Effect of the Nearfield on the Cavitation Limit of Transducers

Abstract

The cavitation-limited acoustic power of a transducer depends on its nearfield structure. Cavitation begins when the pressure amplitude reaches a certain value, but the pressure distribution is usually not uniform, and only the pressure component in phase with the velocity contributes to radiated power. In estimating cavitation limits, these near field effects must be considered as well as those effects that depend on the properties and condition of the medium. An analysis of cavitation-limited power that clearly separates the nearfield effects from other effects is presented here. A parameter γ that determines the nearfield effect on the cavitation limit is defined, and γ is calculated for circular pistons, hemispherical pistons, flexural plates, and multipole spheres. The values of γ are usually in the range 0.25–1.0, where unity corresponds to no near-field effect, and a value less than unity means that the cavitation-limited power per unit area is reduced by that factor.