Nonlinear acoustics and industrial applications

The nonlinear phenomena, which are linked to finite-amplitude waves, are directly involved in the mechanisms that determine a great number of practical applications. In fact, high-intensity applications of sonic and ultrasonic energy constitute a wide field wherein the acoustic waves are used to produce permanent effects on the medium through which they propagate. This field is termed macrosonics. The use of finite-amplitude waves in industrial processing is generally based on the exploitation of high pressure variations together with the associated nonlinear effects, such as radiation pressure, streaming and cavitation, and a series of secondary effects, such as heat, agitation, mechanical rupture, etc. For technological applications the knowledge and control of these effects is essential in order to maximize or suppress them according to the application needs. The development of the systems for industrial use also requires a proper generation and distribution of finite amplitude acoustic fields. There is a wide range of potential macrosonic processing applications, but the majority of them still remain at laboratory stage. This is probably because of the problems related to the development of adequate macrosonic systems and to the deep knowledge of the mechanism of the processes. This paper reviews the main nonlinear problems involved in the development of macrosonic systems for industrial applications as well as the nonlinear effects related to the mechanisms of some specific applications.