Research On Sonoluminescence Threshold Pressure Of Bubbles At Different Frequencies And Gas Component

Ultrasound cavitation and sonoluminescence (SL) generation have gained great interests in recent years, in this paper, we attributed to discuss the influence of ultrasonic frequency and the gas component inside on the SL threshold pressure and have gotten some value results. In addation, the method for measuring the ultrasonic pressure intensity dynamically by the means of SL image is also discussed.In the first chapter, the background of sonoluminescence was introduced. It includes the introduction of the bubble dynamics, the mechanism of SL, the theory of SL and the potential applications of SL have been reviewed in the thesis.In the second chapter, the main experiment setup is introducted. Based on the back illuminated cooled CCD, we have designed an experiment device with high quantum efficiency, high sensitivity and low noise. The lowest detectable light flux of our equipment is 0.09 photons/sec*pixel.With the equipment, we have done the following work:In the third chapter, the thresholds of the ultrasonic pressure for MBSL at different ultrasonic frequencies were measured by experiment, for the first time, respectively. And the dependence of MBSL on ultrasonic frequency was analyzed. Results show that, at any frequency, the MBSL field changes with the ultrasonic intensity, and the thresholds of ultrasonic pressures are increased with the ultrasonic frequency. The reason is that, the ultrasound with higher frequency needs higher pressure to make the bubbles provide enough energy to dissociate the water molecules.In the forth chapter, the SL threshold pressures for bubbles with different noble gases were measured experimentally. Results show that the threshold pressure increases with the decrement of molecular mass for gases inside the bubbles. The simulating temperature values at collapse are almost equal to each other for different gas bubbles at the threshold pressures, however, when the pressure above the threshold one, the SL mechanism satisfies the bremsstrahlung. On the base of the experiments and simulations, we found that firstly water molecules dissociate in theprocess of cavitation and follow with light emission, then, the noble gases ionize with the increase of temperature and the bremssthahlung occurs. SL is a process from molecular emission to bremsstrahlung.In the fifth chapter, we record the SL image resulted from ultrasonic cavitation and studied the relationship between the SL intensity and ultrasonic intensity. The results show that the SL image can reflect the distribution of ultrasound, accordingly. The SL imaging can be considered a new method to measure the intensity of ultrasound dynamically.Finally, the appliation of SL in biology and medical treatment was analysized. SL not only has strong penetrability that the virtue sound has, but also can show the medical matter by optical means. So, SL imaging will be applied widely.