Bio-inspired micro/mini propulsion at air-water interface: A review

This paper reviews and discusses the propulsion of water-floating natural creatures and man-made devices at the air-water interface. Natural creatures with a large ratio of body weight to surface tension force normally propel themselves by repeatedly slapping and stroking their feet while natural creatures with a small ratio of body weight to surface tension force are floated dominantly by surface tension and are propelled by various propulsion mechanisms. Some animals developed unique walking and propelling methods such as leaping, sailing, meniscus climbing, and utilizing of Marangoni effect. Inspired by the natural creatures, a large number of water walking robots and propulsion methods have been developed. Many of them are based on the walking and propelling of water striders, although they require complicated fabrication and structures. Some of the recently developed devices are propelled by the gradient of surface tension (via addition of heat or surfactant) or by streaming flows (induced from oscillations of bubbles or interfaces). These methods need relatively simple mechanical structures and fabrication but are effective only in limited conditions. The bio-inspired water floating and propelling systems can be applied to environment monitoring systems, surveillance security systems, educational robots, and toys. In particular, this paper suggests applying those systems to “smart dust” sensory robots and pollutant collecting devices.