Active control of the dynamic density of acoustic metamaterials

All attempts to develop acoustic metamaterials with prescribed characteristics are based on utilizing the concepts of resonance frequencies of the metamaterial cell structure or on the spatial arrangement of two-or multi-phase domains to realize density or bulk modulus values on the micro scale that influence the wave propagation on the macro scale. In here, a radically different concept is presented whereby active acoustic metamaterial cell has been developed to manipulate the incompressible material dynamic density and reach relative stable values of 0.35–13 times the original fluid domain in which the cells are embedded. Piezoelectric ingredients have been added for density control and internal pressure gradient measurements as part of the control loop. Arbitrary density values have been achieved and a metamaterial cell with truly programmable dynamic density has been developed shifting incompressible fluids from passive to active domains. © 2021