Researchers have developed smart textiles that use acoustic waves instead of electronics to measure touch, pressure, and movement precisely.

Imagine wearing a T-shirt that measures your breathing or gloves that translate your hand movements into commands for your computer.

Researchers at ETH Zurich, led by Daniel Ahmed, professor of acoustic robotics for life sciences and health care, have laid the foundations for just such smart textiles.

Unlike many previous developments in this area, which usually use electronics, the researchers rely on acoustic waves passed through glass fibers. This makes the measurements more precise and the textiles lighter, more breathable, and easier to wash.

“They are also inexpensive because we use readily available materials, and the power consumption is very low,” says Ahmed.

The researchers call their development SonoTextiles.

“While research has already been conducted into smart textiles based on acoustics, we are the first to explore the use of glass fiber in combination with signals that use different frequencies,” explains Yingqiang Wang, the first author of the study.

The researchers have woven glass fibers into the fabric at regular intervals. At one end of each glass fiber is a small transmitter that emits sound waves. The other end of each of the glass fibers is connected to a receiver that measures whether the waves have changed.

Each transmitter works at a different frequency. This means it requires little computing power to determine which fiber the sound waves have changed on. Previous smart textiles often struggled with data overload and signal processing issues, since each sensor location had to be evaluated individually.

“In the future, the data could be sent directly to a computer or smartphone in real time,” says Ahmed.

When a glass fiber moves, the length of the acoustic waves passing through it changes, as they lose energy. In the case of a T-shirt, this can be caused by body movement or even breathing.

“We used frequencies in the ultrasonic range, around 100 kilohertz—well beyond the range of human hearing, which is between 20 hertz and 20 kilohertz,” Wang emphasizes.

The researchers have shown that their concept works in the lab. In the future, SonoTextiles could be used in a variety of ways: as a shirt or T-shirt, they could monitor the breathing of asthma patients and trigger an alarm in an emergency.

In sports training and performance monitoring, athletes could receive real-time analysis of their movements, to optimize their performance and prevent injuries. The textiles also have potential for sign language: gloves with this technology could simultaneously translate hand movements into text or speech. They could also be used in virtual or augmented reality environments.

“SonoTextiles could even measure a person’s posture and improve their quality of life as an assistive technology,” adds Chaochao Sun, who shares first authorship of the study. People who want to improve their posture could receive targeted feedback to correct poor posture. The textiles could also indicate when a wheelchair user needs to change position to prevent pressure ulcers.

Although the everyday usability of SonoTextiles is potentially very high, Ahmed adds that there is still room for improvement in terms of practical application. Glass microfibers worked well as sound conductors in the lab, but they could potentially break in everyday use.

“The beauty is that we can easily replace the glass fibers with metal. Sound also propagates effectively through metal,” explains Ahmed. “We would like to expand our research in this direction and also into other applications.”

The researchers now want to make the system more robust and examine how the electronics can be better integrated into the textiles.

The research appears in Nature Electronics.

Source: ETH Zurich

Related

‘Living electronics’ monitor and heal inflamed skin

Team mimics spiders to make fibers for smart textiles

Smart clothing monitors the wearer’s heart

New “smart clothing” uses conductive nanotube thread to continuously monitor the heart.

Researchers sewed the fibers into athletic wear to monitor the heart rate and take a continual electrocardiogram (EKG) of the wearer.

The fibers are just as conductive as metal wires, but washable, comfortable, and far less likely to break when a body is in motion.

On the whole, the enhanced shirt was better at gathering data than a standard chest-strap monitor taking live measurements during experiments. When matched with commercial medical electrode monitors, the carbon nanotube shirt gave slightly better EKGs.

“The shirt has to be snug against the chest,” says Lauren Taylor, a graduate student at Rice University and lead author of the study in Nano Letters. “In future studies, we will focus on using denser patches of carbon nanotube threads so there’s more surface area to contact the skin.”

The researchers note the nanotube fibers are soft and flexible, and clothing that incorporates them is machine washable. The fibers can be machine-sewn into fabric just like standard thread. The zigzag stitching pattern allows the fabric to stretch without breaking them.

The fibers provide not only steady electrical contact with the wearer’s skin but also serve as electrodes to connect electronics like Bluetooth transmitters to relay data to a smartphone or connect to a Holter monitor that can be stowed in a user’s pocket, Taylor says.

Zigzag gives nanotube thread its stretch

The lab of Matteo Pasquali, a professor of chemical and biomolecular engineering, of chemistry, and of materials science and nanoengineering, introduced carbon nanotube fiber in 2013.

Since then the fibers, each containing tens of billions of nanotubes, have been studied for use as bridges to repair damaged hearts, as electrical interfaces with the brain, for use in cochlear implants, as flexible antennas, and for automotive and aerospace applications.

The original nanotube filaments, at about 22 microns wide, were too thin for a sewing machine to handle. Taylor says the researchers used a rope-maker to create a sewable thread, essentially three bundles of seven filaments each, woven into a size roughly equivalent to regular thread.

“We worked with somebody who sells little machines designed to make ropes for model ships,” says Taylor, who at first tried to weave the thread by hand, with limited success. “He was able to make us a medium-scale device that does the same.”

She says it’s possible to adjust the zigzag pattern to account for how much a shirt or other fabric is likely to stretch. Taylor says the team is working with Mehdi Razavi and his colleagues at the Texas Heart Institute to figure out how to maximize contact with the skin.

Better than Kevlar

Fibers woven into fabric can also be used to embed antennas or LEDs, according to the researchers. Minor modifications to the fibers’ geometry and associated electronics could eventually allow clothing to monitor vital signs, force exertion, or respiratory rate.

Taylor notes other potential uses could include human-machine interfaces for automobiles or soft robotics, or as antennas, health monitors, and ballistic protection in military uniforms.

“We demonstrated with a collaborator a few years ago that carbon nanotube fibers are better at dissipating energy on a per-weight basis than Kevlar, and that was without some of the gains that we’ve had since in tensile strength,” she says.

“We see that, after two decades of development in labs worldwide, this material works in more and more applications,” Pasquali says. “Because of the combination of conductivity, good contact with the skin, biocompatibility, and softness, carbon nanotube threads are a natural component for wearables.”

The wearable market, although relatively small, could be an entry point for a new generation of sustainable materials that can be derived from hydrocarbons via direct splitting, a process that also produces clean hydrogen, Pasquali says.

“We’re in the same situation as solar cells were a few decades ago,” Pasquali says. “We need application leaders that can provide a pull for scaling up production and increasing efficiency.”

Additional coauthors are from the University of Pennsylvania and Rice. The US Air Force, the American Heart Association, the Robert A. Welch Foundation, the Department of Energy, the Department of Defense, and a Riki Kobayashi Fellowship from the Rice Department of Chemical and Biomolecular Engineering funded the work.

Source: Rice University

Related

Heart and lung sensor chip is smaller than a ladybug

‘Smart’ fabric boosts wearable device signals to save power

Stretchy electronic ‘tattoo’ monitors heart disease