Reduced-weight near-cloaks for underwater invisibility

TL;DR

This paper explores strategies to create underwater acoustic cloaks with reduced weight by combining impedance mismatched and near-cloak approaches, balancing buoyancy and scattering reduction.

Contribution

It introduces a novel combination of existing cloaking strategies to reduce weight while maintaining effective acoustic invisibility.

Findings

Combining eikonal and near-cloak strategies reduces cloak weight.

Properly designed mismatch improves the balance between buoyancy and scattering.

Radially varying mismatch further enhances performance.

Abstract

Limiting the total weight of an acoustic cloak is of fundamental importance in underwater applications, where buoyancy of the cloaked object is desirable. Unfortunately, it is well known that traditional cloaking strategies imply either a mass tending to infinity or a total weight equal to the Archimedes' force, thus making a perfect cloak that preserves the buoyancy of the target impossible. In this paper, we discuss strategies to reduce the weight of the cloak seeking a good compromise between weight reduction and acoustic performance. In particular, we compare and combine two existing strategies: the so-called eikonal cloak, where an impedance mismatched cloak is adopted, and the near-cloak, where a non-singular transformation makes the target equivalent to a smaller obstacle. We show that properly combining these strategies allows to reduce the mass of the cloak while maintaining a scattering reduction in line with the existing literature. We also investigate radially varying mismatch as a way to further improve the balance between scattering reduction and buoyancy.