06.04.17

Touch sensitive fibres could be the key to wearable device control

Touch sensitive clothing that can interface with devices could be made from elastic fibres developed by researchers at North Carolina State University. Scientists outlined the fibres, which are made from tube-like strands that are only slightly thicker than a human hair and contain liquid metal, in a recently published paper.

Michael Dickey, a professor of chemical and biomolecular engineering at NC State and corresponding author of a paper describing the work, explained: “Touch is a common way to interact with electronics using keyboards and touch screens. We have created soft and stretchable fibres that can detect touch, as well as strain and twisting. These microscopic fibres may be useful for integrating electronics in new places, including wearable devices.”

Each fibre consists of three strands. One is completely filled with liquid metal, one is two-thirds filled, and one is only one-third filled with EGaIn. The slim tubes are then twisted together into a tight spiral.

The method uses capacitance, in much the same way as many touchscreens. In this case when a finger touches the fibre it changes the capacitance between the finger and the metal inside the polymer strands. If a finger is moved along the fibre the capacitance will vary, depending how many of the strands contain EGaln at that point in the fibre.

Researchers also developed a sensor using two polymer strands, both of which are completely filled with EGaIn.

Again, the strands are twisted into a tight spiral. Increasing the number of twists elongates the elastic strands and brings the EGaIn in the two tubes closer together. This changes the capacitance between the two strands.

“We can tell how many times the fiber has been twisted based on the change in capacitance,” Dickey said. “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.”

The work was detailed in a paper, “Stretchable Capacitive Sensors of Torsion, Strain, and Touch Using Double Helix Liquid Metal Fibers,” published in the journal Advanced Functional Materials.