Researchers at the Massachusetts Institute of Technology and University of Potsdam in Germany have pioneered a new way to continually monitor the physical condition of bridges, aircraft, buildings and other large structures. They have produced a material, or skin, that varies its electrical charge whenever it experiences a change in pressure.
"We have just demonstrated that we can use this skin to locate and detect cracks," said Simon Laflamme, who led the research as a graduate student in the MIT Department of Civil and Environmental Engineering. "It is a very large stress gauge."
They have proposed developing patches of the material that can be affixed to areas where cracks and stresses are likely to appear, such as the undersides of bridges. The skins would detect any potential problems and relay their findings back through a wireless network.
Such sensors, should they be widely adopted, would add to the tsunami of sensor data that is expected to flood networks and computer systems in the years to come.
The technology could help better gauge the condition of the world's bridges, buildings and other structures. Today, most structures are inspected visually, a process that is expensive, time-consuming and inexact. A sensor network covering such structures could eliminate, or at least reduce, the need for visual inspections.
Each patch would be electronically charged and able to detect stress or other problems by a change in its capacitance, or the amount of electricity it holds.
"The patch is very sensitive. If there is some elongation of the sensor, or a change in curvature through a crack or a load, its capacity to store energy can change dramatically," Laflamme said.
The researchers built prototypes using commercially available silicon fabric, but found it too thin and flexible for the task. So they fashioned a new material using a flexible thermoplastic polymer mixed with titanium dioxide, a mixture that should be very electronically sensitive to changes in pressure.
The researchers will continue to work on commercializing the system. The polymer still needs to be fine-tuned, but they are confident it could eventually be produced in large rolls at low cost. "It is cheap to produce," Laflamme said. They must also figure out how to recharge the wireless radios that each patch will need to communicate. The patches themselves will need no power once charged, Laflamme said.
Thus far, the researchers have been issued one U.S. patent on their technology and have written their results up in two scientific journals, "Structural Control Health Monitoring" and the "Journal of Materials Chemistry."
Overall, the U.S. infrastructure of bridges, tunnels and roads is in very poor shape, the American Society of Civil Engineers (ASCE) declared in 2009 (though some U.S. government stimulus funding has since been allocated for improvements). In 2007, a Minnesota bridge spanning the Mississippi river collapsed, killing 13 people.
Laflamme and his team are not the only ones to develop systems to continually monitor infrastructure. The Johns Hopkins University Applied Physics Laboratory developed a wireless embedded sensor platform that could monitor the corrosion of bridges and relay the results back for analysis.