Numerical investigations of single bubble oscillations generated by a dual frequency excitation

The oscillations of a single bubble excited with a dual frequency acoustic field are numerically investigated. Computations are made for an air bubble in water exposed to an acoustic field with a linearly varying amplitude. The bubble response to an excitation containing two frequencies f(1) = 500kHz and f(2) = 400kHz at the same amplitude is compared to the monofrequency case where only f(1) is present. Time -frequency representations show a sharp transition in the bifrequency case, for which the low frequency component f(2) becomes resonant while the high frequency component f(1) is strongly attenuated. The temporal evolution of the power spectra reveals that the resonance of the low frequency component is correlated with the time varying mean radius of the bubble. It is also observed that the total power of the bubble response in the bifrequency case can reach almost twice the power obtained in the monofrequency case, which indicates a strong enhancement of the cavitating behavior of the bubble for this specific frequency combination.