Acoustic Levitation: Scientists Use Sound Waves To Move And Mix Objects In Midair, Create First Airborne Instant Coffee [VIDEO]
Acoustic levitation is the process of suspending solid or liquid objects in midair using sound waves. Sound waves create changes in air pressure as they travel, making some air molecules closer together and others further apart. When an object is placed at a certain point within a sound wave, the force of gravity is counteracted by the force exerted by the sound wave, allowing the object to float in midair. From io9:
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The two opposing waves (emitted and reflected) interfere with one another, creating a standing wave. Certain parts of the wave, called nodes, don't move. And when the standing wave is parallel with gravity, some portions of it have a constant downward pressure and other portions have a constant upward pressure - the nodes, however, have very little (virtually zero) pressure.
Find that sweet spot in the sound wave tunnel and voila! Acoustic levitation.
While the technology of acoustic levitation has been around for years, scientists have grappled with how exactly to move objects around once they are suspended. Any object made airborne using acoustic levitation was static. But recently, scientists figured out how to actually manipulate them in a 3D space.
Extreme Tech reports that researchers at the Swiss Federal Institute of Technology in Zurich, Switzerland, have succeeded in taking acoustic levitation one step further by not only suspending small objects using sound waves, but also moving them up and down and side to side. They even collided a granule of coffee with a droplet of water to make the first midair instant coffee (of course, you'd probably need at least a thousand of them to make a full cup).
The Swiss scientists designed tiny sound wave transducers powerful enough to float objects but small enough to be lined up shoulder to shoulder. "By slowly turning off one transducer just as its neighbor is ramping up, the new method creates a moving sweet spot for levitation, enabling the scientists to move an object in midair," Fox reports.
The new system of acoustic levitation is able to lift heavier objects (until larger equipment is made, "heavier" means anything with a density close to that of a toothpick) and allows scientists to mix airborne solutions without them splitting apart. The sound waves used in acoustic levitation are set to 160 decibels - about as loud as if you were standing next to a helicopter. But, the sound waves are operated just above the normal hearing range for humans.
How can this type of acoustic levitation be applied to scientific research? For one, it allows scientists to mix solutions in a completely sterile environment. It also allows them to evaporate solutions without them crystallizing, which could lead to the production of drugs that are more efficiently absorbed into the body.
In this video from Argonne National Lab, scientists are seen levitating drops of a solution using acoustic levitation:
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