Energy focusing of flexural waves via algorithmically optimized coding metasurface lenses

Efficient elastic wave focusing is crucial in materials and physical engineering. Elastic coding metasurfaces, which are innovative planar artificial structures, show great potential for use in the field of wave focusing. However, elastic coding lenses (ECLs) still suffer from low focusing performance, thickness comparable to wavelength, and frequency sensitivity. Here, we consider both the structural and material properties of the coding unit, thus realizing further compression of the thickness of the ECL. We chose the simplest ECL, which consists of only two encoding units. The coding unit 0 is a straight structure constructed using a carbon fiber reinforced composite material, and the coding unit 1 is a zigzag structure constructed using an aluminum material, and the thickness of the ECL constructed using them is only 1/8 of the wavelength. Based on the theoretical design, the arrangement of coding units is further optimized using genetic algorithms, which significantly improves the focusing performance of the lens at different focus and frequencies. This study provides a more effective way to control vibration and noise in advanced structures.