Scientists created a "microscopic sonic screwdriver" composed of acoustic vortices that grip and spin microparticles suspended in water.
The vortices act like "tornadoes of sound," and manipulate microscopic particles by drawing them to the core of the vortex, the University of Bristol reported.
"We have now shown that these vortices can rotate microparticles, which opens up potential applications such as the creation of microscopic centrifuges for biological cell sorting or small-scale, low-power water purification," said Bruce Drinkwater, Professor of Ultrasonics in the Department of Mechanical Engineering and one of the authors of the study. "If the large-scale acoustic vortex devices were thought of as sonic screwdrivers, we have invented the watchmakers sonic screwdriver."
To create the tiny vortices, the researchers employed the use of a number of ultra-sonic loudspeakers arranged in a circle to create a "swirling" of sound waves. When a mixture of microparticles and water were exposed to these waves, they were observed to slowly rotate around the vortex core. Larger microparticles (household flour) were found to spin at higher speeds than smaller ones, and also tended to get stuck in a series of circular rings as a result of acoustic radiation forces.
"Previously researchers have shown that much larger objects, centimetres in scale, could be rotated with acoustic vortices, proving that they carry rotational momentum," said ZhenYu Hong, of the Department of Applied Physics at Northwestern Polytechnical University in China.
The findings were published in a recent edition of the journal Physical Review Letters.
