Adaptive acoustic metasurfaces for the active sound field control

Active acoustic metasurfaces (AAMSs) have been recently recognized as very efficient sound shielding structures, which can have large lateral dimensions perpendicular to the direction of the sound wave propagation but very short lateral dimension along the direction of the sound wavevector. The sound shielding principle of AAMSs is based on control of the specific acoustic impedance (SAI). This is achieved by means of an active tuning of elastic properties of piezoelectric transducers, which, therefore, represent the core element of the AAMSs. Using this approach, it is possible to actively control the acoustic coefficients of transmission and reflection of AAMSs. An important point, which has been recently discovered, is the fact that the great suppression of the transmission coefficient can be achieved in the regime, when the SAI of the AAMS is negative. The function of the AAMS in varying operational conditions or in a wide frequency range, however, put delicate stability conditions on the negative val...