Shedding a new light on earthquake damage

Detecting structural damage caused by earthquakes will be 100 times easier thanks to a new optical strain gauge, according to its US developers.

Most buildings, bridges, roads and pipelines in earthquake-prone areas are already fitted with electrical strain gauges which track expansion or contraction levels in structures due to temperature changes.

But the new optical gauge uses a waveguide system with coatings of semiconductors, making it up to 100 times more sensitive.

Prof William Euler from the University of Rhode Island, who developed the gauge, claims it is cheaper and more effective than existing ones, and by detecting strains that others miss, it could hold the key to ensuring public safety.

It is made from glass tubes with an inner diameter of just 500 microns. These are coated with layers of semiconductors and then embedded in, or attached to, a structure. Laser light is then beamed into one end of the tube.

If the structure is strained, the tubes are effectively bent and a change in the intensity of light is detected at the opposite end. The difference in the light signal correlates with the amount of strain affecting the structure.

Each layer of semiconductor consists of materials with different light refraction capabilities. The researchers have used polyimide, silicon, aluminium, and ITO coatings and each coating gives different results in terms of sensitivity and dynamic range.

The semiconductors and the waveguide system of hollow tubes are unique to the gauge, making it ultra sensitive. The system, which is relatively inexpensive, also makes the gauge entirely independent of temperature – a problem that hampers the functioning of electrical gauges.

The researchers claim that the gauge has numerous other potential uses – as a pressure-sensitive gauge to trigger traffic lights, as a load sensor to indicate truck weights, in the manufacture of aircraft wings, landing gear, or any other equipment prone to flexing and fatigue.

The gauge is ready for commercial production and can be fitted to already existing structures.