Highly efficient isolation of waterborne sound by an air-sealed   metasurface
  Underwater sound isolation has been a long-standing fundamental issue in industry and military fields. Starting from a simple theoretical model, here an air-sealed metasurface is proposed to overcome this problem. Comparing with the sample without filling air, the effective impedance of the air-sealed one is greatly reduced and strikingly mismatch with water, accompanying another merit of low sound speed. Deeply suppressed sound transmission (~10-5) through such a metasurface is observed experimentally over a wide range of ultrasonic frequencies and incident angles. 
Xiaoxue Bai, Chunyin Qiu, Xinhua Wen, Shasha Peng, Manzhu Ke, and   Zhengyou Liu
physics.class-ph