A planar lens based on the electrowetting of two immiscible liquids

• Published in: Journal of micromechanics and microengineering Vol. 18; no. 3; pp. 035023 - 035023 (7)
• Main Authors: Liu, Chao-Xuan, Park, Jihwan, Choi, Jin-Woo
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.03.2008; Institute of Physics
• Subjects: Applied fluid mechanics; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Fluid dynamics; Fluidics; Fundamental areas of phenomenology (including applications); Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Micromechanical devices and systems; Physics; Precision engineering, watch making; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Wetting; Electrocapillarity; Liquids; Wettability; Wetting; Aqueous solutions; Active system; Silicone oil; Hydrophobic compound; Droplets; Contact angle; Strain control; Fluidics
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/18/3/035023

This paper reports the development and characterization of a planar liquid lens based on electrowetting. The working concept of electrowetting two immiscible liquids is demonstrated with measurement and characterization of contact angles with regard to externally applied electric voltages. Consequently, a planar liquid lens is designed and implemented based on this competitive electrowetting. A droplet of silicone oil confined in an aqueous solution (1% KCl) works as a liquid lens. Electrowetting then controls the shape of the confined silicone oil and the focal length of the liquid lens varies depending upon an applied dc voltage. A unique feature of this lens design is the double-ring planar electrodes beneath the hydrophobic substrate. While an outer ring electrode provides an initial boundary for the silicone oil droplet, an inner ring works as the actuation electrode for the lens. Further, the planar electrodes, instead of vertical or out-of-plane wall electrodes, facilitate the integration of liquid lenses into microfluidic systems. With the voltage applied in the range of 50-250 V, the confined silicone oil droplet changed its shape and the optical magnification of a 3 mm-diameter liquid lens was clearly demonstrated. Moreover, focal lengths of liquid lenses with diameters of 2 mm, 3 mm and 4 mm were characterized, respectively. The obtained results suggest that a larger lens diameter yields a longer focal length and a wider range of focal length change in response to voltage. The demonstrated liquid lens has a simple structure and is easy to fabricate.