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Lamb Waves Topological Imaging of Multiple Blind Defects in an Isotropic Plate

The study investigates the feasibility of the Lamb wave topological imaging method for detecting multiple blindholes in an isotropic plate. The topological imaging method is performed based on the computations of two
wave fields, a forward and an adjoint, in the defect-free reference medium using different emitting sources. The
image is computed by multiplying the forward and adjoint wave fields together and integrating them over time or
frequency. The interferences of multimode aliasing and the scattering effect can thus be eliminated at the defectfree positions with an improved image resolution. To investigate the physical mechanism, the refocusing process of
the multimode Lamb waves at the defect positions is presented by a face-to-face comparison between the snapshots
of the forward and adjoint wave fields using the finite element simulation. The Lamb wave topological imaging
method is numerically and experimentally verified to identify multiple blind-holes in an isotropic aluminium plate.
The results demonstrate that the topological imaging method enables the suppression of the sartefacts resulting
from the mode conversion and achieve high-resolution imaging of the blind defects