Nonlinear mechanical metamaterial cloaks

Mechanical cloaking in the linear regime has been achieved using different strategies from transformation elasticity to data-driven optimization approaches. However, cloaking in structures supporting large-amplitude nonlinear elastic responses remains an open challenge. In this work, we extend cloaking to the nonlinear regime by formulating it as a behavior-mimicking optimization problem for both static and dynamic responses. We showcase how such conceptual generalization enables the creation of cloak structures that can neutralize the effect of structural alterations and excitation disturbances. Through simulations and experiments, we realize highly deformable structures capable of hosting 'unfeelable' inclusions, shielding point excitations from being detected in the bulk, and creating stress-free regions in metamaterial domains. This research opens new avenues for the creation of soft material responses that are unaffected by the presence of embedded objects and can host mechanical decoupling of different subdomains with a monolithic design. Potential applications include shielding of unwanted vibrations, protection of sensitive sensors, and rendering desired haptic feedback in highly-deformable robotic systems.