Detecting invisible layers in layered composites

Lamb waves propagating in a layered structure consisting of layers with equal acoustic impedances, is studied by a variant of Cauchy sextic formalism and the exponential fundamental matrix method. It is shown that the dispersion portraits provide enough information to distinguish individual layers, even if their acoustic impedances are identical, making such layers indistinguishable by the pulse - echo method. It is revealed that the developed methodology is adequate for determining geometrical and physical properties of the individual layers with equal acoustic impedances.

Automated summary

Lamb waves propagating in a layered structure with equal acoustic impedances are studied. The dispersion portraits can distinguish individual layers, even if their acoustic impedances are identical. The developed methodology is adequate for determining geometrical and physical properties of the individual layers with equal acoustic impedances.