Magnetic-acoustic biphysical invisible coats for underwater objects

Magnetic fields and acoustic waves are the two fundamental measures to perceive underwater objects, which, however, have never been simultaneously handled before. In this work, we propose and demonstrate a biphysical submillimeter-thick metamaterial coat that can simultaneously make underwater objects invisible to both magnetic fields and acoustic waves. The conformal coat is a subtle integration of an open-cavity acoustic absorber made of a dissipative acoustic metasurface (AMS) and a bilayer magnetic cloak. Experimentally, a magnetic cloaking effect with a field disturbance ratio of <0.5% is obtained over a broad-frequency range (10–250 kHz), and the compound metamaterial coat can strongly attenuate ultrasonic waves with a near-unity absorptivity. The magnetic subcoat can be freely combined with various AMS layers to achieve a wideband acoustic stealth effect for different spectral regimes. This work may open up a new way to build multifunctional devices for various waterborne applications.