A checkerboard of rigid electronic components have been embedded into a flexible surface that can be stretched three times its normal length. The technique makes it possible to keep stiff circuit boards safe from kinks, while at the same making wearable flexible computers more feasible.
"We want to put this on something like
rubber," André Studart told Discovery News. Studart is a professor
of complex materials at Swiss Federal Institute of
Technology (ETH) and one of the co-authors of the paper in Nature Communications outlining
Rather than try to make the electronics stretch, Studart and his colleagues decided to make a surface for the electronics to sit on that had both stretchy and stiff regions. The stretchy areas give the flexibility while the stiff regions protect the rigid electronic circuits.
The surface is comprised of polyurethane, the same substance used in skateboard wheels and floor
coatings. Polyurethane can me made stiffer or softer depending on what
it's mixed, or doped, with. The researchers used laponite, which is a
kind of clay, and micrometer-sized bits of aluminum. The polyurethane doped with aluminum is stiffer than that with laponite, which in
turn is stiffer than polyurethane not mixed with anything.
To make their polyurethane both stretchy and stiff, the team made a sheet of it that consisted of several layers. The bottom layer is the most flexible, and made of undoped polyurethane. The middle layer is made of polyurethane doped with laponite. The very top layer is the the most rigid, the one doped with aluminum. While the stretchiest layer on the bottom is a large sheet, the stiffer ones are laid down in cut-out squares and bonded to the undoped polyurethane layer.
The team tested the surface by installing an LED circuit on the stiff island. The LED stayed lit even
when the sheet was stretched to 150 percent of its length.
This isn't the only way to do
flexible electronics. John Rogers, at the University of Illinois, has been
work here is "a
nice, new addition to the toolbox."
Rogers said his lab has been
focused at the level of designing systems, which sometimes involves coming up with new
ways to build semiconductors. In one case he used a serpentine pattern of
metal wires, which could stretch like a spring on the surface of a
balloon. "The latest work from Switzerland
could have value in the context of an application of this sort, as an
alternative to the interconnection wiring that we used."
Credit: Rafael Libanori, Randall M. Erb and André R. Studart