Sound Visualization: The theory works! – Part IV

So in this (last) episode of our quest to visualize sound we have to do some sound-vis experiment; right? Well, I did the experiment with an ultrasonic manipulator I was working on a couple months ago. I built a Z-Type shadowgraph (turns out I didn’t have enough space on the optical table for a knife edge because the camera I used is so enormous) with the following characteristics (see part II for nomenclature):

\displaystyle f_2=2m

\displaystyle g=1m

\displaystyle L=0.13m

For this first experiment I used a phased array device with 64 ultrasonic transducers:

When I give all transducers the same phase, they are supposed to produce a plane-like wave. This is how the wave looks like in this shadowgraph setup:

Where the oscillation levels are plus and minus 50 levels from the background level. Thus, we have N_{lv}=100 and the expected pressure fluctuation at 40kHz is 257 Pa, corresponding to a SPL of 142.2dB. Quite loud!

A measurement with a very good microphone (B&K 4939) gave me a pressure fluctuation of 230 Pa – which is quite close to the expected value from the shadowgraph!

I made a little video explaining the details of the setup and there’s some really nice footage of acoustic manipulators I built on it. Perhaps you can find some inspiration on it:

So this post was rather short. Most of the content is in the video, so I hope you have a look!

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