Making acoustic half-Bessel beams with metasurfaces

Unlike the well-known Airy beams that can be deformed beyond paraxial angles, the half-Bessel (HB) Beams can bend to steeper angles. Here we propose an effective metasurface design for constructing two-dimensional acoustic HB beams. The design is based on an array of spatially varied coiling-slit units, each of which mimics the wave responses derived from the analytical expression of the acoustic HB beam. A tradeoff method is utilized here to simplify the variable amplitude responses. The full-wave simulations and experimental measurements consistently manifest the effectiveness of this design process. Potential applications, such as the large-angle bending transport of particles, can be anticipated.