Inducing dispersion curves with negative group velocity in inertially amplified phononic crystals through the application of an external state of prestress

In this paper, we report about the effect of the application of a state of prestress on the band structure of a periodic phononic crystal characterized by an inertial amplification mechanism. Through a numerical example, we show the possibility of inducing negative group velocity in an isolated branch of the dispersion diagram. A 2-step Updated Lagrangian scheme is adopted to calculate the dispersion diagram of the structure. The proposed method include (i) the static geometrically nonlinear analysis of a representative unit cell undergoing the action of an applied external load and (ii) the Bloch-Floquet decomposition applied to the linearized equations of the acousto-elasticity for the unit cell in the deformed configuration. The dispersion analysis is performed in terms of small amplitude motions superimposed on a deformed state, once the desired load has been applied