Underwater stealth metasurfaces composed of split-orifice–conduit hybrid resonators

The development of sound-absorbing materials for noise reduction in daily life has been a prolonged issue that also applies to a recognized need for submarine anechoic tiles to stay independent from SONAR (SOund NAvigation Ranging). Here, we present an underwater stealth metasurface that uses split-orifice–conduit (SOC) hybrid resonators to significantly reduce its acoustic reflectance. A theoretical analysis of SOC elements provides an approach to quantifying acoustic characteristics using the transfer matrix method in a single metasurface. The findings confirm that we can tune the absorption with respect to a resonating frequency by adjusting geometrical parameters. Utilizing a hybrid mechanism that enables easy access to coupled resonances, we obtain broadband absorption spectra even in the presence of a covariant sound speed profile in the deep sea and a thermoviscous effect on unit cells of the metasurface. Such a metasurface will provide a further step toward developing feasible underwater stealth technologies for submarines and remains to be experimentally demonstrated.