Cavitation usually refers to the generation and subsequent dynamic behaviors of cavities when liquid suffers from a sufficient pressure drop. It has been widely used in sonochemistry, biomedical, environmental science and other areas. 

Over the past decades, cavitation intensity has already been used as a self-evident definition charactering the activity or strength of cavitation. Chemical, acoustic, optical and mechanical methods were developed to measure the cavitation intensity.

However, measurement results using different methods could be hardly compared with each other. It is necessary to confirm a clear and universal definition of cavitation intensity. 

Recently, from the point of view of energy, researchers from the Institute of Acoustics of the Chinese Academy of Sciences (IACAS) proposed a generalized definition of cavitation intensity, and derived an appropriate formula to calculate the cavitation intensity.

The cavitation intensity was defined by the power density of cavitation (i. e. the cavitation energy  in unit time and unit space). Researchers found that the cavitation intensity could be characterized by q, namely the state variable of cavitation, which denotes the instantaneous ratio of the volume cavitation bubbles occupies a space.

The influence factors of cavitation intensity were intricately related to the surrounding liquid environment, ultrasonic frequency and pressure, bubble size and so on. Therefore, in the fixed liquid environment and bubble nuclei condition with certain sound pressure amplitude, a specific ultrasonic frequency might maximize the cavitation intensity. 

The study, published in Ultrasonics Sonochemistry, was supported by the National Natural Science Foundation of China.

Illustration on the definition of cavitation intensity and its measure method (Image by IACAS)