A metamaterial antenna that harvests energy in the air through radio waves

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There is electricity in the air… Literally, this time. A team of researchers has indeed developed a small antenna capable of collecting radio waves present in the air to convert them back into reusable energy.

The study, published in Optical Material Express, demonstrates the ability of this antenna to exploit waves deeply rooted in our daily lives. Those of our telephone networks, our GPS, or even our devices that work in Bluetooth…

Indeed, the radio waves that circulate in the air carry an untapped amount of energy. It is possible to capture this energy via an antenna, and convert it to transform it into usable electric current. The idea is not new and many innovations go in the direction of this “recovery” of energy.

The interest of such an antenna would be to be able to remotely recharge machines that consume little energy, such as LEDs, or sensors… “By eliminating the connections cables and batteries, these antennas could help reduce costs, improve reliability and make certain electrical systems more efficient”, explains the chief from research team Jiangfeng Zhou, University of South Florida, in a statement from Optica. “ This would be useful for powering smart home sensors such as those used for temperature, lighting and motion, or sensors used to monitor structure buildings or bridges, where replacing a battery may be difficult or impossible”.

If the scientists are so satisfied with their results, it is because in comparison with different experiments, their antenna manages to extract energy with great efficiency. Two elements change the game in this performance. First, simply the increasing amount of waves present in the air. “ With the huge explosion of radio wave based technologies, there will be a lot of unused electromagnetic emissions that could be collected,” says Jiangfeng Zhou. “ This, combined with advances in metamaterials, has created a ripe environment for new devices and applications that could benefit from harvesting this waste energy and its use “.

A material with “supernatural” properties

The second element, which is directly linked to innovation, it is indeed the use for this antenna of a metamaterial. Metamaterials, to put it simply, are artificially engineered materials that have properties not found directly in nature.

The The material used in this antenna is therefore specially designed for “perfect” absorption of the wavelengths, and to allow the proper voltage circulating inside to be increased. “Metamaterials use small, carefully designed structures to interact with light and radio waves in a way that is different from natural materials”, explains the press release from Optica. The antenna, thanks to these properties, is particularly adapted to be effective against low intensities.

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Les chercheurs ont testé leur antenne à base de métamatériaux dans une chambre anéchoïque. L’onde radio est émise par l’antenne cornet à gauche et reçue par l’antenne à métasurface montée sur le cadre en bois à droite. La chambre anéchoïque élimine les signaux de fond provenant d’autres sources et empêche les signaux parasites de la source d’ondes radio de rebondir dans la pièce et de perturber les mesures. L’image de l’antenne à base de métamatériaux est agrandie à droite.
© Jiangfeng Zhou et al.

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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. © Jiangfeng Zhou et al.78019

The scientists claim in the report that the laboratory tests were indeed satisfactory. To verify the effectiveness of their design, they measured the amount of energy harvested, while changing the power and frequency of a radio source between 0.7 and 2.0 GHz. In doing so, they managed to harvest 169 microwatts of energy from radio waves, with an intensity of only 0.4 microwatts per square centimeter.

In other words , an intensity sufficient to operate appliances that consume little electricity. As a concrete example, they also placed a phone calling very close to the antenna. This one actually managed to power an LED. However, the antenna still needs to be improved, in particular its size, since it currently measures 100 cm².

Source: Optical Materials Express78019