In the present work, nonlinear acoustic oscillation of a single spherical gas bubble immersed in an unbounded thixotropic fluid is studied numerically. Using Moore's structural model as the constitutive equation of the liquid surrounding the bubble, the general Rayleigh-Plesset integro-differential equation, which governs bubble dynamics, is solved numerically using the Gauss-Laguerre Quadrature (GLQ) method. It is shown that at sufficiently high pressure amplitudes, typical of medical ultrasound applications, a second harmonics may be observed in the bubble's response.

In the present work, the dynamics of a single spherical gas bubble surrounded by an elastic thixotropic liquid is addressed at the presence of an acoustic pressure field. The well-known Dullaert and Mewis' rheological model is used to represent different aspects of the fluid's thixotropic and elastic behavior. A numerical method based on Gauss-Laguerre quadrature is adopted to integrate the integro-differential equation governing bubble dynamics. The numerical results suggest that bubble response is significantly affected by the thixotropic properties of the surrounding fluid. A competition between the time constant set forth by the fluid's elasticity and the time constant related to the fluid's thixotropicity is predicted to give rise to the generation of second harmonics in the bubble's response for certain range of model parameters.