Newswise — Following an earthquake, it's often difficult to determine which buildings, roads or bridges have sustained enough structural damage to make them dangerous. Identifying potentially damaged natural gas pipes and pipelines may be even more important.
An advanced optical strain gauge just developed by two University of Rhode Island researchers may be the key to ensuring public safety under these and other circumstances.
Otto Gregory, associate dean and professor of chemical engineering, and William Euler, professor of chemistry, say that electrical strain gauges are commonly used in many types of structures, but the optical strain gauge they have perfected is up to 100 times more sensitive and can detect strains the more common gauges might miss.
Strain is a basic physical measurement, according to the researchers, which is derived by determining thermal displacement -- expansion or contraction due to temperature changes -- or mechanically by determining the displacement when a load is applied.
"The uniqueness of our gauge is that it is entirely temperature independent," said Gregory. "Regardless of the temperature, it's going to operate effectively without needing to compensate for expansion due to temperature changes. Electrical gauges are annoyingly sensitive to temperature, so they need all sorts of additional circuitry and software to compensate for it. Ours doesn't, so it's cheaper to use, as well as being much more sensitive."
The gauges have been designed to be compatible with fiber optic technology. Thin glass tubes with an inner diameter of just 500 microns (one micron equals one millionth of a meter) are embedded in or attached to a structure, and laser light is pumped into one end of the tube. If the structure becomes strained, the tube is effectively bent and a change in the intensity of light is detected at the opposite end of the tube. The difference in the light signal correlates with the amount of strain affecting the structure.
The patent-pending technology that Gregory and Euler developed is the series of coatings on the tubes that capture and change the intensity of transmitted light. Thin films of semiconductors or polymers are layered on the tubes, and each different layer consists of materials with different light refraction capabilities. "The coatings enhance the responsiveness of the gauges. We wanted coatings that reflect or absorb light, or that lets light leak out," Euler said.
The researchers anticipate the gauges will be used primarily in civil structures like buildings, roads and bridges. In earthquake-prone areas, especially, they believe that use of such a device should become required in building codes. A typical home application would cost approximately $100, similar to installation of a common carbon monoxide detector.
In addition, there are a number of specialty uses for the gauges. Aerospace applications include use on airplane wings, landing gear, and other equipment prone to flexing and fatigue.
The devices can also be used as pressure-sensitive gauges to trigger traffic lights, for instance, or as load sensors to indicate truck weights, elevator overloads, or for anything else that uses an industrial scale.
Gregory and Euler say their gauge is ready for commercial use and can be easily mass produced.
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