Ultrasound is a frequency beyond the human hearing range of 20 kHz or more of sound waves. Ultrasound propagation depends on the elastic medium, its propagation, so that the particles in the elastic medium oscillation, and through the medium according to the direction of ultrasound transmission energy, this wave can be divided into longitudinal waves and transverse waves. In the solid, both can be transmitted, while in the gas and liquid, only the longitudinal wave can be transmitted. Ultrasound can cause the mass to vibrate, the acceleration of the mass vibration and the square of the ultrasound frequency is proportional. Therefore, several tens of kilohertz of ultrasound will produce a great force, strong ultrasound in the liquid propagation, due to the non-linear effect, will produce acoustic cavitation. In the cavitation bubble suddenly closed when the shock wave can be issued around it to generate thousands of atmospheric pressure, the direct and repeated impact on the dirt layer, on the one hand, destroy the dirt and cleaning the surface of the adsorption, on the other hand, will also cause the destruction of the dirt layer from the surface of the cleaning parts and make them scattered to the cleaning fluid. Air bubble vibration can also be scrubbed on the solid surface. Bubbles can also "drill" into the cracks to do vibration, so that dirt off. For greasy dirt, due to the role of ultrasonic cavitation, the two liquids in the interface quickly dispersed and emulsified, when the solid particles are wrapped in oil and adhering to the surface of the cleaning parts, oil is emulsified, the solid particles that fall off. Cavitation bubble in the vibration process will make the liquid itself to produce a circular flow, that is, the so-called acoustic flow. He can make the vibration bubble surface there is a high velocity gradient and viscous stress, prompting the destruction of the cleaning surface dirt and off, ultrasonic cavitation in the solid and liquid surface generated by the high-speed micro-jet can remove or weaken the boundary layer of dirt, corrosion of the solid surface, increase the role of agitation, accelerate the dissolution of soluble dirt, strengthen the cleaning effect of chemical cleaning agents. In addition, ultrasonic vibration in the cleaning fluid caused by a large mass of vibration speed and acceleration, but also the surface of the cleaning parts of the dirt by frequent and intense impact.