On the acoustic radiation pressure on circular discs: Inertia and diffraction corrections

Abstract

In supersonic radiation fields the acoustic radiation pressure on a circular disc may be measured by means of a suitably designed torsion balance. In order to interpret such measurements it is necessary to have available an exact formula for this pressure in various types of radiation fields. It is found that the radiation pressure on a disc, however small compared with the wave-length, depends on the nature of the field as a whole as related to the made of generation of the sound-waves. In a progressive plane wave the magnitude of the radiation pressure on a small disc is very much less than that in a stationary wave. The disc shares these peculiarities as regards pressure with the sphere, for which exact formulae may be obtained in certain types of radiation fields including plane progressive and stationary waves. For discs, the exact evaluation of the radiation pressure involves the complete solution of the associated diffraction problem, To avoid unduly complex analysis, the problem is here dealt with by means of cylindrical wave functions, although the solution arrived at is limited to discs of circumference considerable less than the wave-length.