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In Their Quest for New Metamaterials, Scientists Have Reached the Point of Delirium: A Material Capable of Counting to Ten

“One, two, three, four…” An inanimate block of rubber might be closer than ever to saying this in real life.

Science
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In the fast-paced race to develop new materials, a group of physicists in the Netherlands has achieved a surprising result: a metamaterial capable of counting to ten and remembering the order in which it was pressed. The scientists have recorded a video showcasing the surprising properties of their creation, making it seem like a peculiar sleight of hand. All they need is a small block.

Now, they’re already considering potential applications.

A metamaterial capable of counting? Sure, it doesn’t sound real. However, a team at Leiden University in the Netherlands claims to have created exactly that. In their study, published by the journal Physical Review Letters, professor Martin van Hecke and doctoral student Lennard Kwakernaak explain how they’ve created a very special block of rubber. The piece, provided with flexible sheets, is a mechanical metamaterial that is capable of counting and remembering the order in which it receives pressure.

What does that mean exactly? “Irreversible metamaterials that count mechanical driving cycles and store the result into easily interpretable internal states,” the study’s abstract reads. While the explanation may seem insufficient, it becomes much clearer when watching the demonstration video recorded by Kwakernaak himself. The video features a small block of rubber composed of 22 pairs of flexible beams.

When the block is pressed, all the bars bend to the left except for the first one, which bends to the right. Repeating the process results in a similar outcome, but with more bars bending to the right. Each one displays a mark to show how many times the block has been pressed. “That first bar then pushes the next pair to the right and that moves along one position each time you push the material. That’s how the material counts to ten,” the Leiden University researcher explains.

A photo of the talking metamaterial.

What’s a metamaterial? This isn’t a new concept. Metamaterials are artificially structured materials with unique properties not typically found in nature. Research in this area has been particularly productive in the last two decades. These materials can act as “acoustic lenses,” absorb vibrations without sacrificing rigidity, and move without any physical contact, using only their response to sound waves.

To be more precise, the rubber block is a mechanical metamaterial, a category of materials whose properties are influenced by both their composition and structure. According to Kwakernaak, one advantage is that materials like the one he proposes are relatively inexpensive, robust, and require little maintenance, making them “interesting for all kinds of applications.”

What applications will it have? “It’s hard to say exactly what those [applications] will be, but we always find a purpose for new materials like this. For example, earlier research into a material that folds like origami inspired the folding of solar panels on a satellite,” Kwakernaak says. At Leiden University, they suggest that a bar capable of adjusting from left to right can be likened to a computer bit, and they point to potential future uses, such as counting cars of different kinds or being used in pedometers.

The potential of the metamaterial extends beyond recording pressures. The Dutch researcher claims that it can also discern them: “I found out that you can cause different reactions in the rubber by pushing with different levels of force. By experimenting with this, I was able to make a metamaterial that only counts to the end if you push on it in the right order, with the right amount of force. A kind of lock, in other words.”

Now what? Kwakernaak’s next step is to create an even more complex structure, with bar interactions that extend not just in a single direction but in a plane. “That would actually be a simple computer,” he says. “How such a thin beam bends exactly is much more complicated than you might think. A computer can barely even simulate it.”

“Our metamaterials are robust, scalable, and extendable, give insight into the transient memories of complex media, and open new routes towards smart sensing, soft robotics, and mechanical information processing,” the study concludes.

Image | Universiteit Leiden

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