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Materials

Materials

New type of origami features ‘topological mode locking’

05 May 2019
Origami
Smooth operator: Morph can shift between eggbox and Miura-ori origami patterns. (Courtesy: Allison Carter)

An origami folding pattern that produces a highly-tuneable metamaterial has been discovered by Glaucio Paulino and colleagues at the Georgia Institute of Technology in the US. They developed the new technique by combining the existing “eggbox” and “Miura-ori” folding arrangements into a single pattern.

Origami is best known as the highly-skilled art form of paper folding, but it has also inspired the design of practical structures such as foldable solar arrays for spacecraft. Origami has been used to create metamaterials with useful properties that can be fine-tuned by adjusting the folds – an example being adjustable acoustic metamaterials for a concert hall.

An eggbox origami metamaterial is a planar lattice of mountain and valleys.  When such a metamaterial is stretched in one direction, it will shrink along the perpendicular direction – an effect that is described by a positive Poisson’s ratio. In contrast, Miura-ori metamaterials resemble a lattice of folded zig-zags and have a negative Poisson’s ratio.

Smooth transition

In their study, Paulino’s team developed a new folding pattern that they named “Morph”, which uses a four-vertex origami cell to combine features of both eggbox and Miura-ori patterns. Morph allows for manual switching between mountain and valley assignments of individual creases and this permits a smooth transition between the two types of origami patterns.

What is more, Morph can have both positive and negative Poisson’s ratios – which is a very useful property that has only recently been achieved in other types of metamaterials. In addition, the team showed that Morph can be completely flattened in two different ways.

Paulino and colleagues showed that unit cells within Morph could be combined in both eggbox and Miura-ori modes to create hybrid origami patterns. These patterns displayed several interesting properties such as “topological mode locking”, whereby the mountain and valley assignments of certain unit cells are preserved while the pattern can be fold smoothly.

A related feature of Morph is that its Poisson’s ratio can be tuned to arbitrary values, which the researchers demonstrated by creating a diverse range of shapes through unique combinations of stretching and out-of-plane bending.

The physicists say that the hybrid folds used in their study could lead to versatile new metamaterial structures. Their potential applications include adjustable acoustics for concert halls and crash protection systems in drones that are tuneable to specific flight conditions.

Morph is described in Physical Review Letters.

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