There is energy all around us, carried by the signals of wireless networks that connect devices, sensors, and systems across today’s digital infrastructure.

Until now, most of that energy has gone untapped. A team of researchers at Georgia Tech is changing that with a lens-based millimeter-wave (mmWave) energy harvester captures and converts these signals into usable power, paving the way for battery-free devices in smart cities. 

“Technology powering technology, that’s the vision,” said Marvin Joshi, a Ph.D. candidate in the School of Electrical and Computer Engineering (ECE) and lead researcher on the project.

The team’s energy harvester marks a big improvement over past designs, which often failed to gather enough power and only worked when signals were perfectly aligned from one narrow direction, according to Joshi. 

Joshi and Emmanouil (Manos) M. Tentzeris, the Ed and Pat Joy Chair Professor in ECE, recently published their findings in Nature Scientific Reports.

A New Optics-Inspired Approach

Their innovation centers on a biconvex dielectric lens—a first-of-its-kind architecture in the mmWave energy-harvesting field—that concentrates mmWave signals used by 5G wireless networks onto a compact antenna array. Compared with earlier mmWave harvesters that operated effectively only within narrow capture zones, this lens enables wide-angle energy collection, supporting more flexible placement.

Its near-hemispherical energy collection capability further distinguishes it from earlier narrow-beam approaches, enabling reliable power capture across a wide range of orientations.

The precision lens targets signals in the 28-gigahertz band—part of the 5G spectrum—where extremely high-frequency waves carry more energy than lower-frequency signals. By focusing these waves, the system transforms 5G’s abundant energy into a practical power source for the first time at tens-of-milliwatt power levels, marking a significant advancement from prior sub-milliwatt systems.

Because the lens architecture is frequency-agnostic (not dependent on a specific frequency) and scalable, the same approach can naturally extend to future NextG and 6G wireless systems.

“Think of it like a magnifying glass focusing sunlight,” Joshi said. “Except here, we’re focusing radio waves. The lens works the same way as optics, just at lower frequencies. It focuses energy onto a tight spot.”

Meeting the Power Demands of Billions of Connected Devices

This advancement is critical as connected cities depend on billions of Internet of Things (IoT) sensors to monitor traffic, air quality, infrastructure health, and more. That number is only growing: currently, there are about 21 billion connected IoT devices globally, with projections showing 40 billion by 2030, according to IoT Analytics' global IoT market forecast.

Today, most of these devices run on batteries, creating challenges like frequent replacements, high maintenance costs, and significant environmental impact.

“Changing batteries for that many sensors is simply not practical,” said Tentzeris. “Our goal is to eliminate batteries altogether.”

Previous energy harvesters could only produce microwatts of power—enough for academic demonstrations but not real-world applications. This limitation has historically been viewed as the fundamental barrier preventing large-scale deployment of battery-free IoT systems at mmWave frequencies, according to Tentzeris.

In lab tests, a single Georgia Tech mmWave energy harvester captured up to 20 milliwatts of power (about ten times more than previous designs), marking a world-leading benchmark and redefining what was thought physically achievable in this frequency band.

When scaled to a 2×2 array, the system harvested 82 milliwatts, enough to power practical devices like sensors or low-power wireless transceivers. Under theoretical conditions using the maximum allowed 5G power levels, the design could reach over 100 milliwatts and operate at ranges up to 120 meter.

“This is the first time we’ve seen mmWave harvesters approach 100 milliwatts,” Tentzeris said. “It removes a major roadblock in how to power smart cities and connected devices.” 

Aligned with the Future

The implications are significant. Tentzeris calls the work a turning point for wireless power harvesting and a realistic way to power dense, city‑scale networks directly from 5G.

And it is not only cities that could benefit. Factories and other Industry 4.0 and 5.0 systems could use the harvesters to run equipment‑tracking sensors and autonomous beacons without constant battery replacements. Everything operates wirelessly, which cuts waste, makes maintenance easier, and supports more tightly managed systems.

“Nobody’s using harvesters like this because they’ve been impractical,” Tentzeris said. “We’re turning the invisible energy around us into something useful for the first time, while also making wireless systems more secure.” 

The timing also lines up with a major shift in wireless technology. New 5G and emerging 6G systems are beginning to integrate sensing and communication functions into one single system—approaches known as Integrated Sensing and Communication (ISAC) and Joint Communication and Sensing (JCAS) systems—to improve spectrum efficiency and reduce device cost and power consumption.

As networks adopt ISAC/JCAS the number of deployed sensors will grow dramatically. That expansion also magnifies the challenge of powering them.

“Battery‑free power becomes essential when millions of sensors must operate continuously,” Tentzeris said. “By harvesting energy directly from 5G signals, we can keep those devices online near-perpetuously and generate the dense, real‑time data streams AI needs to make smarter decisions.”