Approach to Quantify Acoustic Cavitation in Absolute Physical Units

In the study of acoustic cavitation it is desirable to quantify the acoustic signals in physical units to allow comparison among different conditions regardless of the equipment used. Motivated by cavitation present in cleaning environments, we have developed a method to measure the acoustics of cavitation in a way that is independent of the instrument used. The proposed method is based on having a point-like pressure sensor (hydrophone) calibrated in magnitude and phase over a broad frequency spectrum (well beyond the driving field frequency), capturing a limited sample of the raw time domain signal (in V), and converting the sample to frequency domain. The spectral decomposition of the raw signal is then used to deconvolve the sensor response to generate the true spectrum of the detected pressure field (in Pa). In the frequency domain, the corrected spectrum reveals the direct field as a single frequency signal, the stable cavitation by the sub-harmonics, harmonics and ultra-harmonics, and transient cavitation in the form of broadband noise above the electronic noise. By selectively integrating the various frequency components it is possible to know the acoustic pressure, in RMS units of pressure (Pa), for the direct field, stable cavitation, and transient cavitation. We present practical examples of measurements under various cleaning conditions where one can observe the effects of driving power, location relative to the source, or distribution of objects to be cleaned in the tank. It is believed that this or other method based on true, absolute pressure measurements will allow more progress in the research of cavitation by providing a means to exchange and compare quantitative data.