Bridge sensors allow for monitoring its safety, but the problem is when you have to change the batteries on the hundreds of sensors across the span.

That is where energy harvesting comes in. An energy-harvesting radio could transmit important data like stress measurements on a bridge without needing a change of batteries, said engineers at Kansas State University, who are working with a semiconductor manufacturer to implement the idea.

“This type of radio technology may exist in your house, for instance if you have a temperature sensor outside that radios data to a display inside,” said Bill Kuhn, K-State professor of electrical and computer engineering. “But those devices need to have their batteries changed. This radio doesn’t.”

San Diego-based Peregrine Semiconductor is looking at possible applications for the technology. This could include monitoring stress, temperature, and pressure on bridges and other structures.

Ron Reedy, Peregrine’s chief technical officer, said the concept requires highly integrated, low power radio chips, which K-State and Peregrine demonstrated to NASA’s Jet Propulsion Laboratory.

K-State engineers are looking at the design challenges of a radio system like this. Kuhn and Xiaohu Zhang, a Master’s student in electrical engineering, have been working on the project for a little more than a year. They are creating a demonstration to test how far the signals can travel from the sensors.

Zhang constructed a demonstration board using solar cells from inexpensive calculators to power the radio. The board has capacitors that capture and store the light energy to power the radio without a battery. Although this prototype captures and stores light energy, Kuhn said energy-harvesting radios could get power a number of different ways, including by electrochemical, mechanical, or thermal energy.

The demonstration board Zhang created includes a microprocessor to store data before transmitting via radio. The radio used is the “Mars chip” Kuhn and his team helped develop for NASA. They developed a micro transceiver to use on Mars rovers and scouts.

Kuhn said the energy-harvesting radio they are working on now is an example of a NASA spinoff.

When the stored data is ready for transmission, the radio sends out a data-burst. In Zhang’s model, this happens every five seconds. It may just sound like a “blip,” but that burst contains data a computer can translate into meaningful information, such as telling an engineer the stress or strain on the underside of a bridge. Kuhn said it is kind of like sending a text message from one cell phone to another: After data transmit through the air, the recipient’s cell phone turns that data back into understandable text.

Kuhn and Zhang are working toward perfecting the radio system design. This includes determining which frequencies to use based on how the environment affects radio waves indoors versus outdoors. They also have to look at how noise and other factors may limit the sensitivity of the receiver that is getting the data from all the sensors.

Because these sensors save data in their microprocessors, Kuhn and Zhang are working on timing and wake-up commands that tell the sensors when to send the stored information to the receiver. Through engineering analysis, they are determining tradeoffs between power requirements, data-rate, and transmission range issues.