Coupled Scholte modes supported by soft elastic plates in water

Localized acoustic surface waves supported by a "soft" elastic plate in water are explored. Unlike many materials, such as aluminum, for soft interfaces the Scholte wave, a localized interface wave, has a speed well below that of sound in water, and the energy of the Scholte wave is no longer mainly localized to the water. We note that the Scholte velocity is largely independent of Poisson's ratio in the solid, and rather than the bulk speeds of sound, the ratio between the Young's modulus and the density of the solid may better indicate whether an interface is soft. The behavior of the coupled Scholte modes along a thin plate with soft interfaces are investigated. It is demonstrated, and experimentally verified using acrylic plates underwater, that for soft interfaces, the symmetric coupled Scholte mode exhibits dispersive behavior, and deviates from the Scholte and the fluid velocities at low frequencies.