A Clever Solution: Sensors That Repair Themselves

I love it when someone comes up with an ingenious solution to a problem, like the self-healing sensor discussed in a paper that came out this month. I won’t go into the entire sensor, but want to explain the “self-healing” part, since that’s what I think is so clever. (The paper itself is here and an overview is here).

First, the problem: engineers who study how various materials and structures behave under stress, use sensors to monitor that behavior. Those sensors are freakin’ worthless if they break. And, sometimes, replacing them is a pain in the, um, neck.

Solution: make sensors that can fix themselves. Here’s how the researchers did it: each sensor contains two glass optical fibers that run through a reservoir filled with ultraviolet(UV)-curable resin. The ends of the glass fibers are aligned with each other, but separated by a small gap. Focused beams of infrared (IR) and UV light run through one of the fibers. When the tightly focused UV beam hits the resin, the resin hardens, creating a thin polymer filament that connects the glass fibers – creating a closed circuit for the IR light. The rest of the resin in the reservoir remains in liquid form, surrounding the filament.

That’s interesting enough, but here’s the cool part: if the polymer filament breaks under stress, the liquid resin surrounding the filament rushes into the gap, comes into contact with the UV beam and hardens – repairing the sensor automatically (see the three-panel image below). Like all elegant solutions, it makes you wonder why no one has thought of it before.

The paper, co-authored by Young Song and Kara Peters, is published in this month’s issue of Smart Materials And Structures.