ABSTRACT
Radiation pressure, or the pressure of ultrasonic radiation, which, in particular, appears in the form of steady ponderomotive forces acting on obstacles in the propagation path of an ultrasonic wave, can in a certain sense be regarded as a nonlinear effect. The difference between acoustic and electromagnetic radiation forces is also related to the fact that under the action of an ultrasonic wave the surface of an obstacle undergoes oscillations, which change the ultrasonic field. This chapter examines a beam of plane ultrasonic waves with cross-sectional area S, and calculates the radiation force acting along the beam on an obstacle with arbitrary shape, which partially absorbs and scatters the incident wave. The velocity of the stationary flow can easily be calculated approximately for the idealized case of a sharply collimated ultrasonic beam, which is uniform over its cross section and at whose boundaries the velocity of the flow vanishes.
