Flexible conductive fibers developed by researchers at Singapore's Nanyang Technological University can cool and contract without producing stress cracks, permitting them to be woven into cotton clothing.
Earlier attempts to produce fibers with a conductive core and a hardwearing covering have failed. Tiny stress cracks can occur from materials cooling and contracting at different rates during manufacture, or from materials being twisted or washed once in a finished product, which can prevent a smart gadget from functioning.
In order to prevent stress cracks, Lei Wei of Nanyang Technological University in Singapore and his associates have now created conductive materials that cool and contract similarly to the aluminosilicate glass found in smartphone screens. The procedure is inexpensive and "industry ready," according to Wei, and it utilizes technology from the production of fiber-optic cable, reports NewScientist.
In this process, a silicon or germanium semiconductor wire is melted to a temperature of approximately 1000°C and then pulled into thin strands. Afterwards, a polymer coating is applied to remove the glass using hydrofluoric acid, enabling a more flexible material. Up to ten kilometers can be covered by the fibers.
After that, little bits of this fiber are woven into a cloth using regular cotton and weaving machinery. Cotton is necessary, according to Wei, to make the clothing comfortable, as the new material feels like "fishing line" next to the skin.
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The researchers have created a number of prototypes using the fiber, which also include electronic sensors and chips that communicate through the conductive material. These items include a jumper that can receive and decode images transmitted by light pulses rather than radio waves, a watch strap that measures the wearer's heart rate, and a hat that detects when traffic lights change color and transmits the information to a smartphone app.
The clothing was worn, cleaned, and dried numerous times over the course of six months of testing, and the fibers held up and kept conducting electricity.
However, there is still a flaw: after a few months, the connection between the stiff circuit boards and the flexible material that house computer chips and other components usually breaks, rendering the smart features inoperable.
“The only part that always leads to the failure of the test is the connection between the fiber and the outer circuit,” says Wei. “To find a stable way to make the connection, that’s the challenge now.”