• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.19-24
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• 2007

The effects of $B_2O_3-SiO_2-R(R;CaO,\;BaO,\;ZnO,\;Bi_2O_3)$ borosilicate glass system on the sintering behavior and microwave dielectric properties of ceramic/glass composites were investigated as functions of modifier, glass addition ($30{\sim}50\;vol%$) and sintering temperature ($500{\sim}900^{\circ}C$ for 2 hrs). The addition of 50 and 45 vol% glass ensured successful sintering below $900^{\circ}C$. Sintering characteristics of the composites were well described in terms of modifier. Borosilicate glass enhanced the reaction with $Al_{2}O_{3}$ to form pores, second phases and liquid phases, which was responsible to component of modifier. Dielectric constant (${\varepsilon}_{r},\;Q{\times}f_{o}$) and temperature coefficient of resonant frequency (${\tau}_{f}$) of the composite with 50 and 45 vol% glass contents($B_{2}O_{3}:SiO_{2}:R=25:10:65$) demonstrated A-CaBS(7.8, 2,560 GHz, -81ppm/$^{\circ}C$), A-BaBs(5.8, 3.130 GHz, -64 ppm/$^{\circ}C$), A-ZnBS(5.7, 17,800 GHz, -21 ppm/$^{\circ}C$), A-BiBs(45 vol% glass in total)(8.3, 2,700 GHz, -45 ppm/$^{\circ}C$) which is applicable to substrate requiring an low dielectric properties.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.85-90
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• 2008

In this paper, we studied on dual reflector adjusted to monopulse antenna system. As a result, when the efficiency of main reflector is more than 70%, The size of reflector is 30 wavelength of maximum frequency and minimum frequency gain is 37.9dBi, and Maximum frequency gain is 38.6dBi. Also, when a radius is D and Focus-distance is $F_e$, a scheme for efficiency improvement of Sub Reflector is to increase the Focus-distance to Diameter Ratio. In this case, Cross polarization in Far field improved and spherical spreading loss in circumference of reflector reduced. The influence of Radiation pattern followed by the side displacement of feed antenna(at $x_sy_s$) is decreased, it is confirmed that performance of scanning is improved.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1455-1461
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• 2008

We implemented a subminiature internal antenna that is around 1 cc volume for the mobile phone. The fundamental type of studied antenna is IFA(Inverted F Antenna), and this antenna is designed to be improved efficiency and gain due to minimum current cancellation by the avoidance of multiple bending pattern. For the implementation of multiple band, helix is applied to compensate for short antenna length for low frequency band, and a 3 dimensional pattern is used for high frequency band. We made two kinds of 3D structure antenna. One is a 1 cc volume antenna for GSM/DCS band on the bare board set, and the other is a 1.5 cc volume for the GSM/USPCS mobile phone set. Measurements showed good gain performance that average gain of two antenna on each band are $-3.46{\sim}-0.45\;dBi$ and $-4.80{\sim}-3.29\;dBi$ respectively.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.170-172
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• 2000

This paper deals with the characteristic analysis of the flux damper with respect to the load, and the stability of Ag/Bi-2223 tapes in a high-Tc superconducting (HTS) synchronous motor. To find out the magnetic field distribution in a detailed model of the actual motor, the experimentally measured currents of the armature and the field windings are used as input parameters. The simulation results show that the flux damper shields the time varying field up to 10%, reduces armature reactance during the motor operation and during load changes, improving the stable motor operation. And it was observed that the flux damper generates loss by means of leakage flux, but this is not significant and it doesn't degrade the performance of the TS synchronous motor.

• Journal of the Korean Geotechnical Society
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• v.29 no.7
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• pp.17-36
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• 2013

In this paper, the empirical relations of skin friction and end bearing resistance with the results of site investigation in soft rock are proposed through the analysis of bi-directional pile load tests of rock socketed drilled shafts performed at large offshore bridge foundations and high-rise building projects (13 test piles in 4 projects). The site investigation and drilling for bi-directional pile load tests were performed at the centers of test piles, and f-w curves for skin friction and q-w curves for end bearing were plotted based on load-transfer measurements. From the above curves, the empirical relations of skin friction and end bearing resistance with the results of site investigation depending on the mobilized displacement are determined by multiple regression analysis and compared with previous studies. Since the f-w and q-w curves of rock-socketed piles in Korea show hardening behavior according to mobilized displacement, the developed empirical relations by the mobilized displacement are more reasonable than those of previous studies which could not consider the mobilized displacement and suggested the ultimate capacity with unconfined compressive strength only. Particularly, the developed equations correlated with unconfined compressive strength show the best correlations among the equations correlated with other parameters.

• Journal of Advanced Navigation Technology
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• v.17 no.6
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• pp.646-651
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• 2013

In this paper, a small inverted-F antenna with adjustable characteristics is proposed with use of lumped elements, capacitor and resistor. Capacitor is inserted between end of the antenna and ground for size reduction and tuning of resonant frequency. On the other hand, $0{\Omega}$ resistor is replaced as the short line connected to ground. The movement of short point due to use of $0{\Omega}$ resistor results in providing variation of input impedance. Therefore optimum characteristics can be obtained only by proper choice of capacitor and short point without redesign of it's geometry. In order to check the validity, the proposed antenna is designed and fabricated for 2.4 GHz frequency band, and then is applied to a product of Zigbee wireless remote controller. As a result, the size of applied antenna is $8.5{\times}4.5mm^2$ and it is observed that the measured bandwidth and antenna gain are 150 MHz and 2 dBi respectively without redesign of the antenna.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.963-967
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• 2001

The effects of the sintering additives such as Bi$_2$O$_3$and V$_2$O$_{5}$ on the microwave dielectric and sintering properties of ZnTiO$_3$system were investigated. Densities of >97% of the theoretical densities have been attained for ZnTiO$_3$at the sintering temperature range of 870~90$0^{\circ}C$ with Bi$_2$O$_3$and V$_2$O$_{5}$ additions of $_3$were obtained with 0.6wt% Bi$_2$O$_3$and 0.5wt% V$_2$O$_{5}$; Qxf$_{o}$ = 48,400 GHz, $\varepsilon$$_{r}$ = 22, and $\tau$$_{f}$ = -43 PPm/$^{\circ}C$. In order to improve temperature coefficient of resonance frequency, TiO$_2$was added to the above system. The optimum amount of TiO$_2$was 15mo1% when sintered at 87$0^{\circ}C$, at which we could obtain following results ; Qxf$_{o}$ = 44,700 GHz, $\varepsilon$$_{r}$ = 26, and $\tau$$_{f}$ = 0 ppm/$^{\circ}C$.EX>.>.EX>.>.>.EX>.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.12 no.3
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• pp.78-86
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• 2013

A hybrid MIMO(Multi Input Multi Output) antenna which is operating both a monopole and a IFA(Inverted F Antenna) is designed. It's applied Vlade(Vertical lade) technique to reduce antenna space, and a diagonally fed MIMO antenna is designed on the bare board for the data communication. Return losses due to variables of antenna length are simulated for the design. Antenna for the hexa-frequency band of LTE700, CDMA, GSM, DCS, PCS and WCDMA is designed and implemented. This antenna is satisfied 3:1 VSWR over the whole design band by the measurement of return loss. And average gains and efficiencies were -3.67 ~ -2.53dBi and 42.06 ~ 55.84% for LTE700/CDMA/GSM frequency band, -3.27 ~ -1.21dBi and 47.08 ~ 75.6% for DCS/PCS/WCDMA frequency band. The isolation between 2 antenna that is one of important factors for the MIMO system was measured good performance as -8.14 ~ -25.77dB over the whole service band.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.377-385
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• 2002

The possibility of $ZrO_2$ thin film as insulator for Metal-Ferroelectric-Insulator-Semiconductor(MFIS) structure was investgated. $SrBi_2Ta_2O_9$ and $SrBi_2Ta_2O_9$(SBT) thin films were deposited on P-type Si(111) wafer by R. F. magnetron sputtering method. The electrical properties of MFIS gate were relatively improved by inserting the $ZrO_2$ buffer layer. The window memory increased from 0.5 to 2.2V in the applied gate voltage range of 3-9V when the thickness of SBT film increased from 160 to 220nm with 20nm thick $ZrO_2$. The maximum value of window memory is 2.2V in Pt/SBT(160nm)/$ZrO_2$(20nm)/Si structure with the optimum thickness of $ZrO_2$. These memory windows are sufficient for practical application of NDRO-FRAM operating at low voltage.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.244-244
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• 2012

Polymer memory devices have attracted considerable attention because of their advantages such as low cost potential, good scalability, flexibility, simplicity in structure, and large capacity for data storage. Metal/poly (4,4'-aminotriphenylene hexafluoroisopropylidenediphthalimide) (6F-TPA PI)/metal system has been found to show an electrical bi-stable behavior. Here, we show a novel set-up of 6F-TPA PI/Al sample in which holes are injected by photoelectron emission process instead of direct charge carrier injection via metal electrode. In this process, an irreversible electrical phase transition of 6F-TPA PI is found, leading to a write-once-read-many (WORM) behavior. The photoelectron spectroscopy results measured before and after the switching process revealed that the irreversible electrical phase transition of 6F-TPA PI is attributed to the chemical modification of the carbonyl group in phthalimide moiety.