Acoustic polarizability-based design of time modulated active metamaterials

Acoustic metamaterials have enabled new and exciting ways to manipulate acoustic waves but, so far, these structures have seen little practical use. Acoustic applications of interest such as acoustic imaging and sound absorption typically require broadband devices. The passive metamaterials considered in the past have fundamental limitations reducing their usefulness in these applications. Active metamaterials, on the other hand, are not subject to the limitations of passive media and are thus promising alternatives. However, their development has been slow, owing to a lack of top-down design methods that provide the metamaterial structure needed to achieve desired acoustic properties. This presentation shows that top-down design tools based on acoustic polarizability concepts are perfect for designing such active structures. The efficacy of these tools is demonstrated in experiments featuring metamaterials with programmable acoustic properties including ultra-fast time modulated Willis materials and media with large anisotropic mass density and on-demand principle axis direction.