Cavitation of liquid due to high amplitude ultrasonic vibration within the liquid is the backbone of ultrasonic cleaning. Liquids have the unique ability to cavitate. In order to cavitate, a material must exhibit three properties -
- It must be relatively inextensible and uncompressible. It can't be able to stretch or expand or be compressed to significantly change it's volume.
- It must have limited tensile strength. If subjected to enough tensile force it will break.
- It must be able to "heal." If divided into two or more pieces, the pieces must be able to re-combine to form a whole that is indistinguishable from the original.
In liquids, as frequency and amplitude are increased, the tensile strength of the liquid is eventually exceeded and the liquid separates or fractures. This phenomenon is called "cavitation."This phenomenon is called "cavitation" and results in a void within the liquid called a "cavitation bubble." Depending on the liquid and its properties, this void may become completely or partially filled with air that was dissolved in the liquid to begin with or with vapor of the liquid itself as the reduced pressure causes the liquid to flash into vapor. For the moment, we will consider the void an area of vacuum created within the liquid. This void is unstable and supported only by the transient (passing) negative pressure or rarefaction portion of the sound wave. We'll talk about the consequences of the pressure wave that follows in an upcoming blog.
- FJF -