①Mechanical effect. The mechanical effect of ultrasound can contribute to the emulsification of liquid, gel liquefaction and solid dispersion. When the ultrasonic fluid medium to form a standing wave, suspended in the fluid of tiny particles due to mechanical forces and cohesion in the wave joints, the formation of periodic accumulation in space. Ultrasonic waves propagate in piezoelectric and magnetostrictive materials, due to the mechanical action of ultrasonic waves caused by the induction of electrodes and induction of magnetization (see dielectric physics and magnetostriction). (ii) Cavitation. Ultrasonic waves acting on liquids can produce a large number of small bubbles . One reason is that the local tensile stress in the liquid and the formation of negative pressure, the reduction in pressure so that the original dissolved in the liquid gas oversaturation, and escape from the liquid, becoming small bubbles. Another reason is the strong tensile stress to the liquid "torn" into a cavity, known as cavitation. Inside the cavity is liquid vapor or dissolved in the liquid of another gas, or even a vacuum. Due to the cavitation effect of the formation of small bubbles with the vibration of the surrounding medium and constantly moving, growing or suddenly burst. When the bursting of the surrounding liquid suddenly rushed into the bubble and produce high temperature, high pressure, at the same time produce a shock wave. With cavitation accompanied by internal friction can form a charge, and in the bubble due to discharge and produce luminescence. Ultrasonic treatment in the liquid technology is mostly related to cavitation. ③ Thermal effect. Due to the high frequency of ultrasound, large energy, absorbed by the medium can produce significant thermal effects. ④ chemical effect. The role of ultrasound can promote the occurrence or accelerate certain chemical reactions. For example, pure distilled water by ultrasonic hydrogen peroxide; dissolved nitrogen in water by ultrasonic nitrite; dyes in aqueous solution by ultrasonic treatment will change color or fade. The occurrence of these phenomena is always accompanied by cavitation. Ultrasound can also accelerate the hydrolysis, decomposition and polymerization of many chemical substances. Ultrasound also has a significant effect on photochemical and electrochemical processes.