Clarkson University researchers have developed a system that uses the vibrations caused by traffic passing over a bridge to power wireless monitoring sensors - without the use of batteries.
The new system "harvests" the vibrations through the use of an aircore tubular linear generator which responds to one of the natural vibration frequencies of the bridge. Each time a car or a lorry passes over the bridge, even in the different lane from the sensor installation, the whole structure vibrates and excites the mover in the generator producing power for the sensor modules.
On each sensor module, the alternating current from the generator is first converted to direct current. Then, energy is accumulated until the power becomes sufficient to perform a useful task. When it is, the sensors perform both measurement and wireless transmission functions.
'Hermetically sealed wireless sensors powered by bridge vibration can remain on the bridge without need of maintenance for decades, providing continuous monitoring of such parameters as ice conditions, traffic flows and health status,' said Assistant Prof Edward S. Sazonov from the university's department of electrical and computer engineering, who developed the technology along with Prof Pragasen Pillay.
An experiment that proved the viability of the concept was conducted in June 2007 using an energy harvester clamped to the bottom flange of a girder on the RT11 bridge in Potsdam, New York.
When the power transferred from the harvester to the sensor module became sufficient, it left sleep mode, made a temperature measurement and then transmitted the datum over a wireless interface. A receiver module connected to a portable computer captured the datum and displayed its reception time, sensor ID and temperature value on screen.
The researchers are now working on using the energy harvesting idea to power sensors in passenger cars.