Combining low-cost LEDs and dyes, the stretchable sensor, say the researchers, could give soft robotic systems - and anyone using augmented reality (AR) technology - the ability to feel the same rich, tactile sensations that mammals depend on to navigate the natural world. The researchers drew inspiration from silica-based distributed fiber-optic sensors, which detect minor wavelength shifts as a way to identify multiple properties, such as changes in humidity, temperature, and strain.
However, while such sensors have been used for monitoring mechanical deformations in stiff infrastructures such as bridges, roads, and buildings, silica fibers aren't compatible with soft and stretchable electronics. Intelligent soft systems also present their own structural challenges, say the researchers.
"We know that soft matters can be deformed in a very complicated, combinational way, and there are a lot of deformations happening at the same time," says doctoral student Hedan Bai, a co-lead author of a paper on the research. "We wanted a sensor that could decouple these."
The researchers' solution was to make a stretchable lightguide for multimodal sensing (SLIMS) - a long tube that contains a pair of polyurethane elastomeric cores. One core is transparent, while the other is filled with absorbing dyes at multiple locations and connects to an LED. Each core is coupled with a red-green-blue sensor chip to register geometric changes in the optical path of light.
The dual-core design, say the researchers, increases the number of outputs by which the sensor can detect a range of deformations – pressure, bending or elongation – by lighting up the dyes, which act as spatial encoders. The researchers then paired that technology with a mathematical model that can decouple, or separate, the different deformations and pinpoint their exact locations and magnitudes.
While distributed fiber-optic sensors require high-resolution detection equipment, SLIMS sensors can operate with small optoelectronics that have lower resolution, making them less expensive, simpler to manufacture, and more easily integrated into small systems.