Energy-harvesting radios remove the need for batteries

Kansas State University engineers are helping a semiconductor manufacturer implement its idea of an energy-harvesting radio that could transmit data without ever needing a change of batteries.

Bill Kuhn, Professor of electrical and computer engineering, and Xiaohu Zhang, master's student in electrical engineering, are developing the radio for Peregrine Semiconductor, a San Diego-based integrated circuit manufacturer.

"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," Kuhn said.

"But those devices need to have their batteries changed. This radio doesn't."

Peregrine is looking at possible applications for the technology, including monitoring stress, temperature and pressure on bridges and other structures.

Ron Reedy, Peregrine's chief technical officer, said that fulfilling this vision of autonomous sensors requires highly integrated, low-power radio chips similar to the kind that K-State and Peregrine have demonstrated to NASA's Jet Propulsion Laboratory on Peregrine's silicon-on-sapphire technology.

Meanwhile, the engineers are looking at the design challenges of a radio system like this. Kuhn and Zhang have been working on the project for over 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 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, Kuhn said that energy-harvesting radios could be powered by different ways, including electrochemical, mechanical or thermal energy.

The demonstration board that Zhang created includes a microprocessor to store data before it's transmitted via radio. The radio used is the ‘Mars chip’ that Kuhn helped develop in a project he and a team from K-State, Cal Tech's Jet Propulsion Laboratory and Peregrine undertook for NASA. The team developed a micro transceiver to use on Mars rovers and scouts.

When the stored data is ready to be transmitted, 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 that a computer can translate into meaningful information, such as telling an engineer the stress or strain on the underside of a bridge.

Kuhn said that it's like sending a text message from one mobile phone to another: after data are transmitted through the air, the recipient's mobile phone turns that data back into text that can be understood.

Kuhn and Zhang are looking to perfect the radio system design. This includes determining which frequencies to use based on and how the environment affects radio waves indoors versus outdoors.

The engineers also have to look at how noise and other factors may limit the sensitivity of the receiver that's getting the data from all the sensors.

Because the 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.