A bunch of drips just got their ticket to stardom. Weiyu Ran and colleagues from Clemson University in South Carolina have levitated droplets of water using an ultrasonic field – and then messed with the field to give the drops starry spikes (see video above).
First the researchers increase the strength of the field, which flattens the floating drops into discs. They then turn the drops into stars by tuning the field to the resonant frequency of the drops – or exact multiples of that frequency. Using a particular multiple produces a star with the corresponding number of spikes.
The starry shapes may look cool but have no known use. However, Ran's team produced them while playing with a set-up that makes drops hover, with the aim of coming up with new ways of removing particles from air. In mines, for example, sprays are commonly used to eliminate dust. However they aren't effective at removing tiny, micrometre-sized particles that are harmful to lungs.
The team's device is too small for such applications – and would need to be scaled up. "Using current techniques would require excessive power so an alternate design would be needed," says team member John Saylor. "It's a proof of concept."
The research will be featured at the American Physical Society's Division of Fluid Dynamics meeting in Pittsburgh, Pennsylvania, next month.
Messing with an ultrasonic field in just the right way can levitate, flatten and then add starry spikes to water droplets
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