Researchers have recently unveiled a new antenna based on metasurface that can capture energy from radio waves (1). Experts have also built a circuit that can harvest energy from graphene, leading to another battery-free power source in a separate development (2).

As more devices offer radio frequencies across cell networks, Bluetooth, and WiFi, there is now an excess of electromagnetic emissions that we can collect. This new antenna based on metamaterial can harvest about 100 microwatts of power from radio waves as far as 100 meters.

Meanwhile, the circuit which harvests energy from graphene’s thermal motion and converts it into an electric current can produce low voltage power for small sensors and devices.

Overall, both advancements will be able to replace traditional batteries with graphene or radio-powered sensors for low-power products like wearables by 2027.

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Metasurface Based Antenna

Researchers have built a new metasurface-based antenna representing a key step towards making it practical to harvest energy from radio waves, like those used in Bluetooth connections or cell phone networks.

This technology can offer wireless power to small devices, LEDs, and sensors that need low energy.

metamaterial antenna
The researchers tested their metamaterial-based antenna in an anechoic room. The radio wave is sent out on the left by the horn antenna and received on the right by the metasurface antenna fixed on the wood frame. The anechoic chamber reduces background signals from other sources while preventing stray radio wave signals from bouncing around the room and interfering with measurements. On the right, a picture of a metamaterial-based antenna has been magnified. Source: Jiangfeng Zhou and Clayton Fowler.

“By removing the batteries and wired connections, these metasurface-based antennas cam electrical systems more efficient, reduce costs, and improve reliability,” said Jiangfeng Zhou, the research team leader from the University of South Florida (3, 4). “It would be useful particularly for powering sensors used in smart homes like those used for lighting, temperature, and motion. We also see applications in sensors used to monitor bridges or building structures, where replacing a battery might be challenging.”

The researchers behind this development reported in the journal Optical Materials Express (5) lab tests of their antenna indicated that it could generate up to 100 microwatts of power, which is enough to power simple devices using low power radio waves.

It was possible because the metamaterial used to make the antenna exhibits ~100% absorption of radio waves and was designed for low intensities.

“Even though more work is required to miniaturize the antenna, our produce crosses a key threshold of 100 microwatts of generated power with high efficiency using ambient power levels seen in the real world,” stated Clayton Fowler, who fabricated the sample and performed the measurements (6, 7). “We could also adopt the technology to use radio waves as a source to power or charge our devices around a room.”

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Capturing Energy From the Air

Scientists have attempted to collect energy from radio waves for a long time, but obtaining enough energy to be useful has proven challenging. This is changing thanks to metamaterials and the ever-increasing number of ambient radio frequency energy sources, such as cell phone networks, WiFi, GPS, and Bluetooth signals.

“There will be a lot of electromagnetic waste emissions that might be gathered with the massive increase of radio wave-based technologies,” Zhou explained. “This, together with breakthroughs in metamaterials, has created a fertile ground for novel gadgets and applications that could benefit from capturing and utilizing waste energy.”

Small, carefully constructed structures in metamaterials interact with light and radio waves in ways that natural materials do not. The researchers employed a metamaterial intended for high absorption of radio waves, which permits a larger voltage to flow across the device’s diode to create the energy-harvesting antenna. It increased its efficiency in converting radio waves into electricity, especially at low intensities.

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Ambient Power Levels Testing

The researchers assessed the amount of power gathered while adjusting the radio source power and frequency between 0.7 and 2.0 GHz for lab tests of the device, which measured 16 cm by 16 cm.

They showed the ability to capture 100 microwatts of electricity from radio waves with an intensity of just 0.4 microwatts per centimeter squared. It is about the same as the strength of radio waves at a distance of 100 meters from a cell phone tower.

“During a phone call, we positioned a cell phone quite close to the antenna, and it gathered enough energy to power an LED,” Zhou explained. “Although harvesting energy from cell phone towers would be more practical, this revealed the antenna’s power gathering potential.”

The researchers aim to make the antenna smaller as it is much larger than most of the devices it could power. They also want to create a version that can simultaneously collect energy from many types of radio waves, allowing them to collect more energy (8).

And it is not the first time researchers have tried something similar.

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Energy-Harvesting Blueprint to Convert Electromagnetic Waves into Usable Power

In 2020, physicists at MIT came up with a blueprint of a decision that they believed would convert a range of electromagnetic frequencies waves into DC (direct current) that can power implants and other household electronics (9).

Their concept leverage the carbon substance graphene’s quantum mechanical, or atomic, nature. They discovered that mixing graphene with another material, in this case, boron nitride, causes the graphene electrons to skew their travel in the same direction.

Any incoming terahertz waves should “shuttle” graphene’s electrons to travel through the material in a single direction, as a direct current, just like several small air traffic controllers.

The researchers have published their observations in Science Advances and work with experimentalists to realize their idea into a working prototype.

“Terahertz electromagnetic waves surround us,” explains lead scientist Hiroki Isobe, a postdoctoral researcher at MIT’s Materials Research Laboratory (10). “If we can transform that energy into a source of power that we can use in our daily lives, that will help us resolve the present energy concerns.”

Liang Fu, a former MIT postdoc now an assistant professor of chemistry at Harvard University, and Su-yang Xu, a former MIT postdoc who is now an assistant professor of chemistry at Harvard University, are Isobe’s co-authors.

Terahertz rectifiers, he believes, might be employed soon to wirelessly power implants in a patient’s body, putting an end to the need for surgery to replace the implant’s batteries. Such devices might convert ambient WiFi signals to power personal electronics like smartphones and laptops (11).

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Circuit Generating “Limitless” and Clean Power from Graphene

Last month, a team of physicists at the University of Arkansas physicists had built a circuit that can capture graphene’s thermal motion and convert it to an electrical current (12).

“A graphene-based energy-harvesting circuit may be put onto a chip to supply clean, infinite, low-voltage power for sensors and small devices,” said Paul Thibado, a physics professor and the lead researcher (13).

The study results, titled “Fluctuation-induced current from freestanding graphene,” published in the journal Physical Review E (14), support a theory developed three years ago by physicists at the University of Arkansas that freestanding graphene, a single layer of carbon atoms, ripples, and buckles in a way that could be used to harvest energy.

The idea of capturing energy from graphene is disputed since it contradicts physicist Richard Feynman’s well-known claim that atoms can’t conduct work due to their thermal motion, known as Brownian motion (15).

At room temperature, Thibado’s team observed that the thermal motion of graphene induces an alternating current (AC) in a circuit, a feat previously deemed unachievable.

The team’s next goal is to see if DC can be stored in a capacitor and used later, requiring miniaturizing the circuit and patterning it on a silicon wafer or chip. Millions of these tiny circuits might be created on a 1-millimeter by 1-millimeter chip and used to replace low-power batteries.

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The Future

Smart home sensors used in thermostats, motion-activated lighting, carbon monoxide detectors, and fire alarms could benefit from these developments, which could lower costs and enhance efficiency.

The next step for both teams is to miniaturize their technology, either to fit on a silicon wafer or a fire alarm. Both of these inventions indicate that sensors will likely replace more devices currently powered by batteries or wires in the future.

Minor devices will have fewer batteries, while those with batteries will be rechargeable over the air. Wearable devices, security cameras, and LED panels might all be powered by your WiFi or 5G connection in the near future.

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