In recent years, a class of artificial sub-wavelength structural unit clusters called metamaterials, have achieved considerable progress, providing a new approach to manipulating wave propagation. Metasurfaces, treated as equivalent two-dimensional metamaterials without sacrificing the ability of wave and vibration control, have the advantages of compactness and simplicity. Through elaborately designing each functional unit, the supercells can achieve a full 2π phase span, and simultaneously possess high transmission coefficients to avoid the unexpected reflection or refraction phenomena. Based on the generalized Snell’s law (GSL), the wavefront of elastic waves can be modulated to achieve anomalous behavior, such as wave focusing, deflection, self-accelerating beam and so on. In spite of the related recent booming researches, the non-perforated or surface-bonded ultrathin elastic metasurfaces have seldom been reported, since there exists a big challenge in designing such a single unit to satisfy the requirements of 2π phase span and simultaneous high transmission. This paper focuses on developing a surface-bonded single-layer elastic meta-structure to implement the peculiar transmission manipulation of asymmetric Lamb waves.In this paper, an elastic meta-structural functional unit is carefully designed, constructed by an aluminum-polylactic acid (PLA) composite stub bonded on an aluminum plate, to enable an effective wave manipulation application for Structural Health Monitoring (SHM) and Non-destructive Evaluation (NDE) community. Through conducting a series of parametric studies, the full 2π phase span and high transmission can be achieved by a single-layer meta-structural unit. When proceeding to calculate the phase profile for realizing the full 2π phase span, the height of the PLA stub is tuned by exploring a finite element model (FEM) using harmonic analysis of a unit cell. Periodic boundary conditions are applied to represent two-dimensional wave propagation in a plate. The nephograms of the phase shift varying with the PLA stub height and excitation frequency exhibit the successful achievement of a full 2π span covering a wide frequency range. Further, to enable a high transmittance at the same time, a series of parametric studies are carried out through adjusting two additional structural parameters, i.e., the width of the composite stub and height of the aluminum stub. Subsequently, various single-layer elastic meta-structures are designed with the proposed unit cell for the peculiar transmission manipulation of asymmetric Lamb waves demonstrated by numerical simulations. The proposed wavefront manipulation capability using the elastic metasurface shows great potential in future SHM and NDE applications. The paper finishes with summary, concluding remarks, and suggestions for future work.Keywords: single-layer elastic metasurface, anomalous transmission, wavefront manipulation, structural health monitoring, non-destructive evaluation

Peculiar Transmission Manipulation of Antisymmetric Lamb Waves via a Surface-Bonded Single-Layer Elastic Meta-Structure

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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