Bianisotropic impedance-engineered metasurfaces for scattering-free, multiplexing acoustic manipulation

Impedance-engineered passive metasurfaces represent an emerging paradigm that enables precise modulation of complex near-field energy flow between neighboring unit cells, facilitating extraordinary acoustic functionalities. However, the majority of existing works are only limited to single-function operation at a fixed frequency, unable to meet the growing demand for multifunctional applications in next-generation acoustic systems. In this work, wavelength-multiplexed impedance-engineered passive metsurfaces are systematically developed using a self-adaptive multiobjective topology optimization method. These metasurfaces achieve multiple wavefront manipulation functionalities at different operational wavelengths through a shared-aperture, including demonstrated scattering-free acoustic focusing and beam steering. The effectiveness of the proposed multiplexing metasurfaces is verified both numerically and experimentally. In addition, the underlying nonlocality mechanisms of these impedance-engineered metasurfaces are comprehensively analyzed and comparisons with conventional designs obtained from phase-gradient control or directly wave-field shaping have been conducted. With their advantages of subwavelength scale, multifunctionality, and high power-efficiency, wavelength-multiplexed impedance-engineered acoustic metasurfaces show good potential in high-precision medical imaging, large-field-of-view remote sensing and large-scale underwater wireless communications.