Pulsation of bubbles in the viscoelastic medium under dual-frequency ultrasound

The pulsation of bubbles under dual-frequency ultrasound is closely associated with their application in medical diagnostics. In this study, we derive the analytical solution of the bubble dynamic equations in viscoelastic media under dual-frequency ultrasound and compare it with numerical solutions. The effects of the surrounding medium's viscoelasticity, bubble equilibrium radius, incident acoustic frequency, and incident sound pressure ratio on the bubble pulsation and its scattered acoustic waves are analyzed. The results demonstrate consistency between the analytical and numerical solutions. Moreover, our analytical solution reveals that an increase in medium viscosity leads to a decrease in the amplitude of bubble pulsation, even at resonance frequency. Additionally, when the sound pressure ratio is 1, both the difference frequency and sum frequency exhibit maximum amplitude in the spectrum of instantaneous bubble radius. Furthermore, for resonance approximation in sparse bubble cluster detection using sum and difference frequencies, it is necessary for incident frequency f₁ to be greater than twice the resonance frequency of the smallest bubble within the cluster.