Characterization of cavitation-radiated acoustic power using single-element detectors

Abstract

Standard approaches to quantifying cavitation activity using emission measurements made by single-element passive cavitation detectors (PCD) would be facilitated by improved quantitative and system-independent characterization techniques. Although the strength of an individual emission source can be determined from absolute pressure measurements by a calibrated PCD, this approach requires spatially resolved detection of single bubbles at known locations. Here, a method is shown for characterizing an ensemble of emission sources, quantified by their radiated acoustic power per unit area or volume of a defined region of interest (ROI). An analytic diffraction-correction factor relating frequency-dependent PCD-measured pressures to cavitation-radiated acoustic power is derived using a spatial integral of the PCD sensitivity. This approach can be applied to measurements made by any PCD without a priori knowledge of the number or spatiotemporal distribution of cavitation bubbles. Simulations show that cavitation-radiated acoustic power per unit ROI volume or area is accurately recovered by compensation of emissions received by focused or unfocused PCDs. Measurements from previous sonophoresis experiments are analyzed, showing that skin permeability changes from 0.41 or 2.0 MHz sonication are comparably correlated to the radiated acoustic power of subharmonic emissions per unit area.