Researchers develop Optical Motion and Strain Sensor for wearable applications

From Optical Strain Sensor for Wearable Tech | Optics & Photonics News

sensors that can measure strain, and thus bodily motions, in real time have become a hot commodity. But figuring out an optical sensor that can stand up to large strains, such as those across a bent elbow or a clenched fist, has proved a tough problem to crack.

A team of researchers at Tsinghua University, China, led by OSA member Changxi Yang, now believes it’s come up with an answer: a fiber optic sensor made of a silicone polymer that can stand up to, and detect, elongations as great as 100 percent—and effortlessly snap back to an unstrained state for repeated use


fibers made of polydimethylsiloxane (PDMS), a soft, stretchable silicone elastomer that’s become a common substrate in stretchable electronics. The team developed the fiber by cooking up a liquid silicone solution in tube-shaped molds at 80 °C, and doping the fiber mix with Rhodamine B dye molecules, whose light absorption is wavelength dependent. Because stretching of the fiber will shrink its diameter, leaving the total volume invariant, a fiber extension has the effect of increasing the optical length for light passing through the dye-doped fiber. That increase, in turn, can be read in the attenuation of the fiber’s transmission spectra, and tied to the amount of strain in the fiber.

This could lead to a new generation of “smart clothing”, especially for sport and medical applications.