Action-at-a-distance’ metamaterials for soft robotics, developed by TU Delft researchers
Mechanical metamaterials are a sub-category of designer materials where the geometry of the material at the small-scale is rationally designed to give rise to unusual properties and functionalities. Here, we propose the concept of “action-at-a-distance” metamaterials where a specific pattern of local deformation is programmed into the fabric of (cellular) materials. The desired pattern of local actuation could then be achieved simply through the application of one single global and far-field force. We proposed graded designs of auxetic and conventional unit cells with changing Poisson’s ratios as a way of making “action-at-a-distance” metamaterials.
We explored five types of graded designs including linear, two types of radial gradients, checkered, and striped. Specimens were fabricated with indirect additive manufacturing and tested under compression, tension, and shear. Full-field strain maps measured with digital image correlation confirmed different patterns of local actuation under similar far-field strains. These materials have potential applications in soft (wearable) robotics and exosuits.
Designer materials, where rationally designed geometry at the small-scale gives rise to unusual material properties at the macro-scale, are often called metamaterials. Depending on the type of the targeted property, such designer materials may be called mechanical metamaterials,optical metamaterials,acoustic metamaterials, or meta-biomaterials. The unusual properties together with other design features could then be used to create advanced functionalities such as shape-morphing and tunable/(re)-programmable mechanical behavior. These and similar functionalities of metamaterials have various potential applications in soft robotics, exoskeletons, and other types of medical devices.
In soft robotics, development of complex actuators is one of the areas that could benefit from such “designer materials.” In particular, the metamaterials could be designed such that specific actuation patterns are programmed into their fabric. This would remove the need to use active materials that need to be locally actuated.