Characterization of Stable and Transient Cavitation in a Dual-Frequency Acoustic Field Using a Hydrophone
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Characterization of Stable and Transient Cavitation in a Dual-Frequency Acoustic Field Using a Hydrophone Mingrui Zhao1, Anfal Alobeidli2, Xi Chen3, Petrie Yam3, Claudio Zanelli3 and Manish Keswani2,* 1
Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721, U.S.A. 2 Materials Science and Engineering, University of Arizona, 1235 E. James E. Rogers Way, Tucson, AZ 85721, U.S.A. 3 Onda Corporation, 1290 Hammerwood Ave, Sunnyvale, CA 94089, U.S.A. * Corresponding author, E-mail: [email protected]; Fax: +1-520-621-8059 ABSTRACT Sonication is a commonly used method for particle removal from various surfaces. There has been a growing interest in the use of combination of two or more acoustic frequencies for cleaning as it is expected to achieve better particle removal efficiency and lower feature damage compared to a single frequency acoustic system. In this study, stable and transient cavitation characteristics in de-ionized water subjected to dual-frequency irradiation have been illustrated using experimentally obtained absolute values of cavitation pressures and pressure-frequency spectra. Comparison of the calculated ratio of stable cavitation pressure to transient cavitation pressure suggests that dual-frequency mode has the potential to reduce feature damage while maintaining the particle removal efficiency compared to low frequency ultrasonic field. These observations are further confirmed from the results of damage studies conducted on aluminum coated glass samples. INTRODUCTION Ultrasonic and megasonic assisted cleaning methods are routinely used for removal of particulate contaminants from various surfaces in liquid media [1]. Ultrasonic cleaning (20 – 200 kHz) is relevant for cleaning of optical parts, lenses, and surgical instruments, while megasonic cleaning (0.5 – 2 MHz) is generally utilized in integrated circuit fabrication [2-3]. Cleaning in the megasonic regime significantly reduces cavitation erosion and offers much thinner boundary layer at solid-liquid interface and higher streaming velocities, which makes it possible to remove sub-micrometer and nano-dimensional particles [4]. However, single frequency systems limit the extent, intensity and tunability of stable and transient cavitation and their relative distribution, which affects the cleaning efficiency. The combination of two or more different frequencies from ultrasonic to megasonic range has been of much interest and is expected to overcome the limitations of traditional single frequency based acoustic cleaning processes. Recent studies have shown that dual-frequency irradiation has the capability to enhance acoustic cavitation effect under suitable conditions. Kanthale et al. measured a significant increase in sonoluminescence (SL) intensity when a cleaning liquid was irradiated with a dualfrequency sound field in comparison to a single frequency field at lower acoustic power levels [5]. Liu and Hsieh observed an extensive increase in number of visible bubbles as well as size
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