Acoustic Radiation Force on a Spherical Fluid or Solid Elastic Particle Placed Close to a Fluid or Solid Elastic Half-Space

The acoustic radiation force acting on a spherical particle placed close to the interface of two infinite half-spaces that is excited by a normally incident traveling wave is investigated using the finite element method (FEM). The medium surrounding the particle is water, whereas different material models are used for the particle itself and the second half-space. Recently, acoustic force spectroscopy has been developed, a technology that uses acoustic forces to measure the mechanical properties of small filaments. If acoustics are used to manipulate particles that are placed very close to an interface then the acoustic interactions between the particle and interface lead to an acoustic interaction force. This interaction force was neglected in previous studies and is included in the total acoustic radiation force obtained by our FEM model. Comparing our results to the primary radiation force that can be obtained using the Gor'kov potential, we found that, for cells (red blood cells or fat cells) immersed in water and placed close to a PMMA, glass, or silicon domain, the magnitude of the acoustic interaction force can exceed 10% of the magnitude of the primary radiation force. In other cases, the acoustic interaction force can be even larger in amplitude and of opposite sign than the primary force.