One of the top value propositions for wearables like Fitbit or Apple Watch is the device’s ability to track a user’s activity levels throughout the day. While these smartwatches can gauge general metrics like steps, heart rate, and calories, they don’t provide biometric specifics that are useful for professional athletes—for instance, the speed of a pitcher’s throw or the gate of a runner’s foot.
Nextiles is a Brooklyn-based startup spun out of MIT that is creating wearables, specifically electronic textiles for athletic clothing, to deliver body- and performance-specific metrics gathered from fabric-based sensors.
A Nextiles fabric-based sensor.
Nextiles has merged materials science, circuit design, and traditional sewing techniques to create these sensors, which measure the pressure, stretch, and bend of limb movements and joint positions. By calculating movement metrics, these sensors provide valuable data to athletes on their performance and technique, so they can optimize their training and even prevent injuries.
The company was recently recognized for its innovation with an induction into both Material ConneXion as well as the Council of Fashion Designers of America’s Innovation Index. All About Circuits interviewed Nextiles CEO George Sun to hear more about the company’s sports-specific e-textiles and its plans for the future.
How Nextile’s E-textile Technology Works
A Nextile’s product largely consists of two main components: e-textile based sensors, which are woven into the clothing, and a central module.
In the textile part of the system, the sensors are constructed by weaving specific electrical patterns into fabric using conductive threads. By weaving the threads in special patterns, Nextiles creates piezo-resistive sensors that vary in resistance based on the mechanical strain imposed on them.
Nextiles’ conductive threads, including polyester, copper, stainless steel, silver, chrome, and a yarn stainless-steel blend.
Similar to a strain gauge, the system works by measuring the strain between each conductive fiber to provide information about a user’s movements. Nextiles organizes patterns of conductive threads into layers of conductive and non-conductive textiles. This might yield, for example, a digitated cross-linked pattern that changes impedance or conductivity when stretched.
“We’re actually using the strain between every conductive fiber and then measuring the mechanical pulls and twists from there,” Sun explains. “For instance, we might determine that a specific change in the fabric meant you bent your arm 45 degrees, or you moved your shoulder by two centimeters in X direction.”
Nextile’s sensors measure fabric deformation to calculate the body’s movements.
These analog signals from the sensors are then sent to a central module. This central module is a flexible PCB consisting of an MCU, a Bluetooth device, and a 3.7 V lithium-ion polymer battery, which holds an 8–12 hours charge with active use. It is in this central module that the sensor readings are converted from analog to digital, interpreted, and then communicated via Bluetooth to a phone or computer. Because the fabric-based sensors are passives, they only draw several hundred µAmps of current to measure changes in the signal.
This central module or “controller” is the only part not actually woven into the fabric; instead, it is stitched into the perimeter in a detachable tab sheet. While this module is still somewhat limited by device size and battery physics, the entire device is about as thick as three quarters to maintain the wearer’s comfort.
What Makes Nextiles Different?
Nextiles’ technology stands apart from other e-textile competitors in two distinct ways.
First, in contrast to many e-textile research confined in university settings, Nextiles has pushed its manufacturability to a production scale.
“We’re not limited to exotic materials or esoteric processes. We can literally use sewing equipment every day to sew our sensors into clothing,” Sun remarks. “As long as you have a needle and thread, you can use our materials and build your own sensors.”
Illustration of how the sewing layout can affect the fabric-based sensor’s sensitivity and conductivity.
This achievement is possible thanks to the standard materials Nextiles uses. Namely, the company develops its sensors using piezoresistive and conductive knit, woven, and nonwoven textiles derived from materials like polyester, nylon, and spandex. Additionally, Nextiles’ conductive threads, largely based on stainless steel or silver, are abundant and readily accessible, decreasing complexity and price for the company’s products.
The second differentiator is the physical patterns the company creates with its threads. Nextiles uses a proprietary technique to interweave its conductive fabrics such that the deformation of each thread (relative to others) can be sensed and understood by an MCU.
In a company whitepaper, Nextiles explains:
“Unlike traditional sensors which are confined to the controller unit itself (e.g. Fitbit, smart watches), the construction of these sensors is entirely divorced from the controller itself. As long as the threads can be threaded between the sensors and controller, the controller can be isolated in an area that is convenient and form-fitting, for example at the waist or back.”
Nextiles’ e-textiles have also undergone testing to determine their resilience to washing and drying. Results revealed that after five cycles, the fabric-based sensors maintained both sensing capability and conductive qualities.
Enhancing Fitness With Fabric
How might Nextiles technology work in action? While wearing a sports tee interwoven with Nextiles’ technology, a user would power the shirt on and connect the controller to a phone or watch via BLE. This way, the users can store data locally or send it to a connected device in real-time. Once the user has finished using the shirt, he or she can remove the controller for USB-C charging and wash the shirt. Nextiles can build custom APIs alongside its e-textiles to store, mine, and deliver biometric data however a partner may like.
Prototype of a motion-sensitive sleeve.
Moving forward, Nextiles has its sights set on professional sports, where its special sensors could provide invaluable feedback to athletes. The company is partnering with (currently unannounced) sports brands to help bring its product to the athlete.
Sun also explained that Nextiles is actively researching the possibility of kinetic energy harvesting to charge the sensors.
“Our fabrics are located over joints that move quite frequently, which puts a lot of power through them,” Sun comments. “Is it possible to collect that kinetic motion and then store that as potential energy in the form of a capacitive charge for a battery?”
Current ambient energy-harvesting materials are too costly and large to embed in fabric, but future advances in materials science may make kinetically charged e-textiles a reality.
All images used courtesy of Nextiles.
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