The idea of my project is to improve on previous experiments by systematically going through the experiment of single bubble sonoluminescence and quantifying and controlling as many of the experimental parameters as is possible. Two systems will be used the first system will have the same basic set-up as before, this will be used as a test system used to verify that the various test liquids will support SBSL and that the liquid has a suitable gas content.
The second system will be the experimental system and will eventually be hooked up to;
Throughout the course of the experiment and supporting research there were a number of improvements and extensions to the project which I would love to have been able to investigate for example;
Young et al (1996) performed experiments into how magnetic field affect light production in sonoluminescence. They found that in a magnetic field sweep at constant acoustic pressure that sonoluminescence was quenched above a certain threshold. In acoustic field sweeps in a constant magnetic field again it was shown that the sonoluminescing region was shifted, needing higher driving force, so that at 20T nearly twice as much power was needed to produce the light. They also noticed different behavior of the light production at different temperatures, at 20°C that the light intensity had a sharp drop off at the upper limit of sonoluminescing region but at 10°C the drop of was gradual and indeed at 20T their amplifier did not have enough power to quench the sonoluminescence. It was thought that the magnetic field acted to produce some king of reduced pressure as seen by the bubble. Attempts to explain this by an effect on the plasma inside the bubble failed because of the small field energy enclosed within the bubble (DiDonna et al 1997). Yasui et al (1999) produced a theoretical paper proposing that the dipole of the water molecules would undergo a torque as they moved through the magnetic field.
N = PH2O × (B × v)
Energy would be transferred from the field to rotation of the water molecules and so a reduced pressure would be seen by the bubble. This paper made rough calculations and the order of magnitude of the effect seems to correspond. This effect is dependant on the cross product of the velocity of the water molecules and the magnetic field, in a spherical field this would mean that the sides of the bubble wall move.
The trapping force that holds the bubble in the acoustic field, the Bjerknes force, also has a subtle directional correction due to the buoyancy of the bubble.
Fbuo= (rg/T) V(t)dt
Where this is integrated over one acoustic cycle, V is the volume of the bubble. This results in a slightly off-centre equilibrium bubble position. The buoyancy force and the acoustic pressure change over the acoustic cycle and this results in a fluctuation in the equilibrium position, these movements are thought to make the bubble aspherical and thus reduce the light production.
We aim to conduct experiments to directly measure the effects of the magnetic field on the bubble dynamics and to further investigate the effect of the temperature on the fall off of light intensity . It may also be interesting to investigate how the spectral shape changes in a magnetic field. Attempts will also be made to use the directional nature of the magnetic effect to further investigate the buoyancy force.
We intend to use organic fluorescent dyes to extend the regime in which the spectra can be measured. Water strongly absorbs photons of wavelengths less than 200nm and so the UV part of the spectra cannot be measured. This inhibits the formulation of a complete theoretical model. Organic fluorescent dyes e.g. Sodium Fluorescein, absorb at short wavelengths and emit at longer wavelengths and so the presence of UV light in the emitted spectra could be inferred.
The spectra of sonoluminescence will be measured with and without the presence of the dye and the spectra compared. The same fluorescence emission spectrum is generally observed irrespective of the excitation wavelength because energy is quickly dissipated in the molecules, however the fluorescence spectrum is usually seen as a mirror image of the absorption spectrum. We are hoping to use these characteristics to learn something of the previously unseen UV spectra of sonoluminescence.
SBSL