The mechanism of the attracting acoustic radiation force on a polymer-coated gold sphere in plane progressive waves
Mayo Clinic College of Medicine, Department of Physiology and Biomedical Engineering, Ultrasound Research Laboratory, 200 First Street SW, Rochester, MN, 55905, USA
2 Laboratoire de Mécanique et d’Acoustique, CNRS-UPR 7051, 31 chemin Joseph Aiguier, Marseille, 13009, France
Revised: 1 April 2008
Published online: 30 June 2008
Acoustic plane progressive waves incident on a sphere immersed in a nonviscous fluid exert a steady force acting along the direction of wave motion. It is shown here that when an elastic gold sphere is coated with a polymer-type (polyethylene) viscoelastic layer, this force becomes a force of attraction in the long wavelength limit. Kinetic, potential and Reynolds stress energy densities are defined and evaluated with and in the absence of absorption in the layer. Without absorption, the mechanical energy density counteracts the Reynolds stress energy density, which causes a repulsive force. However, in the case of absorption, the attractive force is predicted to be a physical consequence of a mutual contribution of both the mechanical and the Reynolds stress energy densities. This condition provides an impetus for further designing acoustic tweezers operating with plane progressive waves as well as fabricating polymer-coated gold particles for specific biophysical and biomedical applications.
PACS: 43.20.+g General linear acoustics – / 43.25.+y Nonlinear acoustics – / 47.35.Rs Sound waves – / 78.66.Qn Polymers; organic compounds –
© Springer, 2008