ACOUSTIC FIELD OF A PULSED CIRCULAR PISTON

The acoustic field, at arbitrary range, of a pulsed, baffled, circular piston is examined from the point of view of the field being composed of a bounded plane wave and a hemi-toroidal edge wave, use being made of a form of linear system theory and of asymptotic expansions. Away from the acoustic axis, asymptotic solutions for the two edge wave components yield waveforms and amplitudes which, for input pulse lengths down to two cycles and piston radii down to a few wavelengths, are in very good agreement with the exact waveforms and amplitudes obtained by numerical convolution. The region in which it is possible to make such comparisons, despite overlap of field components, is extended by a technique of removal of the plane wave. The phase distributions in the edge wave field are clarified, and the interpretation by Robinson et al. of the field components in terms of Replica Pulses with time shifts is shown to be inappropriate, the semblance of bodily shifts being due to phase shifts associated with curvature of the radiator rim. © 1994 Academic Press Limited.