Tailoring arbitrary convex self-bending and low-diffraction elastic waves via deep-subwavelength metasurfaces

Precise control over elastic wave propagation paths, particularly for complex trajectories with preserved beam integrity, remains a significant challenge in various applications. Here, we present a deep-subwavelength elastic metasurface strategy for theoretically tailoring arbitrary convex self-bending elastic waves with remarkably low diffraction over extended distances. Our approach leverages a multi-objective inverse design methodology to optimize deep-subwavelength unit cells, ensuring uniformly high transmission and widely tunable phase shifts. These optimized unit cells are then arranged according to desired phase profiles to sculpt the prescribed curvilinear trajectories. Both numerical simulations and experimental measurements are conducted to validate the exceptional performance of the proposed metasurfaces in shaping complex wavefields. The intensity distribution of the self-bending beams in the vicinity of the mainlobe transversely resembles a squared Airy function while preserving the low-diffraction features along the propagation path within a prescribed range. This unprecedented customization of both the wavefront trajectory and its low-diffraction range opens new avenues for sophisticated elastic wave engineering, promising transformative applications in areas requiring remote, precise energy delivery, enhanced sensing capabilities, and advanced wave-based communication.