Radio waves

Metasurface-based antenna transforms ambient radio waves into electrical energy

The technology could make it possible to use radio emissions from mobile phone networks to wirelessly power sensors and LEDs.

Researchers have developed a novel metasurface-based antenna that represents an important step in making practical the harvesting of energy from radio waves, such as those used in cell phone networks or Bluetooth connections. This technology could potentially provide wireless power to sensors, LEDs, and other simple low-power devices.

“By eliminating wired connections and batteries, these antennas could help reduce costs, improve reliability and make some power systems more efficient,” said research team leader Jiangfeng Zhou of the University of South Florida. “This would be useful for powering smart home sensors such as those used for temperature, lighting and motion or sensors used to monitor the structure of buildings or bridges, where replacing a battery may be difficult or impossible. .”

In the review Express Optical Materials, the researchers report that lab tests of their new antenna have shown it can harvest 100 microwatts of power, enough to power simple devices, from low-power radio waves. This was possible because the metamaterial used to make the antenna has perfect absorption of radio waves and was designed to work with low intensities.

Antenna based on metamaterials in an anechoic chamber

The researchers tested their metamaterial-based antenna in an anechoic chamber. The radio wave is transmitted by the horn antenna on the left and received by the metasurface antenna mounted on the wooden frame on the right. The anechoic chamber eliminates background signals from other sources and prevents spurious signals from the radio wave source from bouncing around the room and interfering with measurements. The image of the antenna made from metamaterials is magnified on the right. Credit: Jiangfeng Zhou and Clayton Fowler

“Although more work is needed to miniaturize the antenna, our device passes a key threshold of 100 microwatts of power harvested with high efficiency using ambient power levels found in the real world,” said Clayton Fowler, the member of the team who fabricated the sample and performed the measurements. “The technology could also be adapted so that a source of radio waves could be provided to power or charge devices in a room.”

Harvest energy from the air

Scientists have been trying to capture energy from radio waves for some time, but it’s hard to get enough energy to be useful. This is changing with the development of metamaterials and the ever-increasing number of ambient sources of radio frequency energy available, such as cell phone networks, Wi-Fi, GPS and Bluetooth signals.

“With the huge explosion of radio wave-based technologies, there will be a lot of waste electromagnetic emissions that could be collected,” Zhou said. “This, combined with advances in metamaterials, has created a ripe environment for new devices and applications that could benefit from collecting this wasted energy and using it.”

Metamaterials using small, carefully designed structures to interact with light and radio waves in ways that natural materials do not. To make the energy-harvesting antenna, the researchers used a metamaterial designed for high absorption of radio waves and which allows higher voltage to flow through the device’s diode. This improved its efficiency in turning radio waves into energy, especially at low intensity.

Testing with Ambient Power Levels

For lab tests of the device, which measured 16cm by 16cm, researchers measured the amount of energy harvested while changing the power and frequency of a radio source between 0.7 and 2.0 GHz. . They demonstrated the ability to harvest 100 microwatts of energy from radio waves with an intensity of just 0.4 microwatts per square centimeter, about the level of radio wave intensity 100 meters from a cell phone tower. .

“We also placed a cellphone very close to the antenna during a phone call, and it picked up enough energy to power an LED during the call,” Zhou said. “Although it would be more practical to harvest power from cellphone towers, it demonstrated the antenna’s power-harvesting capabilities.”

Since the current version of the antenna is much larger than most devices it could potentially power, researchers are working to make it smaller. They would also like to create a version that could simultaneously collect energy from multiple types of radio waves so that more energy can be collected.

Reference: “High-Efficiency Ambient RF Energy Harvesting by a Perfect Metamaterial Absorber” by Clayton Fowler, Sinhara Silva, Grija Thapa, and Jiangfeng Zhou, February 28, 2022, Express Optical Materials.
DOI: 10.1364/OME.449494