Using liner surface modes in ducts to make obstacles reflectionless

TL;DR

This paper proposes an acoustic cloaking method using liner surface modes in ducts, enabling reflectionless obstacle hiding across a wide frequency range by curving waves around objects with minimal backscattering.

Contribution

It introduces a novel acoustic cloaking technique employing resonant liners to achieve reflectionless obstacle concealment in ducts over broad frequencies.

Findings

Resonant liners create a zone of silence for hiding objects.

The cloaking effect is effective over a wide frequency band.

Self-cloaking enhances concealment for smooth-shaped obstacles.

Abstract

Acoustic cloaking for the suppression of backscattering inside ducts is proposed in the audible range where plane waves are curved around the object using the surface modes of the liner. It is numerically shown that a slowly varying resonant liner (e. g. based on an array of tubes) creates a zone of silence in which an object of arbitrary shape can be acoustically hidden for a wide range of frequencies. And then, a resonant liner has deflecting properties without reflection of the wavefront, which are close to an ideal invisibility cloak. This kind of cloaking is effective in a wide frequency band and the cloaking band is a function of the impedance and height of the obstacle relative to the conduit. For smooth shaped obstacles, there is an ability of the object to help hide itself, which increases the cloaking frequency band (self-cloaking). Dispersion effects lead to slow sounds and distortion of the wave phase.