Negative-Stiffness Inclusions as a Platform for Real-Time Tunable Phononic Metamaterials

Tunable phononic metamaterials, which change their response to elastic wave propagation upon actuation, have important applications in cloaking, wave guiding, active noise reduction, superlensing, and acoustic mirrors. Most systems either require substantial morphological changes for actuation, or exhibit only high-frequency band gaps. The authors present a framework for developing tunable phononic metamaterials with low-frequency band gaps, using negative-stiffness inclusions in an elastic matrix, and demonstrate two implementations of this concept. The designs are robust and achieve substantial band-gap manipulation, without elastic instability or significant structural changes.