Effects of Collapsing Bubble in Ultrasonic Field on Soft Material

Abstract

To investigate the physical effects of a collapsing bubble on a soft material, the bubble collapse phenomenon on agar gel under ultrasonic irradiation was experimentally examined. Using a high-speed video camera, we observed two effects of the bubble on the agar gel. One effect was the formation of a hole on the agar surface by "microjet generation". It was revealed that the hole was formed under the initial condition of resonant bubble size. The other effect was the local surface fluctuation of the agar gel by "bubble vibration". This surface fluctuation is the first observed phenomenon in our observations and indicates that a localized pressure stimulus was generated on the agar surface by bubble vibration. These revealed effects show the significant contributions of the bubble techniques in ultrasonic therapy techniques, e.g., ultrasonic drug delivery.