Surface Wave Characterization in Soft Solids Using Ultrafast Ultrasound Imaging

Abstract

Soft solid incompressible materials support the propagation of longitudinal, shear, and surface waves. The latest is the least studied among all. In this work, we reported experimentally the direct observation of planar surface waves propagating at the free interface of a bovine gelatin sample, using ultrafast ultrasound imaging at a frame rate of 10000 frames per second. Employing a 1D+1D correlation-based tracking algorithm, operating over the RF-data high frame-rate movie, maps of the two-dimensional inter-frame displacement were computed. In agreement with theoretical prediction, it has been measured that surface waves produce particle movement along the axial direction as well as the direction of propagation, in a combination that the local trajectory followed by the material is ellipsoidal. Additionally, the wave energy appears highly concentrated at the surface. The motion produced by the wave was characterized as a function of the frequency, obtaining a power-law (with an exponent of 0. 1S) as a dispersion relation. Our results are compatible with the theoretical prediction given by Currie et al in [1], [2], more than forty years ago, in which two different surface waves can be propagated within the gelatin sample when a viscoelastic material is considered.