Effects of concave curvature on the formation and propagation of capillary wave induced by electrowetting-on-dielectric

Abstract

Capillary-wave propellers (CWPs) based on the phenomenon of electrowetting-on-dielectric (EWOD) have shown great potential for floating-object propulsion, heat-transfer enhancement, and fluid thermophysical property measurement. However, the small amplitude of the EWOD-induced capillary-wave limits the performance of the CWP in practical applications. Herein, a CWP with a concave curvature is proposed to enlarge the capillary-wave amplitude. The formation and propagation of the capillary wave are visualized by using a high-speed camera and a free-surface synthetic schlieren method. The wave amplitude and wave propagation are modeled theoretically. The effects of the concave curvature and the frequency of the electrical signal are investigated, and the results show that the concave curvature increases the wave amplitude, velocity vector, and wave intensity as compared with flat EWOD units. In addition, the results show that 20 Hz electrical signals are favorable for pursuing large wave energy density. The underlying mechanism for increasing the wave energy via concave CWPs is revealed experimentally and explained theoretically. The proposed concave CWP is helpful for increasing the propulsion speed of small-scale floating objects and is promising for improving the performance of CWPs in other applications.