Underwater Carpet Cloak for Broadband and Wide-Angle Acoustic Camouflage Based on Three-Component Metafluid

Acoustic camouflage, which is realized by controlling wave propagation, has attracted great attention in recent years. Aided by a reflecting surface, the acoustic carpet cloak has become one of the most practically feasible invisibility devices and captured much experimental research enthusiasm. However, owing to the difficulty in the realization of ideal material parameters, the implemented underwater carpet cloaks could only work for a small incident angle. Here we design an underwater carpet cloak using a three-component metafluid composed of syntactic foam, steel, and water. The proposed syntactic foam, which is synthesized from epoxy resin and hollow glass microspheres, exhibits lower mass density and higher sound velocity relative to water. By periodically embedding the syntactic foam and steel rods in water, a carpet cloak is constructed and experimentally demonstrated in an anechoic water tank. Experimental results indicate that the designed carpet cloak works well under both normal and oblique incidences for broadband frequencies. The implementation of the designed underwater carpet cloak paves the way for future applications. Moreover, the introduction of syntactic foam in the design of the carpet cloak provides an extra degree of freedom for the acoustic parameter regulation of the metafluid in underwater acoustic devices.