The oblique reflexion of sound pulses

Abstract

It is observed that the classical theory of reflexion of plane sound waves breaks down in the case in which a sound pulse is incident on a plane surface of separation of two media at an angle such that total reflexion is to be expected. A sound wave is imagined to be generated by the supersonic motion of a thin wedge, and the motion when the wave meets the surface of separation is investigated by assuming dynamic similarity in the motion. It is shown that the solution of the problem is not of quasi-steady type, and that there is a diffused wave in the denser medium, with a wave front which precedes the incident wave near the surface of separation. This wave is due to diffraction in the lighter medium round the edge of the incident wave. A further result is that there is still a reflected wave, and that its amplitude is equal in magnitude but opposite in sign to that of the incident pulse.