Measurements of Shape Oscillations on a Micro Bubble Surface by Ultrasonic Excitations

In this study, Lamb's equation and pulsation amplitude threshold theory was compared with measured data on the shape oscillation modes of microbubbles when various frequencies of ultrasonic excitation were applied. Micro air bubbles passing through a channel were excited by a piezoelectric element connected to a function generator. The oscillating mode on the bubble surface and the size of the bubbles were visualized using a high-speed camera and a microscope. Then, the changes in oscillation mode according to the bubble size and excitation frequency were observed using the recorded images. The results show that Lamb's equation gives similar data only for low excitation frequency and low mode number. On the other hand, the pulsation amplitude threshold theory agrees in general with the present experiment except for very low excitation frequency. In particular, the slope of mode number variations according to the excitation frequency is well estimated by the pulsation amplitude threshold theory.