How does acoustic levitation use sound waves to make objects float?

[jedishrfu]

https://curiosity.com/topics/acoustic-levitation-makes-objects-float-with-sound-waves-curiosity/

There's a YouTube video that's shows the effect:

 

[scottdave]

I don't think I had ever seen this effect demonstrated before. Thanks for sharing. I subscribe to Smarter Every Day, and I have gone back and watched a lot of his old videos, but I must've missed this one.

 

[PeterO]

Don't forget that sound is a longitudinal wave, so rather than "shaking" the air, between the horns, from side to side, it moves it up and down. I assume the "levitated" styrene balls stabilise themselves at a displacement node, where it is calm, a bit like the sand on those Chladni plates.

 

[jedishrfu]

Don't forget that sound is a longitudinal wave, so rather than "shaking" the air, between the horns, from side to side, it moves it up and down. I assume the "levitated" styrene balls stabilise themselves at a displacement node, where it is calm, a bit like the sand on those Chladni plates.

Yes, they show that in the video.

 

[rumborak]

It's interesting though how they are able to do more than one. I could see a single placed object disrupting the shape of the standing wave.

 

[jedishrfu]

The placement isn't disrupting the standing wave though because this is the zero point where nothing moves.

 

[rumborak]

It is, but if you look at the video, the spheres are very sizeable in relation to the wavelength. From some size on, I would think, they will influence the wave itself.

Btw, maybe I missed this in the video, but how do they achieve the horizontal confinement?

 

[jedishrfu]

The top and bottom plates vibrate and they have a good sized diameter larger than the balls being suspended.

 

[PeterO]

It's interesting though how they are able to do more than one. I could see a single placed object disrupting the shape of the standing wave.

But the object is not disrupting the standing wave, the standing wave is disrupting the object's normal motion it prevents it from falling.