An engineer at University of Maryland in College Park has developed a wireless, self-powered safety sensor for bridges, and started a company to take the device to market. Electrical engineering researcher Mehdi Kalantari says the sensor can provide public works authorities with an effective structural monitoring system for bridges at about 1 percent of the cost of current wired technology.
Kalantari’s sensors — each about the size of a playing card — measure variables related to structural integrity of a bridge, such as strain, vibration, tilt, acceleration, deformation, and cracking. Each sensor is deployed at a strategic point on the support structure, and feeds back measurements about every minute to a central computer, where the data are analyzed.
The sensors are less than five millimeters thick and have four thin, flexible layers, each layer with a specific function. The first layer senses and measures structural parameters. The second layer stores energy. The third layer communicates data. The fourth and outer layer harvests energy from ambient light and radio waves.
The data analysis flags serious structural problems that are more obvious and easier to interpret, and thus trips an alarm very quickly. For problems in their early stages, the analysis is more subtle, and may take a few days for the system to gather enough data to report a structural integrity issue.
Kalantari is working with the Maryland Department of Transportation to test the sensors. Since August 2010, Kalantari has had eight sensors installed on a bridge on the Maryland section of heavily traveled Capital Beltway around Washington, D.C. A second test involves a bridge on I-70 near Frederick in the western part of the state.
The deterioration of older bridges in the U.S. is highlighted in the periodic report card issued by the American Society of Civil Engineers, that indicates more than one in four U.S. bridges are either structurally deficient or functionally obsolete. The 2007 collapse of the I-35 bridge in Minneapolis that killed 13 people dramatized the problem in more graphic terms.
The bridge over I-35 that replaced the one that collapsed has an electronic monitoring system, but the sensors are all hard-wired. To install wired sensors on existing bridges would be prohibitively expensive, says Kalantari, noting that wireless sensors could do the job at about one percent of the cost of wired technology. He calculates that an average-sized highway bridge would need about 500 sensors at $20 each, for a total cost of about $10,000.
Kalantari believes the sensor technology and economic arguments for it are both sound, and has started the company Resensys LLC to take the product to market. He anticipates beginning production of the devices in September.
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