Reconfigurable wave manipulation in smart cellular solids

Abstract

Metamaterials are man-made materials designed to display properties which are not attainable by conventional materials. They owe their behavior to their mesoscale architecture, which often revolves around the periodic arrangement of a repetitive volume element, or unit cell. A particularly prominent application of metamaterials is in the context of wave control, where they have been used as mechanical filters, energy steering devices, and optical and acoustic cloaks. This thesis work tackles a few open problems within this fertile and fast-growing field. Specifically, one of our main aims is to unveil the relationship between the symmetry of the unit cell of a given periodic medium and the symmetry of its wave response, and to provide a mechanistic rationale for the generation of anisotropic wave patterns in specific frequency ranges. We then propose two strategies to modify these patterns in the context of periodic cellular solids (lattice structures). The first strategy, based on the concept of cell symmetry relaxation, relies on a symmetry-driven microstructural design of the unit cell, in which the geometric and material characteristics of certain microstructural features are modulated to modify the symmetry landscape of the cell. The second one, that we named anisotropy overriding, is based on the interplay between the intrinsically anisotropic wave patterns of the medium and the corrective action of a small number of strategically-placed resonators. We also propose tunable implementations of these strategies, which are achieved by incorporating into the periodic architectures smart material inserts (e.g., shunted piezoelectric patches and curlable dielectric elastomers) which are activated using external non-mechanical stimuli. The resulting wave manipulation effects are illustrated through a series of numerical simulations and experimental tests.