High‐Resolution Manifold Acoustic Holography Based on High‐Pixel‐Array Binary Metasurfaces

Acoustic holograms using artificial materials have become an area of intense interest in acoustics due to the great potential in various applications such as medical imaging, underwater detection and object manipulation, etc. In this article, a general approach is proposed for designing high-pixel-array binary metasurfaces and then fabricating the intricate ultrathin structures via picosecond laser processing for implementing high-resolution manifold holograms in far fields. The angular spectrum propagation is utilized in combination with the forward optimization, instead of the Rayleigh-Sommerfeld integral, to efficiently simulate far-field holograms at the target plane. To obtain manifold acoustic holograms in the planes at different depths, zero-padding is utilized to break the tight constraint of sampling theorem. Benefiting from the realizable high-pixel-array binary metasurface, e.g., the number of pixels ≈90 000 or even more, high-resolution complicated holograms can be readily achieved. As an example, multi-depth holography, multi-frequency holography, and sophisticated holography are generated via binary metasurfaces. The functional meta-devices based on ultrasound amplitude modulations provide more opportunities for exploring practical applications of acoustic metamaterials.