Effect of Local Intermediate Coating Thickness on Metastructure-Induced Guided-Wave Redistribution: A Two-Dimensional Finite-Element Study

Protective coatings change the cross-section through which guided waves travel, and metastructures redistribute those fields. When a metastructure is bonded through a coating rather than directly to its host, the coating enters the integration path. This two-dimensional finite-element study asks how increasing an idealized, perfectly bonded and undamped local intermediate layer from 1 to 2 mm modifies the redistribution that an unchanged metastructure adds. In an Abaqus/Explicit model of a 2 mm aluminum plate excited at 60 kHz, the same single-sided 6Cell metastructure is bonded directly or through a 24 mm local coating patch, and a symmetry-resolved displacement-parity observable is evaluated at three receiver pairs over two windows. Matched controls without the metastructure account for coating-only baseline changes. With the prescribed coating modulus of 5.5 GPa, increasing the thickness from 1 to 2 mm reduced the mean matched incremental response by approximately 25.8%; with the 6.15 GPa modulus reported in an earlier coating study, the reduction was approximately 19.9%. At both tested moduli the interaction was negative in all six receiver/window conditions, whereas its magnitude depended appreciably on the modulus. Local coating thickness is therefore an integration variable for this model system; the tested 0/1/2 mm set establishes no optimum.