IoT Bounces Back

Large sensor networks, whether deployed across vast regions of the world or a manufacturing facility, are making it possible to collect tremendous amounts of data in a way that was previously impossible. And that data is quite valuable as it offers us insights into how we can optimize manufacturing processes, prevent equipment failures, improve the yields of farming operations, better manage the environment, and much more.

But whenever large networks of devices are deployed, there are going to be challenges with keeping them powered up. Transmitters used in wireless communication, in particular — which are essential in reporting collected sensor data — are notorious for drawing a lot of power. The batteries that power these transmitters must be recharged and periodically replaced, and alternative options like solar and wind are not always available or practical for every use case. As such, what we really need is an alternative to these traditional alternatives.

Backscattering is emerging as an energy-efficient communication technique that enables nodes to transmit data back to a central receiver without any power of their own. Nodes modulate RF energy received from the transmitter to encode data, before reflecting it back. But despite its promise, current backscatter designs are constrained to sub-6 GHz bands or narrowband operations in the millimeter-wave range, limiting their capacity to support many low-power, interference-free users simultaneously.

A frequency-agile wideband backscatter design in the sub-terahertz (sub-THz) range could greatly improve these networks by enabling spatial reuse through directionality and frequency multiplexing through the abundant bandwidth available. Until now, no such system existed. But just recently, a team led by researchers at Princeton University introduced the first sub-THz backscatter architecture operating above 100 GHz. The additional bandwidth available at these frequencies makes it possible for many more devices to communicate without interference.

At the center of the team’s novel architecture are devices called leaky-wave antennas. These antennas work by guiding signals through a structure called a waveguide, which has a small opening that allows the signals to “leak” out into free space. The direction in which the signal is emitted depends on its frequency, making these antennas inherently frequency-agile — they can shift their operations to different parts of the frequency band as needed. This flexibility allows the system to avoid interference and support multiple users simultaneously.

To make this architecture efficient, the researchers exploited a unique property of leaky-wave devices called reciprocity. This means the same path used for transmitting signals can also be used for receiving them, enabling a simple, low-power, and effective way for devices to communicate. The system does not rely on complex or power-hungry components like amplifiers or oscillators. Instead, it reflects and modulates ambient signals, making it ideal for densely packed IoT networks where energy efficiency is essential.

The design also incorporates narrow-beam directional transmission, which focuses the signal in a specific direction. This feature helps overcome the high energy losses that otherwise occur at sub-THz frequencies and allows many devices to operate simultaneously in the same physical space without interfering with each other. By combining these elements, the team created a backscatter system that is not only energy-efficient but also capable of supporting the growing demand for wireless connectivity in dense IoT environments like factories, agricultural operations, and smart cities.