• Question: Can sound waves used to Levitate objects?

    Asked by usman100 to Chris, Dave, David, Fiona, Jack on 22 Jun 2013.
    • Photo: David Freeborn

      David Freeborn answered on 22 Jun 2013:

      Yes!

      It’s called acoustic levitation, and it works by using the air-pressure created by sound waves.

      Amazingly, there might be applications in the pharmaceuticals industry:
      http://www.anl.gov/articles/no-magic-show-real-world-levitation-inspire-better-pharmaceuticals

      There are some really cool videos of droplets of liquid being levitated. They’re worth taking a look at:

    • Photo: Jack Miller

      Jack Miller answered on 22 Jun 2013:

      Great question! As David says, yes!

      We can also use sound to do some other pretty cool things. I use sound waves on a regular basis to both mushing up biological cells (to look at their contents) and help look at heart function (with ultrasound). People have also tried to use really, REALLY high intensity, focussed ultrasound to kill cancer tissues in the liver.

      It’s also possible to cool things using sound: a sound wave at a particular frequency creates a pressure wave, with alternating areas of compression and rarefaction of air. This pattern of compression/expansion can be used to make metal plates put in the right place heat and cool. A temperature gradient can be generated by putting a stack of plates in the right place in a tube in which the sound wave is bouncing around. Some plates in the stack will get hotter and others colder. All it takes to make a refrigerator out of this system is to attach heat exchangers to the ends of the stack!

    • Photo: Dave Farmer

      Dave Farmer answered on 23 Jun 2013:

      Dear Usman,

      Yes! In fact I’ve done it myself as you can see from the video on my profile.

      It’s actually very simple to understand as long as you are aware of what a sound wave actually is. A sound wave can also be thought of as a pressure wave. This means that whatever material (air for example) it is travelling through is compressed in some areas and expanded in others.

      The way the acoustic levitator works is by setting up a standing sound wave by reflecting it from the speaker off an aluminium block. This means that the compressed (high pressure) areas of the sound wave stay in the same place. When you get this, you can essentially ‘sit’ objects on a cushion of very high air pressure, so they levitate.

      The levitator I built is still a bit of a work in progress, I can levitate solids easily, but am still having trouble with getting liquids stable. If I can do that, then there’s a whole range of experiments I want to try.

      Please let me know if you have any other questions about acoustic levitation!

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