"We have created soft and stretchable fibres that can detect touch, as well as strain and twisting,” says Professor Michael Dickey. “These microscopic fibres may be useful for integrating electronics in new places, including wearable devices."
The fibres are made of polymer strands that contain a liquid metal alloy, eutectic gallium and indium (EGaIn). Each fibre consists of three strands. One is filled with EGaIn, one is two-thirds filled with EGaIn, and one is one-third filled with EGaIn. The slim tubes are then twisted together into a tight spiral.
According to the team, when a finger touches the elastic fibre, it changes the capacitance between the finger and the EGaIn inside the insulating polymer strands.
By moving a finger along the fibre, the capacitance will vary, depending on how many of the strands contain EGaIn at that point in the fibre. Different electronic signals can be sent, depending on which part of the fibre is touched.
The researchers also developed a sensor using two polymer strands, both of which are completely filled with EGaIn. 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 fibre has been twisted based on the change in capacitance," prof Dickey explains. "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 than existing torsion sensors."