Acoustic radiation force dependence on properties of elastic spherical shells in standing waves

Abstract

In this study, we theoretically investigate the acoustic radiation force acting on elastic spherical shells in standing waves in the dimensionless frequency range of 0<ka<0.7 (k is the wave number in the host fluid and a is the outer radius of the spherical shells), we show that in the low-frequency range (0<ka<0.2), the acoustic radiation force on core–shell spheres can vary from positive to negative by decreasing the effective density and effective bulk modulus of the spherical shells, while the effective density and bulk modulus are dependent on the hollow ratio of the core–shell spheres, the density and bulk modulus ratios of the shell to the core. Thus, the core–shell spheres cannot only be trapped from the pressure node to the pressure antinode by increasing the hollow ratio or decreasing the shell’s density or longitudinal or shear velocity, but are also unresponsive to ultrasound waves with an optimal hollow ratio, density, or acoustic velocity of the shell. We further show that in the relatively low-frequency range of0<ka<0.7, the acoustic radiation force on core–shell spheres can be significantly enhanced around resonant frequencies. The acoustic radiation force could be enhanced at lower frequencies by increasing the hollow ratio or decreasing the shell’s density or shear wave velocity. Our results pave the way for optimising the design of core–shell particles for efficient ultrasound-mediated drug delivery.