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Developed at the University of South Florida, technology based on the antenna could potentially provide wireless power to sensors, LEDs and other simple devices with low energy requirements.
“By eliminating wired connections and batteries, these antennas could help reduce costs, improve reliability and make some electrical systems more efficient,” said research team leader Jiangfeng Zhou.
“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 might be difficult or impossible.”
Laboratory tests of the new antenna showed it can harvest 100 microwatts (μW) of power from low power radio waves, enough to power simple devices.
“This was possible because the metamaterial used to make the antenna exhibits perfect absorption of radio waves and was designed to work with low intensities,” a research announcement said.
“Although more work is needed to miniaturise the antenna, our device crosses a key threshold of 100μW of harvested power with high efficiency, using ambient power levels found in the real world,” said researcher Clayton Fowler. “The technology could also be adapted so that a radio wave source could be provided to power or charge devices around a room.”
Scientists have been trying to capture energy from radio waves for some time, but it has been difficult to obtain enough energy to be useful. This is changing thanks to the development of metamaterials and the ever-growing number of ambient sources of radio frequency energy available, such as mobile phone networks, Wi-Fi, GPS, and Bluetooth signals.
“With the huge explosion in radio wave-based technologies, there will be a lot of ‘waste’ electromagnetic emissions that could be collected,” said Zhou. “This, combined with advancements in metamaterials, has created a ripe environment for new devices and applications that could benefit from collecting this waste energy and putting it to use.”
Metamaterials use small, carefully designed structures to interact with light and radio waves in ways that naturally occurring materials do not. To make the energy-harvesting antenna, the researchers used a metamaterial designed for high absorption of radio waves, which also allows a higher voltage to flow across the device’s diode. This improved its efficiency, particularly at low intensity.
In laboratory tests of the device, which measured 16x16cm, the researchers measured the amount of power harvested while changing the power and frequency of a radio source between 0.7-2GHz. They demonstrated the ability to harvest 100μW of power from radio waves with an intensity of just 0.4μW per centimetre squared, approximately the level of intensity of radio waves 100m from a mobile phone tower.
“We also placed a cell phone very close to the antenna during a phone call, and it captured enough energy to power an LED during the call,” said Zhou. “Although it would be more practical to harvest energy from cell phone towers, this demonstrated the power-capturing abilities of the antenna.”
Because the current version of the antenna is much larger than most of the devices it would potentially power, the researchers are working to make it smaller. They also aim to make a version that could collect energy from multiple types of radio waves simultaneously, so more energy can be gathered.
The research was published in Optical Materials Express.
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