Researchers have found a low-power, inexpensive way for large numbers of devices, such as machines in factories and equipment in labs, to share information by efficiently using signals at untapped high frequencies.
The technology could immediately enable low-cost, efficient real-time monitoring in industrial settings, such as tracking the condition of manufacturing robots or detecting gas leaks in refineries, by eliminating the need for power-hungry signal transmitters. The researchers said that with some engineering improvements, the technology could be used for large-scale applications like smart cities and agriculture.
The technology is an advanced version of a device that transmits data in a wireless system, commonly known as a tag. The new tag can support data transmission for a large network of devices using a technique called backscattering. This is where 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. Backscattering is already used in simple systems like smart payment and 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. Conventional backscatter designs also have slow communication speeds, as lower frequency signals have limitations on how much information can travel back and forth at once.
The new tag, developed by researchers at Princeton, Rice University and Brown University, is the first of its kind that can use backscattering in the sub-terahertz 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,” said Yasaman Ghasempour, assistant professor of electrical and computer engineering at Princeton and the study’s principal investigator. “Despite the conventional wisdom, this paper shows that it is possible to have low-power, scalable communication in the sub-terahertz range.”
The paper was published Oct. 9 in Nature Communications.
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. “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. That’s the real challenge,” Ghasempour said.
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. Ghasempour said that achieving sub-terahertz backscattering required the team to rethink the entire architecture of the tag. “It wouldn’t work to use the same old hardware design and scale it up,” she said.
To address these limitations, the researchers came up with 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. In other words, the interference footprint of each tag is limited in spatial and spectral domains.
Ghasempour said she hopes that others will read this paper and find engineering improvements for advanced applications. By implementing a way to amplify signals in the system at low costs, for example, the technology could power sensor networks across cities to monitor air quality or traffic flow.
The tags could be placed on traffic signs to be detected by self-driving cars, as they can use radio waves to convey messages like “stop” or “yield” even when visibility is blocked by fog or snow. In agriculture, the technology could help create expansive networks of soil sensors across fields or forests, providing real-time data on moisture levels or temperature.
Ghasempour said that developing low-power data modulators in these kinds of systems is an active area of research, and that this innovation is a step toward decreasing cost and power consumption for the entire wireless system.
The paper “A frequency-agile retrodirective tag for large-scale sub-terahertz data backscattering” was published Oct. 9 in Nature Communications. Besides Ghasempour, authors include Atsutse Kludze, Junichiro Kono and Daniel M. Mittleman. Support for this research was provided in part by the National Science Foundation and the U.S. Air Force Office of Scientific Research.
