Magnetic Levitation Stabilized by Streaming Fluid Flows.

We demonstrate that the ubiquitous laboratory magnetic stirrer provides a simple passive method of magnetic levitation, in which the so-called "flea" levitates indefinitely. We study the onset of levitation and quantify the flea's motion (a combination of vertical oscillation, spinning and "waggling"), finding excellent agreement with a mechanical analytical model. The waggling motion drives recirculating flow, producing a centripetal reaction force that stabilized the flea. Our findings have implications for the locomotion of artificial swimmers and the development of bidirectional microfluidic pumps, and they provide an alternative to sophisticated commercial levitators.