"Smart fabric" strain sensor combines strength and sensitivity
In order to monitor their wearers' movements, smart fabrics typically incorporate strain-measuring sensors. And while such sensors are often impractically fragile, Harvard University scientists have created a new one that can really take a beating.
At the heart of the prototype device is an array of electrically conductive carbon fibers, sandwiched between two pre-strained sheets of an elastic polymer. The individual fibers are arranged in a pattern known as a serpentine meander. This means that like a snake's undulating body, they go back and forth from side to side.
As a result, the carbon fiber array is sort of like a flat Slinky, which stretches apart when pulled from either end. As the fibers are pulled farther away from one another, however, the electrical conductivity of the sensor decreases correspondingly. Therefore, by continuously monitoring an electrical current that is passed through the device, it is possible to determine how much strain it's experiencing.
What's more, the sensor is very sensitive, with even tiny movements of the fabric producing a reading. According to the researchers, there's usually a trade-off with such devices, in that their fragility increases along with their sensitivity. This highly-sensitive strain sensor, however, can reportedly survive being hit with a hammer, run over by a car, stabbed with a scalpel, and going through 10 washing machine cycles.
Additionally, unlike other sensors that offer similar sensitivity, the Harvard one doesn't incorporate expensive materials, not does it require specialized production facilities.
In lab tests, the device was incorporated into a fabric sleeve worn by a volunteer. By detecting changes in strain associated with the flexing of that person's forearm muscle, the technology was able to identify hand gestures including a fist, open palm, and a pinching motion.
A paper on the research, which is being led by Oluwaseun Araromi, was recently published in the journal Nature.
The sensor is demonstrated in the video below.