一种新型介电弹性体仿生可调焦透镜的变焦分析

介电弹性体 (dielectric elastomer) 是电活性聚合物智能材料的一种,在外加电场作用下,可产生多种形式的响应.在驱动柔性透镜的变焦方面,相对于传统的机械操控变焦方法 显示出独特的优势.针对一款在电压激励下可高效调节焦距的介电弹性体仿人眼变焦透镜,该透镜由上下两层介电弹性薄膜和固定框架构成,并在封闭腔内充入盐水,上层薄膜涂覆环形柔性电极.在电压激励下,上层膜发生变形,由于盐水的体积保持恒定,引 起下层膜随之变形,使得透镜的焦距发生改变.采用 neo-Hookean 模型,利用变分原理导出了该透镜的控制方程、边界条件和连 续条件.利用打靶法求解了该非线性问题并高效地处理了非线性问题的界面连续条件. 理论分析结果与实验结果相吻合. 利用此模型开展了广泛的参数分析,研究表明,透镜的几何形状、初始焦距、介电弹性体薄膜的预拉伸率、涂覆的电极面积、材料的剪切模量等对透镜焦距的调节性能都有重要的影响.所建立的理论分析模型可为柔性仿生透镜的设计和参数优化提供有效的分析方法. 

THEORETICAL NONLINEAR ANALYSIS OF A BIOMIMETIC TUNABLE LENS DRIVEN BY DIELECTRIC ELASTOMER

Dielectric elastomer (DE) is a class of electroactive polymer smart materials. Under the external electric field, it can produce various forms of responses. Comparing with the traditional lens with which the focus length is manipulated by the mechanical controls, the DE soft tunable lenses exhibit the distinct advantages in the tuning way of the focal length. The DE soft tunable lenses tune the focal length by mimicking the eyeball of human beings. The lens is composed of two circular DE films which are fixed on the rigid frame. The salty water is filled in the enclosed space and forms a convex lens. The top DE film is coated by the annular compliant electrodes. Under the voltage excitation, the upper film is deformed. Accordingly, the lower film is deformed due to the incompressibility of the salt water sealed in the enclosed space. Subsequently, the focal length of the tunable lens is changed. By employing the variational principle and the neo-Hookean model, we obtain the governing equations, boundary conditions and the continuity conditions of the biomimetic lens when driven by the dielectric elastomers. The nonlinear governing equations are solved by the shooting method and the continuity conditions at the interface are treated with in an effective way. The theoretical results agree well with the experimental data. The extensive parametric analysis is carried out based on the presented model. The numerical results show that the geometrical configuration, the initial focal length, the area of the coated annular compliant electrodes, the pre-stretch of the top DE film and the shear modulus of the bottom film have significant effect on the adjusting performance of the tunable lens. The presented theoretical model provides an effective tool in designing and optimizing the biomimetic adaptive focus lens.