Reconfigurable Acoustic Coding Metasurface for Bidirectional Wavefront Manipulation across the Water-Air Interface

• A reconfigurable coding metasurface enables efficient bidirectional wavefront control across the water-air interface. • Sidewall-induced flexural resonance in discrete units simultaneously ensures high transmission and tunable phase modulation. • The compact single-layer design supports programmable functions like focusing, splitting, and Airy-beam generation. • Experiments confirm enhanced transmission and reconfigurable field control in both propagation directions. Bidirectional high-efficiency sound control across the water-air interface is essential for cross-medium communication and remote sensing. However, conventional quarter-wavelength impedance matching imposes a strong trade-off between transmission efficiency and phase tunability, limiting flexible control in both directions. Here, we propose a reconfigurable acoustic coding metasurface that enables efficient bidirectional wavefront manipulation within a single-layer architecture. Discrete solid units with vibro-acoustic coupling harness sidewall flexural vibrations, facilitating effective velocity transfer between water and air. This underlying mechanism overcomes the conventional constraint, enabling simultaneous high transmission and phase modulation. Through mechanical reconfiguration of the coding units, the metasurface supports flexible switching among various acoustic functions, such as focusing, beam splitting, and Airy-beam generation, for both propagation directions. Full-wave simulations and experimental results validate its versatility and reconfigurability. This work opens new possibilities for compact, programmable platforms in intelligent cross-domain acoustic communication and adaptive sensing.