Sensors provide answers in emergencies

An earthquake strikes a large city, wrecking roads and bridges, stranding rush-hour commuters, trapping office workers inside high-rise buildings.

As director of the city's transportation authority, you have minutes to make a momentous decision. What is the safest, fastest route that rescue teams can take to travel to hard-hit areas of the city? Which bridges, even if damaged, can still support traffic loads?

Questions like these are increasingly on the minds of structural engineers and emergency personnel as the world faces continuing unpredictable weather conditions.

The answers to the questions, says Yunfeng Zhang, an assistant professor of civil and environmental engineering at Lehigh University, can be provided by sensors "“ networks of tiny sensors with built-in computer chips that are attached to a bridge to monitor its safety and performance.

Sensors deployed strategically on a bridge, says Zhang, can provide a high-resolution, multi-dimensional picture of the health of a structure, giving engineers vital information about a bridge's performance and, in the aftermath of a catastrophe, its ability to carry traffic.

To be useful in the event of an earthquake or other emergency, says Zhang, sensor data must be transmitted in real time, virtually without delay, to remote processing centers for interpretation and then to decision-makers.

Wired sensors can transmit data in real time but they have limitations, says Zhang. Installing and maintaining the wires is costly and labor-intensive. Wires degrade and are prone to interference from electro-magnetic signals. And wires themselves might get damaged in earthquakes.

Zhang recently received a five-year, $400,000 CAREER Award from the National Science Foundation to develop wireless sensor networks for bridges and other structures with the aim of improving the transmission of sensor data and the ease in accessing the data. The project is titled "Integrated Research and Education in Smart Sensing and Intelligent Structures Technology."

Wireless sensor networks, which are relatively new, avoid many of the problems that hamper wired sensors. But they face obstacles. The relatively narrow communication bandwidth available for civil-engineering wireless sensors can reduce download rates to one kilobyte per second, not nearly fast enough to crunch the enormous amounts of data generated by a bridge in operation.

"Using the sensor data compression algorithm I'm developing," he says, "we can minimise data-downloading time and ultimately download data in real time and evaluate it in near real-time basis."

Zhang's research draws on structural engineering, systems science, information technology, as well as electrical engineering.