Membrane smart metamaterials for unidirectional wave propagation problems

Abstract

Acoustic metamaterials can be realised by the periodic distribution of features that vary from rigid inclusions and discontinuous cuts to sub-wavelength resonators. The use of lightweight elements in the resonator design gave rise to membrane-type acoustic metamaterials (MAMs), which exhibit relevant attenuation on a narrow frequency range. The use of smart materials, resulting in smart MAMs, paves the way towards tunable systems that can improve the attenuation performance at different frequency ranges. This work presents a numerical and experimental investigation on the use of smart MAMs for addressing unidirectional acoustic perturbation through the combination of a prestressed membrane with shunted piezoelectric elements. A concept unit cell has been modelled using fully coupled electro-vibroacoustic finite elements and verified experimentally in an impedance tube, adapted for sound transmission loss (STL) measurements. Then, a novel acoustic metamaterial is proposed by arranging a number of the proposed unit cells along the wave propagation direction. Numerical exercises, based on the validated unit cell model, show the formation of an electroelastic attenuation band around the first open-circuit membrane mode. The smart MAM is capable of delivering large STL, not only at the membrane anti-resonance, as expected, but also at a band around the first resonance frequency, showing a promising application for an effective, lightweight acoustic barrier.