• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.3
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• pp.215-221
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• 2009

In this paper, a slotted trapezoidal microstrip fractal patch antenna is designed and fabricated for the vehicle GPS antenna. We designed air substrate patch antenna to obtain gain improvement by the elimination of dielectric loss. By applying fractal structure with crossed slot to trapezoidal patch, we obtained 42.5 % as much patch size as conventional triangular patch antenna. Measured bandwidth was 200 MHz on GPS band under VSWR 2:1 And gain was 4.31 dBi at resonant frequency that is 2$\sim$5 dB higher gain than conventional ceramic patch antenna on GPS band.

• Journal of the Korean GEO-environmental Society
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• v.11 no.11
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• pp.77-85
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• 2010

Unconfined compressive strength tests were performed to evaluate curing characteristics of controlled low strength material(CLSM) made with coal ashes. It is found that unconfined compressive strength normalized by curing times, increases as decreasing the water contents of CLSM particularly during first three days. Dynamic cone penetrometer tests were also carried out to evaluate cost-effective CLSM lump strength characteristics with time. It takes around 10 days to reach target strength, 500kPa (penetration rate, 20mm/blow). Curing rate significantly decreases after 10 days elapsed regardless of CLSM formulation.

• Journal of the Korean GEO-environmental Society
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• v.11 no.12
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• pp.37-45
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• 2010

The particle size of microfine cement(MC) is so small that it can be injected into silt layer. But the more particle size is miniaturized, the more the cohesion increases. This phenomenon results in the decrease of the perviousness of MC. In this study, the grouting effects of microfine cement with superplasticizer to maintain cohesion low and that of normal cement were investigated in rock. To estimate the grouting effects, TCR/RQD test for rock quality, lugeon test, borehole loading test for coefficients of elastic and deformative stress, borehole shear test for shear stress, detection p~q~t(pressure~flow~time) chart tests were carried out. The results using MC show a better permeability, modulus of elasticity, deformation, charge per unit, and recover efficiency of grouting material than those of ordinary portland cement except shear stress.

• Proceedings of the KIEE Conference
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• summer
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• pp.1285-1287
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• 2004

본 논문은 20kV 10kW급 고전압 직류 전원장치와 원격제어기의 개발에 대해서 기술하고 있다. 개발된 고전압 직류 전원장치는 다양한 고전압 시스템에 적용하기 위해서 출력전압이 최대 20kV까지 가변 가능하도록 설계되었으며 먼저, 펄스파워 시스템에 필요한 고전압 캐패시터 충전용 전원장치로서 사용하여 동작특성과 신뢰성을 확인하였다. 고전압 직류 전원장치는 단상 고주파 공진형 인버터 방식을 채용하였으며 스위칭 주파수를 최대 100kHz까지 가변시켜 출력전류를 제어하였다. 또한 인버터 출력이 인가되는 고전압 변압기에 2대의 단상 변압기를 사용하여 각각의 출력부담과 전기적 절연내력을 낮출 수 있었다. 한편, 고전압 시스템에 적용 할 때, 조작자의 안전성을 높이고 동작상태를 실시간으로 진단하기 위해서 원격제어기를 개발하였으며 다양한 조건에서의 시뮬레이션과 실험을 통해 개발된 고전압 전원장치와 원격제어기의 동작특성을 확인하였다

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.373-374
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• 2017

최근 개발 및 출시되고 있는 전기자동차(EV) 충전시스템은 3상 AC전원을 입력받아 입력역률개선과 고효율 AC/DC변환을 위한 Interleaved PFC컨버터, Bridgeless PFC컨버터, 3-Level 비엔나정류기(VIENNEA Rectifier) 등의 Topology가 사용되고 있으며, 변환된 DC전압을 입력받아 배터리를 충전하기 위한 절연된 고주파 DC/DC컨버터로 LLC 공진컨버터, 3레벨 컨버터 등이 사용되어 사이즈저감 및 경량화를 꾀하고 있다. 본 논문은 기존 입력역률 개선을 위한 PFC 컨버터와 배터리 충전을 위한 절연형 DC/DC 컨버터 2단으로 구성되어진 충전시스템 대신에 사이즈저감 및 효율개선 그리고 넓은 범위의 출력전압제어(200Vdc~430Vdc)에 대응 할 수 있도록 '단일전력단 3레벨 하이브리드 AC/DC 컨버터'를 제안하였고, 2kW 시제품을 제작하여 실험을 통해 적용 가능성을 입증하였다.

• Electrical & Electronic Materials
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• v.7 no.5
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• pp.403-408
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• 1994

Dielectric and structural properties of $Ba_{1-x}$(Z $n_{1}$3/T $a_{2}$3/) $O_{3}$+1 mol% Mn $O_{2}$ (x=0, 0.01, 0.02, 0.03, 0.04) ceramics was investigated at microwave frequencies. With $Ba_{+2}$ shortage, the sinterability and the unloaded Q( $Q_{u}$) were much improved, and the ordering in B site and the lattice distortion was greatly enhanced and the structure approached the completely ordered structure. $Q_{u}$ was strongly correlated with these factors such as ordering ratio, lattice distortion and sinterability, and had the maximum value of 7500 at x=0.01. The dielectric constant was near 30 and the temperature coefficient of the resonant frequency was 2 ppm/.deg. C at x=0.01.1.1.1.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1821-1823
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• 2003

We propose a high voltage dc-dc converter for CW(continuous wave) $CO_2$ laser system using a current resonant half-bridge inverter and a Cockcroft-Walton circuit. This high voltage power supply includes a 2-stage voltage multiplier driven by a regulated half-bridge series resonant inverter. The inverter drives a step-up transformer and the transformer secondary is applied to the voltage multiplier. Thus, it has high efficiency because of the less switching losses by virtue of the current resonant half-bridge inverter, and also compact size, small parasitic capacitance in the transformer stage owing to the low number of a winding turn of the step up transformer secondary by combining with Cockroft-Walton circuit. We could be obtained the maximum laser output power of 44 W and the maximum system efficiency of over 16 %.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.116-125
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• 1995

Higher order nonlinear transfer functions are applied to model the nonlinear responses obtained Inn dynamic analysis of single degree of freedom systems (SDOF) subjected to wave and current loadings. The structural systems are subjected to single harmonic, two wave combination and irregular wave loading. Three different sources of nonlinearities are examined for each of the wave loading condition and it is shown that the nonlinear response appear at the resonance frequencies of the SDOF even when virtually no wave energy exists at those resonance frequencies. Higher order nonlinear transfer functions based on Volterra series representation are used to model the nonlinear responses mainly f3r the flexible systems and clearly shows the degrees of nonlinearity either as quadratic or cubic.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.8 no.2
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• pp.128-132
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• 2015

In this paper, a microstrip dual mode band pass filter with doubly fed line is proposed. The proposed filter consists of a corner truncated patch with right crossed slots and doubly fed lines. In general, the resonator with the right crossed slots simultaneously has size reduction and spurious response suppression. In order to improve the rejection performance in out of its higher stop band, the dual mode resonator is excited by using doubly fed line. Details of the filter characteristics are described, and both simulated and measured results of the designed filter are presented.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.4
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• pp.815-820
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• 2007

In this paper, a small internal antenna for dual-band(RFID, PCS) applications is presented. The proposed antenna is a basic PIFA type and has a deformed ground plane under the main radiator. The modified ground plane is spreading the surface current and the antenna miniaturization can be achieved due to the coupling effect. The antenna is manufactured according to the simulation results and the resonance frequency move to low frequency band by 150MHz. And the surface current on the radiator and ground plane is evenly distributed so our suggested antenna can be used for better SAR and HAC performance.