Study on Characteristics of Sound Absorption of Underwater Visco-elastic Coated Compound Structures

Visco-elastic damping materials containing kinds of air-filled, fluid-filled microspheres or cylindrical cavities have been widely used in various areas involving the coating of water-borne structure to reduce acoustic echoes to active sonar systems. As a special damping material, rubber has attracted great interest in the field of vibration and noise for its low Young’s modulus and high strain recovery features. Based on wave transfer propagation theory in infinite layered medium, sound absorption performance for underwater compound damping structures is investigated using transfer matrix method.A new anechoic coating containing different varying sectional cavities is proposed. Simulation results show that the new anechoic coating keeps good absorption performance in high frequency and its sound absorption coefficient is increased notably in low frequency. Simulations also show that the property of rubber material influences structural sound absorption greatly. Soft rubber as well as those with large loss factor may improve sound absorption performance of the whole structure remarkably. New anechoic coating containing varying sectional cavities have great advantages over the uniform compound structures. It's a good way to make different varying sectional cavities inside multi-layered rubber compound structures for improving sound absorption property. The sound absorption coefficient can be modulated by changing the thickness of the three different varying sectional cavities, and not the more the cavities are, the better sound absorption will achieve. As a new kind of complex multilayered rubber compound structures, compound structure containing varying sectional cavities has better sound absorption property than rubber interlayer with cylindrical cavities compound structure and homogeneous rubber compound structure.