title: Acoustic radiation torque and the conservation of angular momentum (L).
abstract: This note concerns the evaluation of the static acoustic radiation torque exerted by an acoustic field on a scatterer immersed in a nonviscous fluid based on far-field scattering. The radiation torque is expressed as the integral of the time-averaged flux of angular momentum over a spherical surface far removed from the scattering object with its center at the centroid of the object. That result was given previously [G. Maidanik, J. Acoust. Soc. Am. 30, 620-623 (1956)]. Another expression given recently [Z. W. Fan et al., J. Acoust. Soc. Am. 124, 2727-2732 (2008)] is simplified to this formula. Comments are made on obtaining it directly from the general theorem of angular momentum conservation in the integral form.
authors.affiliation: Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814, USA.
authors.forename: Likun
authors.initials: L
authors.lastname: Zhang
authors.forename: Philip L
authors.initials: PL
authors.lastname: Marston
mesh_terms: D000162:Acoustics; D008962:Models, Theoretical; D011827:Radiation; D012996:Solutions; D013696:Temperature; D019415:Torque; D014783:Viscosity
chemical_list: D012996:Solutions