Bubble dynamics from High Intensity Focused Ultrasound (HIFU): high speed photography and numerical simulations
* Presenting author
We present an experimental study of High Intensity Focused Ultrasound (HIFU) using a parabolic shaped transducer and high speed photography. The transducer (Sonic Concept Inc.) has a diameter of 60 mm, and a resonant frequency of 250kHz. When it is driven between 120 to 150 Volt peak-to-peak, concentrated rings of bubbles are formed on top of the transducer. The distance between the rings is about 3 mm, which is half the wavelength of the sound wave produced by the transducer at 250 kHz. The bubbles within the rings are not stable. They move between the rings, or coalesce, or float toward the free surface. We captured the nucleation and oscillations of the bubbles using the high speed photography and a long distance microscopic lens. In an attempt to understand some of these observed phenomena, we employed numerical simulations based on the Boundary Element Method (BEM). Recently a new desingularized Boundary Integral equation has been proposed and implemented. This breakthrough significantly reduces the computational complexity and cost.A three-dimentional BEM code is used to solve the Helmholtz equation. The code could simulate the ultrasound field generated by the HIFU transducer which is used in the experiments previously mentioned.