Fig. 1: The schematic of generating acoustic vortex knots with metamaterials.
a, b plot the amplitude and phase distribution of the initial wavefront with 24-by-24 pixels to generate the Hopf link vortex line. c, d present the distribution of amplitude and phase on the initial wavefront with 24-by-24 pixels for the generation of the trefoil knot vortex line. e The structure of a single unit cell. The operation wavelength is λ0 = 57.17 mm (6000 Hz). The width of the structure is a = λ0/3 = 19.07 mm. Here geometric parameters of CUC boundary layers are chosen as d1 = 8.17 mm, t1 = 6.17 mm, and L1 = 13.3 mm. And geometric parameters of the CUC center layer are d2 = 43.66 mm and t2 = 2 mm. The relative phase shift of the transmitted field can be tuned from 0 to 2π with L (the orange line) changing from 2 to 16.05 mm. The length of PP is Lp =λ0/4 = 28.585 mm. The width of PP is W. f The schematic of creating acoustic vortex knots by using 2D metamaterial-based hologram with both phase and amplitude control.
