Float me up, Scottie.
Researchers at the University of Bristol have crafted a tractor beam that uses acoustic vortices — basically sound tornadoes — to keep small objects aloft, a good step toward potentially levitating humans.
"Acoustic researchers had been frustrated by the size limit for years, so it's satisfying to find a way to overcome it," Asier Marzo, a research associate in Bristol's Department of Mechanical Engineering, said in a statement released by the university.
Talk about a flotation device
Acoustic tractor beams have proven capable of trapping and holding particles in midair, but anything larger than the sound wave used to create the beam and it would spin about in an unstable fashion until it was ultimately ejected from the vortex. Improving acoustic tractor beams, however, was a worthwhile pursuit since they could levitate non-metal objects that magnetic tractor beams couldn't.
What the Bristol researchers did was create multiple vortices that would rapidly fluctuate their spinning directions. These changes in directions create stability for whatever object is floating in the vortices.
The reason why an object larger than the sound wave would originally spin out of control was because some of the force from the sound wave would cause a little bit of the spin levitating the object. That extra spin would make it unstable and zip right out of the vortex.
This new tractor beam, with its multiple vortices, changes up the directions of the sound waves, and that in turn creates stability for the object. The result is that the tractor beam is able to keep a polystyrene sphere measuring about 2 centimeters, or more than twice the size of the 40hkHz-pitched wavelengths (audible to bats, not humans), stable and aloft.
It's the largest object ever to be kept in the air by a tractor beam, according to the university statement.
For now, let's focus on the practical
From a practical standpoint, the researchers see their tractor beam as a way to improve the construction processes for assembling delicate machinery and to assisting in precision medical procedures.
"In the future, with more acoustic power it will be possible to hold even larger objects. This was only thought to be possible using lower pitches making the experiment audible and dangerous for humans," Mihai Caleap, a senior research associate at Bristol, said in the statement.
So while human levitation may be a ways off, the only way for the science to go from here is up, up, up.