Design and realization of nonlinear mechanical metamaterial cloaks

Based on flexible mechanical metamaterial platforms that have been proven to be experimentally realizable, that support nonlinear deformations and waves, and that possess a large number of adjustable geometrical design parameters, we propose here to realize mechanical metamaterials for cloaking in the nonlinear regime. Mechanical cloaking in the linear regime has been previously achieved using various strategies, from transformation elasticity to data-driven optimization approaches. However, cloaking in structures that support large-amplitude nonlinear elastic responses remains an open challenge due to the difficulty to design the nonlinear elastic properties of metamaterials. The key point is to implement differentiable simulations for our metamaterial dynamical response and solve an optimization problem to systematically find optimal cloaking structures. The latter is then fabricated and tested under both static and dynamic excitations. Specifically, we realize highly deformable structures capable of hosting “undetectable” inclusions, shielding point excitations, and creating stress-free regions within metamaterial domains. Potential applications include shielding against unwanted vibrations, protecting sensitive sensors, and generating desired haptic feedback in highly deformable robotic systems.