Ultrasound underwater coherent perfect absorbers

In this paper, we propose a coherent perfect absorber for the underwater ultrasound regime (MHz frequencies), inspired by the mechanism of Salisbury, which relies on reflective conductive sheets. By leveraging a silicon-based acoustoelastic metasurface with thin periodic slits acting as Fabry-Pérot resonators, and by focusing on realizing an efficient ultrasound underwater steel bandgap mirror, we observe coherent perfect absorption (CPA) both numerically and experimentally at frequencies around 0.6 and 1.2 MHz, with the latter exhibiting strong absorption of coherent acoustic wave energy by the water due to the intense spatial confinement of pressure within the slits. The robustness of this CPA device is also demonstrated, in particular with respect to oblique incidence. Due to the simplicity of our design, we expect it to open avenues in underwater ultrasonics, with many applications for ultrasound imaging and stealth, to name a few.