Refined acoustic holography via nonlocal metasurfaces

Holography can provide the desired wavefront phase and/or amplitude for imaging, particle manipulation, bacteria trapping, and cell patterning in optics and acoustics. However, previous work on acoustic holography is mostly based on local design optimization, either using active control of the sound source or relying on the structural design to provide the desired wavefront. Achieving precise control over the acoustic field remains a significant challenge. Here, we realize refined single-plane symmetric binary amplitude, asymmetric intensity gradient amplitude, and bi-objective hologram through the non-local holographic imaging theory that considers the acoustic coupling of structural units in detail. By taking into account the self-radiation and mutual radiation between many small units on a plate of well-designed thickness, as well as the transmission through the plate's apertures, we can effectively regulate the sound field behind the plate. We demonstrate the effectiveness of our approach through numerical simulations and experiments, showcasing a circle, a black hole, and a bi-objective with a circle and a square hologram. Notably, the acoustic black hole hologram precisely reconstructs the intensity gradient distribution at two bright spots. This non-local holographic imaging theory is valuable for the fine-intensity regulation of the sound field and is expected to be applied in ultrasound diagnosis and treatment, medical imaging, and other fields.