A programmable metasurface for real time control of broadband elastic rays

Real-time engineering of elastic rays in solid materials is crucial for several applications relevant to active noise and vibration cancellation and to inverse methods aiming to either reveal or dissimulate the presence of foreign bodies. Here, we introduce a programmable elastic metasurface for the first time with sensing-and-actuating units, allowing to adapt and reprogram its wave control functionalities in real time. The active units behave following decoupled 'feedforward' sensor-to-actuator control loops governed by local transfer functions encoded into a digital circuit and offering highly flexible phase and amplitude engineering of transmitted and/or scattered waves. The proposed metasurface is concretized numerically and experimentally by achieving, for the first time, real-time tunable ray steering of flexural waves in a host plate. Various other significant demonstrations have been included to strongly illustrate the multifunctional adaptability of the design. In particular, one-way non-reciprocal blocking of waves is observed experimentally whereas skin cloaking of voids is tested numerically. Finally, operability across broad wave frequency ranges is demonstrated (5-45 kHz). The design will pave a new efficient way in the field of sensing and actuation of elastic waves.