Star Trek-style tractor beam could levitate HUMANS

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Star Trek-style tractor beams that can levitate humans have moved a step closer to reality.

For the first time, engineers in Bristol have shown they can hold a large object steady in mid-air using only sound.

Researchers have been attempting to use the power of rotating sound fields to do this for decades. Up until now, this has proved impossible.

Now, instead of using a spinning field of sound to keep an object steady, researchers have created a device that creates ‘mini tornadoes’ out of sound waves.

The discovery opens the door to the manipulation of drug capsules within the body. It also makes the levitation of human beings or vehicles a possibility. 

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For the first time engineers have shown it is possible to stably trap objects larger than the wavelength of sound in an acoustic tractor beam. Using this technique, researchers held a two-centimetre polystyrene sphere in the tractor beam (pictured)

Previous attempts to trap particles larger than the wavelength of sound had been unstable, causing them to uncontrollably spin.

A rotating sound field transfers some of its spinning motion to the objects causing them to orbit faster and faster until they are ejected. 

‘Acoustic researchers had been frustrated by the size limit for years, so its satisfying to find a way to overcome it. I think it opens the door to many new applications’, lead author Dr Asier Marzo said.

The new approach, published in Physical Review Letters, uses rapidly fluctuating sound vortexes.

Tractor beams helped the crew of the USS Enterprise in a number of sticky situations in Star Trek (pictured) and enabled the Empire capture the elusive Millennium Falcon in Star War

Tractor beams helped the crew of the USS Enterprise in a number of sticky situations in Star Trek (pictured) and enabled the Empire capture the elusive Millennium Falcon in Star Wars

HOW DO TRACTOR BEAMS WORK?

Sound waves are made of areas of high and low pressure. When they travel through a medium such as air they produce a force.

Sonic tractor beams are created by a sequence of sound waves creating a region of low pressure.

Essentially this counteracts gravity, meaning that they can trap an object in midair.

If the object tries to move up or down, zones of high pressure push it back into the low-pressure zone.

The size of the low-force region depends on the size of the wavelength – the longer the wavelenth the larger the area of pressure.

Previous attempts to trap particles larger than the wavelength of sound had been unstable, causing them to uncontrollably spin.

The new approach uses rapidly fluctuating sound vortexes.

These are similar to tornadoes of sound, made of a twister-like structure.

By quickly changing the rotational direction of the mini-tornadoes, researchers found the core increased in size, allowing larger objects to levitate.

These are similar to tornadoes of sound, made of a twister-like structure with a loud sound surrounding silent core.

This silent core is where the object can hover. 

By quickly changing the rotational direction of the mini-tornadoes, researchers found the core increased in size, allowing larger objects to levitate.

‘In the future, with more acoustic power it will be possible to hold even larger objects’, said Dr Mihai Caleap, Senior Research Associate.

‘This was only thought to be possible using lower pitches making the experiment audible and dangerous for humans’, he said.

Working with ultrasonic waves at a pitch of 40kHz, a similar pitch to that which only bats can hear, the researchers held a two-centimetre polystyrene sphere in the tractor beam

Working with ultrasonic waves at a pitch of 40kHz, a similar pitch to that which only bats can hear, the researchers held a two-centimetre polystyrene sphere in the tractor beam

Working principle of virtual vortices, intertwined short vortices of opposite directions are emitted to trap and stabilize the particle

Working principle of virtual vortices, intertwined short vortices of opposite directions are emitted to trap and stabilize the particle

Working with ultrasonic waves at a pitch of 40kHz, a similar pitch to that which only bats can hear, the researchers held a two-centimetre polystyrene sphere in the tractor beam. 

This sphere measures over two acoustic wavelengths in size and is the largest yet trapped in a tractor beam.

The research suggests that, in the future much larger objects could be levitated in this way.

‘Acoustic tractor beams have huge potential in many applications’, said Dr Bruce Drinkwater, Professor of Ultrasonics from the Department of Mechanical Engineering and supervisor of the project.

I’m particularly excited by the idea of contactless production lines where delicate objects are assembled without touching them’, said Dr Drinkwater.  





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