Rainbow trapping of acoustic skyrmions with subwavelength gradient metastructure

Acoustic skyrmions, topological quasiparticles with nontrivial vector configurations promising for data storage and information processing, have been explored in various acoustic metastructures. However, configuring skyrmionic modes with different frequencies at distinct locations of the structure remains challenging. Here, we propose a cylinder metastructure with gradient grooves to realize rainbow trapping for acoustic skyrmions. By theoretical analysis and numerical calculation, we propose a mathematical mapping from three-dimensional (3D) parameter sphere to two-dimensional (2D) vector ring-shaped surface, and a Néel-type skyrmionic mode of velocity field vectors can be stably formed in ring-shaped grooves with uniform depth. With this mapping relation, we construct the binary and gradient groove structures, and demonstrate that the skyrmionic modes can be stationed at different subareas with different groove depths for different working frequencies for enhancing data storage capacity. The rainbow trapping for acoustic skyrmions not only enables high-density storage of broadband acoustic signals but also ensures data integrity and stability in complex acoustic environments, paving the way for partitioned data storage and information processing in advanced acoustic functional devices.