Enhanced energy trapping in a nonreciprocal phononic crystal cavity

Abstract

Acoustic energy trapping using defect modes in the band gap frequencies of acoustic metamaterials has been widely explored. Unlike this extensively used mechanism, the present work demonstrates the use of non-reciprocity in the transmission band to trap energy inside a phononic crystal cavity. A phononic crystal with broken parity and time reversal symmetry can be used to generate linear nonreciprocal transmission of the ultrasound waves. A gradient induced differential dissipation (GIDD) based passive non-reciprocal phononic crystal with asymmetric scatterers was employed to create three configurations of cavities. The parity of the present system is broken by the asymmetric shape of the scatterers, and the time reversal symmetry is naturally broken by viscous dissipation. The cavity configurations were based on the orientations of the asymmetric scatterers in part of the crystal that allowed utilization of non-reciprocity involved in only one of the cavities' configurations. Enhancement of energy trapping at a frequency of 622.5 kHz was observed experimentally for the cavity utilizing nonreciprocity compared to other cavity configurations. Experimental results were further confirmed and comprehended using finite element method based computational outcome. This energy trapping device is linear, robust, and allows sound energy trapping without an external energy source.