1. Theory of Apparatus

1
Sonoluminescence
1. Theory of Apparatus The function of the
apparatus is to create of strong 3-dimensional
standing wave within a resonance chamber. This
will effectively trap the bubble within the nodes
of the chamber and force a bubble to collapse on
its self and emit light. In order to produce SL,
there are three key aspects of the apparatus that
need to be taken into account. First is the
Piezo-Electric Transducer (PZT), which is the
driving element of the apparatus. A driving rod
is connected to the PZT, forming an ultra-sonic
horn (USH). The next element is the resonance
chamber, which is a simple open ended plexi-glass
rectangular box. The last element is the
electrical circuit of the system. Due to the
strong driving force required to produce this
phenomena, all elements of the system must
resonate at the same frequency.
7. Making the Bubble Glow Before the bubble
glows, the frequency of the apparatus must be
fine tuned using the PZT microphone to find the
frequency which corresponds to the greatest
amplitude. Once this is found the driving
amplitude needs to be slowly raised. Much like
the trapping threshold, there exists a SL
threshold. The window for the SL threshold is
fairly small and if breeched will immediately
cross the destruction threshold, resulting in the
bubbles destruction. Once the driving amplitude
reaches the SL threshold, a small bluish colored
light should emit from the bubble. The intensity
of the light will slowly increase as the
amplitude is slowly raised. The light from the
bubble can only be seen if in a dark room with
the lights from the electronics covered. It is
necessary to wait a few minutes for your eyes to
adjust to the darkness, then the light from the
bubble should be very noticeable.
Multi-Meters
Oscilloscope
Ultra-Sonic Horn
Resonance Chamber
Power Amplifier
Function Generator
Circuit Board
8. Why does the Bubble Glow? This is still a
mystery to the scientific community. Several
theories exists as to what causes this phenomena
ranging from small jet streams that fracture as
they hit the bubbles surface to hawking radiation
(similar to black hole theories) to thermonuclear
fusion. All of these theories have some validity,
but are improvable to date due to the small scale
of the bubble. What is known is that in order for
any object to emit blue light, the temperature of
the object will exceed the surface temperature of
the sun which is about 10,000 K or 17,540 F (Hot
enough to melt steel!!!).
5. Water Preparation For the bubble to be in a
stable state, the water must be clear of
particles, ions and gasses. We use
distilled-deionized water and place it into a
vacuum chamber. We boil it under vacuum for a
period of about 30 minutes. By this time the
water should stop boiling and be in a pure state.
Next the water has to be put into the chamber
with extreme care to avoid not putting bubbles
into the water while pouring it. The temperature
of the water does change the operating frequency,
but can easily be compensated for by fine tuning
the function generator periodically. A good
temperature range for SL was found to be
13-19 degrees Celsius
9. Future Studies Now that sonoluminescence can
be achieved consistently, many new experiments
can be preformed. The actual temperature of the
bubble can be determined using spectroscopy. The
range of sizes of the bubble and the pulse time
can be determined using laser scattering.
Temperature dependence and multi-bubble
sonoluminescence are also now possible to study.
In the next year, these experiment will hopefully
shed some new light on this amazing phenomena.
6. Trapping a Bubble With the water prepared and
electronics in place, trapping a bubble should
not be difficult. Using the signal from the PZT
microphone, there exist a certain amplitude known
as the trapping threshold which correspond to the
ultrasonic pressure needed to trap the bubble.
Any pressure above this threshold should be
enough to ensure the capability of trapping a
bubble at center node of the chamber. Straight
injection of a bubble was first thought to be the
easiest method, however the bubble size became to
large and floated to the top. The most reliable
method for introducing a bubble was to drop a few
droplets of water onto the waters surface. The
sonic pressure of the system was strong enough to
pull a small bubble created by the droplet into
the center node. This bubble is very small, but
still should be visible to the unaided eye. When
trapped, the bubble creates a small interference
pattern on the PZT microphone as seen in the
diagram.
Acknowledgements Dr. Bruce Bolon, Hamline
University Dr.
Andy Rundquist, Hamline University
Dr. Tom Kramer, Hamline
University Dr.
Richard Peterson, Bethel University