This is the first trial run, with the flask filled with tap water, untreated in any way.
After tuning the circuit with the water in the flask, we’re achieving electrical resonance at about 26.4khz – this is where the voltage across the transducer is at its peak (the transducer is a capacitor connected across a transformer coil, giving a resonant circuit). To find the resonance frequency I just swept up from 25khz and observed the voltage. I could not do any acoustic flask resonance measurements at this point, having fried my piezo disks. (I have sent off for a 25khz ultrasonic receiver which I think will work better as a mic).
The trace below shows the voltage across the transducer, with the probe x10 attenuated, so each square is 100v, I think we’ve got enough drive voltage with this amplifier now!
And here’s what’s going on in the flask, certainly something.
I noticed little bubbles spontaneously formed and danced around, some seemed to gravitate towards certain points in the flask – these must the antinodes (areas of low pressure). Other bubbles that formed in this vicinity would coalesce into larger bubbles, until buoyancy won out and the bubble would rapidly ascend to the surface. This is all quite promising..
The next step may be to de-gas the water and see if we can get some stable bubbles, I’m pretty happy with the rig, but I am wondering if it is possible to side step all the degassing and achieve sonoluminescence in plain old tap water. Reading around a bit, Krefting et al (2003) made a study of sonoluminescence in air saturated water, and found that stable bubbles exist in water that has not been degassed. This should be properly explored and documented – certainly if it is repeatable.
- Effect of drive amplitude.
- Effect of frequency tuning around resonance.
- Measurements of bubble position.
- SBSL / MBSL
I have videoed one of the dancing bubbles – yes the resolution is all wrong.. but you can see bubble dancing in the field, dispersing, growing and reforming.