For Additional Information:
Fred Seeley, (205) 890-6276 x 251
Phillip Gentry, (205) 890-6414
Students 'harmonize' with a star in a jar
Using $1.29 acrylic boxes from a dime store and simple electronics,
undergraduate students and their UAH lab instructor are doing cutting
edge research into sonoluminesence, a little understood phenomenon
sometimes referred to as "a star in a jar."
In a back corner of a teaching lab, the student-built apparatus uses
acoustic waves to suspend a microscopic bubble in water. Stretched and
compressed by the force of sound waves, the bubble expands to a diameter
of only 100 microns, then collapses to one one-millionth of that volume.
It does that 30,000 times a second, focusing acoustic energy by a factor
of one trillion, generating temperatures hotter than the surface of the
Sun and releasing with each cycle a faint flash of light that lasts 30
trillionths of a second.
While scientists at some of the most pretigous laboratories in the U.S.
try to explain how sonoluminesence works, UAH physics instructor Fred
Seeley and his students may be on the threshold of explaining why the
tiny glowing bubble can't be made brighter.
The answer may be in harmonics. When the team looked at harmonics
(secondary acoustic waves) in the water-filled vessel without the bubble,
it found weak harmonic feedback.
"When you add the bubble, however, you get a rich harmonic structure,"
Seeley said. "And some harmonic frequencies are almost as powerful as the
fundamental wave.
"Our hypothesis is that these harmonics are generated by the shock of the
bubble's collapse. The bubble wall collapses at the speed of sound until
the water reaches its 'hard core' and can't go anywhere else."
Harmonic waves set up by that periodic shock may destructively interfere
with the fundamental drive, limiting the light that is released, Seeley
said. The team is trying to control destructive harmonics to see if a
brighter bubble can be made.
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