마이크로 미러 구동기의 디자인 및 해석에 대한 수치적 연구

권기남 (權起楠) 弘益大學校 大學院 2006 국내석사

MEMS는 기존의 반도체 공정을 이용하여 수 ㎛ 크기의 기계부품을 제작 하는 분야이다. 화학공학이나 전기 분야에서 반도체 공정 기술이 발전하였기 때문에 공정 등 많은 부분에서 기계 분야 외적의 지식이 많이 필요하다. 하지만 반도체 공정의 부과 물로 여겨졌던 MEMS가 새로운 분야로 재탄생하게 됨으로써 반도체공정과는 다르게 기계 분야의 기술이 많이 필요 하게 되었다. 이중 마이크로 구동기는 직접적인 기계적 특성을 지니고 있기 때문에 기계분야에서 크게 다룰 수 있는 연구 분야가 될 것이다. 또한 이 마이크로 구동기로 작동되는 마이크로 미러는 기계적 동작 특성 연구가 매우 필요하므로 기계분야에서 적합한 분야로 평가된다. 마이크로 미러는 광신호를 바로 광신호로 바꾸는 OXC(Optical Cross Optical)방식의 광스위치의 핵심 부품이다. 인터넷 트래픽의 폭발적인 증가 등을 배경으로 최근 전 세계적으로 광 네트워크 인프라에 대한 투자가 적극적으로 이루어지고 있고 WDM(Wavelength Division Multiplexing)을 이용한 광 백본망이 폭 넓게 보급되고 있는데, 그러한 네트워크에 없어서는 안 될 존재가 광 스위치이다. 마이크로 미러를 이용한 광 스위치기술이 앞으로의 광통신 시장을 좌우하게 될 것이다. 하지만 아직 까지 마이크로 미러의 제작과 제어등의 부분에서 광 스위치로 사용 될 만한 수준에 이르지 못했다. 따라서 본 연구에서는 좀 더 나은 구동기를 설계하고 이것을 마이크로 미러에 접목하여 광 스위치에 알맞은 미러 제작을 목표로 하였다. 정전기력 구동기를 이용한 광스위치는 판과 판 사이에 발생하는 정전기력을 이용하여 발생되는 변위를 이용한 마이크로 미러 이다. 기존의 구동기는 캔틸레버 (Cantilever) 형태의 단순한 구조지만 토션바 (Torsion Bar) 형태의 지지대를 만들어 접촉각을 크게 만들어 주었고, 또한 디자인을 변경하여 최적의 설계조건을 찾아내었다. 열팽창 구동기의 구동형태에는 차동저항방식과 바이메탈방식이 있다. 차동저항 방식의 열팽창 구동기는 구동기의 면적차에 따른 저항 차이에 발생되는 열팽창 변위의 차이에 따라 구동 변위가 발생한다. 차동저항의 구동기가 최대 효율을 얻을 수 있도록 최적 설계를 한 후 최대허용온도로 제한된 변위를 늘려주기 위해서 바이메탈 방식과 차동저항방식을 결합한 형태인 Metal/Poly-Silicon 구동기를 설계하였다. 본 구동기는 최대 항복응력과 최대허용온도의 한계점까지 최대 구동변위로 작동 되도록 제작 되었다. 바이메탈 방식의 열팽창 구동기는 서로 다른 열팽창률을 갖는 두 물질이 발생하는 변위차를 이용하여 구동하는 변위이다. 기존의 구동기는 한 가지 움직임을 갖는데 비하여 서로 다른 방향의 변위를 갖도록 2개의 구동기를 설계하여 미러 지지대가 굽힘이 아닌 비틀림 변형하도록 설계하였다. 본 연구에 의한 마이크로 미러는 폭 20㎛, 길이 100㎛밖에 안되는 크기의 구동기, 폭 100㎛, 길이 100㎛밖에 안되는 크기의 마이크로 미러의 경우에도, 11V DC에서 28㎛의 변위, 28°의 구동각을 얻을 수 있었고, 이는 구동각 약 5°의 종래기술에 비하여 엄청난 향상이다. MEMS (Micro Electro mechanical systems) technology has generated a significant a mount of interest in the business sectors. This interest is focused on the potential performance and cost advantages with micro scale device fabricated based on silicon processing technology. It is a technique to fabricate micro scaled devices which is often mechanically actuated. Our micro mirrors are fabricated MEMS technique. Micro mirrors are used optical switch for optical communication system. Micro mirrors for a new optical communication method like WDM (Wavelength Division Multiplexing) and OXC (Opticl Cross Connect), which be needed to study the switching speed and large deflection for using the MEMS optical switching device. The goal of this study is to demonstrate micro actuators having a large deflection and rotating angles for requiring micro mirrors. Micro actuators are essential for micro electromechanical systems of movable components. Optimization of their dynamic properties is conducted using the Intellisuite. Actuators for driving micro mirrors are classified into those using electrostatic forces and using thermal expansion effects. Electro mechanical actuators are actuated the electrostatic force to create motion. Thermomechanical actuators use the physical expansion or contractionthat occurs in materials as they undergo temperature changes. Electrostatic actuators are designed adapting torsional springs to avoid plastic deformation during the actuation with large tilting angles. If externally imposed voltages increases greater than 550V, a local plastic deformation occurs. Thermal actuators of length, 200μm and thickness, 2μm, with a 40μm long flexure and a 15μm wide cold arm deflect up to 13μm at the tip around 10V We also design thermal expansion type actuators for driving micro mirrors. Actuation mechanisms of the thermal expansion type are classified into different-resist and bi-metal ones. For obtaining larger deflections, metal/poly-silicon actuators combining both methods are devised. Numerical simulations using the commercial software show that metal/poly-silicon actuators can result in deflections twice as large as the conventional poly-silicon actuators can. We also design thermal bimetal type actuators for driving micro mirrors. It reports the design and simulation of thermal double-cantilever beam bimorph(TDCB) actuators that can be used to drive micromirrors. TDCB actuators combine two paralleled bimorph actuators acting in opposite directions for rotational control of micromirrors. Each actuator is structured by nickel and silicon dioxide thin film with an embedded polysilicon line as a heat source. With a size of only 20μm width and 100μm length, TDCB actuators result in vertical displacement of 20μm at 20V DC which is a significant improvement, comparing to the conventional thermal bimorph actuators.

사각채널내에 배열된 반원 리브의 열·유동특성에 관한 연구

이경환 경상대학교 대학원 2011 국내박사

The various shapes of artificial attachments like fin or rib, dimple are fitted in the flow channel to create flow separation and reattachment; vortices and recirculation near the wall and these effects are the main reasons for heat transfer enhancement in such channels. The rib geometry and arrangement in the channel also alter the flow field resulting in different the convective heat transfer coefficient and the overall thermal performance. When the spacing of artificial attachments is too dense to yield enough reattachment, it affects inversely to increase heat transfer. on the other hand if the spacing is too large between periodically arranged ribs, heat transfer efficiency does not improve significantly. because boundary layer was developed from the reattachment point. Therefore, heat transfer efficiency can be increased by moderately using the rib shapes, sizes and spacing. The point is to be noted not only to the enhanced heat transfer but also perspective of huge pressure drop because of artificial flow interruptions in the flow channel. So the heat transfer enhancement and pressure drop both factors should be chosen as a fact of overall performance. The turbulent flow characteristics and heat transfer augmentation on the periodically arranged semi-circular ribs in a rectangular channel have been investigated. The aspect ratio of the rectangular channel was AR=5, the rib height-to-hydraulic diameter rate was 0.07. The rib height-to-channel height rate was set as e/H=0.117 for various PR(rib picth-to-rib height rate) between 8~14, respectively. The SST k-ω turbulence model and v2 - f model were used to find out the heat transfer and flow characteristics of near the wall which are suited to obtain realistic phenomena. The numerical analysis results show turbulent flow characteristics, heat transfer enhancement and friction factor as observed experimentally. The results predict that turbulent kinetic energy(k) is closely relative to the diffusion of recirculation flow. and v2 - f model simulation results have a good agreement with experimental values.

열간 단조 공정의 폐열을 이용한 온수 획득에 관한 연구

김철표 경상대학교 대학원 2009 국내석사

Nowadays, the world is facing environmental crisis and shortage of resource problem at the same time. In particular, climate changes not only induce weather disasters but also cause the subsequent destruction of the ecosystem essentially and this threatening the survival of mankind. It was predicted that the annual economic loss due to the climate change will be reach 5~20% of whole world GDP, if overconsumption of energy system continues as recent state. (2006, Stern report). The economic development of developing countries and continuous increasing of the world's population will be instigating the shortage of energy resources and accelerating price increases of energy. Hence, reduce the primary energy consumption in other hand development and introduction of application technology with environment-friendly energy are needed. Recently, since the energy problem, application of renewable energy was highlighted such as solar energy, wind power energy and so on. Many researches focus on develop alternative energy and energy conservation technologies and these research are actively under going. Among these include numerous on energy conservation technologies through waste heat recovery. However, most of the technology is limited to industrial facilities and large capacity boiler device so that broad expansion on applications technologies is required. In this research, investigate the hot water acquisition through waste heat recovery in small capacity of boiler. Furthermore, validate efficiency of waste heat recovery respect to various capacities of boiler use commercial software and finally intent to contribute to design optimal heat exchange system. Therefore, in this study conduct both experimental and numerical analysis and the results can be summarized as follow: 1. The temperature of water heated by exhaust gas from furnace and maintain steady state after 8 hours experiment running. 2. It shows that the obtained heat of cooling water is tending upwards with the change of times. 3. During experiment cooling water can be obtain maximum difference of temperature by 25 ℃. 4. Total amount of recovered heat with the steady state reach around 40,000 kJ/h. 5. Comparison results show that experiments and numerical simulation have a good agreement within the range of 10% on temperature distribution. 6. Based on the verified numerical model, the feasibility of hot water acquisition according to flow rate of the cooling water and the effluence of different season condition were investigated. As the results, the flow rate of cooling water and season condition has no significant effect on of acquisition of the hot water. 7. According to experiments and numerical analysis results it can be consider that in case of recycling the waste heat(temperature range: 300 ~ 400℃) from small capacity of furnace have high benefits to supply necessary hot water used for heating and throughout industrial field.

나노 구리 입자를 이용한 히트파이프의 열전달 향상에 관한 연구

정현권 경상대학교 대학원 2012 국내박사

The paper focuses on the pressure characteristics inside single loop oscillating heat pipe (OHP) which have 8.0 mm inner diameter copper tube with loop height of 725 mm. Piezoresistive absolute pressure sensor (Model-Kistler 4045A5) has been used to get data. Distilled water is used as working fluid inside the OHP with different filling ratios of 40%, 60%, 80% of total inside volume. Experimental results show that the thermal characteristics are significantly inter-related with pressure fluctuations as well as pressure frequency. And the pressure frequency also depends upon the evaporator temperature maintained in the range of 60℃ to 90℃. The investigation shows that 60% filling ratio gives the highest inside pressure magnitude and highest number pressure frequency at any of setting evaporator temperature and the filling ratio of 60% filling shows the lowest thermal resistance. The main purpose of this research is the investigation of thermal performance of water based copper nanofluids charged into single loop oscillating heat pipe (OHP). The effects of filling ratios and copper particle concentration over thermal resistance and pressure fluctuation inside oscillating heat pipe have been investigated. Experimental results show that the thermal characteristics are significantly inter-related with pressure fluctuations as well as pressure frequency with different nanofluid concentration. The pressure frequency also depends upon the evaporator temperature which has been maintained from 60℃ to 90℃. The experimental results show the 60% filling ratio gives the highest inside pressure magnitude of highest number pressure frequency at any of setting of evaporator temperature and 5wt% results had the lowest thermal resistance.

리튬브로마이드 수용액막의 흡수특성에 대한 실험적 연구

이준규 弘益大學校 大學院 2001 국내석사

흡수식 열펌프에서 유하액막에 의한 가스나 증기의 흡수과정은 난방 및 냉방 성능을 결정하는 중요한 열 및 물질전달과정이다. 본 연구에서는 농도 60%의 리튬브로마이드 수용액이 관외측을 따라 유하액막으로 흘러내릴 때 수증기 흡수과정에 대하여 수용액막의 레이놀즈수(80-200)와 비흡수가스의 체적농도 (O%-lO%)가 흡수과정의 열 및 물질전달에 미치는 영향을 실험적으로 연구하였다. 수용액막 레이놀즈수 100 이상의 영역에서 6열의 수평관 외측에 액막이 완전하게 형성됨을 확인하였다. 수용액의 농도가 증가함에 따라 열전달특성과 물질전달특성이 감소하였다. 흡수과정중 레이놀즈수 150에서 비흡수가스의 체적농도가 증가함에 따라 유하액막의 열 및 물질전달율은 감소하였다. 특히 열 및 물질전달 특성은 순수 수증기에 소량의 비흡수가스가 유입되었을 때 그 저하율이 심각하였다. In the present study, the effects of film Reynolds number (80~200) and volumetric content of non-absorbable gases (0~10%) in water vapor on the absorption process of aqueous LiBr solution were investigated experimentally. The formation of solution film on the horizontal tubes of six rows were observed to be complete for Re>100. The heat and mass transfer coefficients were measured as a function of film Reynolds number at different volumetric concentration of non-absorbable gases. Increase of solution concentration resulted in the decrease of heat transfer and mass transfer characteristics. As the concentration of non-absorbable gases increased at Reynolds number 150, mass transfer rate decreased. The degradation effects of non-absorbable gases seemed to be significant especially when small amount of non-absorbable gases were introduced to the pure water vapor.

有限要素法에 의한 流體素子 內部 流動解析 및 熱特性에 關한 硏究

노헌영 弘益大學校 1986 국내석사

自然冷媒를 利用한 二元 冷凍시스템의 性能特性에 관한 硏究

장석준 경상대학교 대학원 2008 국내석사

CFCs developed in the 1930's have been most widely used in the field of refrigeration since they almost perfectly satisfy the requirements for good thermodynamic properties, chemical stability, non-flammability, non-toxicity etc (Kim et al., 1998). However, these CFC refrigerants will cause disruption of the Ozone Layer, which is known as the main cause of a global warming phenomenon. Due to this, various abnormal weather phenomena such as El-Nino and La-Nina have occurred on the earth. After awakening the danger of the abnormal weather phenomena, CFCs usage in the field of refrigeration is strongly prohibited to protect the global circumstance. However, with the development of living environment and industry, a super low temperature technology is required with an Eco-friendly refrigerant. Considering of its wide application in the present and the future, study of the super-low temperature refrigeration system should be actively carried out. This study is aimed to investigate the characteristic of two stage refrigeration system which can accomplish the super low temperature under -70 ℃ using by R290 and R170 Eco-friendly refrigerant. Generally, a one stage refrigeration system is common application in the refrigeration system. However, that system cannot be used when a more low temperature is required. Therefore, for the super low temperature, a two stage refrigeration cycle system should be applied. Giovanni et al. (2005)1 and Agnew (2004) et al.2 reported on the cascade heat exchanger for achieving a super low temperature with Eco-friendly refrigerant. In this study, two stage refrigeration system was set up; the understanding of the operating characteristics was tried from the experiment; the COP of the system was investigated by using Propane(R290) - Ethane(R170) refrigerant. In addition, the experiments was carried out for figuring out the performance characteristic by changing the heat transfer area of the Hp condenser and by changing the Le evaporating pressure. From the experiment, the super low temperature near -75 ℃ could be obtained in the pressure of under 1.1 bar in the two refrigeration system with the natural refrigerant (R290/R170); if the pressure is maintained in 0.5 bar, the temperature of -75 ℃ is stably obtained. In general, as the heat transfer area of the condenser reduces, the condensing temperature increases and this makes the compressor discharge temperature and pressure increase. Accordingly, the flash gas amount in the evaporator inlet is increased and the refrigerant flow rate is increased with a high quality and the COP is decreased, consequently. If the same phenomenon is occur in the high temperature side of the two stage refrigeration system, the COP reduction is occur in the Le cascade by the same reason. Moreover, the experimental results show that the COP is decrease with the reduction of a heat transfer area because it gives the bad effect to the heat exchange capacity in the cascade. In the refrigeration cycle, if the evaporating temperature increases, the specific volume of the refrigerant from the compressor suction decreases and the refrigerant flow rate inside the system increases, which makes the refrigeration capacity and working power increase. Hence, the COP is increased due to the decrease of the compression ratio. However, in the two stage refrigeration system, the refrigeration capacity of the low temperature side is increased by the evaporating pressure change and the condensing heat duty of Le condenser is increased by the Le refrigeration flow rate increase. It makes the Hp refrigeration capacity decrease. Accordingly, the total refrigeration capacity of the two stage refrigeration rather decreases with the Le evaporating pressure increase.

Numerical Study on The Sound Pressure Level Attenuation during Muzzle Blast

Handry Afrianto 경상대학교 대학원 2013 국내석사

The artillery fired with a high pressure and temperature propellant gas shoots out will created strong radiation, noise and the blast wave. The impulsive sound from the artillery has several negative effects such as damage of environmental, structural, social problem and firing accuracy. Hence, a lot of researchers have investigated and developed design of artillery or guns in order to reduce the effect negative of firing. Silencer is used to reduced the muzzle blast flow noise, silencer have to be design properly, so that it allows gun gases to expand into chamber volumes properly to get maximum pressure reduction. The purpose of this study was to determine the utility and effectiveness of several techniques for reducing gun blast far-field noise using numerical method. The techniques that were investigated are in general applicable to guns of all sizes, from pistols and rifles to very large artillery and naval guns. Primary interest is suitable devices for use on artillery 40 mm caliber. The effectiveness of each noise reduction technique was judged according to the amount of reduction in SPL (Sound Pressure Level) that was achieved. It is generally agreed that, for occasional noise events, unaided human hearing cannot reliably detect differences in SPL smaller than about 3 dB. On the other hand, a change of 10 dB seems to correspond roughly to a factor of two changes in subjective noisiness or annoyance. Thus, any noise reduction technique that yields a change in noise level of less than 3 dB is of little or no value in terms of reducing human annoyance. A reduction of at least 10dB was the goal of the present study. The first case, tank gun of large calibre 7.62 mm NATO rifle G-3 with DN-41 round was selected about the flow field in the form of shadowgraph images analysis from references data reported by D.L. Cler21 in order to validate of numerical method. Moreover, the numerical method of artillery 40 mm calibers has been validated with experimental sound pressure result. After getting validation of the above shadow graphs and sound pressure level, numerical method has been applied to analysis the supersonic blast flow. The basic domain has been made from the specifications and data of 40 mm caliber artillery. The second case, the silencer models has been installed on the muzzle in order to reduce sound pressure from the blast wave. The third case is acoustic insulation materials have added inside silencer with the thickness and materials characteristics variation to enhanced sound attenuation.

유동상에서 산기부의 영향에 대한 실험적 연구

이기수 홍익대학교 1998 국내석사

太陽熱 溫水 시스템用 버블펌프 性能에 관한 硏究

이광성 경상대학교 대학원 2009 국내박사

Our country has a very good prospects for the solar energy due to the geographical position and seasonal weather conditions. As an alternative energy, the development of the technology for solar radiation utilization is very important and recently, is becoming popular in industrial and agricultural field all over the world. After investigating the characteristics and applying optimum design and operating conditions of the bubble pump in solar water heating system, the experiment was carried out and the same setting electric pump was installed instead of bubble pump and did the same experiment. The results obtained from this experiment are following. 1. When the slug flow occurs in the vertical pipe, the ideal flow and performance characteristics of the bubble pump are functional according to temperature variation. The slug flow occurs from 90℃, and then it is created rapidly for increasing temperature. At that time, the velocity of a moving fluid in the pipe is about 7.69~14.28 ㎝/s, and the maximum size of the slug flow is about 100㎜. Also the maximum mass flux rate is 6.7~8.3g/s. 2. When a connecting pipe is put between the separator and the condenser, the flux is increased by 16%. If the condenser's pressure is lower than the pressure in the container of the electric heater, there is a possibility of backward fluid flow. Due to increasement of the condenser pressure and remain in safety, a connecting pipe is installed between the separator and the condenser and it made hot gas in the separator condensed. Consequently, the efficiency of the bubble pump increases when connecting tube is installed in the experiment. 3. The highest flow rate reached when the riser was in the highest position (h=10mm), and it was increased by almost 0.4g/s for every 10㎜ increment of height of the water level in the riser. There generated high pressure in the condensor and separator as 68kPa, 59kPa as water level in the riser at 10mm. In this condition, the mass flow rate was 1.8g/s. 4. When the smaller diameter of pipe is set, the more bubble is obtained. But the average flow rate reached the highest when the diameter was 10㎜. 5. There were a few variations on values according to vertical pipe lengths of the bubble pump. The mass flow rate was increased by 0.17g/s when it was short as 200mm long pipe. But when vertical pipe length was 500㎜, it could reach the normal temperature quickly because the slug flow occurred in this case at initial stage. Consequently, the author find out that 500㎜ of the vertical pipe length is optimum. 6. We analyzed the bubble pump efficiency in winter and summer season. The 2,320㎉/day heat energy was stored in the water tank in winter season and 3,200㎉/day was in summer season. 7. We compared the efficiency of the bubble pump with the electric hot water pump. Any control device is not necessary for the bubble pump. In this case, the electric pump generated 5,760㎉/day of the heat energy in the tank and that for the bubble pump was 2,080㎉/day on Feb 10~18, 2009. Therefore, the bubble pump was able to store 39.50% of heat energy in the storage tank comparing to the electric pump. Consequently, there is a possibility of energy saving of 40% by the bubble pump using the solar energy.