Radio waves

Metamaterial antenna harvests energy from radio waves

Researchers have developed a new antenna based on the metasurface, an advance that can harvest energy from radio waves such as those used in mobile phone networks.

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 metamaterial-based antenna is magnified on the right (Image: Jiangfeng Zhou and Clayton Fowler)

The technology could potentially provide wireless power to sensors, LEDs, and other 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 Express Optical Materials, the researchers report that lab tests of their new antenna have shown that it can harvest 100 µW of power 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.

“Although more work is needed to miniaturize the antenna, our device passes a key threshold of 100 µW of harvested power with high efficiency using ambient power levels found in the real world,” said Clayton Fowler, 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.”

Scientists have tried to capture energy from radio waves before, but it has been difficult to get enough energy to be useful. According to the Florida team, this is changing due to the development of metamaterials and available ambient sources of radio frequency energy, 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 electromagnetic waste emissions that could be collected,” Zhou said in a statement. “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 use 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 is said to have improved its efficiency in turning radio waves into energy, especially at low intensity.

For lab tests of the 16cm by 16cm device, the researchers measured the amount of energy harvested while changing the power and frequency of a radio source between 0.7 GHz and 2.0 GHz. They demonstrated the ability to harvest 100 µW of power from radio waves with an intensity of 0.4 µW/cm2approximately the intensity level of radio waves 100 m 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. “While harvesting power from cell towers is more practical, it demonstrated the antenna’s power-harvesting capabilities.”

The researchers are working on making their solution smaller, and they would like to create a version that could collect energy from multiple types of radio waves simultaneously.