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A Clever Solution: Sensors That Repair Themselves

An elegant design for a sensor that heals itself. What's not to like about that?

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.

The image on the left shows the polymer filament connecting the glass fibers in the sensor. The middle image shows where the filament has snapped off. The image on the right shows where the resin has rushed into the gap, been exposed to UV light and reconnected the filament - effectively repairing itself.