The Influence of Material Dissipation and Imperfect Bonding on Acoustic Wave Reflection from Layered Solids

It is well known that layered solids can support dispersive, layer guided waves whose propagation characteristics are strongly dependent upon the material properties of the solids. Thus, accurate measurements of the propagation characteristics of guided waves can lead to the development of excellent nondestructive evaluation tools for coated solids, composite laminates and other electronic as well as structural materials which are being used with increasing frequency in modern engineering applications. Two recently developed experimental arrangements [1,2] which provide the means for such measurements are sketched in Figure 1. In the arrangement shown in Figure la, the platelike specimen is fully immersed in a fluid, while in that shown in Figure 1b, the fluid is present on only one side of the specimen. In both cases, a beam of acoustic waves is launched at a specific angle of incidence and the reflected acoustic field is recorded by a symmetrically placed second transducer. The recorded signals in both experiments consist of the spatially reflected waves and for sufficiently large angles of incidence, leaky waves radiated by the layer guided waves in the solid. After appropriate signal processing to remove the noise and Fourier analysis, the spectrum of the total reflected field is obtained