Invisible design and acoustic scattering of metamaterial plates with active feedback control

The work targets a limitation of anechoic tiles for active sonar, where low-frequency detection can still occur. It proposes active mechanical metamaterial plates that use periodic four-link mechanisms with local resonators to control the plates’ dynamic effective density. The authors derive a theoretical model for how sound waves scatter from these active plates, accounting for fluid–structure interaction and vibroacoustic coupling. The goal is an “invisible design” effect for submarines by reducing scattered sound pressure in a negative density region. They report that scattered sound pressure is effectively reduced when appropriate acceleration and displacement feedback coefficients are used. The theoretical derivation is supported by finite element simulation and acoustic scattering experiments.