'Bigger is different'—the unusual physics of mechanical metamaterials exposed

September 26, 2017 by Research Amolf And Universities Leiden And Amsterdam Reveals Striking Scale Effects, AMOLF
Indentation on a two-dimensional mechanical metamaterial. Credit: AMOLF

Mechanical metamaterials, which exhibit unusual properties such as shape morphing and programmability, have been found to display further surprising features. When the materials are a step in size larger, new rules seem to apply. This was discovered by researchers at AMOLF, Leiden University and the University of Amsterdam. Their findings will be published in Nature Physics on 25 September.

"In standard materials such as a , we understand what happens when you add more material," says first author Corentin Coulais. "If you make the rubber band twice as long, then it is twice as easy to stretch. That is basic mechanics. But are different. The exact opposite can happen. For example, we discovered that a long metamaterial can actually be stiffer than a short one."

Until now, the research into metamaterials was focused on relatively small systems in which aspects such as programmability are easily investigated. "However, we suspected that different effects would occur in larger systems," says Coulais. "We have now studied that extensively."

As a postdoc in the group for Mechanical Metamaterials of Martin van Hecke, Coulais examined a relatively simple strip of metamaterial together with Leiden University master's student Chris Kettenis. This unidimensional metamaterial, built up from stiff elements that can rotate slightly with respect to each other, unexpectedly became stiffer when its length was doubled. The striking scale effect also occurred in the case of the more complex two- and three-dimensional metamaterials.

The strip of metamaterial used in the experiments. Credit: AMOLF

The team also discovered that there was also a characteristic length scale that marked the transition from small to large. Coulais says, "We see that above this scale, the special functionality of the metamaterials wears out, so to speak. The special effects of the geometric structure become spread out."

Coulais emphasizes that only the design of the metamaterial is responsible for the characteristic length scale. Take, for example, the influence of the flexibility of the pivot points between squares. The intrinsic properties of the rubber that the metamaterial is made from are not relevant. "This really is a phenomenon that we have now been able to reproduce in computer simulations as well."

It is clear that designers of should take the characteristic length scale into account. However, this does not limit the possibilities, says Coulais. "On the contrary, the new that we now describe in Nature Physics actually introduces a whole new range of possibilities."

Another consequence of the effects also came to light. When the material is larger, a small offset in the position of the pressure point will give rise to a completely different response of the material. This opens possibilities to design materials that incorporate different types of behavior. An example is a material that can be both flexible and stiff depending on how it is constricted. Coulais is now employed at the Institute of Physics of the University of Amsterdam (UvA), where he is continuing his pioneering work with his own research group. "There is still a lot to discover about these unusual materials."

Explore further: New mechanical metamaterials can block symmetry of motion, findings suggest

More information: Corentin Coulais, Chris Kettenis and Martin van Hecke, A characteristic length scale causes anomalous size effects and boundary programmability in mechanical metamaterials, Nature Physics, 25.09.17 online, DOI: 10.1038/nphys4269

Related Stories

Legos and origami inspire next-generation materials

March 29, 2017

Inspired by the fun of playing with Legos, an international team of researchers from Tianjin University of Technology and Harvard University have used the idea of assembling building-blocks to make the promise of next-generation ...

Recommended for you

Fiber optic sensor measures tiny magnetic fields

September 19, 2018

Researchers have developed a light-based technique for measuring very weak magnetic fields, such as those produced when neurons fire in the brain. The inexpensive and compact sensors could offer an alternative to the magnetic ...

The hunt for leptoquarks is on

September 19, 2018

Matter is made of elementary particles, and the Standard Model of particle physics states that these particles occur in two families: leptons (such as electrons and neutrinos) and quarks (which make up protons and neutrons). ...

Researchers push the boundaries of optical microscopy

September 19, 2018

The field of optical microscopy research has developed rapidly in recent years. Thanks to the invention of a technique called super-resolution fluorescence microscopy, it has recently become possible to view even the smaller ...

Searching for errors in the quantum world

September 19, 2018

The theory of quantum mechanics is well supported by experiments. Now, however, a thought experiment by ETH physicists yields unexpected contradictions. These findings raise some fundamental questions—and they're polarising ...

Extremely small and fast: Laser ignites hot plasma

September 19, 2018

When light pulses from an extremely powerful laser system are fired onto material samples, the electric field of the light rips the electrons off the atomic nuclei. For fractions of a second, a plasma is created. The electrons ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.