Dielectric elastomer (DE) is an emerging electroactive polymer material capable of significant deformation under an external electric field and is widely used in the fields of soft robotics and tactile sensors. Based on its electrically induced deformation properties, researchers have developed dielectric elastomer actuators (DEAs), which consist of a DE film coated with flexible electrodes on both surfaces. When a voltage is applied to the flexible electrodes, the electric field induces lateral expansion and thickness contraction of the film. DEAs offer advantages such as large strain, fast response, and low power consumption, making them well-suited for applications in liquid tunable lenses. Although the existing DE-based liquid tunable lenses can achieve a certain range of focus adjustment, the development of DE-driven liquid lenses with simple structure, good stability, and strong zooming ability still faces many challenges. In this paper, a dual-cavity dielectric elastomer zoom lens structure based on the principle of electrodeformation of dielectric elastomer is designed, featuring a compact structure, good stability, large aperture, strong zoom ability and fast response speed. This work provides new ideas and methods for the design and optimization of dielectric elastomer liquid lenses.

In this paper, a dual-cavity dielectric elastomer tunable lens structure is designed, which mainly consists of upper and lower cavities, transparent conductive liquid and DE films. The DE film between upper and lower cavities acts as an active film to realize the electrically induced deformation. The DE film on the top of the upper cavity acts as a passive film, with its curvature directly determining the focal length of the lens, and the DE film on the side of the lower cavity also acts as a passive film to equalize the pressure inside and outside the cavity. Upper and lower cavities are filled with the same kind of transparent conductive liquid, which serves as the driving electrode of the DE film. The zoom principle of the lens is theoretically analyzed, and a lens model is built in COMSOL to study the influence of the liquid volume parameters in upper and lower cavities on the lens’s focal length tuning performance. Based on the simulation results, the fabrication of the tunable lens is completed, and focal lengths of the liquid lens under different voltages are measured by a focal length meter and compared with simulation results. The focusing ability, imaging quality, focal spot size, and light intensity distribution of the liquid lens under different driving voltages are tested using a charge-coupled device (CCD). Additionally, an optical system is set up to evaluate the dynamic response performance of the lens.

Theoretical analysis reveals that in this dual-cavity lens structure, the liquid volumes in upper and lower cavities determine the initial focal length of the lens and the direction of focal length adjustment (Fig. 1). Based on COMSOL simulation results, the influence of liquid volume parameters on the zooming performance of the liquid lens is analyzed. It is found that within a 100 mm focal length range, when the total liquid volume is 3.15 mL and the volume ratio of the upper cavity is 0.21, the lens achieved the largest focal tuning range (Fig. 4). Based on the optimized parameters obtained from simulation, the liquid lens is fabricated (Fig. 5). The focal length of the lens is measured using a focal length meter, showing a decrease from 97.69 mm to 79.72 mm under a voltage of 5 kV, which closely matched the simulation results (Fig. 6). By adjusting the driving voltage, the liquid lens can clearly focus on objects at different distances (Fig. 7). With the increase of the driving voltage, the imaging resolution of the lens improves from 35.919 lp/mm at 0 kV to 45.255 lp/mm at 5 kV (Fig. 8). The imaging spot of the lens exhibits an approximately circular distribution, and the spot diameter gradually decreases with increasing voltage, reaching 178.68 μm at 5 kV (Fig. 9). Using ImageJ software, the light intensity distribution of the spot under different voltages is obtained. The full width at half maximum (FWHM) of the spot decreases with increasing voltage, reaching 93.12 μm at 5 kV, indicating that the focusing ability of the lens gradually enhanced. Under square wave excitation, the average response time of the lens reaches 56 ms (Fig. 10).

In this paper, a dual-cavity dielectric elastomer tunable lens structure is designed. The structural design and working principle of the liquid lens are introduced, and the deformation of the DE film under the driving voltage is simulated. The influence of the liquid volume parameter on the focusing performance of the lens is analyzed, and the focusing ability, imaging quality, focal spot size, light intensity distribution, and response time of the liquid lens under different driving voltages are tested. The results show that the initial focal length and the focusing ability of the liquid lens can be precisely controlled by adjusting the total volume and the volume ratio in the upper cavity. As the driving voltage increases, the focal length and focal spot diameter of the lens decrease, image details become clearer, and imaging resolution and energy concentration of the focal spot improve accordingly. When upper and lower cavities are filled with 0.66 mL and 2.49 mL of liquid, the focal length of the liquid lens is reduced from the initial 97.69 mm to 79.72 mm under the voltage drive of 5 kV, with a focal length variation of 17.97 mm, a resolution of 45.255 lp/mm, a focal spot diameter of 178.68 μm, and a response time of approximately 56 ms. The introduction of the passive film on the side wall of the lower cavity simplifies the design of the liquid lens structure and improves the zoom capability and control accuracy of the lens. Above results provide a theoretical reference and experimental basis for the optimal design and further practical application of liquid tunable lenses.