Degradation of meridional ray backscattering enhancements for tilted cylinders by mode conversion: Wide-band observations using a chirped PVDF sheet source

High-frequency backscattering measurements are discussed for a thick-wailed hollow finite cylindrical shell. The frequency range examined is above the coincidence frequency where energy coupled to supersonic Lamb-type waves d ominates the backscattering for off-beam aspect. One particular mechanism, involving a meridional leaky ray, leads to large enhancements along well-de fined arcs in frequency-aspect angle space. It is shown that the backscatte red levels for the flexural mode meridional ray drop dramatically above a c ertain frequency. This degradation of the energy in the return signal is fo und to be correlated with mode conversion at the truncation of the shell of the lowest order flexural mode into the next higher flexural mode. An appr oximate calculation utilizing simply supported boundary conditions does not display the observed degradation since it fails to allow for mode conversi on.