Pushing the potential of piezoelectric devices
Imagine a future in which simply driving on the highway generates electricity to power our homes and businesses. California thinks that may be possible. The state’s Energy Commission announced last month that it is investing $2 million to study whether devices that employ piezoelectric crystals -- which transform mechanical pressure into electricity -- can be seeded into roadways and used to generate power.
California hasn’t yet chosen a company or university to develop and test the technology, however, and some experts are skeptical about the potential for “piezo” to be sufficiently cost effective.
“I think piezo is actually fairly impractical” for roadway generation of electricity, University of Washington professor of civil and environmental Joe Mahoney said. Using piezo in roadways is unlikely to be cost effective, he said, because while the piezo devices are themselves very durable they would have to be replaced every time the highway is repaved. And since the piezo devices require a relatively soft roadway -- asphalt rather than concrete -- repaving would be needed every 10 to 20 years. Given the numbers of piezo devices required to generate a reasonable amount of electricity, those costs could be prohibitive.
Still, while Mahoney isn’t optimistic about piezo as a source for gathering energy from roadways, he is energized by their potential as infrastructure sensors. “It has been proven that piezo has a lot of applications in monitoring,” he said.
That’s what Shantanu Chakrabartty, professor of computer science and engineering at Washington University in St. Louis, is exploring. Instead of using piezo devices’ ability to generate electricity for harvesting, Chakrabartty is testing how the devices can detect stress on structures such as bridges and buildings. An added advantage is that, since piezo devices generate their own power when they are compressed by infrastructure, they do not require batteries and can, as a result, be embedded deep in infrastructure.
Under a four-year, $1.1 million grant from the National Science Foundation, Chakrabartty and his team are currently deploying piezo sensors underneath the deck of the Mackinac Bridge in Michigan, the largest suspension bridge in the western hemisphere. According to Chakrabartty, the bridge authority wants to use the sensor network to better understand how cracks propagate and the impact of varying traffic patterns.
The tiny charge that is generated when one of Chakrabartty’s piezo devices is compressed is recorded in the sensor’s on-board flash memory. The tiny sensors -- which range in size up to a few centimeters -- are connected to a telemetry box that is about 10 centimeters long. “We can collect data from the sensors just by driving over the bridge,” Chakrabartty said.
Data collection will likely become even easier. Under the NSF grant, the team will construct a virtual cloud-based infrastructure for the sensors that will allow data to be collected and accessed remotely and on moment’s notice.
The piezo sensors aren’t suited only to monitoring bridges. According to Chakrabartty, his team is also working with the transportation departments in Michigan and Texas to deploy piezo sensors to monitor pavement conditions. While the embedded sensors would have to be replaced when repaving occurs, the number of piezo sensors used for monitoring conditions would amount to only a fraction of those required for generating electricity, making the solution more economical. “For our purposes, we are looking at one sensor per cubic meter,” Chakrabartty said. His goal is to get the cost of the sensors down to less than a dollar each.
Chakrabartty also said he has another grant from the NSF to develop the technology for use in buildings to detect earthquake damage or structural weaknesses. “The hope is to do forensics after a seismic event or an explosion,” he said. What’s more, data from the sensors may be used before an event to give engineers critical data to determine where there are vulnerabilities.
Posted by Patrick Marshall on Oct 28, 2016 at 1:39 PM