EXPERIMENTAL DEMONSTRATION OF THE PSEUDO-RAYLEIGH (A(0)) WAVE

It is well known that the circumferential waves supported by thin cyli ndrical, water-loaded shells correspond closely to those on a water-lo aded 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 so und 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) wave s, whose high attenuation also rendered their multicircuit resonances too broad to be individually observable. In the present experiment, ca rried out with ultrashort, spark-generated acoustic pulses whose diffr action 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 dispe rsion curves uniquely characterized it as being the A(0) wave. (C) 199 8 Acoustical Society of America. [S0001-4966(98)01910-9].