Ultrasound interacts with the medium in the propagation process, and the phase and amplitude change, which changes some of the physical, chemical and biological properties or states of the medium, or accelerates the process of this change, thereby producing a series of effects, such as mechanics and heat. , Chemical and biological effects, etc. These effects can be attributed to the following functions:
Cavitation bubbles grow in the negative pressure zone formed by the longitudinal propagation of ultrasonic waves, forming a bubble interface.
It closes quickly in the positive pressure zone and is compressed and stretched under alternating positive and negative pressures.
The impact of the high-speed microjet on the side of the distal air bubble produces a water hammer impact, that is, a shock wave.
The shock wave spreads radially outwards, hits the solid surface of the sample, is reflected to the bubbles, and the bubbles become vortex convection towards the solid surface, forming a huge instantaneous pressure; this huge instantaneous pressure can make solid particles suspended in the liquid or The surface of biological cell tissue is severely damaged.
In addition to the above effects, there are mechanical, thermal and other effects:
During the propagation process of ultrasound, the medium particles will compress and stretch alternately, which constitutes a pressure change, and the pressure change will cause a mechanical effect. Although the displacement and velocity of the medium particle movement caused by ultrasound are not large, the particle acceleration proportional to the square of the ultrasonic vibration frequency is very large, sometimes exceeding tens of thousands of times the acceleration of gravity. Such a large acceleration is enough to cause a powerful mechanical effect on the medium. effect.
If the ultrasonic wave acts on the medium and is absorbed by the medium, there is energy absorption. At the same time, due to the ultrasonic vibration, the medium generates strong high-frequency oscillation, and the medium rubs against each other to generate heat. This energy raises the temperature of the liquid and solid. When ultrasound penetrates the interface between two different media, the temperature rises even more. This is because the characteristic impedance on the interface is different, which will cause reflection, forming a standing wave, causing relative friction between molecules and heating.
The cavitation of ultrasound can cause oxidation, for example, hydrogen peroxide is produced after a short period of ultrasound treatment in distilled water. Nitric acid is produced after ultrasonic treatment in nitrogen-dissolved water. Ultrasound also has a reducing effect and affects the electric decomposition of metals.
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