5E-3 Experimental Evidence for a Growing Surface Wave and Acoustic Beam Narrowing upon Reflection from Fluid-Solid Interfaces

The secular equation for acoustic waves at fluid-solid interfaces yields the common leaky wave and its complement. This complementary wave grows instead of decays with propagation and is time-reversed compared to the leaky wave. Moreover, this growing wave has not yet been observed experimentally, perhaps due to difficulty of its excitation. Experimental observation of this wave was one goal of our work. The second goal was to study mirror reflection of an acoustic beam of special shape when the incident angle is equal to the Rayleigh critical angle. An obliquely incident beam is known to split after reflection into two components: a specular beam and a broad beam generated by the leaky waves. The interference of these two components results in "Schoch displacement" of the reflected beam along the interface and overall beam broadening. Our hypothesis was that by time reversing the reflection at the critical angle, the reflection beam can be made narrower rather than broader.