Unveiling the frequency-dependent dynamics of acoustic radiation force on lipid-coated ultrasound bubbles

Ultrasonic contrast agent bubbles are a good medium for particle manipulation due to their high acoustic contrast factor. As a kind of widely used acoustic contrast agent, the surface tension of lipid bubbles is complicated, so the solution of its oscillation is normally obtained numerically rather than analytically. Another issue is that the Gorkov's formula for acoustic radiation force (ARF) used for the manipulation of small particles do not apply to bubbles in some frequency ranges. In this paper, the analytical solution of the oscillation of lipid-coated bubbles excited by ultrasound of different frequencies is given, and the frequency dependent ARF of lipid bubbles is obtained theoretically and verified by experiments. The theory complements the widely used Gorkov force, addressing the limitation that Gorkov force is only applicable when the particle density and compressibility are similar to the medium. The results have theoretical significance for the biomedical application of lipid bubbles and may provide theoretical basis for particle manipulation, particularly for the emerging field of manipulating biological particles containing gas bubbles.