A review of acoustic metamaterials for naval and underwater defense applications: from historical concepts to new trends

Since World War II, there have been many efforts worldwide to design hull coatings for naval and underwater defense applications in order to reduce either noise radiated from the hull (discretion) or acoustic reflection from the hull (stealth). This paper presents a non-exhaustive review of concepts that have emerged since the iconic Alberich coating and highlights new trends and promising candidates, such as metamaterials, to improve the discretion and stealth performance of underwater defense systems. The need for acoustic materials for naval and underwater applications is first explained, along with some specific design requirements for acoustic coatings. Two coatings technologies, called micro-inclusion coatings and macro-inclusion coatings, are then successively reviewed. New trends in materials design for naval and underwater defense applications are also presented in the following section. This paper concludes by introducing the need for acoustic materials in the frame of new threats to the naval industries as well as other non-naval areas, opening new possibilities for their design.