Main Page/PHYS 4210/SonoluminescenceDev

Sonoluminescence

Sonoluminescence is the process by which a gas bubble trapped at the antinode of an ultrasonic standing wave emits visible radiation. This strange phenomenon will be the platform on which 3-dimensional standing waves and black-body radiation will be investigated.

Introduction

Single bubble sonoluminescence, hereafter abbreviated as SL, was discovered in the late 1980's and has received a great deal of attention. This remarkable process involves the trapping of gas bubble at the antinode of a ultrasonic standing wave in a liquid.

3D Standing Waves

In order for the trapping of gas bubbles, a 3-dimensional ultrasonic standing wave need to be attained. The resonant frequency of a the standing wave will occur if each of the 3 dimensions has a length which is equal to an integer number of half wavelengths of the acoustic wave. One will notice that the shape of the liquid cell is rectangular, having the length and width being equal. The height of the cell, and hence a value of great importance for this experiment, is set by the volume of water added to the cell.

The Ultrasonic Horn

The ultrasonic horn is used to deliver acoustic power to the volume of water. Internally, the horn contains a series of annular shaped disc transducers which are bolted into its base. The basic structure and shape of the horn is designed to efficiently couple the pressure waves generated from the transducers to the narrow stem of the horn. All of the transducers are the same. They consist of a ceramic material which has been prepared in such a manner as to have a permanent polarization. In other words,there are specialized capacitors. As a charged is placed across this capacitor there is a force generated across the ends, and the capacitor wants to separate. Since the transducers are compressed, this repulsive force does not physically expand the disc but does produce dynamic pressure. As the charge across the transducer is reversed, there is now an attractive force which results in a negative pressure amplitude.

The particular ultrasonic horn used has components which make it tunes for a frequency from 25kHz to 27kHz. Outside of those ranges, the acoustic energy available in the horn is