Ultrasound-induced nonlinear oscillation of a spherical bubble in gels of different gelatin concentrations

The viscoelasticity of soft tissue surrounding bubbles play an important role in bubble dynamics in the context of medical applications. In this study, we experimentally observe the (finite-amplitude) nonlinear oscillations of a spherical gas bubble in gels under 28-kHz ultrasound irradiation; we treat the gelatin concentration, the equilibrium bubble radius, and the pressure amplitude of the ultrasound as experimental parameters. A spherical bubble is generated by focusing a laser pulse into an air-supersaturated gel; the nucleated bubble shows gradual growth due to mass influx of the dissolved gas. 28-kHz ultrasound with varying its pressure amplitude is irradiated toward the bubble and resonant curves regarding the bubble oscillation amplitude as a function of the equilibrium radius are constructed. The viscosity and rigidity of the gel can be estimated from a comparison between the linearized Rayleigh--Plesset theory and the experimental result for small-amplitude oscillations. In the presentation, we will present the experimental results for finite-amplitude oscillations and compare them to the extended Rayleigh--Plesset calculations that account for nonlinear elasticity and dissipative effects that result from viscosity, compressibility, and heat and mass transfer.