Ultrasonic effect and power ultrasound

　As we all know, sound waves below 20HZ and above 20HZ are sound waves that are inaudible to human ears. Ultrasound refers to waves with a frequency above 20KHZ. Ultrasonic surge has a cavitation effect, which usually refers to a series of dynamic processes such as oscillation, growth, shrinkage, and collapse of microbubbles present in the liquid activated by ultrasonic waves. As early as 100 years ago, when the British first destroyer launched the water test, it was found that the propeller propeller caused severe vibration in the water. THORNYCRO and HARNABY studies showed that a large number of bubbles were generated due to the rotation of the propeller in the water. This is the first time in history that the physical nature of cavitation has been described under the pressure of water, that is, the direct shrinkage of shrinkage. After that, the British improved the design several times, but could not get rid of the vibration problem. Officially invited the classic acoustic master, the Lord to study this problem. In 1917, RAYLEIGH published the title "The pressure generated by the collapse of the spherical hollow in the liquid" The research papers of the Ming Dynasty laid the foundation for the study of the theory of backspace.