PICTURE A RECTANGLE of fabric cut from a standard grey t-shirt. It’s stretchier than most tees, because it’s made from a mix of nylon and spandex, not cotton. And it stands out in another way, too: If you flip back a corner of the cloth, one side has an unexpected metallic sheen.
This textile isn’t the creation of a sci-fi costume director. It’s called shieldex, and it was exactly what textile engineer Asli Atalay and her team at Harvard needed to develop a soft, stretchable, motion-measuring sensor. The metallic shine comes from silver coating the flexible fibers, so the fabric can stretch and conduct electrons at the same time. Rather than slapping silicon chips into bracelets, these electronics could give wearables more of the stretchability and comfort of the best sweatpants.
While the roboticist’s arsenal of metal components and silicon chips accomplishes a lot, softer robotic wearables could be friendlier for injuries, or older users, driving down the risks to humans while still providing help with, say, opening a jar. Think gloves that boost grip, or sleeves that act as assistive exoskeletons. “You put on a t-shirt, a sweater, a pair of socks—you could have these types of sensors embedded in them,” says bioengineer Conor Walsh, a co-author of the paper.
To make the sensors, Atalay first sandwiches two layers of souped-up fabric around a film of soft, electrically insulating silicone. Then, a trusty laser cutter slices the sandwich into whatever shape she wants. She runs a hot iron over an adhesive to attach the electrical leads—like attaching an iron-on patch to your jean jacket, except she’s sticking a tiny wire to each layer of silver spandex.
Technically, what she’s building is a parallel plate capacitor—each side of the metal-plated fabric is an electrode, holding equal but opposite charges. As the fabric stretches, the insulating silicone between the electrodes thins out and the electrodes get bigger and closer together, changing the sensor’s capacitance (that’s the the charge on each conducting plate divided by the voltage difference between them). That capacitance change is used to measure how far the fabric stretches. And voila: a batch of stretchy, flexible motion sensors.