Sound sieve lets you choose what to levitate

[Nipuna]

[media]https://www.youtube.com/watch?v=rGvPiOA0HeU[/media]

Sieves made of sound could one day amp up the power of nano-manufacturing and cell therapy.

Ultrasound waves have been used before to levitate and mix small objects or droplets, but these devices were limited to moving just a few objects at a time. A team led by Hairong Zheng of the Shenzhen Institutes of Advanced Technology in China has now used sound wave pressure to lift and sort many objects at once.

The team etched a thin brass plate with rectangular strips and suspended it in a tank of water. Ultrasound blasted from above sends acoustic waves through the water that cause the plate to resonate with the bottom of the tank. The resulting sound pressure lifts objects placed below the plate according to size and density.

Acoustic filter
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The team sorted small glass beads from larger ones and pulled glass beads away from tin beads of the same size. Zheng says that in principle the device could be tuned to sort a range of nano-scale objects, including building blocks for tiny structures, or cells that need to be selectively targeted for medical treatments.

Adapting the sieve to work in air might be difficult, says Bruce Drinkwater at the University of Bristol, UK. Right now the sieve needs to run in liquid to create the right acoustic resonance. It might be useful for sampling water to check for pollutants, he says, provided the team can find a way to clear away the particles that stick to the plate so the device could run continuously.

Journal reference: Physical Review Applied, DOI: 10.1103/PhysRevApplied.1.051001