Researchers have developed a novel device that can convert energy from Wi-Fi signals into electricity. A new paper describing the new groundbreaking technology was published on 28 January in the journal Nature (1). According to the authors, this latest work “provides a universal energy-harvesting building block that can be integrated with various flexible electronic systems.”
A rectenna is a special type of receiving antenna capable of converting electromagnetic energy into direct current (DC) electricity and are commonly used in wireless power transmission systems that transmit power by radio waves. The new paper describes the design, fabrication, and testing of one such device, an “atomically thin and flexible ultrafast Schottky diode based on a so-called MoS2 phase heterostructure with a cutoff frequency of 10GHz, and integrated with a flexible Wi-Fi-band antenna.
In other words, the rectenna works by capturing electromagnetic waves as alternating current (AC) waveforms, including the waves that transmit Wi-Fi signals. Then, by connecting it to an extremely thin two-dimensional semiconductor ― a molybdenum disulfide film just a few atoms thick ― the signal is converted into DC voltage, which is the kind of voltage typically used to power electronics and charge batteries.
The technology, developed by an international team of researchers from Massachusetts Institute of Technology (MIT), Technical University of Madrid, the Army Research Laboratory, Charles III University of Madrid, Boston University, and the University of Southern California could potentially be used to power flexible and wearable electronics, medical devices, sensors for environmental monitoring, and the “internet of things.” For example, radio-frequency signals such as WiFi can pass through people, therefore, the energy-harvesting devices could provide power to implants enabling them to collect important health data and send it back to an external receiver.
At present, the device has an efficiency of 30–40 per cent, whereas other existing high-end rectennas, such as those made from more expensive and rigid silicon or gallium arsenide, can achieve about 50–60 per cent. In addition, the researchers were only able to produce around 40 microwatts per 150 microwatts of WiFi power in the laboratory. However, although this may seem like a relatively small amount of power, the flexible semiconductor material can be rolled into large sheets that if made large enough have the potential to capture valuable quantities of energy.
The breakthrough could pave the way for energy-harvesting covers, including wrappers that cover entire buildings, that could potentially extract energy from the environment to power sensors and other electronics, lead researcher Prof Tomás Palacios from MIT told the Guardian. Many sensors operate on a single-microwatt level, moreover, the energy could be collected and stored in batteries for later use. He adds that “when you have one of these energy-harvesting devices you are collecting energy 24/7 and you could be storing that in a battery to use later,” which is what will make this technology so useful.
Furthermore, the authors suggest the work is a stepping stone toward a high-speed flexible platform of the future for wirelessly charging everyday electronics by using existing Wi-Fi infrastructure as an “energy hotspot.”
(1) Zhang, X. et al. Two-dimensional MoS2-enabled flexible rectenna for Wi-Fi-band wireless energy harvesting. Nature (2019). DOI: 10.1038/s41586-019-0892-1