Applied Acoustic Metamaterials
Speaker: Steve Cummer, Duke University
Abstract: While acoustic wave propagation in periodic structures is an old topic, modern research in acoustic metamaterials began with efforts to mimic progress in electromagnetic metamaterials with a focus on exotic material parameters, such as negative modulus and negative effective mass. The field has since branched into a wide range of topics including phononic bandgap materials, transformation acoustics, active materials, and thin metasurfaces. This presentation will focus on recent results from acoustic metamaterials research in my group, following two main paths. The first focus will be on transformation acoustics, focusing on the design and experimental demonstration of structures based on fluid-based anistropic acoustic metamaterials. Truly broadband devices have been demonstrated in air, for which the high contrast with solid materials makes it relatively easy to realize many useful effective parameters. We will also describe our initial work in developing the needed materials for the more challenging environment of water. The second focus will be on the development and use of labyrinthine metamaterials, a concept first described by Jensen Li in which the intra-cell coiling of propagation distance enables the control of transmission phase to create a wide range of properties and effects. This approach is proving particularly useful in the development of thin diffractive structures for manipulating acoustic wave transmission and reflection.