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Analytical expressions for the axial and transverse acoustic radiation forcesas well as the radiation torque per length are derived for a rigid ellipticalcylinder placed arbitrarily in the field of in plane progressive,quasi-standing or standing waves. The rigid elliptical cylinder case isimportant to be considered as a first-order approximation of the behavior of afluid particle suspended in air, because of the significant acoustic impedancemismatch at the particle's boundary. Based on the partial-wave series expansionmethod in cylindrical coordinates, non-dimensional acoustic radiation force andtorque functions are derived and defined in terms of the scatteringcoefficients of the elliptic cylinder. A coupled system of linear equations isobtained after applying the Neumann boundary condition for an immovable surfacein a non-viscous fluid, and solved numerically by matrix inversion afterperforming a single numerical integration procedure. Computational results forthe non-dimensional force components and torque, showing the transition fromthe progressive to the (equi-amplitude) standing wave behavior, are performedwith particular emphasis on the aspect ratio a/b, where a and b are thesemi-axes of the ellipse, the dimensionless size parameter, as well as theangle of incidence ranging from end-on to broadside incidence. The results showthat the elliptical geometry has a direct influence on the radiation force andtorque, so that the standard theory for circular cylinders (at normalincidence) leads to significant miscalculations when the cylinder cross-sectionbecomes non-circular. Moreover, the elliptical cylinder experiences, inaddition to the acoustic radiation force, a radiation torque that vanishes forthe circular cylinder case. The application of the formalism presented here maybe extended to other 2D surfaces of arbitrary shape.

Radiation forces and torque on a rigid elliptical cylinder in acoustical plane progressive and (quasi)standing waves with arbitrary incidence