Touch-sensitive fibres put new twist on controlling electronic devices
We are used to touchscreens, but now researchers have created new, touch-sensitive fibres that can be used to interact with electronic devices. The microscopic fibres are soft, stretchable and capable of detecting touch, strain and twisting, all of which could lead to new sorts of wearable devices and sensing applications.
The fibres created at North Carolina State University are made of an extremely thin strands of a tube-like polymer filled with a liquid metal alloy of eutectic gallium and indium (EGaIn). The strands are a few hundred microns in diameter, or just a little thicker than a human hair.
To create the fibre shown in the video below, three strands are twisted together to form a tight spiral. Each of the tubes are filled to different degrees with the liquid metal alloy – one is completely filled, one is two-thirds full and one is just one-third of the way filled.
The fibre responds to touch in the same way that many phone’s screens do by interpreting variations in capacitance between your finger and the electronic components of your phone. This works because both sides of this interaction are conductors of electricity and they’re separated by an insulator. In the case of your phone the insulator is the screen. In the case of the fibres, your finger and the liquid metal alloy are conductors and the polymer tubes are insulators.
Just as touching a different part of your touchscreen can be translated into different actions on your mobile device, touching a different section of the fibre can also produce different electronic signals, based on how many strands contain the metal alloy in a particular section of the fibre.
We’ve seen some similar approaches to creating flexible, wearable electronics using silver nanowires and conductive ink, but the use of liquid metal in this case is particularly interesting.
two-strand version of the fibre can also be twisted together to measure rotation.
“We can tell how many times the fibre has been twisted based on the change in capacitance,” explains Michael Dickey, a professor of chemical and biomolecular engineering at NC State. “That’s valuable for use in torsion sensors, which measure how many times, and how quickly, something revolves. The advantage of our sensor is that it is built from elastic materials and can therefore be twisted 100 times more – two orders of magnitude – than existing torsion sensors.”
Dickey is lead author on a paper detailing the research in the journal Advanced Functional Materials.
A video can be watched here