If the smart textiles of the future are going to survive, their components are going to need to be resilient. Researchers have developed an ultra-sensitive, resilient strain sensor that can be embedded in textiles and soft robotic systems.
The researchers created a design that looks and behaves very much like a Slinky — a solid cylinder of rigid metal that when patterned into a spiral shape, becomes stretchable. The researchers started with a rigid bulk material — in this case carbon fiber — and patterned it in such a way that the material becomes stretchable. The pattern is known as a serpentine meander because its sharp ups and downs resemble the slithering of a snake. The patterned conductive carbon fibers are then sandwiched between two pre-strained elastic substrates.
The overall electrical conductivity of the sensor changes as the edges of the patterned carbon fiber come out of contact with each other, similar to the way the individual spirals of a Slinky come out of contact with each other when you pull both ends. This process happens even with small amounts of strain, which is the key to the sensor's high sensitivity.
Unlike current highly sensitive stretchable sensors that rely on exotic materials such as silicon or gold nanowires, this sensor doesn't require special manufacturing techniques or even a cleanroom. It could be made using any conductive material. The researchers tested the resiliency of the sensor by stabbing it with a scalpel, hitting it with a hammer, running it over with a car, and throwing it in a washing machine 10 times. The sensor emerged from each test unscathed.
To demonstrate its sensitivity, the researchers embedded the sensor in a fabric arm sleeve and asked a participant to make different gestures with their hand including a fist, open palm, and pinching motion. The sensors detected the small changes in the subject's forearm muscle through the fabric and a machine learning algorithm was able to successfully classify these gestures. Such a sleeve could be used in everything from virtual reality simulations and sportswear, to clinical diagnostics for neurodegenerative diseases like Parkinson's Disease.
Another aspect that differentiates the technology is the low cost of the constituent materials and assembly methods. The researchers are exploring how the sensor can be integrated into apparel due to the intimate interface to the human body it provides. The sensor could make biomechanical and physiological measurements throughout a person's day, which is not possible with current approaches.