What tiny surfing robots teach us about surface tension by Staff Writers Houghton MI (SPX) Oct 11, 2020
Spend an afternoon by a creek in the woods, and you're likely to notice water striders - long-legged insects that dimple the surface of the water as they skate across. Or, dip one side of a toothpick in dish detergent before placing it in a bowl of water, and impress your grade schooler as the toothpick gently starts to move itself across the surface. Both situations illustrate the concepts of surface tension and propulsion velocity. At Michigan Technological University, mechanical engineer Hassan Masoud and PhD student Saeed Jafari Kang have applied the lessons of the water strider and the soapy toothpick to develop an understanding of chemical manipulation of surface tension.
Their vehicle Tiny surfing robots. Beyond the obvious implications for future Lucasfilm droids designed for ocean planets (C-H2O?), what are the practical applications of surfing robots? "Understanding these mechanisms could help us understand colonization of bacteria in a body," Masoud said. "The surfing robots could be used in biomedical applications for surgery. We are unraveling the potential of these systems."
Hunting for Answers and the Marangoni Effect "During a conversation with a physicist, it occurred to me that what we had observed then was due to the release of a chemical species that changed the surface tension and resulted in motion of particles that we observed," Masoud said. That knowledge has led Masoud to continue analyzing the propulsion behavior of diminutive robots - only several microns in size - and the Marangoni effect, which is the transfer of mass and momentum due to a gradient of surface tension at the interface between two fluids. In addition to serving as an explanation for tears of wine, the Marangoni effect helps circuit manufacturers dry silicon wafers and can be applied to grow nanotubes in ordered arrays. For Masoud's purposes, the effect helps him design surfing robots powered by manipulating surface tension chemically. This solves a core problem for our imagined C-H2O: How would a droid propel itself across the surface of water without an engine and propeller? Detailed in research findings published recently in the journal Physical Review Fluids, Masoud, Jafari Kang and their collaborators used experimental measurements and numerical simulations to demonstrate that the microrobot surfers propel themselves in the direction of lower surface tension - in reverse of the expected direction. "We discovered that negative pressure is the primary contributor to the fluid force experienced by the surfer and that this suction force is mainly responsible for the reverse Marangoni propulsion," Masoud said. "Our findings pave the way for designing miniature surfing robots. In particular, knowing that the direction of propulsion is altered by a change in the surrounding boundary can be harnessed for designing smart surfers capable of sensing their environment."
Stability Studies on the Horizon "We have just scratched the surface of learning the mechanisms through which the surfers - and other manipulators of surface tension - move," Masoud said. "Now we are building understanding toward how to control their movement."
First tests for landing the Martian Moons eXploration Rover Berlin, Germany (SPX) Oct 01, 2020 The Japan Aerospace Exploration Agency (JAXA) Martian Moons eXploration (MMX) mission will have a German-French rover on board when it is launched in 2024. The rover will land on the Martian moon Phobos and explore its surface for approximately three months. Initial landing tests are currently underway at the German Aerospace Center Landing and Mobility Test Facility (Lande- und Mobilitaetstest Anlage; LAMA) in Bremen. Using a first preliminary development model, the engineers are determining how robust ... read more
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