Acoustic metasurfaces have enabled unprecedented control over acoustic waves, offering opportunities in areas such as holographic rendering, sound absorption, and acoustic communication. Despite the steady progress made in this field, most acoustic metasurface designs are passive in that they only provide static functionalities. Here, a reconfigurable active acoustic metalens is implemented to showcase scanning of the focus along arbitrary trajectories in free space with the help of a previously developed active acoustic metasurface platform. Each unit cell of the metasurface contains a cavity, whose size can be tuned continuously by a dynamic control system to adjust the phase of the reflected wave. While this work focuses on beam focusing, it could hold great promise for a wide range of applications including acoustic levitation and tweezers.

Time-domain digital coding metasurfaces have been proposed recently to achieve efficient frequency conversion and harmonic control simultaneously; they show considerable potential for a broad range of electromagnetic applications such as wireless communications. However, achieving flexible and continuous harmonic wavefront control remains an urgent problem. To address this problem, we present Fourier operations on a timedomain digital coding metasurface and propose a principle of nonlinear scattering-pattern shift using a convolution theorem that facilitates the steering of scattering patterns of harmonics to arbitrarily predesigned directions. Introducing a time-delay gradient into a time-domain digital coding metasurface allows us to successfully deviate anomalous single-beam scattering in any direction, and thus, the corresponding formula for the calculation of the scattering angle can be derived. We expect this work to pave the way for controlling energy radiations of harmonics by combining a nonlinear convolution theorem with a time-domain digital coding metasurface, thereby achieving more efficient control of electromagnetic waves.

Fabricating materials with customized characteristics for both electromagnetic (EM) and acoustic waves remain a significant challenge using the current technology, since the demand of multiphysical manipulation requires a variety of material parameters that are hard to satisfy in nature. However, the emergence of artificially structured materials provides a new degree of freedom to tailor the wave–matter interactions in dual physical domains at the subwavelength scale. Here, a bifunctional digital coding metamaterial (MM) is proposed to engineer the propagation behaviors of EM and acoustic waves simultaneously and independently. Four kinds of rigid pillars with various material properties are employed to serve as 1-bit reflection-type digital meta-atoms with antiphase responses in both frequency spectra, thus offering the opportunities for independent field control as desired. The MM demonstrates excellent performance of scattering manipulations from 5700 to 8000 Hz in the acoustic region and 5.80–6.15 GHz in the microwave region. The bifunctional MM is verified through full-wave simulations and experimental measurements with good agreement, which stands out as a powerful tool for related applications in the future.

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