• Composites Research
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• v.27 no.4
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• pp.146-151
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• 2014

In this study, the experimental study has been performed by varying the polarization of the electric field and impact force to check the piezoelectric characteristics of piezoelectric paint sensor. Piezoelectric paint sensor used in this study is composed of epoxy resin with a hardener and PNN-PZT powder in 1:1 weight ratio. The dimensions of the paint sensor specimen are $40{\times}40{\times}1mm^3$ and regular specimens were made using a mold. The voids are removed from the specimen in the vacuum desiccator. Both upper side and bottom side of the paint sensor were coated with silver paste for making an electrode and then dried at room temperature for a day. The poling treatment has been carried out under controlled conditions of the electric field in order to check the effect of piezoelectric sensitivities, while the poling temperature was fixed at room temperature and the poling time was set to 30 min. The piezoelectric sensitivities have been measured by comparing output voltage from paint sensor with output force from impact hammer when the impact hammer hits the paint sensor. In result, the effect of the electric field has been evaluated for the sensitivity and describe the result.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1340-1350
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• 2009

The design and implementation of planar Active Phased Array Antenna System are described in this paper. This Antenna system operates at X-band with its bandwidth 10 % and dual polarization is realized using dual slot feeding microstrip patch antenna and SPDT(Single Pole Double Through) switch. Array Structure is $16\times16$ triangular lattice structure and each array is composed of TR(Transmit & Receive) module with more than 40 dBm power. Each TR module includes digital attenuator and phase shifter so that antenna beam can be electronically steered over a scan angle$({\pm}60^{\circ})$. Measurement of antenna pattern is conducted using a near field chamber and the results coincide with the expected beam pattern. From these results, it can be convinced that this antenna can be used with control of beam steering and beam shaping.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.890-899
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• 2014

Austenitic stainless steel is widely used in various industries due to its excellent corrosion resistance. However, Cr carbides precipitation along the grain boundaries after heat treatment or welding may develop Cr depleted zone, which acts as a preferential site for intergranular corrosion attack. To resolve this, carbon stabilizing element such as Ti or Nb are added to suppress formation of Cr carbides. However, there are few reports on corrosion characteristics under seawater environment of the stabilized stainless steel. This study investigated the effects of alloying contents on the electrochemical characteristics in seawater of stainless steel containing stabilizing element(Ti and Nb). To achieve this, the changes on the microstructure due to alloying were observed with microscope, and the electrochemical characteristics were determined by measurement of natural potential and potentiodynamic polarization experiments. The microscopic observation revealed that all specimens had inclusions other than the austenite matrix phase due to the addition of alloying elements. Such inclusions are considered to have different electrochemical characteristics from those of the matrix, and thus a clear distinction was found according to the type of stabilizers and the contents. The results of this study suggest that it is important to consider the effects of alloying contents on the electrochemical characteristics in seawater with the addition of Ti or Nb into austenitic stainless steel.

• Journal of Satellite, Information and Communications
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• v.2 no.2
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• pp.41-47
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• 2007

The first geostationary satellite made by Korea, COMS, has the three different payload ; Meteorological sensor, Oceanographic sensor and Ka-band communication payload. There are Meteorological & Ocean Data Communication Subsystem(MODCS) and Telemetry, Command and Ranging Subsystem(TC&R) as other RF radiation sources. MODCS transmits and receives Meteo and Ocean measurement data from/to earth using L-band and TC&R using S-band. The Ka-band communication payload will provide high-speed multimedia services and communication services for natural disaster such as prediction, prevention, and recovery services in the government communications network.Ka-band beacon is for the earth antenna pointing and the experiment of rain fading. This paper gives the analysis results about the mutual radiation effect on Ka-band communication payload, Ka-band beacon, MODCS and TC&R. Up/Down link power and coupling factor including the geometrical position and distance of antenna, filter rejection and degradation factor due to the different polarization are considered. The results show MODCS and TC&R are compatible for Ka-band communication payload and Ka-band beacon does not interfere with MODCS and TC&R normal operation.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.5
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• pp.17-23
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• 2017

Optical current sensors are suitable for operation in high voltage and high current environments such as power plants due to they are not affected by electromagnetic interference and have excellent insulation characteristics. However, as they operate in a harsh environment such as large temperature fluctuation and mechanical vibration, high reliability of the sensor is required. Therefore, many groups have been working on enhancing the reliability. In this work, an integrated optical current sensor incorporating polarization-rotated reflection interferometer is proposed. By integrating various optical components on a single chip, the sensor exhibits enhanced stability as well as the solution for low-cost optical sensors. Using this, we performed the characterization for the actual field application. By using a large power source, the current of 0.3 kA~36 kA was applied to the photosensor and the linear operation characteristics were observed. The error of the sensor was within $0{\pm}.5%$. Even when operating for a long time, the error range of the sensor was kept within $0{\pm}.5%$. In addition, the measurement of the frequency response over the range of 60 Hz to 10 kHz has confirmed that the 3-dB frequency band of the proposed OCT is well over 10 kHz.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.84-84
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• 1999

최근 큰 잔류분극을 가진 강유전체 Pb(Zr, Ti)O3 박막을 이용한 비휘발성 기억소자의 연구가 활발히 진행되고 있다. 그러나 Pb(Zr, Ti)O3 박막을 비휘발성 기억소자로 응용하는 경우 분극피로(polarization fatigue), imprint, 누설전류 등의 문제점이 나타나는 것으로 알려져 있다. 특히 분극반전 횟수가 증가할수록 잔류분극이 감소하는 분극피로 현상은 비휘발성 기억소자의 응용에 있어서 치명적인 장애가 되므로 기억소자의 실용화를 위해서는 분극피로 현상의 개선이 무엇보다 중요하다. 본 연구에서는 Pb(Zr, Ti)O3 강유전체 박막의 분극피로 현상을 규명하고 개선하기 위해서 다음과 같은 세가 실험적 방법으로 접근하였다. 먼저 Pt와 금속산화물인 LaNiO3을 이용하여 상·하부 전극을 달리하여 제조한 축전기에 대해서 분극피로 특성을 관찰하고 이로부터 분극피로 현상에 대한 전극의 효과를 조사하였다. 여기서 금속산화물인 LaNiO3 박막과 Pt 박막은 r.f. 스퍼트 법으로 증가하였으며 Pb(Zr, Ti)O3 박막은 LaNiO3/Si(100)/와 Pt/Ti/SiO2/i(100) 기판위에 졸겔법으로 제조하였다. 다음으로 분극피로된 박막의 상부전극에 극성이 다른 직류전압을 인가해주었을 때 나타나는 분극회복 현상을 광범위하게 관찰하였으며, 특히 직류전압의 극성에 따라 비대칭적인 분극회복 특성을 보였다. 마지막으로 이와 같은 직류전압에 대한 비대칭적인 분극회복현상에 착안하여 양과 음의 방향으로 바이어스된 스윗칭 펄스를 인가하여 분극피로 특성을 조사한 결과 비대칭적인 분극피로 현상을 관찰할 수 있었다. 이와 같은 Pv(Zr, Ti)O3 박막의 분극피로와 회복의 비대칭적인 현상은 분극피로 현상의 기구를 밝히는 중요한 근거가 되었으며, 본 연구에서는 하부 계면에서의 산소빈자리의 역할로 분극피로 현상을 모형화하였다.식각하기 시작하였으며, 19.5J/cm2에서 유리기판의 rudraus(격벽 두께 130$\mu\textrm{m}$)까지 식각하였다. 대한 정보(RDF)는 명확하게 얻을 수 있었다.nospec과 SEM으로 관찰하였다. 또한 Ge 함량 변화에 따른 morphology 관찰과 변화 관찰을 위하여 AFM, SEM, XRD를 이용하였으며, 이온주입후 열처리 온도에 따른 활성화 정도의 관찰을 위하여 4-point probe와 Hall measurement를 이용하였다. 증착된 다결정 SiGe의 두게를 nanospec과 SEM으로 분석한 결과 Gem이 함량이 적을 때는 높은 온도에서의 증착이 더 빠른 증착속도를 나타내었지만, Ge의 함량이 30% 되었을 때는 온도에 관계없이 일정한 것으로 나타났다. XRD 분석을 한 결과 Peak의 위치가 순수한 Si과 순수한 Ge 사이에 존재하는 것으로 나타났으며, ge 함량이 많아짐에 따라 순수한 Ge쪽으로 옮겨가는 경향을 보였다. SEM, ASFM으로 증착한 다결정 SiGe의 morphology 관찰결과 Ge 함량이 높은 박막의 입계가 다결정 Si의 입계에 비해 훨씬 큰 것으로 나타났으며 근 값도 증가하는 것으로 나타났다. 포유동물 세포에 유전자 발현벡터로써 사용할 수 있음으로 post-genomics시대에 다양한 종류의 단백질 기능연구에 맡은 도움이 되리라 기대한다.다양한 기능을 가진 신소재 제조에 있다. 또한 경제적인 측면에서도 고부가 가치의 제품 개발에 따른 새로운 수요 창출과 수익률 향상, 기존의 기능성 안료를 나노(nano)화하여 나노 입자를 제조, 기존의 기능성 안료에 대한 비용 절감 효과등을 유도 할 수 있다. 역시 기술적인 측면에서도 특수소재 개발에 있어 최적의 나노 입자 제어기술 개발 및 나노입자를 기능성 소재로 사용하여 새로운 제품의 제조와 고압 기상 분사기술의 최적화에

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.6
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• pp.1006-1014
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• 2000

Hemisphere type Luneberg lens antenna with a reflector(frequency : 9.375 GHz, -3 dB beam width 6$^{\circ}$, diameter 30.3 cm(about 10 A), which is miniaturized and lightweightized by attaching a reflector on a section of half the Luneberg lens antenna, is designed and fabricated on the basis of Luneberg lens antenna from which easy beam pointing is acquired only by movement of 1st radiator. Measurement shows -3dB beamwidth is 6.1$^{\circ}$ in case of E-plane and 5.5$^{\circ}$ in case of H-plane. These are good agreements with expected value. Gain of this antenna is 26dBi(Aperture efficiency for uniform distribution : $\pi$ = 44.97%) which is greater than that of 1st radiator(Rectangular microstrip antenna) by 20.4 dB. And, after calculating the approximated pattern of the 1st radiator, far-field pattern, whose source is the second aperture source farmed from the approximated pattern of the 1st radiator is computed. Comparing this far-field pattern with the expected pattern, a (relatively) good agreement is observed. Circular polarization Luneberg lens antenna is also manufactured by making 1st radiator so that it has the characteristics of LHCP and RHCP radiation. The results are as followings : -3 dB beamwidth 5.8$^{\circ}$ , side lobe level -15.3 dB, isolation between LHCP and RHCP radiation 2543, axial ratio 2 dB bandwidth about 1.4 GHz(14.9%).

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.409-417
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• 2014

Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas in a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of most parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum weldment for these parts is very important to prolong their lifetime in a economical point of view. In this study, four types of filler metals such as Inconel 625, 718, 1.25Cr-0.5Mo and 0.5Mo were welded with SMAW and GTAW methods in the forged steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected zone and base metal were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H2SO4 solution. The weld metal and base metal exhibited the best and worst corrosion resistance in all cases of filler metals. In particular, the weld metal welded with filler metals of Inconel 718 revealed the best corrosion resistance among the filler metals, and Inconel 625 followed the Inconel 718. Hardness relatively indicated higher value in the weld metal compared to the base metal. Furthermore, Inconel 625 and 718 indicated higher values of hardness compared to 1.25cr-0.5Mo and 0,5Mo filler metals in the weld metal.

• Corrosion Science and Technology
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• v.13 no.1
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• pp.28-35
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• 2014

Recently, the fuel oil of diesel engines of marine ships has been increasingly changed to heavy oil of low quality as the oil price is getting higher and higher. Therefore, the spiral gear attached at the motor of the oil purifier which plays an important role to purify the heavy oil is also easy to expose at severe environmental condition due to the purification of the heavy oil in higher temperature. Thus, the material of the spiral gear requires a better mechanical strength, wear and corrosion resistance. In this study, the heat treatment(tempering) with various holding time at temperature of $500^{\circ}C$ was carried out to the alloy of Cu-7Al-2.5Si as centrifugal casting, and the properties of both hardness and corrosion resistance with and without heat treatment were investigated with observation of the microstructure and with electrochemical methods, such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram, and a.c. impedance. in natural seawater solution. The ${\alpha}$, ${\beta}^{\prime}$ and ${\gamma}_2$ phases were observed in the material in spite of no heat treatment due to quenching effect of a spin mold. However, their phases, that is, ${\beta}^{\prime}$ and ${\gamma}_2$ phases decreased gradually with increasing the holding time at a constant temperature of $500^{\circ}C$. The hardness more or less decreased with heat treatment, however its corrosion resistance was improved with the heat treatment. Furthermore, the longer holding time, the better corrosion resistance. In addition, when the holding time was 48hrs, its corrosion current density showed the lowest value. The pattern of corroded surface was nearly similar to that of the pitting corrosion, and this morphology was greatly observed in the case of no heat treatment. It is considered that ${\gamma}_2$ phase at the grain boundary was corroded preferentially as an anode. However, the pattern of general corrosion exhibited increasingly due to decreasing the ${\gamma}_2$ phase with heat treatment. Consequently, it is suggested that the corrosion resistance of Cu-7Al-2.5Si alloy can be improved with the heat treatment as a holding time for 48 hrs at $500^{\circ}C$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.7
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• pp.678-685
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• 2013

In this paper, we propose a design of dual-band patch antennas for Global Positioning System(GPS) applications, and the designed antenna is used as an individual element of GPS arrays. A low distortion and a high isolation of the array are achieved by adjusting rotating angles of each array element. The antenna consists of two radiating patches that operate in the GPS $L_1$ and $L_2$ bands, and the two ports feeding network with a hybrid chip coupler is adopted to achieve a broad circular polarization(CP) bandwidth. The rotating angles of each antenna element are varied with four directions(${\phi}=0^{\circ}$, ${\phi}=90^{\circ}$, ${\phi}=180^{\circ}$, ${\phi}=270^{\circ}$) in order to minimize the pattern distortion and maximize the isolation among array elements. The measurement shows bore-sight gains of 0.3 dBic($L_1$) and -1.0 dBic($L_2$) for the center element. Bore-sight gains of 1.6 dBic($L_1$) and 1.0 dBic($L_2$) are observed for the edge element. This results demonstrate that the proposed antenna is suitable for GPS array applications.