# Nonlinear mechanical metamaterial cloaks

## TL;DR

This paper introduces a novel nonlinear mechanical cloaking method using optimization and differentiable simulation to design metamaterials that effectively hide internal features and shield against external disturbances in static and dynamic conditions.

## Contribution

It presents the first optimization-based approach to nonlinear mechanical cloaking, utilizing a differentiable simulation framework for designing cloaks in complex metamaterials.

## Key findings

- Optimized cloaks effectively mask inhomogeneities.
- Cloaks shield against external disturbances in static and dynamic regimes.
- Physical experiments validate simulation results.

## Abstract

The concept of cloaking -- hiding objects from external detection -- has seen wide success in linear systems. Yet, translating these advancements to nonlinear mechanical systems remains an open challenge. Here, we present a new approach to nonlinear mechanical cloaking that frames cloaking as an optimization problem aimed at replicating a target mechanical response. We solve this problem using a differentiable simulation framework coupled with gradient-based optimization. We implement this approach in a class of mechanical metamaterials constructed from rigid units with elastic couplings that support large deformation and contact interactions. Using both numerical simulations and physical experiments, we design optimal cloak structures that effectively mask internal inhomogeneities and shield against external mechanical disturbances both in static and dynamic regimes. This approach provides a versatile design paradigm for creating mechanical systems with integrated cloaking functionality across a broad range of loading scenarios.