and ECG had a sampling rate of 300 Hz with 8-bit resolution. The maximum power consumption was 100 mW. The microprocessor computed pulse transit time (PTT) between the R-wave of ECG and the peak of PPG. To increase the resolution of PTT, analog peak detectors obtained the peaks of ECG and PPG whose interval was calculated using an internal clock cycle of 921.6 kHz. The device was designed to be operated by 3-volt battery. Biosignals can be measured for $2{\sim}3$ days continuously without the external interruptions and data is stored to an on-board memory. Our system was successfully tested with human subjects.

• Journal of Biomedical Engineering Research
• /
• v.29 no.4
• /
• pp.286-294
• /
• 2008

This work investigates the characteristics of brain interactions of experienced Zen-Buddhist practitioners by obtaining multichannel EEG (electroencephalogram) data. Brain interactions were compared among three phases-40-minute meditation (M), 5-minute Chakra-focusing practice (Z) and rest with closed eyes (R). The similarity index S, developed in nonlinear dynamical system theory, was employed to measure the degree of possibly asymmetric coupling. Meditators exhibited, overall, stronger interactions among multiple cortical areas in meditation stages M and Z than in the R state. This enhancement was greater in the M stage when the meditator was accompanied by a thought-free and fully consciousness state. In the high-frequency band (>13Hz), the interdependence was also higher in both meditation stages than at baseline rest. However, the interaction strength, especially in the posterior regions, was greatest in the Z stage, which involved internal attention. Few electrode pairs were observed with significant pair-wise asymmetry in the Z state. The similarity is a possible characteristic of dense reciprocal and strong mutual interactions between multiple cortical areas during meditation - especially in the Z state in the high-frequency band. These results demonstrate that profound Zen meditation induces various dynamic states in different phases of meditation, possibly reflected by nonlinear interdependence measure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.264-265
• /
• 2008

While the reliability of bulk insulation has become important particularly in multilayer boards and embedded boards, electronics are to be used under various environments such as at high temperature and in high humidity. We observed internal space charge behavior for two types of epoxy composites under dc electric fields to investigate the influence of water at high temperature. In the case of glass/epoxy specimen, homocharge is observed at water-treated specimen, and spatial oscillations become clearer in the water-treated specimens. Electric field in the vicinity of the electrodes shows the injection of homocharge. In aramid/epoxy specimens, heterocharge is observed at water-treated specimens, i.e. negative charge accumulates near the anode, while positive charge accumulates near the cathode. Electric field is enhanced just before each electrode. In order to further examine the mechanism of space charge formation, we have developed a new system that allows in situ space charge observation during ion migration tests at high temperature and high humidity. Using this in situ system.

• Journal of IKEEE
• /
• v.19 no.3
• /
• pp.407-414
• /
• 2015

Electrical impedance tomography is an imaging technique to reconstruct the internal conductivity distribution based on applied small currents and measured voltages through an array of electrodes attached on the boundary of a domain of interest. In this paper, an analytical solver with complete electrode model is derived and the analytical voltage data are calculated. Moreover, the voltage data are also computed with existing numerical solvers such as finite element method and boundary element method. The forward solutions using homogeneous and inhomogeneous conditions are compared with phantom experiments through the root mean square errors.

• Journal of the Optical Society of Korea
• /
• v.17 no.3
• /
• pp.269-274
• /
• 2013

The effect of diffusing substrate and pillow lenses on the outcoupling efficiency of organic light-emitting diodes (OLEDs) was studied by optical simulation based on the point-dipole model. The diffusing substrate included Mie scatterers by which the condition of total internal reflection could be broken. The finite-difference time-domain method was used to obtain the intensity distribution on the transparent electrode of an OLED, which was used as a light source to carry out a ray-tracing simulation of the OLED and the diffusing substrate. It was found that the outcoupling efficiency of the OLED was sensitive to the thickness of organic layers and could be increased by 21.0% by adopting a diffusing substrate in which Mie scatterers whose radius was $2.0{\mu}m$ were included at the density of $10^7mm^{-3}$ and by 65.5% by forming one pillow lens with the radius of 2 mm on the front surface of the glass substrate. This study revealed that the outcoupling efficiency could be improved by adopting diffusing substrate and pillow lenses along with the optimization of the thickness of each layer in the OLED.

• Proceedings of the KWS Conference
• /
• 1997.10a
• /
• pp.184-193
• /
• 1997

Aluminium and aluminium alloys have the high electrical and heat conductivity. It gives rise to difficulties for a choice of electrodes material for their contact electric welding. This paper describes the investigations performed to solve the above problem. The purpose of this investigation was to obtain dispersion-hardening alloys by the internal oxidation method, to optimize their contents and treatment modes, to produce electrodes of these alloys and to test them. The strengthing effect of alloys with oxide particles depends on their size stability at high temperatures. Despite of the fact, that oxides are the most stable of all the non-metallic phases their coagulation takes place. Based on the early results, we chose two types of alloys, first No. 1 Cu - 0,4%Al and second No. 2 Cu - 0,2%Be for production of electrodes. These alloys had not additional alloying elements. These alloys were prepared as 1 mm plates and flake-formed 200 m thick, and also No. 1 as a powder of size 100 mkm (received from Korea). The large samples for electrodes were produced by three methods : explosive welding method, dynamic one including the explosion compression of electrode blank and the quasi-dynamic method including the high-speed compression of dense briquest and the further hot extrusion of a rod.

• Korean Journal of Materials Research
• /
• v.13 no.12
• /
• pp.779-784
• /
• 2003

Nickel powders were obtained by various preparation methods, and their sintering characteristics were investigated. Nickel powders made by wet chemical process (WCP) had a higher surface area and more narrow size distribution than that of chemical vapor deposition (CVD) method. Nickel-oxide powders by the WCP method were prepared at $200^{\circ}C$ for 3 hr. The oxidation behaviour of nickel-oxide powder is similar with that of the CVD method. Nickel powders made by the WCP method showed a higher shrinkage in the range of $600^{\circ}C$∼$900^{\circ}C$ than that of commercial powder made by the CVD method. The similar results were observed on the surface microstructure of sintered bodies by SEM measurements.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11b
• /
• pp.525-528
• /
• 2001

ZnO:Al thin film can be used as a transparent conducting oxide(TCO) which has low electric resistivity and high optical transmittance for the front electrode of amorphous silicon solar cells and display devices. This study of electrical, crystallographic and optical properties of Al doped ZnO thin films prepared by Facing Targets Sputtering(FTS), where strong internal magnets were contained in target holders to confine the plasma between the targets, is described. Optimal transmittance and resistivity was obtained by controlling flow rate of $O_2$ gas and substrate temperature. When the $O_2$ gas rate of 0.3 and substrate temperature $200^{\circ}C$, ZnO:Al thin film had strongly oriented c-axis and lower resistivity( < $10^{-4}{\Omega}-cm$ ).

• Transactions of Materials Processing
• /
• v.19 no.5
• /
• pp.283-289
• /
• 2010

Extrusion process in the bulk material for fabrication of miniature helical gears has problems such as a high forming load and short tool life because the cross-section is complex and asymmetry. To overcome these problems, in this study, miniature helical gears were fabricated by Zn-22Al powder hot extrusion. The included die angle for minimum extrusion load and improving die filling was determined by FE-simulation. The Zn-22Al spheroidal powder produced by gasatomization were compacted and sintered for extrusion experiment. The dimension of helical-gear is 0.3mm in module, 3.35mm in pitch diameter, $15^{\circ}$ in helix angle and the number of teeth is 12. All of the extrusion experiments were performed with internal helical gear die which was machined by precision electric discharge machining using the electrode. The experiment was conducted at $190^{\circ}C$ to $310^{\circ}C$ to obtain extrusive and mechanical properties. The extruded helical gears were analyzed through extrusion load, Vickers hardness and SEM images for each extrusion temperature. The powder hot extrusion process was successfully applied to fabricate a miniature helical gear.