Transcript Sonoluminescence - University of Rochester

Sonoluminescence
Chris McFarland
Ryan Pettibone
Emily Veit
The Basics
• Set up a standing pressure wave in some
fluid.
• Trap a bubble at the antinode of the wave.
• The pressure waves alternately compress
and rarefy the bubbles adiabatically.
• The compressed gas in bubbles reaches a
high temperature, and radiates by some
unknown process.
• Easy enough, right?
WRONG!
Experimental Setup/Procedure
• Set L=0, set signal
generator to flask
resonance.
• Adjust inductor to
achieve RLC
resonance.
• Pull water out of
flask, drip back in
to make bubbles.
Amp.
L
Sig. Gen.
Flask
Osc.
Syringe
Our objectives:
Find Resonance of flask, “trap” a bubble,
and…
MORE POWER!!
Innovation: Resonance
• We found powerful resonant peaks at
52KHz, 77KHz, 270 KHz.
• We believe that these are resonances
because: The input to the transducers was
constant over this range, and when you
change the water level, the resonant
peaks change.
Resonance Frequencies Found
2.5
Amplitude (V)
2
1.5
1
0.5
0
0
20
40
60
Driving Frequency (kHz)
80
100
Resonance Properties
Predicted
Harmonic
Frequency
1st
34.9 kHz
2nd
55.7 kHz
3rd
74.6 kHz
Q
Measured
Q Factor
Frequency
32.3 kHz
15.6
51.6 kHz
50.4
77.0 kHz
39.2
Energy Stored
Power Loss
Innovation: The Amplifier
Rf
Ri
Vi
Vo
Vo/Vi=-Rf/Ri
We used this circuit to boost Vo.
Innovation
• Inductor: With the inductor tuned, we
achieved 80Vpp across the transducers,
and an 8Vpp microphone signal.
• RLC Resonance was achieved with L ~ 8
mH. Thus, C transducers ~ 5 nF.
• Cleaned flask/syringes with ethanol
• Water: Degassed, distilled water was
used.
• Put up more curtains
Qualitative Observations
• We did “trap” bubbles, that is, bubbles
hovered at the flask at antinodes.
• When this occurred, changing the
frequency caused the bubbles to abruptly
move, indicating that sound waves were
influencing the motion of bubbles in flask.
• Bubbles appear to “quiver,” indicating a
change of radius.
Experimental Issues
• Chris: His hair caused the infamous
“Dandruff Effect” in the last lab: this time
he broke an expensive lab amplifier.
• When you pull water out of flask to make a
bubble, the flask falls out of resonance.
• It’s hard create bubbles without hitting the
flask with the syringe.
Conclusion
• We achieved a mic voltage of up to 8Vpp,
higher than the last group. This and
qualitative observations suggest we were
very close to achieving SL.
• The only difference: We used the 52 KHz
resonant peak. Why didn’t we see a
strong resonance at 31 KHz??
Suggestions to Next Group
•
•
•
•
•
Fix our experimental issues
Use argon gas to make bubbles
Find a way to cool flask
Glue more transducers to flask?
Pray.
QUESTIONS??