Magneto-Mechanical Bilayer Metasurface with Global Area-Preserving Density Tunability for Acoustic Wave Regulation

Abstract: Metasurfaces have extensive potential in acoustic cloaking, optical scattering, and electromagnetic antenna due to their unprecedented properties and the ability to conform to curved substrates. Active metasurfaces have attracted significant research attention because of their on-demand tunable properties and performances through shape reconfigurations. They normally achieve active properties through internal structural deformations, which often lead to changes in overall dimensions. This also demands the corresponding alterations of the conforming substrate, which could be a significant limitation for their practical applications. To date, achieving area-preserving active metasurfaces with distinct shape reconfigurations remains a prominent challenge. In this paper, we present magneto-mechanical bilayer metasurfaces that demonstrate area density tunability with area-preserving capability. The bilayer metasurfaces primarily consist of two arrays of magnetic soft materials with distinct magnetization distributions. Under an external magnetic field, each layer behaves differently, which allows the metasurface to reconfigure its shape into multiple modes and thus significantly tune its area density without changing its overall dimensions. The area-preserving multimodal shape reconfigurations are further exploited as active acoustic wave regulators to tune bandgaps and wave propagations. The bilayer approach thus provides a new concept to design area-preserving active metasurfaces for broader practical applications.