Although many groups are developing power-generating "smart fabrics," the technology is often too complex to be scaled up to commercial use. Now, however, scientists have devised a simple method of embroidering electrical generators onto regular fabric.
The new technique is being developed at North Carolina State University, by a team led by Asst. Prof. Rong Yin.
It incorporates a special yarn, made of commercially available copper wires coated in polyurethane. That yarn gets embroidered onto a base of regular cotton fabric – or potentially any other material. In the area where the yarn is being added, though, the cotton is overlaid with a fabric made of a synthetic polymer called PTFE (polytetrafluoroethylene). There's a tiny gap between the PTFE and the copper wires.
In a final step, a protective layer of regular cotton yarn is embroidered over top of the copper-wire yarn.
When the wearer of a garment incorporating the yarn subsequently moves around, the wires and the PTFE come in and out of contact with one another. When they touch, electrons are transferred between them, generating an electrical current. This phenomenon is known as the triboelectric effect, and it's what's responsible for the static charge that occurs when you're combing your hair. Small devices that utilize the effect to generate usable electricity are called triboelectric nanogenerators (TENGs).
In lab tests, some of the copper-wire TENGs were embroidered onto denim which was worn on the palm of the hand, at the elbow, under the arm and at the knee. In all cases, the devices generated electrical signals that could be used to track the movement of the respective body part. Additionally, when one of the TENGs was attached to the insole of a shoe, it functioned as a pedometer, generating electrical signals of varying strengths depending on whether the wearer was walking, running or jumping.
Finally, the technology was used to create an arm-located numeric keypad, in which each number was individually embroidered onto the base fabric. Depending on which number the user pushed, a different electrical signal was produced.
And as an added benefit, the embroidered TENGs are inexpensive to apply, and were found to retain their functionality after multiple wash cycles.
"Our technique uses embroidery, which is pretty simple – you can stitch our yarns directly on the fabric," said Yin. "During fabric production, you don’t need to consider anything about the wearable devices. You can integrate the power-generating yarns after the clothing item has been made."
A paper on the research was recently published in the journal Nano Energy.
Source: North Carolina State University