Wireless charging is increasingly common in phones and other devices, but it's still held back by a very short range – usually the device needs to sit on top of a charging pad, which cancels out some of the benefits of going wireless. In a new step towards truly wireless charging, engineers have developed an ultra-thin device that captures Wi-Fi signals and converts them into electricity.
The new system is based on existing devices called rectifying antennas, or rectennas. These capture AC electromagnetic waves in the air – such as Wi-Fi signals – and convert them into DC electricity. But most of them are rigid and, being made with silicon or gallium arsenide, are best suited to powering small electronics. So the team on the new study set out to develop a new rectenna that's flexible enough to be scaled up to much larger sizes.
For the new design, the team made the rectifier – the component that converts the current – out of molybdenum disulfide (MoS2). This semiconducting material measures just three atoms thick, making it extremely flexible while still holding its own in the efficiency department. The team says the MoS2 rectifier can capture and convert up to 10 GHz of wireless signals with an efficiency of about 30 percent. That's much higher than other flexible designs, and the researchers also say it's faster.
That said, it doesn't quite stack up against other rectifiers, which can reach efficiencies of up to 60 percent. It's also generating a relatively small amount of electricity, producing about 40 microwatts from about 150 microwatts of Wi-Fi power. Although that isn't much, it should be enough to power small wearable or medical electronic devices, removing the need for batteries.
The team hopes that these disadvantages will be outweighed by the other benefits of the new design, including its flexibility and scalability.
"What if we could develop electronic systems that we wrap around a bridge or cover an entire highway, or the walls of our office and bring electronic intelligence to everything around us?" says Tomás Palacios, co-author of the study. "How do you provide energy for those electronics? We have come up with a new way to power the electronics systems of the future – by harvesting Wi-Fi energy in a way that's easily integrated in large areas – to bring intelligence to every object around us."
Next up, the team is planning on improving the efficiency and building more complex systems.
The research was published in the journal Nature.
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