Radiation torque produced by an arbitrary acoustic wave

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. Copyright (C) EPLA, 2012