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The acoustic impedance mismatch between water and air limits the acoustic communication through the water–air interface. Here, based on the resonances of bubbles, we propose a metasurface consisting of bubbles sealed with membranes for perfect sound transmission at the water–air interface. We have experimentally achieved sound transmission enhancement of over 20 dB at 380–510 Hz, with the thickness of the metasurface about 1/180 times air wavelength. By flexibly adjusting the immersion depth, the metasurface is able to operate at multiple frequencies. The effects of viscosity and geometry of bubbles are discussed simulatively. The present work is relevant to the practical design of advanced acoustic devices for transmedia communication. [ABSTRACT FROM AUTHOR]

Self-accelerating beams have applications in optic and acoustic fields due to their peculiar properties. As a promising artificial two-dimensional metamaterial, a metasurface can be used as the generator of self-accelerating beams. However, restricted by the generalized Snell's law, most research hotspots focus on flat metasurfaces. In this Letter, the generalized Snell's law on an arbitrary curved reflective surface is discussed. Then, the phase profile for the self-accelerating beams generated from the curved reflective surface is derived based on the caustic theory. The metasurface consisting of the tunable spiral path units is constructed, and numerical and experimental validations are performed. The methodology developed in the present letter extends the applications of the self-accelerating beams. [ABSTRACT FROM AUTHOR]