| In this work, we develop microboats and microsubmarines, which are capable of moving on and under water, respectively.;The microboat is propelled due to the difference between surface tensions around stern and bow. This difference is generated by releasing a liquid with lower surface tension than water from the stern. We explore both horizontal and vertical motions of the microboats through a combination of experimental and theoretical investigations. It has a length of 8 mm and weight of 20 mg with the highest speed of 25 cm/s and travel distance of 85 cm. Moreover, we design, fabricate and test microboats with rudders. Such a microboat is capable of having a radial motion in an open water area. The radii of the motion are controlled by lengths of the rudders.;The microsubmarine is also designed, fabricated and tested. It is driven by thermally oscillatory bubbles. A submarine has a length of 8 mm and weight of 40 mg. Its thrust can be as large as 67.6 nN when applied voltage, pulse frequency and duty are, respectively, 16 V, 100 Hz and 50%. Its travel distance is 1.28 cm with the highest speed of 1.8 mm/s. A micro submarine is further incorporated with micropillars to be able to float up from the under water. After this incorporation, micro submarine may still rise up to water surface from the bottom of water tank even if it is denser than water. |
