Mechanism of the quasi-zero axial acoustic radiation force experienced by elastic and viscoelastic spheres in the field of a quasi-Gaussian beam and particle tweezing

F. G. Mitri (1) , Zine El Abiddine Fellah (2)

1 Los Alamos Natl Lab,
2 O&I - Ondes et Imagerie

The present analysis investigates the (axial) acoustic radiation force induced by a quasi-Gaussian beam of progressive (traveling) waves centered on an elastic and a viscoelastic (polymer-type) sphere in a nonviscous fluid. The quasi-Gaussian beam is an exact solution of the source free Helmholtz wave equation and is characterized by an arbitrary waist w0 and a diffraction convergence length known as the Rayleigh range. Examples are found where the radiation force unexpectedly approaches closely to zero at some of the elastic sphere's resonance frequencies for kw0  1 (where this range is of particular interest in describing strongly focused or divergent beams), which may produce particle immobilization along the axial direction. Moreover, the (quasi)vanishing behavior of the radiation force is found to be correlated with conditions giving extinction of the backscattering by the quasi-Gaussian beam. Furthermore, the mechanism for the quasi-zero force is studied theoretically by analyzing the contributions of the kinetic, potential and momentum flux energy densities and their density functions. It is found that all the components vanish simultaneously at the selected ka values for the nulls. However, for a viscoelastic sphere, acoustic absorption degrades the quasi-zero mean force.

Mots clés: Radiation force; Quasi-Gaussian beam; Acoustic scattering; Elastic and viscoelastic sphere

Domaines: Acoustique [physics.class-ph]; Acoustique [physics.class-ph]

F. G. Mitri, Zine El Abiddine Fellah. Mechanism of the quasi-zero axial acoustic radiation force experienced by elastic and viscoelastic spheres in the field of a quasi-Gaussian beam and particle tweezing. Ultrasonics, 2013, 54 (1), pp.351-357. ⟨10.1016/j.ultras.2013.04.010⟩. ⟨hal-00813136⟩