Radiation torque produced by an arbitrary acoustic wave
Physical Acoustics Group, Instituto de Física, Universidade Federal de Alagoas - Maceió, AL, Brasil 57072-970
2 Los Alamos National Laboratory, Materials Physics and Applications Division, MPA-11, Sensors & Electrochemical Devices, Acoustics & Sensors Technology Team - MS D429, Los Alamos, NM 87545, USA
Accepted: 30 January 2012
Acoustic waves may force a suspended object in the wavepath to spin by exerting a radiation torque. Generally, this torque depends on how the incident wave is scattered and absorbed by the object. We derive a general formula for the Cartesian components of the acoustic radiation torque produced by an arbitrary incident beam on an object of any geometrical shape in a nonviscous fluid. To illustrate the method, we calculate the acoustic radiation torque produced by a zero- and a first-order Bessel beam on an absorbing sphere in the off-axis configuration. Unexpectedly, the results show that some radiation torque components reverse their directions depending on the beam offset and the sphere size factor.
PACS: 43.25.Qp – Radiation pressure / 43.20.Fn – Scattering of acoustic waves / 43.55.Ev – Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
© EPLA, 2012