Magnetics Business & Technology - July/August 2021 - 20

RESEARCH & DEVELOPMENT
Silicon & Magnetic Powder Yield Programmable Metamaterial at EPFL
puter devices like hard drives. These devices contain bits of data
that can be written to and read from in real time. The cells in his
programmable metamaterial, called m-bits, work like the bits in a
hard drive - they can be switched on, making the material stiffer,
or off, making it more flexible. And researchers can program various
combinations of on and off to give the material exactly the
mechanical properties they need at any given time.
To develop his material, Chen drew on methods from both computer
science and mechanical engineering. " That's what makes
his project so special, " says Pauly. Chen also spent a considerable
amount of time testing his material in each of its different
states. He found that it could indeed be programmed to achieve
various degrees of stiffness, deformation and strength.
Scientists at EPFL in Switzerland have developed a metamaterial
made of silicon and magnetic powder whose mechanical
properties can be reprogrammed on demand and whose internal
structure can be modified by applying a magnetic field.
Over the past 20 years, scientists have been developing metamaterials,
or materials that don't occur naturally and whose
mechanical properties result from their designed structure rather
than their chemical composition. They allow researchers to create
materials with specific properties and shapes. Metamaterials
are still not widely used in everyday objects, but that could soon
change. Tian Chen, a researcher EPFL in Switzerland, has taken
metamaterials a step further. Details of the work were recently
published in the journal, Nature.
A single material with several mechanical functions
" I wondered if there was a way to change the internal geometry
of a material's structure after it's been created, " says Chen. " The
idea was to develop a single material that can display a range
of physical properties, like stiffness and strength, so that materials
don't have to be replaced each time. For example, when you
twist your ankle, you initially have to wear a stiff splint to hold the
ankle in place. Then as it heals, you can switch to a more flexible
one. Today you have to replace the entire splint, but the hope is
that one day, a single material can serve both functions. "
Silicon and magnetic powder
Chen's metamaterial is made of silicone and magnetic powder.
It has a complicated structure that allows mechanical properties
to vary. Each cell within the structure behaves like an electrical
switch.
" You can activate and deactivate individual cells by applying a
magnetic field. That modifies the internal state of the metamaterial,
and consequently its mechanical properties, " says Chen. He
explains that his programmable material is analogous to com20
Magnetics Business & Technology * July/August 2021
Located in Switzerland, EPFL is one of Europe's most vibrant
and cosmopolitan science and technology institutions with five
campuses.
Many research horizons
Programmable metamaterials are akin to machines, such as
robots, that employ complicated, energy-intensive electronic
mechanisms. With his research, Chen aims to find the right balance
between static materials and machines.
EPFL is one of Europe's most vibrant and cosmopolitan science
and technology institutions with five campuses. Chen works at
two labs there, the Geometric Computing Laboratory headed by
Mark Pauly and the Flexible Structures Laboratory headed by
Pedro Reis.
Reis sees a lot of potential for further research using Chen's
technology. " We could design a method for creating 3D structures,
since what we've done so far is only in 2D, " he says. " Or
we could shrink the scale to make even smaller metamaterials. "
According to EPFL, Chen's discovery marks a fundamental step
forward, as it is the first time scientists have developed a truly reprogrammable
mechanical metamaterial, opening many exciting
avenues for research and cutting-edge industrial applications.
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Magnetics Business & Technology - July/August 2021

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