Self-healing sensor measures strain in structural materials

The sensor could be used to help make decisions about structural safety in the wake of earthquakes, explosions or other events.

Engineers use sensors to measure the strain exerted on materials, but a flaw in such sensors is that they can break under stress. However, a sensor that can no longer provide information to users doesn’t necessarily mean that the material they were monitoring has been irreparably harmed.

‘To address this problem, we’ve developed a sensor that automatically repairs itself, in the event that it is broken,’ said Dr Kara Peters, an associate professor of mechanical and aerospace engineering at NC State and co-author of a paper describing the research.

The sensor can reportedly stretch and compress along with the material it monitors. An infrared (IR) light wave runs through the sensor and detects these changes in length, which tells how much strain the material is undergoing.

The sensor contains two glass optical fibres that run through a reservoir filled with ultraviolet (UV)-curable resin. The ends of the glass fibres are aligned with each other, but separated by a small gap. Focused beams of IR and UV light run through one of the fibres. When the tightly focused UV beam hits the resin, the resin hardens, creating a thin polymer filament that connects the glass fibres, creating a closed circuit for the IR light. The rest of the resin in the reservoir remains in liquid form, surrounding the filament.