Axial acoustic radiation force on an elastic spherical shell near an impedance boundary for zero-order quasi-Bessel–Gauss beam*

Abstract

Shell structures have increasingly widespread applications in biomedical ultrasound fields such as contrast agents and drug delivery, which requires the precise prediction of the acoustic radiation force under various circumstances to improve the system efficiency. The acoustic radiation force exerted by a zero-order quasi-Bessel–Gauss beam on an elastic spherical shell near an impedance boundary is theoretically and numerically studied in this study. By means of the finite series method and the image theory, a zero-order quasi-Bessel–Gauss beam is expanded in terms of spherical harmonic functions, and the exact solution of the acoustic radiation force is derived based on the acoustic scattering theory. The acoustic radiation force function, which represents the radiation force per unit energy density and per unit cross-sectional surface, is especially investigated. Some simulated results for a polymethyl methacrylate shell and an aluminum shell are provided to illustrate the behavior of acoustic radiation force in this case. The simulated results show the oscillatory property and the negative radiation force caused by the impedance boundary. An appropriate relative thickness of the shell can generate sharp peaks for a polymethyl methacrylate shell. Strong radiation force can be obtained at small half-cone angles and the beam waist only affects the results at high frequencies. Considering that the quasi-Bessel–Gauss beam possesses both the energy focusing property and the non-diffracting advantage, this study is expected to be useful in the development of acoustic tweezers, contrast agent micro-shells, and drug delivery applications.