Architecture and Hardware

Trying On Smart Clothes

The fingertips of a glove woven with conductive fibers developed at Purdue University glow when the wearer’s hand approach a live cable, enabling safe wireless voltage detection.

Wearables have been a "next big thing" in personal computing for several years now. From smartglasses to smartwatches and fitness trackers, computing devices have been growing smaller and more mobile, making it feasible to have one on us all the time.

One thing those examples have in common is that they are standalone devices that you put on like jewelry—accessories to whatever else you are wearing. That could change soon, though: wearables are on the cusp of a transition in which your clothing itself will become the mobile computing device.

One approach to such "smart clothing" relies on sensors and other devices that are woven into the clothing, sort of like the way you might lace your earbud cord through your buttonholes. That's the approach of the Canadian company Hexoskin, whose shirt is designed to monitor physiological functions like breathing and heartbeat. According to Marc Paquin, Hexoskin's vice president of strategic development, "We embed cardiac silver-plated electrodes and respiratory inductance plethysmography sensors in a form factor that looks like a t-shirt." The sensor-embedded shirt works with a separate recording device that supplies power and sends data to personal computers or mobile phones.

Similarly, the Nadi X yoga pants from Wearablex incorporate accelerometers and haptic motors that guide the wearer into the proper yoga position by varying the frequency and intensity of vibrations. A separate unit with a battery clips onto the pants behind the knee to provide power.

Conductive textiles

Embedded electronics with separate devices for power are still add-ons to garments. In the latest wave of smart clothing, the fabric of the garment itself is made up of the electronics. "The field has definitely seen a resurgence of interest and activity focused on new materials for electronic fibers and fabrics," says John Ho, assistant professor at the Institute for Health Innovation & Technology of the National University of Singapore. "This stands in contrast with work in previous decades that focused more on integrating existing electronic modules with clothing."

One reason for the shift in focus, says Ramses Martinez, assistant professor in the School of Industrial Engineering and Weldon School of Biomedical Engineering at Purdue University, is that "Until now, there was no need for such a thing. Now we are discovering that it is actually a wonderful way to interface with humans, as humans are full of curved surfaces and we tend to move a lot."

The 2018 book Wearable Technology in Medicine and Health Care described the challenge for conductive fabrics to be "seamlessly integrated into textiles using traditional textile manufacturing techniques while not disrupting the primary functions of clothing, for example, comfort." Several manufacturers produce e-textiles these days. Bally Ribbon Mills, for example, mixes thin metal strands or metal-coated material strands with the filaments of yarn, or spins a common fiber and then impregnates it with a metal-based powder.

That kind of textile is the basis for Ho's work. "In our work, we use commercially available conductive fabrics, which incorporate conductive metals such as nickel, gold, carbon, or stainless steel," says Ho. They cut the fabrics into specific shapes and apply them to other fabrics. "Typical substrate materials include cotton, polyester, or nylon," he says.

The overlain pieces of e-textile create a "wireless body sensor network"—a Wi-Fi network closely surrounding the wearer's body. The restricted nature of the network means wearable electronics will require less power and will be able to detect weaker signals. After discussing options with various companies, Ho's group decided to commercialize the technology.

Martinez's group at Purdue, on the other hand, is working on ways to make the e-textiles. "Conductive threads can be quite good at conducting electricity, but they are actually quite painful to incorporate into sewing machines," Martinez says. "We wanted to create a conductive thread that was compatible with existing embroidery systems. We developed a new textile filament made of silk reinforced with carbonaceous material, which is very conductive."

The carbonaceous material comes from the combustion of seafood shells, which creates a dust that Martinez compares to laser printer toner. That dust is mixed with silk protein, which resembles egg whites. "It mixes quite nicely," says Martinez, "and if you dry it carefully, you can pull it into wires, which are the conductive threads we are using."

The new fiber offers several benefits. "It minimizes the friction on embroidery systems and facilitates embroidery at higher speed," Martinez says. The thread also can be coated with hydrophobic molecules to make it washable. Finally, circuits made with the embroidery thread can harvest the static electricity generated by the textiles rubbing together. "They are able to power the electronics in the textile and do not require any external source of power—just wearing the garment is enough"

Future directions

Both Ho and Martinez think about what will push e-textiles and smart clothing into the mainstream.

"This is the key question that everyone in the field is trying to answer," says Ho. "There are at least two important features the 'killer app' will have. First, it will take advantage of the fact that the textile covers a large fraction of the body—this is critical to differentiate from existing wearable devices. Second, it will target applications where standardized clothing is culturally acceptable. Examples include athletic wear, hospital gowns, and military uniforms."

Martinez agrees with that assessment. "I believe the market will be going first toward athletes and people that want to monitor their athletic performance. You want to have a sector of the population happy to pay extra, because all your prototypes are going to be more expensive than conventional stuff." That early adopter premium also will make e-textiles more appropriate for garments that are expected to last and won't go out of fashion, he said.

In addition, Martinez says, "There's some but not a lot of fashion involved in athletic wear—your yoga pants are not going to look that different from this year's. There's also very little fashion involved in medical monitoring wear."

The next step he sees after going after such unchanging fashion will be items like coats and jackets, where fashion is involved but on a relatively slow cycle. "T-shirts and things like that will probably be the last territory to conquer."

Beyond all that, Martinez also looks toward the ability of e-textile-based smart clothing to provide feedback or assistance to the user, as the Nadi X pants can. "One of the things we are working on is developing wearable fabrics that are capable of emitting frequencies that will drive away mosquitoes. That is a very good way of transforming energy that otherwise gets dissipated as heat into an activity that you prefer."

The group is also working on a smart diaper. "The diaper will tell if the baby is having any urinary tract infection," Martinez explains. "It will also hopefully distinguish pee from poop, and give parents a sense of emergency in terms of when the diaper needs to be changed."

Jake Widman is a San Francisco, CA-based freelance writer focusing on connected devices, smart homes and smart cities, extended reality, and other emerging technologies.

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