PRINCETON, NJ—Engineers at Brown University, Princeton University and Rice University have developed a low-power, inexpensive way for a large number of devices, such as machines in factories, to share information wirelessly by efficiently using signals at untapped frequencies.

The new tag is the first of its kind that can use backscattering in the subterahertz range, a high frequency portion of the radio spectrum. This range can support high-speed data transmission across broad bandwidths.

The development means it could be possible to power signal transmission for dense networks of devices using passive tags, saving significant power and infrastructure compared to conventional wireless systems.

“I believe this technology will find applications in many interesting settings,” says Yasaman Ghasempour, Ph.D., assistant professor of electrical and computer engineering at Princeton University. “Despite the conventional wisdom….it is possible to have low-power, scalable communication in the subterahertz range.”

According to Ghasempour, the new technology could enable low-cost, efficient real-time monitoring in industrial settings, such as tracking the condition of robots, by eliminating the need for power-hungry signal transmitters.

Backscattering occurs when a central reader sends a signal to a sensor tag to gather information, and the tag reflects this ambient signal directly back to the reader. It is already used in simple systems like building entry cards, but until now has only been possible at low frequencies.

The low frequency limit poses a problem when many devices try to communicate at the same time, because when more signals are introduced, they are more likely to run into one another and get jumbled up. Traditional backscatter designs also have slow communication speeds, because lower frequency signals have limitations on how much information can travel back and forth at once.

“Using backscattering at higher frequencies is challenging, because the signals are more susceptible to fading as they propagate and must be very precise to travel long distances,” says Ghasempour. “The reader has to form a narrow pencil-shaped beam to shine into the tag’s precise location, and the low-power tag should do the same without consuming any power."

Traditional backscatter tags reflect signals back to their source using simple antennas that typically broadcast the energy in all directions, causing only a portion of the energy to reach back to the reader. While some advanced tags can adjust the direction of their signal, their ability to do so is limited, and they’re restricted to a narrow range of frequencies.

Achieving subterahertz backscattering required Ghasempour and her colleagues to rethink the entire architecture of the tag. They also developed an entirely new antenna structure.

The new antennas allow the direction of the signal to change automatically in response to changes in frequency. By doing this, the tag can “steer” the signal to enable longer range communication and avoid interference from other signals.