Ultrasonic energy acting on the medium will cause high-speed fine vibration of the mass, resulting in changes in mechanical quantities such as velocity, acceleration, sound pressure, and sound intensity, thus causing mechanical effects. Ultrasound is a form of mechanical energy propagation, and the fluctuation process will produce a linear effect of vibration. Ultrasound propagation in the medium, the mass displacement amplitude is very small, but the acceleration of the mass caused by ultrasound is very large. If 20kHz, 1W / cm2 of ultrasound propagation in water, the sound pressure amplitude of 173kPa, which means that the sound pressure amplitude per second to change between plus and minus 173kPa 20,000 times, the maximum acceleration of the mass up to 1440km / s2, about 1500 times the acceleration of gravity, such intense and rapid changes in mechanical motion is the power of ultrasound mechanical vibration effect. When the ultrasound medium is not a uniform layered medium (such as biological tissue, human body, etc.), the acoustic impedance of each layer of the medium is different will make the propagation of sound waves to produce reflections, the formation of standing waves, standing waves of the wave belly, wave section caused by changes in pressure, tension, and acceleration. Due to the different masses of different media (such as biomolecules), there are differences in the vibration speed caused by pressure changes, so that the pressure changes caused by the relative motion between the media masses are another reason for the mechanical effects of ultrasound. The use of ultrasound mechanical effect should be processed (perforation, cutting cutting, compaction, surface strengthening, welding, cleaning, polishing, and removal of undesired film and dirt, etc.), also used to accelerate the dispersion, homogenization, emulsification, crushing, sterilization, and other processes.
Table of Contents
The examples of ultrasonic mechanical action
Mechanical StirringThe high-frequency vibration and radiation pressure of ultrasound can form effective stirring and flow in gas and liquid. The cavitation bubble vibration produces strong jets and local micro-impulse on the solid surface, which can significantly reduce the surface tension and friction of the liquid, and destroy the surface layer of the solid-liquid interface, thus achieving the effect that ordinary low-frequency mechanical stirring cannot achieve. This effect is the physical basis for the application of drug penetration, cosmetic product introduction to the skin, ultrasonic degassing, food, and cosmetic blending and refinement.
InterdiffusionUsing ultrasonic vibration and the pressure and high-temperature effect of cavitation induces the interpenetration of molecules between two liquids, two solids, or liquid-solid or liquid-gas interfaces to form new material properties. Ultrasonic welding of metals or plastics, ultrasonic emulsification, cleaning, and atomization can be classified as such effects.
The local shock wave generated by the closure of cavitation bubbles can crush the particles in the liquid and make them fine; make the crystals uniform; disperse the larger, uneven milk droplets into tiny uniform agents (such as medical contrast agents, cancer treatment agents, etc.); and even include the role of dissolving blood clots.