in recent years, but only to levitate very small objects. A new breakthrough could lead to new futuristic and distant uses for technology and open the door to the levitation of much larger objects, including humans.
Engineers at the University of Bristol have been able to catch (essentially levitate) objects using an acoustic tractor beam that is larger than the wavelengths of sound used by the device.
"The acoustic researchers have been frustrated by the size limit for years, so it is satisfying to find a way to overcome it, I think it opens the door to many new applications," said Asier Marzo from the Department of Mechanical Engineering of Bristol. March is the main author of an article published on Monday in the journal Physical Review Letters.
Such applications could include the non-contact control of drug capsules or microsurgical instruments within the human body using beams of sonic tractors. It may also be possible to move and manipulate fragile items in a completely new way.
"I am particularly excited about the idea of non-contact production lines where delicate objects are assembled without touching them," said Bruce Drinkwater of Bristol, who oversaw. the play.
The breakthrough comes from the use of rapidly fluctuating acoustic vortices, which the team describes as being similar to "sound tornadoes, made of a tornado-like structure with a strong sound surrounding a silent core".
By changing the direction of torsion of the vortices, the researchers were able to stabilize the tractor beam and increase the size of the silent core, which allows it to hold larger objects. Using this technique and 40kHz ultrasonic waves (similar to a tone that only bats can hear), they were able to levitate a two-centimeter polystyrene sphere, the largest object trapped in a tractor beam of the real world.
Perhaps most impressive is that the research suggests that this technique could be scalable to the proportions of people.
"In the future, with more acoustic power it will be possible to hold even larger objects," said associate researcher Mihai Caleap. "This was only thought possible with lower tones, which makes the experiment audible and dangerous to humans."
Soon, "floating in the air" could go from being simply a saying to the way we sleep when there is no bed available.
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