In 2006 Federal Highway Administration listed 25.8% of nation’s 596,842 bridges either as structurally deficient or functionally obsolete. While many of these bridges will remain in service for many years, they need monitoring and rehabilitation.
Presently, bridge monitoring is performed through periodic visual inspections. In the tragic example of I-35W Mississippi River bridge collapse, the bridge passed a visual inspection a year prior to failure.
Many researchers are suggesting installing wireless monitoring sensors that can continuously monitor bridge condition and report any changes that may lead to failure. Wireless sensors are easy to install and can be applied to existing highway infrastructure.
The problem arises in proving power.
Replacing millions and millions of batteries would become a huge logistic problem and add to the expense of maintaining bridges. Another important factor is environmental impact of discarding used batteries.
Intelligent-Systems suggests using vibration of bridges caused by passing traffic, wind and microtremors to power the bridge monitoring sensors.
The battery is completely eliminated from the equation. Hermetically sealed sensors powered by bridge vibration can remain on the bridge for decades and provide continuous monitoring.
Vibration of the bridge is harvested by an aircore tubular linear generator which responds to one of the natural vibration frequencies of the bridge. Each time a car or a truck pass over the bridge, even in the different lane from the sensor installation, the whole structure vibrates and excites the mover in the generator thus producing AC voltages on the output.
A wireless self-powered sensor has the following key tasks:
- Effectively convert AC voltage from the generator to DC voltage that can be used for powering of the sensors. Active intelligent conversion may raise the amount of available energy upto 500%.
- Store the accumulated energy until the level becomes sufficient to perform a useful task.
- Effectively use stored energy to perform a measurement and wireless transmission.
An early prototype of a wireless platform that is now known as AmbioMote a product manufactured and sold by AmbioSystems under a license from Clarkson University.
The devices handles intelligent energy (AC->DC) conversion, significantly boosting the efficiency of energy harvesting. Compared to a regular rectifier-capacitor pair, AmbioMote is capable of capturing 400% greater energy.
According to Crossbow, wireless sensor networks are finding increasing roles in industrial automation, environmental control, asset tracking, and other applications. However, without a seamless link to standard Ethernet networks, data-rich sensor networks are often difficult to analyze, and application development can be time-consuming. The Stargate NetBridge ($449), based on a Linksys NSLU2, may change all that by integrating sensor network management, data visualization and web server, data logging, and traffic management into a single compact package.
Related DailyWireless stories include; Wireless River Monitoring, Low Power WiFi Sensor, Hyperspectral Search, Solar Man, Solis Solar Powered Hotspots, Solar Powered WiMAX & WiFi, Wireless Bridge Monitoring, and Minneapolis Bridge Collapse & Emergency Communications.
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