Remote infrastructure monitoring via 'smart skin' sensors

As structures such as bridges and parking garages age, the need for improved methods for detecting deterioration is much needed to be able to save lives and prevent economic disorder. In fact, the major bridge failures in recent years have called upon the much needed attention to monitor America's highway bridges and other infrastructures.

Researchers at the Georgia Institute of Technology are developing a novel technology that would facilitate close monitoring of structures for strain, stress and early formation of cracks. Their approach uses wireless sensors that are low cost, require no power, can be implemented on tough yet flexible polymer substrates, and can identify structural problems at a very early stage. The only electronic component in the sensor is an inexpensive radio-frequency identification (RFID) chip.

Moreover, these sensor designs can be inkjet-printed on various substrates, using methods that optimise them for operation at radio frequency. The result would be low-cost, weather-resistant devices that could be affixed by the thousands to various kinds of structures.

"For many engineering structures, one of the most dangerous problems is the initiation of stress concentration and cracking, which is caused by overloading or inadequate design and can lead to collapse—as in the case of the I-35W bridge failure in Minneapolis in 2007," said Yang Wang, an assistant professor in the Georgia Tech School of Civil and Environmental Engineering. "Placing a 'smart skin' of sensors on structural members, especially on certain high-stress hot spots that have been pinpointed by structural analysis, could provide early notification of potential trouble."

Wang is collaborating with a team that includes professor Manos M. Tentzeris of the School of Electrical and Computer Engineering, and Roberto Leon, a former Georgia Tech professor who recently moved to Virginia Tech. The work is supported by the Federal Highway Administration.

Antennas as sensors
The Georgia Tech research team is focusing on wireless sensor designs that are passive, which means they need no power source. Instead, these devices respond to radio frequency signals sent from a central reader or hub. One such reader can interrogate multiple sensors, querying them on their status at frequent intervals.

The researchers' approach utilises a small antenna mounted on a substrate and tuned to a specific radio frequency. This technique enables the antenna itself to function as a stress sensor.