Ultrasonic effect

Ultrasonic effect: When the ultrasonic wave propagates in the medium, due to the interaction between the ultrasonic wave and the medium, the medium changes, resulting in a series of mechanical and electromagnetic ultrasonic effects, including the following two effects:

① Mechanical effects. The mechanical action of ultrasound can promote the emulsification of liquids, the liquefaction of gels and the dispersion of solids. When a standing wave is formed in the ultrasonic fluid medium, the tiny particles suspended in the fluid are condensed at the nodes due to mechanical force, forming periodic accumulation in the space. When ultrasonic waves propagate in piezoelectric materials and magnetostrictive materials, induced electrical polarization and induced magnetization are caused by the mechanical action of ultrasonic waves.

② Cavitation. When ultrasonic waves act on liquids, a large number of small bubbles can be generated. One reason is that partial tensile stress occurs in the liquid to form a negative pressure. The decrease in pressure makes the gas originally dissolved in the liquid supersaturate and escape from the liquid and become small bubbles. The other reason is that the strong tensile stress "tears" the liquid into a cavity, which is called cavitation. Inside the cavity is liquid vapor or another gas dissolved in the liquid, and it may even be a vacuum. Small bubbles formed by cavitation continue to grow or burst suddenly. When it bursts, the surrounding liquid suddenly rushes into the bubble to generate high pressure, and at the same time, a shock wave is generated. The internal friction accompanied by cavitation can form electric charges and cause light emission in the bubbles due to discharge. The technology of ultrasonic treatment in liquid is mostly related to cavitation.