Time-resolved monitoring of cavitation activity in megasonic cleaning systems

Abstract

The occurrence of acoustic cavitation in the cleaning liquid is a crucial precondition for the performance of megasonic cleaning systems. Hence, a fundamental understanding of the impact of different parameters of the megasonic process on cavitation activity is necessary. A setup capable of synchronously measuring sonoluminescence and acoustic emission originating from acoustically active bubbles is presented. The system also includes a high-speed-stroboscopic Schlieren imaging system to directly visualize the influence of cavitation activity on the Schlieren contrast and resolvable bubbles. This allows a thorough characterization of the mutual interaction of cavitation bubbles with the sound field and with each other. Results obtained during continuous sonication of argon-saturated water at various nominal power densities indicate that acoustic cavitation occurs in a cyclic manner, during which periods of stable and inertial cavitation activity alternate. The occurrence of higher and ultraharmonics in the acoustic emission spectra is characteristic for the stable cavitation state. The inertial cavitation state is characterized by a strong attenuation of the sound field, the explosive growth of bubbles and the occurrence of broadband components in the acoustic spectra. Both states can only be sustained at sufficiently high intensities of the sound field. At lower intensities, their occurrences are limited to short, random bursts. Cleaning activity can be linked to the cavitation activity through the measurement of particle removal on standard 200 mm silicon wafers. It is found that the particle removal efficiency is reduced, when a continuous state of cavitation activity ceases to exist.

Influence of surface tension on cavitation noise spectra and particle removal efficiency in high frequency ultrasound fields

“…PRE tests have been carried out at those optimal conditions, chosen on the basis of the previously reported hydrophone measurements, and are presented in Table I. Hauptmann 17 recently reported that under continuous sonication and at low acoustic power densities the obtained particle removal efficiency is limited. Cavitation activity can be enhanced when pulsing the acoustic field, as shown in Sec.…”

“…A more detailed description and illustration of the experimental setup can be found elsewhere. 17 Once the acoustic spectrum is recorded and averaged, the ultraharmonics (from 2.5 to 5.5 times the resonant frequency) are evaluated. Different types of cavitation are often 114322-2distinguished when evaluating acoustic noise spectra.…”

Size Distribution of Cavitation Bubbles

“…The hydrophone signal was amplified using a homemade amplifier based on the AD8066 FastFET operational amplifier (Analog Devices) (Hauptmann et al 2012).…”

Low-frequency low energy ultrasound combined with microbubbles induces distinct apoptosis of A7r5 cells

“…The data were fourier transformed to obtain the fundamental frequency of acoustic fields and the amplitude of the 2nd, 3rd and 4th harmonic acoustic pressure. The amplitude of fundamental frequency was set as the standard to normalize the data, where the normalized data represented the acoustic cavitation according to the method of Hauptmann et al (17). The experiments were repeated four times.…”

“…The acoustic cavitations were detected according to the method of Hauptmann et al (17). Hydrophones were placed into tubes which were filled with A7r5 cells treated with ultrasound (US group) or ultrasound combined with microbubbles (US+MB group), and the change of acoustic fields was detected over time.…”