Acoustic Levitation

When sound waves are focused at the same space, repeating standing waves can form with areas of low amplitude (nodes) and areas of high amplitude (antinodes)

If the sound signal is focused just right, it is possible to trap particles in the “quiet” zones (nodes) and cause them to levitate. Of course, it isn't quite as simple as that, check out this Action Lab video for a better description.

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The Demo

This is one of the most amazing demonstrations that I've seen. Even though I know it's real, it still somehow seems like an animation of some kind. I've learned that the "wow factor" is about 1000 times better if you let students do this on their own rather than a teacher demo.

I use the following prompt when doing this as a station lab:
"Use the tweezers to levitate Styrofoam beads in the standing sound wave (start by placing one bead in the center) and take a photo of your final configuration. (Please be careful with this set up - the electronics are precise & fragile)"

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The Materials

This has been on my project dream list for a while and it was finally possible with the right materials. I have purchased each of the acoustic levitation offerings listed at StirlingKit.com and they are both amazing. 

Link to purchase at StirlingKit.com

The small model works right out of the package without any assembly required but it is limited in the amount that you are able to levitate. It isn't quite as impressive as the larger model but it doesn't require nearly as much technical assembly.

The larger model comes with the 3D Printed fixture, 72 ultrasonic speakers, and a board to drive it all. While this includes all of the materials, there is A LOT of assembly required!

One down, 71 to go...

Lots of installing and prepping the speakers. Each one has a polarity so the assembly is very detail oriented...

More soldering than I've done in my life! It might not look like it at first glance but the wiring is basically just connecting them all up in parallel with all of the positives connected to the red wired and negatives connected to the black wire.

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Science Investigations

If you are looking for a little more than the fun and games of making things float, here are a couple of ideas to add a little more science :)

1. Using dry ice, Pat Counts was able to make the standing waves visible in a really cool way!

Visualizing standing sound waves with dry ice. Finished this little project just in time. My students start longitudinal standing waves on Monday! #iteachphysics pic.twitter.com/2usGZ1EiNU

— Pat Counts (@Misterfizzx) March 28, 2019

2. Dan Burns was able to measure the distance between nodes to calculate a frequency

Thanks for sharing. Had a chance to check mine out today. Assuming they are at adjacent nodes, I get 1 wavelength = 0.0087 m. If speed of sound is 345 m/s, frequency is 39655 Hz. pic.twitter.com/j5Ojjnz4vx

— Dan Burns (@kilroi22) January 21, 2022

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