Electrowetting for Variable Focus Liquid Lenses

Electrowetting is the process of deforming a conductive liquid droplet placed on a dielectric substrate by applying an electric field. The feasibility of electrowetting for creating variable focus liquid lenses was investigated.  It was hypothesized that the change in shape experienced by a droplet due to electrowetting would be sufficient to cover the range of focal lengths typically required for human vision correction (-6.5 to 6.5 diopters). To test the hypothesis, a 1.5-mm water droplet was placed on a glass substrate consisting of an indium tin oxide conductive layer with a 300-nm-thick Parylene-HT dielectric coating. DC voltage was applied across the droplet and the conductive layer.  The droplet was photographed at different applied voltages (0-45 V) using a digital camera and the contact angle was determined by image processing. The experiment was repeated with an added surfactant and then with the droplet immersed in silicone oil. The change in the radius of curvature of the droplet and focal length of the liquid lens was calculated. By changing the applied voltage from 0 to 45 V the contact angle changed from 65 to 48 degrees for water, 35 to 22 degrees with the surfactant, and 109 to 70 degrees with oil. Based on the contact angle measurements, a 25-mm-diameter water-oil lens can cover -4.5 to 4.5 diopters with vertical sides. This range can expand to -6.5 to 6.5 diopters by changing side angles by +/- 20 degrees, indicating that electrowetting can be employed to develop variable focus lenses for human vision correction.