Identification of shear wave parameters of viscoelastic solids by laboratory measurements of Stoneley-Scholte waves

International audienceThis paper deals with the problem of viscoelastic solid characterization by acoustical means and in particular with the recovery of the shear wave parameters. It has been previously shown, in the Underwater Acoustics field, that the shear wave parameters of the sea floor could be recovered by using inverse techniques applied to propagation characteristics of interface waves such as Stoneley-Seholte waves, which can propagate in water/sedi ment configurations. The goal of the study presented in the paper is then to test models, commonly used for seabed identification, on media whose properties arc well-controlled by laboratory tank experiments, contrary to in situ bottoms. It is shown that the viscoelastic medium parameters can also be identified from the characteristics of interface waves, generated experimentally in laboratory on very attenuating synthetic materials. The paper presents results about the estimated shear wave parameters obtained from both numerical and experimental data by applying Brent's method on the characteristics of the interface waves. The observation and the discussion of differences between theoretical and experimental results are the goa] of the paper. The study presented here validates the forward model previously developed and it can be considered as a first step towards the direction of acoustic classification of sea bottoms

Theoretical study of the Stoneley-Scholte wave at the interface between an ideal fluid and a viscoelastic solid

International audienceThe propagation of the Stoneley-Scholte wave is analysed at the boundary between an ideal fluid and a viscoelastic solid. The theoretical study is developed using the approach of the inhomogeneous plane waves: the interface wave is thus regarded as a linear combination of one evanescent wave in the fluid and two heterogeneous waves in the solid. The main interest of the paper is the introduction of the viscoelastic solid, which is a medium characterized by physical attenuation, in the study of the propagation of the interface wave. Its mechanical viscosities are expressed in terms of acoustical attenuations, more easily determined by means of acoustical measurements. Existing mathematical tools are then used for solving the dispersion equation determined in this case. The study presented in the paper deals only with some aspects of the direct problem, that is the determination of the propagation properties of the Stoneley-Scholte wave, established for two different interfaces. A comparison of these characteristics in the presence and in the absence of attenuation, and a parametric study of the effect of attenuation, are included. The validity of the theoretical results are finally well demonstrated with some experimental ones, obtained with synthetic resins modelling viscoelastic solids

Excitation of the Stoneley-Scholte wave at the boundary between an ideal fluid and a viscoelastic solid

International audienceThe predicted properties of the Stoneley- Scholte wave, deduced from a previous theoretical study, are experimentally verified at the boundary between an ideal fluid and a viscoelastic solid, respectively represented by water and synthetic resins (PVC and B2900). In particular, it is quantitatively shown that the damping of the energy of the interface wave increases with the distance from the interface and with the distance of propagation. The method of generation of the Stoneley- Scholte wave is based on the association of a shear wave transducer with a solid wedge. The method, previously developed for the ideal fluid-elastic solid interface, is here adapted for the boundary between water and a viscoelastic solid