A new fiber-optic sensor made from stretchy rubber rather than glass can be integrated into wearable electronics and measure movement. The sensors can also quantify the force of stretching, bending, and pressing movements, so they could be used to gather data for sports medicine and physical therapy.
Most wearable sensing technology detects motion but can’t measure the associated forces, says Robert F. Shepherd, an expert in soft materials at Cornell University who led the sensor development team. Force can provide useful information, like where a repetitive stress injury is likely to occur.
Scientists have alreadycreated stretchable force sensors that work by detecting changes in electrical resistance or charge. Shepherd says optical devices have advantages. “When you use photons instead of electrons, you have a whole different materials space you can work with. Instead of having to put conductive particles in rubber, you just need the rubber itself.” Avoiding electronic materials should also make the sensors impervious to electromagnetic interference and moisture.
Shepherd’s sensors are made of two polyurethane cores wrapped together in a silicone casing. One core has areas that contain colored organic dyes (Science 2020, DOI: 10.1126/science.aba5504). Stretching, bending, or pressing the sensors changes the intensity and the color of the light that travels through them, indicating how the sensors deform and the force of that deformation. “A big advantage of this system is that it uses really simple elements and raw materials that you can get off the shelf,” says Hedan Bai, a graduate student who developed the sensor.
The researchers made a glove outfitted with the fiber-optic sensors. Such a device could be used to track how much force, for example, an ace pitcher’s hand experiences when throwing a fastball. Shepherd’s company Organic Robotics has licensed the sensors.
Zhenan Bao, an expert in wearable electronics at Stanford University, calls the work “a great advancement for optical fiber-based sensors for soft robotics.” Using different colors to read out information from different locations is a creative idea, she says in an email. “I can see a lot of new possibilities with this approach.”