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

The growing interest in marine renewable energy and ocean-related human activities are the main causes of an alarming increase of the noise level in the oceans and seas. Nevertheless, the performance of underwater noise mitigation systems has since long been (and still is) limited by the fact that dissipation in linear systems is inherently poor at the sub-wavelength scale. 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 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.POSEIDON will take the risk of exploring two unconventional and ground-breaking 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, exploring 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, assigning crystalline properties to non-crystalline materials by breaking precise classes of symmetries over multiple length scales.Both approaches are supported by the innovative assumption that (3) underwater wave control through metamaterials be already exploited by Nature.If successful, POSEIDON will fill the gap in the knowledge of underwater acoustics and significantly advance the frontiers of bottom-up material design.