介电润湿驱动的变焦液体透镜电动力学分析

Electrodynamic study of variable-focus liquid lens driven by electrowetting on dielectric

为增进对液体微透镜变焦的动力学特征的理解,将晶格玻尔兹曼方法与电动力模型相结合,提出了一种晶格玻尔兹曼-电动力(LB-ED)方法研究介电润湿(EWOD)驱动的变焦液体微透镜原理.采用晶格玻尔兹曼方法求解Navier-Stokes方程以研究透镜的变焦过程,引入新的分布函数求解电场分布以计算驱动透镜变焦的电场力.首先数值分析了EWOD效应,并与理论分析及实验结果进行对比,验证数值方法的准确性;然后研究了电压对EWOD驱动的变焦液体透镜焦距的影响;分析了透镜变焦的动态过程;最后讨论了绝缘液体黏度对透镜响应时间及系统稳定性的影响.研究表明:不仅低电压下接触角变化与Lippmann-Young方程吻合良好,且高电压时出现接触角饱和现象,与实验结果一致,数值方法正确;根据数值计算和理论推导,建立了电压与焦距的关系;施加电压的初始时刻,电场力引起接触角突变,透镜需要延迟时间响应接触角的变化;发现绝缘液体黏度过小,系统处于振荡状态,黏度过大,系统处于过阻尼状态.合适的液体黏度可以使系统性能达到最佳.

With the development of micro-optical electromechanical systems, micro-lenses with adjustable focal length have become a research hotspot in the industry. In order to improve our understanding of the dynamic feature of variablefocus liquid micro-lens, a lattice Boltzmann-electrodynamic (LB-ED) method combining the lattice Boltzmann method and electrodynamic model was proposed to study the transient process of lens driven by electrowetting on dielectric (EWOD). The multi-component lattice Boltzmann method (LBM) was used to study the motion of the lens during a focusing action which is governed by Navier-Stokes equation, and then a new distribution function was introduced to calculate the electrical force. Firstly, the EWOD effect was numerically analyzed and compared with theoretical values and experimental results. Then the influence of voltage on the focal length was studied, and the dynamic process of zoom of the lens was analyzed. Finally, effects of the viscosity of the insulating liquid on the response time and stability of the lens were investigated. Results show that the change of contact angle agreed well with Loppmann-Young equation under low voltage and saturation occurred under high voltage, which indicated that the change of contact angle was consistent with the theoretical values and experimental results and verified the correctness of the numerical method. The relationship between applied voltage and focal length was established. When the voltage was switched, the contact angle changed abruptly but it cost the system some time to respond to the change in the force at the contact point. It was found that the system was in an oscillating state when the viscosity of the insulating liquid was small, and in an over-damped state when the viscosity was large. A suitable liquid viscosity could optimize the system performance.