Focused-Ultrasound-Induced Cavitation Removes Material in a Controlled Fashion

Most HIFU-induced cavitation applications use low frequencies (< 5 MHz), limiting the spatial precision of material erosion. Here, high-frequency (12 MHz) HIFU-induced cavitation was used to locally remove material from aluminium and thin film samples. Control over pit volume and surface area (pits with 20 - 200 µm diameter) was demonstrated by varying sonication parameters. Pit surface areas and volumes were quantified with a scanning acoustic microscope. Increasing the number of bursts increased the eroded volume but also caused a greater variation in pit area, owing to the stochasticity of inertial cavitation. Increasing the sonication amplitude increased the erosion area, as a larger area of the beam exceeded the local cavitation threshold. These results will be used to find suitable sonication parameters for localized HIFU surface-sampling.