Acoustic cloaking and mirages with flying carpets

TL;DR

This paper introduces floating acoustic carpets that enable cloaking and mirages by mimicking objects' scattering properties, using non-singular, multi-layered isotropic fluids for practical underwater and radar applications.

Contribution

It extends the concept of acoustic cloaking to floating carpets that can hide objects or mimic other obstacles without singular parameters, using multi-layered isotropic fluids.

Findings

Carpets can hide objects and mimic other obstacles' scattering.

Non-singular, multi-layered carpets work over finite wavelength ranges.

Applications include underwater detection evasion and antenna protection.

Abstract

Carpets under consideration here, in the context of pressure acoustic waves propagating in a compressible fluid, do not touch the ground: they levitate in mid-air (or float in mid-water), which leads to approximate cloaking for an object hidden underneath, or touching either sides of a square cylinder on, or over, the ground. The tentlike carpets attached to the sides of a square cylinder illustrate how the notion of a carpet on a wall naturally generalizes to sides of other small compact objects. We then extend the concept of flying carpets to circular cylinders. However, instead of reducing its scattering cross-section like in acoustic cloaks, we rather mimic that of another obstacle, say a square rigid cylinder. For instance, show that one can hide any type of defects under such circular carpets, and yet they still scatter waves just like a smaller cylinder on its own. Interestingly, all these carpets are described by non-singular acoustic parameters. To exemplify this important aspect, we propose a multi-layered carpet consisting of isotropic homogeneous fluids with constant bulk modulus and varying density which works over a finite range of wavelengths. We have discussed some applications, with the sonar boats or radars cases as typical examples. For instance, we would like to render a pipeline lying on the bottom of the sea or floating in mid-water undetectable for a boat with a sonar at rest just above it on the surface of the sea. Another possible application would be protecting parabolic antennas.