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Variable focus lens for a mobile phone by using electrowetting on dielectric
Byung Do Oh(오병도) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
A small actuator for a mobile phone was required for added functions on a small camera module such as autofocus and zoom, digital still camera (DSC) having the function already. To meet high end need for DSClike miniaturized camera, a lens set equipped with a classical mechanical actuator like a small version of motor, voice coil motor or piezoelectric actuator was downsized into a mobile phone, lowered than just 10 ㎣. Recently, electrowetting technique is applied to this filed, showing a great potential and sufficient performance compared with a mechanical actuator. In this paper, application of electrowetting on a variable focus lens will be introduced and miniaturized camera module including the liquid lens be presented. Especially focused on a design factor, a camera module, and the realization of liquid lens will be discussed.
Isothermal Compression Molding for a Polymer Optical Lens
오병도(Byung Do Oh),권현성(Hyun Sung Kwon),김순옥(Sun Ok Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
Aspheric polymer lens fabrication using isothermal compression molding is presented in this paper. Due to increasing definition of an image sensor, higher precision is required by a lens which can be used as a part of an imageforming optical module. Injection molding is a factory standard method for a polymer optical lens. But achievable precision using injection molding has a formidable limitation due to the machining of complex mold structure and melting and cooling down a polymer melt under high pressure condition during forming process. To overcome the precision requirement and limitation using injection molding method, isothermal compression molding is applied to fabrication of a polymer optical lens. The fabrication condition is determined by numerical simulations of temperature distribution and given material properties. Under the found condition, the lens having a high precision can successfully be reproduced and does not show birefringence which results often in optical degradation
2상류용 전류형식 전자기유량계 이론 및 환상류에서의 3차원 가상포텐셜 분포의 수치적 계산
오병도,김무환,안예찬,Oh, Byung-Do,Kim, Moo-Hwan,Ahn, Yeh-Chan 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.6
The theory of the current-type electromagnetic flowmeter for a high temporal resolution was developed for two-phase flow measurements. To predict the output of the current-type flowmeter, the three-dimensional virtual potential distribution C and the newly introduced flow pattern coefficient f were derived and computed. The output of flowmeter depends on the liquid conductivity (sensitive to temperature) and flow configurations of the two-phase flow with the sinusoidal excitation over 100 Hz. The flow pattern coefficient was specially devised to separate the dependency on the flow configuration of the two-phase flow from that on the liquid conductivity which can be expressed with the calibration of single-phase flow. Using the finite difference method, the three-dimensional virtual potential distributions were computed for the electrode of finite size. By taking derivative of the virtual potential, the weight functions were evaluated and compared with existing analytic series solution for the point-electrode. There was a reasonable correspondence between the present and existing results. In addition, the flow pattern coefficients were evaluated for annular flows with various film thicknesses, and compared with the experimental results by the impedance spectroscopy. The numerical results agreed well with the experimental data.
김정배(Jeongbae Kim),이한춘(Han Choon Lee),오병도(Byung Do Oh),김무환(Moo Hwan Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Nucleate boiling experiments with constant wall temperature of heating surface were performed using R113 for almost saturated pool boiling conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain a constant wall temperature condition and to measure the heat flow rate with high temporal and spatial resolutions. Bubble images during the bubble growth were taken as 5000 frames a sec using a high-speed CCD camera synchronized with the heat flow rate measurements. The geometry of the bubble during growth time could be obtained from the captured bubble images. The bubble growth behavior was analyzed using the new dimensionless parameters for each growth regions to permit comparisons with previous results at the same scale. We found that the new dimensionless parameters can describe the whole growth region as initial and later respectively. The comparisons showed good agreement in the initial and thermal growth regions. The required heat flow rate for the volume change of the observed bubble was estimated to be larger than the instantaneous heat flow rate measured at the wall. Heat, which is different from the instantaneous heat supplied through the heating wall, can be estimated as being transferred through the interface between bubble and liquid even with saturated pool conditions. This phenomenon under a saturated pool condition needs to be analyzed and the data from this study can supply the good experimental data with the precise boundary condition (constant wall temperature).
강덕홍(Deok-Hong Kang),안예찬(Yeh-Chan Ahn),김종록(Jong-Rok Kim),오병도(Byung Do Oh),김무환(Moo Hwan Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
The transient nature and complex flow geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et al.). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. To do this, the velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for the simulated slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are required for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.