Figure 2. Geometry and experimental design of the acoustic microswimmers.

(a) Fluorescent images of four types of swimmer: linear microswimmers with a single (false-coloured yellow) or double (red) indent that is symmetric about the central axis, rotational microswimmers with off-centred (purple) indent and directional microswimmers with (green) indents of different diameter. (b), A piezoelectric transducer injects acoustic energy into a chamber that is filled with fluid, lined with acoustically-absorbent putty, and enclosed on top and bottom by glass slides. (c), An image sequence recorded at 360,000 frames per second showing bubble oscillation within the conical indentation, fitted to a sine function. (d), Acoustic oscillation of the microswimmer bubbles generates substantial acoustic microstreaming in water. Both ends of indentations are open.