Unconventional principles of underwater wave control in the sub-wavelength regime

Introduction

The growing interest in marine renewable energy and ocean-related human activities are the main causes of an alarming increase in the noise level in the oceans and seas. Nevertheless, the performance of underwater noise mitigation systems has long been (and still is) limited by the fact that dissipation in linear systems is inherently poor at the sub-wavelength scale.

Problem Statement

Consequently, a viable solution to attenuate underwater waves over low, broadband, and multiple frequencies does not exist yet. POSEIDON aims to tackle the intrinsic reasons for such a scientific/technological delay and declares an ambitious goal: to develop a new class of meta-screens allowing zero-transmission/zero-radiation over low and broadband frequencies. This will be achieved by exploiting rather than avoiding complexities stemming from heavy-fluid/structure interaction and exhibiting practical structural requirements, such as being compact, lightweight, and efficient under hydrostatic pressure.

Innovative Approaches

POSEIDON will take the risk of exploring two unconventional and groundbreaking approaches in the challenging context of extremely sub-wavelength underwater acoustics to design a new class of metamaterials allowing unprecedented low and broadband wave reflectivity and absorption:

1. Anti-auxetic underwater metamaterials: This approach explores the intimate relationship between the micro-structure and the macroscopic vibrational properties of a multi-scale metamaterial immersed in a heavy fluid and exhibiting Poisson's ratios > 0.5.

2. Topologically protected and impedance adapted underwater metamaterials: This method assigns crystalline properties to non-crystalline materials by breaking precise classes of symmetries over multiple length scales.

Nature's Inspiration

Both approaches are supported by the innovative assumption that underwater wave control through metamaterials is already exploited by Nature.

Conclusion

If successful, POSEIDON will fill the gap in the knowledge of underwater acoustics and significantly advance the frontiers of bottom-up material design.