An example of a 3D reconfigurable metamaterial.
Metamaterials are an almost magical class of materials that can do things that seem impossible, but they can only perform one miracle at a time. Now Harvard researchers have come up with a toolkit for constructing metamaterials that flow from one shape and function into another, like origami.
Metamaterials have been around since the 1940s, but only in recent years has their development taken off. Unlike conventional substances, metamaterials have functions and properties that are independent of what they're made of. Instead, their repetitive microstructures allow them to do the seemingly impossible – think flat lenses that act like they're curved, structures that shrink instead of expanding when heated, and even invisibility cloaks.
The problem is that the substructures that metamaterials rely on are very specific, so each metamaterial can only do one thing at a time. Last year, Harvard researchers demonstrated a way to overcome this limitation with reconfigurable metamaterialsmade of thin polymer sheets. Now a team from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute of Biologically Inspired Engineering at Harvard University have developed a more general framework to help engineers to create metamaterials that can change shape and function.
"In terms of reconfigurable metamaterials, the design space is incredibly large and so the challenge is to come up with smart strategies to explore it," says Katia Bertoldi, John L. Loeb Associate Professor of the Natural Sciences at SEAS. "Through a collaboration with designers and mathematicians, we found a way to generalize these rules and quickly generate a lot of interesting designs."
Starting with simple shapes, such as extruded cubes, the team developed computer models that allowed them to create and assess almost a million designs and select the ones with the desired functions. With this toolkit, the Harvard team was able to create reconfigurable thin-walled structures with complex geometries that shape-shift quickly and smoothly. The designs are also scale independent, meaning they could be applied to things on the meter-scale, like transforming solar panels, to the nano-scale, like reconfigurable metamaterials.
From the computer models, the team used laser-cut cardboard, double-sided tape, and multimaterial 3D printing to construct working prototypes. The result is 3D metamaterial models that fold along the edges to change shape, like origami.
"Now that we've solved the problem of formalizing the design, we can start to think about new ways to fabricate and reconfigure these metamaterials at smaller scales," says James Weaver, a senior research scientist at the Wyss Weaver Institute.
The research is published in Nature.