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Surfing on a wave of sound allows controlled movement of levitating objects


July 19, 2013

The movement of levitated objects - here a toothpick - is possible by varying the acoustic...

The movement of levitated objects - here a toothpick - is possible by varying the acoustic waves of several parallel emitter-reflector modules (Photo: Daniele Foresti / ETH Zurich)

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With the exception of magic, the process of levitating objects generally relies on magnetism or electric fields. However, sound waves can also be used to cancel out the effects of gravity to suspend objects and droplets of liquid in mid air. For the first time, researchers at the Swiss Federal Institute of Technology Zurich (ETH) have been able to control the movement of such levitating objects. Besides looking cool, the technology has implications for the study of various chemical reactions and biological processes and the development and production of pharmaceuticals and electronics.

Unlike the acoustic levitator developed at the US Department of Energy’s Argonne National Laboratory, which is able to suspend droplets in mid air between two small speakers, the new technology developed by postdoctoral researcher at the Laboratory of Thermodynamics in Emerging Technologies at ETH, Daniele Foresti, allows the movement of suspended droplets and objects to be controlled so multiple droplets can be mixed in mid air or objects can be transported.

This allows droplets – both magnetic and non-magnetic – to be mixed without any potential contamination or interference from surfaces. It is also allows experimentation on certain substances that disintegrate when coming into contact with surfaces.

While it was discovered over 100 years ago that sound waves can exert enough force to keep an object suspended, controlling the motion of the suspended object through the air has proven more difficult. Forest succeeded where others had failed by switching on multiple emitter-reflector modules in parallel to each other. By varying the acoustic waves from module to module, he was able to transfer particles or droplets of liquid from one module to the next – essentially surfing them on a wave of sound.

Foresti told us that his system uses ultrasounds at 24 kHz, so is beyond the 20 kHz limit of human hearing – but within the hearing range of dogs. He says this wavelength limits the size of objects that can be levitated to 4 to 5 mm in diameter, but that the length of the object is theoretically unlimited. Also, “louder” acoustic waves allow denser materials, such as glass, ceramic, aluminum and steel to be levitated.

So far, Foresti and his team have successfully levitated drops of water, hydrocarbons, various solvents and even toothpicks. In one test they levitated a granule of instant coffee and a droplet of water before combining the two in mid air, while in another two droplets of liquid with different pH values were brought together to create a droplet that contained a fluorescent pigment that only glows at a neutral pH value.

Foresti says the technology could have a wide variety of applications including chemical and biological experiments that require particles or droplets to be initially processed and then analyzed without worrying about any chemical changes that can occur due to contact with a surface. The technique can also run in parallel with several objects, strengthening its potential for industrial applications.

A video demonstrating the controlled movement of levitating droplets can be found here.

Source: ETH

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick

Can it be used to make self cleaning floors and counters?

19th July, 2013 @ 02:21 pm PDT

The Jetsons Anti Gravity car is soon 2 be here from this experiment alone IF mass producible/.

Stephen N Russell
19th July, 2013 @ 06:30 pm PDT

"In one test they levitated a granule of instant coffee and a droplet of water before combining the two in mid air,"

It makes the world's smallest and most expensive coffee.

Gregg Eshelman
20th July, 2013 @ 02:22 pm PDT

Re:Gregg Eshelman

I picked up on the coffee comment too.

You do realize that if this technology matures to viable product, they may create a machine that creates the best tasting coffee. :)

1. Raw coffee beans are suspended in a chamber and exposed to a heating coil to bake them perfectly

2. Baked beans are exposed to a fundamental frequency to shatter them like crystal, leaving small suspended shards

3. In another chamber a stream of the finest filtered water levitates gently while being boiled.

4. The two ingredients are then blended together gently, then poured into a pre-heated ceramic coffee cup.

In all seriousness, ultrasonic technology is a goldmine. It is the graphene of sound, and I'm surprised it does not have more common place applications other then just for making water fog in people's ponds.

21st July, 2013 @ 09:11 am PDT
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