• 비파괴검사학회지
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• 제21권2호
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• pp.182-188
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• 2001

대부분의 실제구조물은 인장과 진동 등이 동시에 작용하는 복합하중 상태가 되며 이러한 환경에서 물체의 거동을 해석하는 것이 중요하다. 이 논문에서는 x축에 대해 $45^{\circ}$ 결함이 있는 평판이 하중을 받고 있을 때, 진동 특성을 시간평균 electro speckle pattern interferometry(ESPI)를 이용하여 해석하였다. 결함이 있는 박판 시험편에 인장력을 증가하면서 물체의 고유진동수 변화와 모드의 형태 변화를 동시에 관찰하였다. 실험결과에서 결함은 저차모드에서는 진동모드에 영향을 주지 않았으나, 고차모드에서는 진동모드에 변화를 주었으며, 특정 진동모드에서 결함의 영향으로 현저하게 고유주파수가 낮아지는 경향을 보였다. 또한 실험결과는 유한요소해석과 비교하여 주파수 비교에서는 5% 이내의 오차율을 보였으며, 진동모드 비교에서는 완전히 일치하였다.

• 한국태양에너지학회 논문집
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• 제32권5호
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• pp.118-123
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• 2012

Water balance has a significant impact on the overall fuel cell performance. Maintenance of proper water management should provide an adequate membrane hydration and avoidance of water flooding in the catalyst layer and gas diffusion layer. Considering the important of advanced water management in PEM fuel cell, this study proposes a simple one dimensional water transportation model of PEM fuel cell for use in a dynamic condition. The model has been created by assumption that the output is the water liquid saturation difference. The liquid saturation change is the total difference between the additional water and the removal water on the system. The water addition is obtained from fuel cell reaction and the electro osmotic drag. The water removal is obtained from capillary transport and evaporation process. The result shows that the capillary water transport of low temperature fuel cell is high because the evaporation rate is low.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1610-1615
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• 2007

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• 대한공간정보학회지
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• 제20권1호
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• pp.65-72
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• 2012

MEMS(Micro Electro Mechanical System)기술이 발전하여 작고 저렴한 IMU(Initial Measurement Unit)와 GPS(Global Positioning System)통합센서가 생산되어 다양한 분야에서 활용되고 있다. 본 연구에서는 모바일매핑시스템을 경량화하기 위해서 MEMS 기반 IMU/GPS 통합센서가 적합할 것으로 판단하고 XSens사 MEMS 기반 IMU/GPS 통합센서(MTi-G)의 특성 분석을 위한 실험을 수행하였다. 차량 대시보드에 통합센서를 고정하고 인천 송도 국제도시 도로구간과 터널구간을 주행하여 후처리 과정을 거치지 않은 좌표성과를 취득하였다. 전반적으로 위치결정 성과가 양호했지만 일부 구간(정지구간, 과속방지턱, 터널구간 등)에서 센서 특성, XKF(칼만필터) 특성 및 GPS 신호 수신환경 제한으로 인해 양호하지 못한 부분이 확인되었다. 실험결과 경량 모바일매핑시스템의 활용 가능성을 확인할 수 있었으며, 향후 다양한 GPS 신호 수신환경과 주행 조건에서의 실험과 보다 정밀한 정확도 분석이 요구된다.

• 한국정보통신학회논문지
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• 제17권7호
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• pp.1645-1652
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• 2013

본 논문에서는 비파괴검사용 고성능 결함탐상기를 위한 압전변환기를 구현하였다. 여기서는 압전변형상수와 전기기계 결합계수 등과 같은 주요 특성에 대한 설계 목표치를 먼저 정하고 유한요소해석을 이용하여 얻은 데이터를 설계 및 제작에 활용하였다. 시편을 이용한 실험 결과, 제작된 PZT 세라믹은 목표치들을 매우 잘 만족시키는 것으로 확인되었다. 이는 공진 주파수에서 매우 향상된 임피던스 특성과 초음파 발생 특성을 가지는 것으로 나타났다. 또한 새로운 압전변환기가 적용된 초음파 결함탐상기는 기존 탐상기보다 증가된 결함 검출이득을 제공한다. 따라서 새로운 결함탐상기는 초음파를 이용한 비파괴검사의 검사 신뢰성 향상에 크게 기여할 수 있을 것으로 사료된다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.1903-1908
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• 2008

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• 한국재료학회지
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• 제12권3호
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• pp.211-214
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• 2002

Properties of 52/48 PZT films with various thicknesses for piezoelectric micro-electro mechanical systems (MEMS) devices fabricated by multi-coating method on $Pt(3500{\AA})/Ti(400{\AA})/SiO_2(3000{\AA})/Si$(525$\mu\textrm{m}$) substrates were investigated. PZT films were deposited by spin-coating process at 3500 rpm for 30 sec, followed by pyrolysis at 45$0^{\circ}C$ for 10 min producing the thickness of about 120nm. These processes were repeated 4, 8, 12, 16 and 20 times in order to have various thicknesses, respectively. Finally, they were crystallized at $650^{\circ}C$ for 30 min. All thick PZT films showed dense and homogeneous surface microstructures. Thick PZT films showed crystalline structures of random orientations with increasing thickness. Dielectric constants of thick PZT films were increased with increasing film thickness and reached 800 at 100kHz for 2.3$\mu\textrm{m}$ thick PZT film. $P_r\; and\; E_c$ of 2.3$\mu\textrm{m}$ thick PZT films were about 20$\mu$C/$\textrm{cm}^2$ and 63kV/cm. Depth profile analysis by Auger Electron Spectroscopy (AES) of 4800 $\AA$ thick PZT film showed the formation of the perovskite phase on Pt layer by Pb diffusion behavior. It was considered that Pb-Pt intermediate layer promoted PZT (111) columnar structures.

• 설비공학논문집
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• 제20권12호
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• pp.820-824
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• 2008

Electret filter media are used in general ventilation filters, disposable respirators, vehicle cabin filters, vacuum cleaners and room air cleaners. There are basic mechanisms of interception, inertial impaction, diffusion, gravitational settling, electrostatic attraction by which an aerosol particle can be deposited onto a fiber in a filter. The ability of fine particle removal strongly depends on the electrostatic forces between particles and polarized fibers. Thus, the stability of the fiber polarization is a major factor in the reliability of electret filters. In this study, the electret filter is made by electrospinning process using Polystyrene which is dissolved by 5 : 5 of Tetrahydrofuran (THF) and Dimethylformamide (DMF). Also the electrical properties and the filtration performances of electrospun filter media are Quantitatively investigated. Electrical properties of electrospun filters have been studied on surface charge potential and surface charge density. Also the filtration performance of the electret filters are evaluated on collection efficiency. The surface charge potential and the surface charge density of electrospun PS filters are increased with increasing applied voltage and saturated at 30 kV of applied voltage. Also collection efficiency of electro spun filters is increased with increasing surface charge potential and surface charge density. But the surface charge potential is decreased by natural decay and it causes deterioration of particle collection efficiency.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1645-1646
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• 2006

Micro ElectroMechanical Systems (MEMS) 기술을 이용한 초미세 유체 제어 시스템 (마이크로 펌프, 마이크로 밸브, 마이크로 채널, 마이크로 믹서 등)은 화학, 생명분야의 DNA 분석, 항원-항체 분석, 질병의 진단 등에 사용되는 lab-on-a-chip, micro total analysis system ($\mu$-TAS) 등에서 화학 및 바이오 유체를 제어하는 분석 시스템의 일부분으로서 사용되며 필수적으로 요구된다. 본 논문에서는 이러한 microchip을 구현하기 위해 초미세 유체 제어 소자인 마이크로 펌프와 밸브를 같은 기관 위에 polydimethylsiloxane (PDMS)와 indium tin oxide (ITO)-Glass를 사용하여 동일한 구조로 집적 하였다. 마이크로 펌프의 pumping rate은 인가 직류 펄스 전력의 주파수와 duty 비를 변화시켜 최적화하였다. 직류 펄스 전력 500 mW를 인가하였을 때 주파수 2 Hz, duty 비 7 %에서 약 $1.05{\mu}l/min$의 최대 유량이 측정되었다. 마이크로 밸브는 ITO 히터에 전력을 인가함으로서 유량의 on/off 제어가 잘 됨을 확인할 수 있었고 유체를 closing하기 위해 필요한 전력은 약 300 mW이다.

• Design & Manufacturing
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• 제11권3호
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• pp.19-24
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• 2017

In these days, increase requirement of TEM (Transmission Electro Microscope) in not only scientific field but also industrial field. Because TEM can measure inner-structure of specimen a variety of materials like metal, bio. etc. When use TEM, specimen should be thin about 50nm. So making for thin specimen, use Ion milling device that include specimen holder. The holder generally made of Aluminium Aluminium holder is worn away easily. For this reason, using time of ion milling with aluminum holder is too short. To solve the problem, we replace aluminium holer to molybdenum alloy holder. In this paper, we design molybdenum alloy holer for CAM and modify CAD modeling for effective machining process. So we array a specimen 3 by 4 and setup orientation for one-shot machining process. Next we make a CAM program for machining. we making a decision two machining strategy that chose condition of tool-path method, step-down, step-over. etc. And then conduct machining using CNC milling machining center. To make clear difference between case.1 and case.2, we fixed machining conditions like feed-rate, main spindle rpm, etc. After machining, we confirm the condition of workpiece and analysis the problems case by case. Finally, case.2 work piece that superior than case.1 cutting with WEDM because that method can not ant mechanical effect on workpiece.