# PT-symmetric scattering in flow duct acoustics

## TL;DR

This paper demonstrates both theoretically and experimentally that airflow duct acoustics with balanced gain and loss exhibit PT-symmetry features such as spontaneous symmetry breaking and unidirectional invisibility, advancing understanding of acoustic PT-systems.

## Contribution

It introduces a novel acoustic PT-symmetric system using flow ducts with diaphragms, combining theoretical analysis and experimental validation of PT-symmetry phenomena.

## Key findings

- Observation of PT-symmetry breaking in acoustic scattering
- Experimental demonstration of unidirectional invisibility
- Validation of scattering matrix formalism in acoustics

## Abstract

We show theoretically and experimentally that the propagation of an acoustic wave in an airflow duct going through a pair of diaphragms, with equivalent amount of mean-flow-induced effective gain and loss, displays all the features of a parity-time (PT) symmetric system. Using a scattering matrix formalism, we observe experimentally the properties which reflect the PT-symmetry of the scattering acoustical system: the existence of a spontaneous symmetry breaking with symmetry-broken pairs of scattering eigenstates showing amplification and reduction, and the existence of points with unidirectional invisibility.