A team from MIT have demonstrated a new fabrication technique that produces comfortable and form-fitting smart textiles able to sense their wearers posture and motions. The process, which is based around innovative digital knitting technology for soft electronics, improves on current approaches of embedding electronic devices into textiles, and could be scaled up for manufacturing with potential applications in sport science, robotics, prosthetics, rehabilitation, gaming, and augmented/virtual reality.
The research, presented at the IEEE Engineering in Medicine and Biology Society Conference, uses a plastic yarn heated until partially melted, known as thermoforming, which significantly improves the precision of pressure sensors woven into multi-layered knit textiles, which they called 3DKnITS. The process depends on a specially developed hardware and software machine-learning system that measures and assesses data from the pressure sensors in real time.
A digital knitting machine weaves together layers of fabric with rows of standard and functional yarn. The multi-layer knit textile has two layers of conductive yarn knit sandwiched around a piezoresistive knit that alters its resistance when squeezed. To a pattern, the machine stitches the yarn throughout the textile in horizontal and vertical rows – where the functional fibers intersect, they create a pressure sensor.
The thermoforming hardens the multilayer textile into one layer by squeezing and melting the whole fabric together, enhancing its accuracy and allowing the creation of 3D forms such as socks and shoes that fit the size and shape of the user. As the fabric is knit as a grid, a wireless circuit scans rows and columns on the textile, measuring the resistance at each point. This circuit was designed to overcome artifacts caused by “ghosting” ambiguities that happen if the user puts more pressure on two or more separate points at the same time. The pressure sensor data is displayed as a heat map, with the images being fed into a machine-learning model taught to detect the posture, pose or motion of the user.
As lead author Irmandy Wicaksono told Materials Today, “With digital knitting, you have this freedom to design your own patterns and also integrate sensors within the structure itself, so it becomes seamless and comfortable, and you can develop it based on the shape of your body”.
The team now hope to work with professionals such as physical therapists, orthopedics, sport coaches and dancers, and to accumulate further data to make the sensor more robust. They also want to investigate how environmental conditions such as temperature and humidity affect its accuracy.
“With digital knitting, you have this freedom to design your own patterns and also integrate sensors within the structure itself, so it becomes seamless and comfortable, and you can develop it based on the shape of your body”Irmandy Wicaksono
Functional fibers and digital knitting produce new smart textiles. Credit: Irmandy Wicaksono/MIT Media Lab