The “sensing skin” technology detects cracks in concrete (as in top image) and reports when and where the damage took place (as in bottom image). Photo: Aku Seppänen.

Researchers from North Carolina State University and the University of Eastern Finland have developed “sensing skin” technology that can be painted onto a structure—like a bridge or nuclear facility—to both detect and report damage. It can be used as an early warning system that allows engineers to respond to a problem before it becomes serious.

“The sensing skin could be used for a wide range of structures, but the impetus for the work was to help ensure the integrity of critical infrastructure such as nuclear waste storage facilities,” says Dr. Mohammad Pour-Ghaz, an assistant professor of civil, construction and environmental engineering at NC State and co-author of a paper describing the work.

“The idea is to identify problems quickly so that they can be addressed before they become big problems and—in the case of some critical infrastructure—so that public safety measures can be implemented,” Pour-Ghaz says.

How it works
The skin is an electrically conductive coat of paint that can be applied to new or existing structures. The paint can incorporate any number of conductive materials, such as copper, making it relatively inexpensive. It is also easy to apply by roller, brush, or spray.

Electrodes are applied around the perimeter of a structure. The sensing skin is then painted onto the structure, over the electrodes. A computer program then runs a small current between two of the electrodes at a time, cycling through a number of possible electrode combinations.

Every time the current runs between two electrodes, a computer monitors and records the electrical potential at all of the electrodes on the structure. This data is then used to calculate the sensing skin’s spatially distributed electrical conductivity. If the skin’s conductivity decreases, that means the structure has cracked or been otherwise damaged.

The researchers have developed a suite of algorithms that allow them to both register damage and to determine where the damage has taken place.

“Determining the location of the damage based on the measured electrode potentials is a challenging mathematical problem,” says Dr. Aku Seppänen, an Academy Research Fellow in the Department of Applied Physics at the University of Eastern Finland and co-author of the paper. “We had to develop new computational methods to more reliably determine where the damage is. Ultimately, I think our work represents an advance over previous algorithms in terms of accuracy.”

The researchers have demonstrated the effectiveness and accuracy of the sensing skin on a small scale, using concrete beams less than a meter wide.

“Our next step is to extend this to large geometries,” Pour-Ghaz says. “We want to show that this will work on real-world structures.”

The paper, “Electrical impedance tomography-based sensing skin for quantitative imaging of damage in concrete,” was published online June 18 in the journal Smart Materials and Structures. The research was supported in part by the Academy of Finland.