Dependence of cavitation, chemical effect, and mechanical effect thresholds on ultrasonic frequency

Abstract

Cavitation, chemical effect, and mechanical effect thresholds were investigated in wide frequency ranges from 22 to 4880kHz. Each threshold was measured in terms of sound pressure at fundamental frequency. Broadband noise emitted from acoustic cavitation bubbles was detected by a hydrophone to determine the cavitation threshold. Potassium iodide oxidation caused by acoustic cavitation was used to quantify the chemical effect threshold. The ultrasonic erosion of aluminum foil was conducted to estimate the mechanical effect threshold. The cavitation, chemical effect, and mechanical effect thresholds increased with increasing frequency. The chemical effect threshold was close to the cavitation threshold for all frequencies. At low frequency below 98kHz, the mechanical effect threshold was nearly equal to the cavitation threshold. However, the mechanical effect threshold was greatly higher than the cavitation threshold at high frequency. In addition, the thresholds of the second harmonic and the first ultraharmonic signals were measured to detect bubble occurrence. The threshold of the second harmonic approximated to the cavitation threshold below 1000kHz. On the other hand, the threshold of the first ultraharmonic was higher than the cavitation threshold below 98kHz and near to the cavitation threshold at high frequency.

Advances in low-frequency ultrasound combined with microbubbles in targeted tumor therapy

“…The cavitation effect of low-frequency ultrasound is affected by many factors, such as ultrasonic frequency, intensity, irradiation time, and method, etc. (Nguyen et al, 2017). The ultrasonic parameters reported in the literatures are not completely consistent.…”

“…Findings obtained by Tezel et al (2002) emphasized the importance of low frequencies (20-100 kHz), because the amplitude of broadband noise induced by the low-frequency transient cavitation correlated well with enhanced skin conductivity. Some studies revealed that the thresholds of cavitation effect increased as the ultrasonic frequency increased, and the duration of the rarefaction phase decreased because the pressure oscillation period decreased (Pétrier and Francony, 1997;Grieser et al, 2015;Nguyen et al, 2017). Consequently, it becomes more difficult for cavitation bubbles to occur.…”

Axial acoustic field along a solid-liquid fluidized bed under power ultrasound

“…Similarly, Uchida et al [28,29] define the cavitation index as the integral of the spectrum over a band located in the high frequency region (here between 1 MHz and 5 MHz). An alternative method is to integrate the spectrum on a wider band, after eliminating the lines corresponding to the (sub/ultra) harmonics and/or the fundamental [30]. This last method is more complex to apply as it needs to detect and eliminate specific parts of the spectrum, but it is more rigorous.…”

“…However, since the Blake threshold is a model describing the behavior of an isolated bubble, using it to locate cavitation zones might be inaccurate. Indeed some authors like Nguyen et al [30] measure a cavitation threshold around kPa 20…”

Preparation of octenyl succinic anhydride‐modified cassava starch by the ultrasonic‐assisted method and its influence mechanism

“…Ultrasonic cavitation is a series of dynamic processes of bubbles in the liquid when they are exposed to the ultrasonic field and it can produce three kinds of mechanical forces, including local ultra-high pressure, high-speed jet, and high-frequency vibration (Nguyen, Asakura, Koda, & Yasuda, 2017). Miano, Ibarz, and Augusto (2017) treated corn kernels by ultrasound and found that the hydration of corn kernels enhanced and the time reduced by about 35%.…”