For years, Erik Thostenson and Thomas Schumacher, faculty members at the Center for Composite Materials at the University of Delaware, have been studying the use of carbon nanotube composites as a kind of “smart skin” for bridge structures. Recently, according to the university, the two researchers have built on that work with a new approach called Electrical Impedance Tomography (EIT), which uses surface electrode measurements to create an image of the conductivity of a material or structure.

The researchers applied the approach to a distributed carbon-nanotube-based sensor that may be able to identify weaknesses in bridge structures before a potential collapse. The sensor uses an EIT algorithm to produce a map of changes in the carbon nanotubes to identify small damages that would be otherwise undetectable.

“While the feasibility of employing carbon-nanotube-based composites as sensors has been validated, the typical approach is to use a series of one-dimensional measurements collected from a two-dimensional sensing area,” says Thostenson, an expert in processing composites for sensor applications. “The problem is that this confines the possible damage locations to the grid points of the measurements. EIT, on the other hand, is a true 2-D algorithm.”

The university says there are a number of advantages to the nanotube composite sensor. It can detect damage to a structure of almost any shape. It is also mechanically robust and contains great electrical properties. However, the research team still believes there is room for improvement.

“Although we did encounter some issues with the size of cracks being overestimated and their shapes not being well represented, overall our EIT methodology was able to detect the initiation of damage well before it was visible with infrared thermography,” Schumacher says. “We are in the process of making improvements to the EIT algorithm to increase its accuracy. After that, we plan to demonstrate it in the laboratory, with an aim toward scaling it up for future monitoring of real structures.”