WHY THIS MATTERS IN BRIEF
As transistors and computing devices continue to shrink it is inevitable we’ll bake more computing power into our clothing, and all that extra compute will need some way to power it.
Today, the majority of smart clothes we use to monitor a person’s vital statistics as they exercise, go about their business or move are still fairly chunky affairs, but while a lightweight, comfortable normal looking clothing that can, for example, generate enough power to light up a jogger at night might sound futuristic, materials scientist Trisha Andrew at the University of Massachusetts Amherst says she could make one today.
In a paper published recently in the journal Advanced Functional Materials Andrew and her team have outlined how they’ve finally managed to integrate breathable, pliable, metal-free electrodes into a variety of new fabrics and off the shelf clothing in a way that not only retains their original look and feel, but that also generates and transmits enough electricity to power electronics and sensors that are embedded into them, or other small electronic devices.
The Power Within
“Our lab works on textile electronics, and we’re aiming to build up our knowledge of materials science so [companies] can give us any garment they want, any fabric, any weave type, and turn it into a conductor. Such conducting textiles can then be built up into sophisticated electronics, and one of our first use cases involved using the new technology to harvest body motion energy and convert it into electricity,” she said.
Electrifying and creating advanced fabrics and clothes that can monitor a person’s health or vital signs is increasingly important to the military, as well as to the traditional health and fitness apparel companies like Adidas and Nike, she notes.
Generating small electric currents using the movement of individual layers of fabric, which is the same effect you get when you rub a comb against a sweater, is called Triboelectric charging, explains Andrew, and it’s this phenomenon that allows materials to become electrically charged as they rub against each other.
“By sandwiching layers of different materials between two conducting electrodes people can generate a few microwatts of power every time they move,” she says.
In the paper the team explain how they used a technique called “Vapour Deposition” to coat 14 different fabrics, including five cottons with different weaves, linen and silk, with a conducting polymer known as Poly(3,4-ethylenedioxytiophene) or PEDOT for short, to make plain-woven, conducting fabrics that are resistant to stretching and wear and remain stable after washing and ironing. The thickest coating they put down was about 500nm, or about a tenth of the diameter of a human hair, which was just enough to retain the fabrics look and feel.
“Our paper describes the materials science needed to make these robust conductors,” said Andrew, “and we showed that they are stable to washing, rubbing, human sweat and a lot of wear and tear.”
“There’s a strong motivation within [industry] to use familiar fabrics rather than having to create a whole new type of fabric,” she added, “so this is a huge leap for consumer products because now you don’t have to convince people to wear something different to what they’re already used to.”
The test results were sometimes a surprise, Andrew notes.
“You’d be amazed how much stress your clothes go through until you try to make a coating that will survive a shirt being pulled over the head. The stress can be huge, up to a thousand Newtons of force. For comparison, one footstep is equal to about 10 newtons, so it’s yanking hard. If the coating isn’t stable, a single pull like that will flake it all off. That’s why we had to show that we could bend it, rub it and torture it. That is a very powerful requirement to move forward.”
Since the paper was submitted Andrews and her team have made a wearable heart rate monitor using an off the shelf fitness bra and eight monitoring electrodes, and she explains that a hospital heart rate monitor has 12 electrodes, while the wrist worn fitness devices popular today, from companies like Apple and Fitbit, have only one, which makes them prone to false positives.
As for what’s next the team say they’ll be testing the bra alone and with leggings that have another four sensors built into them to see if sensors can match the accuracy and sensitivity of the hospital heart rate monitors, and as they go on to say in their paper “flexible, body worn electronics represent a frontier of human interface devices that make advanced physiological and performance monitoring possible,” so if the new breakthrough stands up to scrutiny then it could pave the way for a whole new range of comfortable smart clothing and wearables that can monitor our health and wellness in real time with the accuracy of hospital equipment. But it could also lead to the creation of a whole new genre of “powered” clothes such as dresses that glow, and trainers that change patterns, like these ones – the possibilities are limitless.
