Beaker on magnetic stirrer

Magnetic stirrers, a commonplace piece of laboratory equipment, can generate a form of magnetic levitation. Credit: Getty

Fluid dynamics

How to achieve levitation with an ordinary piece of laboratory kit

Castor oil allows for stable magnetic levitation of a laboratory ‘flea’.

The humble magnetic stirrer, which is found in labs worldwide, can levitate a small magnet — a capability that could lead to new applications of magnetic levitation.

A stirrer’s rotating magnetic field spins a bar magnet placed inside a vessel of liquid. As the field rotates faster, the magnet lags behind and is repelled upward, causing it to waggle and hop — earning the device its nickname, the ‘flea’.

David Fairhurst at Nottingham Trent University, UK, and his colleagues found that a flea placed in castor oil and in other fluids of a similar viscosity hops upward when it reaches a critical speed. It then remains suspended, waggling and spinning as it levitates. Simulations and experiments showed that the flea’s complex motion creates streams of circulating fluid, which stabilize its levitation.

Most forms of magnetic levitation require the magnets to be cooled to very low temperatures. The authors’ technique operates at room temperature and could be used in submersibles or micro-scale pumps.