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Acoustic Levitation Makes Objects Float With Sound Waves

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Levitation. At its best, the word brings up images of a sci-fi future; at its worst, it evokes memories of weird street magicians. But in fact, levitation is here, now. The most promising version of it may be acoustic levitation: using sound to make objects float in the air.

Scientist Chris Benmore demonstrates his acoustic levitator, which could help to improve the development of pharmaceuticals.

Floating On A Sound Wave

We have several methods of levitation today, including electrostatic forces, magnetism, and light. But they all have their drawbacks: magnetism requires the object to be, well, magnetic, and light can only levitate super-small particles of matter. Sound waves, however, can levitate objects up to a few kilograms in weight. 

To do that, scientists place the object in between an acoustic emitter and a reflector, which interfere with one another to create a standing wave. Some parts of that wave pull down, others push up, but if you get it just right, certain areas—called nodes—don't move at all. 

The vibrational force of sound waves keep drops of liquid stationary in an air column.

A World Of Possibilities

Acoustic levitation isn't just a cool party trick. It has important real-world applications. In pharmaceutical labs, for instance, scientists could evaporate drugs without having them crystallize, making them easier for the body to accept. Floating droplets of liquid also make it easy for chemists to conduct risky chemical reactions without the chemicals ever touching a container. Isn't the future cool?

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Key Facts In This Video

  1. Two identical sound waves projecting in opposite directions can create a standing wave, which has neutral areas that don't oscillate. 01:22

  2. Acoustic levitation "floats" objects in the neutral areas of a standing wave. 01:43

  3. Water droplets undergoing acoustic levitation will explode when the amplitude of sound is increased beyond a certain threshold. 03:42

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