Number density of bubbles under ultrasonic horn measured from stroboscopic images

Abstract

Although image measurement is essential in the analysis of acoustic cavitation bubbles, it is impossible to determine the position of the bubble along the optical axis of the imaging system from the images. Thus, the number density of the bubbles cannot be measured from the image. This paper proposed a method to determine bubbles’ positions along the optical axis using the bubble image brightness. The relationship among the bubble position along the optical axis, the bubble diameter, and the bubble image brightness is clarified using the bubble in the single bubble system. A measurement method of the bubble number density based on this relationship is established. Using this method, the time-averaged spatial distribution of bubble number density under ultrasonic horn is revealed.

Characterization as measurement sound source of acoustic cavitation noise from bubble clusters under ultrasonic horn

“…[17][18][19] The ultrasonic horn, which has a very high tip vibration velocity, generates bubble clouds with a high bubble number density in the vicinity of the horn tip. [20][21][22] The collapse of this cluster emits strong spherical shockwaves. The peak sound pressure of the shockwave is more than 1000 kPa within a distance of 2 mm from the bubble cluster, and the frequency bandwidth of the shockwave is more than 10 MHz.…”

Theoretical analysis and experimental verification of spatial coherence of acoustic cavitation noise from bubble clusters under ultrasonic horn

“…Under the ultrasonic horns, which emit ultrasound with a huge sound pressure amplitude, acoustic cavitation bubbles arise with a high number density and form bubble clusters. [18][19][20] The oscillation of the bubble cluster under the horn emits strong spherical shockwaves [21][22][23] with a peak sound pressure of 1 MPa at 2 mm from the shockwave origin and the frequency components ranging from 0 to 30 MHz or higher. 24) A broader bandwidth of ultrasound can be beneficial for ultrasonic particles 25,26) and biological 27) measurements because it provides more spectral information and generally achieves higher temporal resolution in propagation time measurement of the ultrasound.…”