| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 103 === Liquid lens has many advantages such as light weight, small volume, variable focus, no fracture. Some imaging devices can apply with liquid lens, such as cell phone, microscope and camera. The lens shape can be adjusted to achieve the purpose of tunable focal length of the liquid lens. The electric force tuning has a higher potential development among the various mecha-nisms of liquid lens because it can adjust the voltage to conveniently control the lens shape. There are two methods for the electric force tuning which are electrowetting and dielectrophoresis respectively. This study is for dielectric liquid lens as the research topic.
The study uses the software of finite element method, COMSOL MUL-TIPHYSICS, to simulate the transient behavior and flow field of the dielectric liquid lens. The numerical simulations are carried out using laminar, two phase flow-level set method for tracking the deformation of the interface. At the same time, the continuity equation and momentum equation of flow field are coupled with Poisson’s equation of static electric field. The simulation results have showed a similar tendency of the contact angles varied with voltages with experimental results. The electric field distribution is related to the electrode pattern and dielectric constant of liquid. In this study, we use the concentric electrode. Therefore, it alternates the strong and weak electric field along r-axis. Moreover, the electric field is relatively weak in large dielectric constant liquid, and relatively strong in small dielectric constant liquid. Using 1000 Hz AC input, it may generate the vibration because of alternating voltage. The simulation results show that the high frequency voltage only causes the relative deviation under 4%. Maybe this is a reason why the experiments used the high frequency voltage. In addition, the dielectric force is varied with time because of AC voltage. Therefore, the flow field changes with different die-lectric force. The surface tension and dielectric force are dominated alter-nately in the flow field. First, the dielectric force is dominated in the flow field when the peak voltage is applied. Therefore, liquid flows inwardly that would generate a vortex in order to squeeze the interface. After that, the sur-face tension is dominated in the flow field when the zero voltage is applied. Liquid flows outwardly to recover the interface shape. In addition, there is some different transient flow field between the low voltage and the high volt-age.
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