Wave control through soft microstructural curling: bandgap shifting, reconfigurable anisotropy and switchable chirality

Abstract

Abstract. In this work, we discuss and numerically validate a strategy to attain reversible macroscopic changes in the wave propagation characteristics of cellular metamaterials with soft microstructures. The proposed cellular architecture is characterized by unit cells featuring auxiliary populations of symmetricallydistributed smart cantilevers stemming from the nodal locations. Through an external stimulus (the application of an electric field), we induce extreme, localized, reversible curling deformation of the cantilevers-a shape modification which does not affect the overall shape, stiffness and load bearing capability of the structure. By carefully engineering the spatial pattern of straight (non activated) and curled (activated) cantilevers, we can induce several profound modifications of the phononic characteristics of the structure: generation and/or shifting of total and partial bandgaps, cell symmetry relaxation (which implies reconfigurable wave beaming), and chirality switching. While in this work we discuss the specific case of composite cantilevers with a PDMS core and active layers of electrostrictive terpolymer P(VDF-TrFE-CTFE), the strategy can be extended to other smart materials (such as dielectric elastomers or shape-memory polymers).

Exploiting Microstructural Instabilities in Solids and Structures: From Metamaterials to Structural Transitions

“…While most of the proposed acoustic metamaterials operate in fixed ranges of frequencies that are impractical to tune and control after the assembly [212][213][214][215][216][217], it has been recently shown that instabilities provide an opportunity to alter in situ their dynamic response [34,35,173,[218][219][220][221].…”

“…Therefore, predeformation allows for the controllable variation of elastic moduli and dispersion properties [221,[223][224][225]. Such tunability can be further enhanced by triggering mechanical instabilities along the loading path, since these result in dramatic geometric reconfigurations.…”

Shear Wave Propagation and Band Gaps in Finitely Deformed Dielectric Elastomer Laminates: Long Wave Estimates and Exact Solution

“…Thus, for example, the effect has been used to control wave propagation in homogenous DEs [11][12][13]. Moreover, microstructured DEs hold even greater potential for active control of elastic waves by an electric field [14,15]. Hence, investigation of wave propagation in composite DEs opens new possibilities in improving of small length-scale devices, for example, micro-electromechanical systems, where an electric field is the preferred operated variable.…”

Introduction

“…12,13 Recently, such instabilities have been exploited to design architected materials with tunable negative Poisson's ratio and effective negative swelling ratio 14 structures capable of switching between achiral and chiral configurations, 14 soft actuators 15 and robots, 16 materials with tunable optical properties, 17,18 and dynamic response. [19][20][21][22] Elastic beams not only buckle but may also snap between two different stable configurations, retaining their deformed shape after unloading. As bistable elastic beams can lock in most of the energy provided to the system during loading, they have been recently used to create fully elastic and reusable energy-trapping architected materials.…”