Experimental demonstration of the pseudo-Rayleigh (A0) wave

It is well known that the circumferential waves supported by thin cylindrical, water-loaded shells correspond closely to those on a water-loaded plate, i.e., to the Scholte-Stoneley wave A and to the Lamb waves A(0), A(1), A(2), ..., and S-0, S-1, S-2 .... Until now, however, it had not been possible to definitely observe the acoustic excitation of the A(0) wave on a shell using steady-state or long-pulse incident sound waves (while excitation of the A and S-0 waves was clearly evident). The reason for this is the rapid decay of the propagating A(0) waves, whose high attenuation also rendered their multicircuit resonances too broad to be individually observable. In the present experiment, carried out with ultrashort, spark-generated acoustic pulses whose diffraction by a steel shell is visualized by the shadowgraph method, the A(0) (''pseudo-Rayleigh") wave could be observed immediately after its excitation, before it had any time to decay. Spectral analysis of its observed re-radiation permitted the extraction of its phase-velocity dispersion curve, which by comparison with previously calculated dispersion curves uniquely characterized it as being the A(0) wave. (C) 1998 Acoustical Society of America. [S0001-4966(98)01910-9].