Watch a ‘metabot’ twist and expand without a power source

A man peers into a device holding small cage-like objects which are tumbling about
Origami-inspired metamaterials deforming within a changing magnetic field. Credit: Aaron Nathans/Princeton University

The fascinating behaviour of origami has inspired engineers to design a structure that twists when compressed and shrinks when twisted.

The structure is a “metamaterial”; a class of engineered materials that exhibit behaviour not seen in nature and whose properties depend on their structure rather than chemical composition. These materials can have applications ranging from heat regulation to robotics and packaging.

This new metamaterial is based on the Kresling origami pattern and is described in a new article in the journal Nature.

Philip Klocke and Professor Larry Howell of Brigham Young University in the US, who were not involved in the research but are the authors of a related Nature News and Views article, explain that a single sheet of paper is folded to form a cylinder in the Kresling design.

“When twisted, the sides of the origami structure fold so that the cylinder is compressed,” they write.

Rather than being made of a single sheet, the repeating units of the new metamaterial are made from thin plastic rods that follow the fold lines of a Kresling origami pattern.

“Soft joints between the rods allow the structures to collapse, expand and rotate like the origami that inspired them,” write Klocke and Howell.

Kresling origami-inspired unit. Credit: Princeton University

By stacking clockwise and anticlockwise units on top of each other, the researchers created columns with upper and lower sections that twist in different directions.

These columns were assembled into a regular array to create a 3D deformable metamaterial, which can be “reversibly compressed to less than half its original height by applying a sequence of clockwise and anticlockwise twists”.

The researchers attached magnets to the plastic rods so that the application of an external magnetic field would cause them to twist, collapse, or pop open. The resulting “metabot” can follow electromagnetic commands like a remotely controlled robot even though it lacks any motor or internal gears.

“The electromagnetic fields carry power and signal at the same time,” says Minjie Chen, co-author of the Nature paper and associate professor of electrical and computer engineering at Princeton University in the US.

Origami-inspired metamaterial moving within a magnetic field. Credit: Princeton University

“Each behaviour is very simple but when you put them together [it] can be very complex.

“This research has pushed the boundaries of power electronics by demonstrating that torque can be passed remotely, instantaneously, and precisely over a distance to trigger intricate robotic motions.”

The potential applications are wide ranging.

“Because of its tuneable response to applied forces, it could be used instead of foam infills for storage containers, or as weighing scales, buttons or retractable staircases,” suggests Klocke and Howell.

“If the metamaterial could be made to respond to heat and light, it could also be used as a heat shield for applications, such as space vehicles, that require protection from extreme temperature variations, or to build a material that contracts rather than expands in response to heat.”

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