• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.12
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• pp.1050-1057
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• 2015

This paper presents the characteristics of broadband double-cone antennas. The antenna is used to measure electromagnetic fields(2~5 GHz) radiated from a primary or a secondary electrode of a pole-transformer when partial discharge occurs inside the pole-transformer. The theoretical analysis is conducted using commercial software based on a finite difference time domain(FDTD) method. The parameters are a radius, and a height of the broadband double-cone antennas, and the number of posts on a ground plane. This paper examines influences of structural parameters of the broadband double-cone antennas on return loss. The results show that a condition for an optimum structure of broadband double-cone antennas exists. It also shows that the broadband double-cone antennas have radiation patterns similar to those of a dipole antenna. Therefore the broadband double-cone antennas are appropriate for the measurement of radiated electromagnetic fields from the pole-transformer. To verify the theoretical analysis, computed results are compared to experimental results.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.945-948
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• 2008

Nanocomposite materials provides efficient reinforcement, thermal endurance, and many other advantages depending on the additives used, with applications in the aerospace, automotive, and biomedical industries. Here, epoxy based nanocomposites were synthesized in the presence of Cloisite 15A and characterized with TEM, XRD, TGA, and DMA. To determine the effect of the clay d-spacing, Cloisite 20A was also used to synthesize the nanocompostes. In addition to the traditional hot plate method, an ultrasonicator was used to investigate the effect of different types of mixing on the properties of the nanocomposite; no significant effect was found. An examination of the nanocomposite morphology revealed that all the nanocomposites synthesized yielded an intercalated structure. When 5 wt% of Cloisite 15A was used with 20 min sonication time, the storage modulus increased 10% over the neat(no clay) nanocomposite. In general, the presence of Cloisite 15A produced a better storage modulus than Cloisite 20A.

• Smart Structures and Systems
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• v.26 no.3
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• pp.331-343
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• 2020

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe₂O₄ and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1779-1784
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• 2010

Net washing in a fishery involves considerable labor and is a time-consuming process; it also causes severe environmental pollution. In this study, we developed a net hauler for washing fishing nets. This hauler can be used to simultaneously haul and wash the net. We devised the revolver structure of the net hauler in order to resolve the net slip problem. The net hauler can be used by itself for washing small-sized nets, or it can be used in an auxiliary washing step in case of a large-sized net. Further, the component installed in the net hauler for unraveling the net improves the net washing performance of an automatic net washer. During the experiments conducted using the prototypes of the new net hauler, the net did not slip and the desired washing performance could be achieved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1043-1050
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• 2010

Fuel stratification and thermal stratification occur in the HCCI combustion chamber on a microscopic scale. They affect the ignition and combustion processes. In this study, the effect of the inhomogeneity in the mixture gas on the HCCI combustion process was investigated. Two-dimensional chemiluminescence images were captured using a framing camera to evaluate the flame structure. DME was used as the test fuel. First, the effect of inhomogeneity in the fuel distribution in the premixture was investigated for the four-stroke optically accessible engine. Then, by comparing the combustion of the homogeneous mixture in the rapid compression machine, which does not contain any residual gas, with the combustion in the four-stroke engine, the effect of inhomogeneity in temperature due to the residual gas was analyzed. The results showed that a time lag appears spatially in combustion under inhomogeneous conditions in the four-stroke engine. The spatial variation in the combustion without the residual gas in the rapid compression machine is less than that in the combustion in the four-stroke engine.

• Proceedings of the Membrane Society of Korea Conference
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• 2004.05a
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• pp.94-97
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• 2004

Micro/nano-sized L $a_{0.6}$S $r_{0.4}$Co $O_{3-}$$\delta$/ particles are considered to improve oxygen permeability in highly selective inorganic oxygen separation membrane. A L $a_{0.7}$S $r_{0.3}$G $a_{0.6}$F $e_{0.4}$ $O_{3-}$$\delta$/ membrane with perovskite structure is fabricated by a conventional solid-state reaction. As the oxygen permeation flux of the L $a_{0.7}$S $r_{0.3}$G $a_{0.6}$F $e_{0.4}$ $O_{3-}$$\delta$/ membrane was lower than commercial gas separation membranes, we coated the L $a_{0.6}$S $r_{0.4}$Co $O_{3-}$$\delta$/ particles to enhance the oxygen permeation flux. It has been demonstrated that the effective area of reactive free surface is an important factor in determining the effectiveness of the introduction of coating layer for oxygen permeation. The introduction of micro/nano L $a_{0.6}$S $r_{0.4}$Co $O_{3-}$$\delta$/ particles was very effective for increasing oxygen flux, as the flux was as much as 2 to 6 times higher than that of an uncoated L $a_{0.7}$S $r_{0.3}$G $a_{0.6}$F $e_{0.4}$ $O_{3-}$$\delta$/ membrane.\delta$/ membrane.>/ membrane.brane.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.10
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• pp.941-944
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• 2016

This paper proposes 24 GHz power amplifier for automotive collision avoidance and surveillance short range radar using Samsung 65-nm CMOS process. The proposed circuit has a 2-stage differential power amplifier which includes common source structure and transformer for single to differential conversion, impedance matching, and power combining. The measurement results show 15.5 dB maximum voltage gain and 3.6 GHz 3 dB bandwidth. The measured maximum output power is 13.1 dBm, input $P1_{dB}$ is -4.72 dBm, output $P1_{dB}$ is 9.78 dBm, and maximum power efficiency is 17.7 %. The power amplifier consumes 74 mW DC power from 1.2 V supply voltage.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.4
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• pp.757-764
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• 2018

This paper describes the design and implementation of a 1hp class two-phase type BLDC fan motor used in an air conditioning system. The BLDC motor, which is implemented in this study, is not a commutator motor type with excellent lifetime and durability and is driven by two phase power source. The most important target specification of a motor used in an air conditioning system is that it has a high efficiency at the rated operating point. For this purpose, we designed the stator shape of the BLDC motor, the design of the rotor magnet, and the control circuit for driving. The BLDC motor has a structure where the motor part, the control part, and the power part are integrated. The finite element analysis was used to calculate the characteristics of the BLDC motors, and the conformity of the design results was confirmed by fabricating and testing the prototype model.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.395-400
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• 2017

The paper discussed the air-to-fuel ratio control of automotive fuel-injection systems using the cerebellar model articulation controller(CMAC) neural network. Because of the internal combustion engines and fuel-injection's dynamics is extremely nonlinear, it leads to the discontinuous of the fuel-injection and the traditional method of control based on table look up has the question of control accuracy low. The advantages about CMAC neural network are distributed storage information, parallel processing information, self-organizing and self-educated function. The unique structure of CMAC neural network and the processing method lets it have extensive application. In addition, by analyzing the output characteristics of oxygen sensor, calculating the rate of fuel-injection to maintain the air-to-fuel ratio. The CMAC may easily compensate for time delay. Experimental results proved that the way is more good than traditional for petrol control and the CMAC fuel-injection controller can keep ideal mixing ratio (A/F) for engine at any working conditions. The performance of power and economy is evidently improved.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.6
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• pp.534-542
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• 2003

Small electric motors in an automobile perform various tasks such as engine cooling, pumping, HVAC etc. At present, most of them are DC motors supplied by 12V or 24V batteries. However, DC motors suffer from low efficiency, life cycles and reliability. Therefore, there is a growing interest in substituting DC motors for advanced at motors including switched reluctance motors(SRM). Although there are several other forms SRM convertors, they are either unsatisfactory to the control performance or unsuitable for the 12V battery source. Especially, a conventional asymmetric converter of SRM provides the best flexible and effective control to the current waveform of SRM, but it has the most switches and produces conducting voltage drops across two power switches during SRM operation. For automotive applications with a 12V battery source, this circuit is inadequate. For considering the requirement for effective operation and simple structure of converter in the limited internal circumstance of automobiles, the author inclines toward selecting Modified C-dump converter and Energy efficient c-dump converter.