PT symmetric sonic crystals: from asymmetric echoes to supersonic speeds

Abstract

Parity-time PT symmetric structures based on balanced distributions of gain and loss have attracted significant attention in acoustic metamaterial research since they allow one to sculpture the flow of sound waves in complete new ways. We compute complex Bloch waves in fluidic non-Hermitian sonic crystals and demonstrate how band coalescence can lead to exceptionally large group velocities permitting supersonic wave propagation in PT symmetric slabs. Further, by controlling the degree of non-hermiticity in such systems, we found that asymmetrically reflected pulses can be readily amplitude-tuned, which might find potential use in echocardiography, sonar and echo suppressors.