The feeling of anxiety over how long your smartphone battery is going to last is one that's familiar to most of us, but a team from the Ohio State University in the US has come up with an unusual source of extra power: radio waves emitted by the devices themselves. In tests, the researchers were able to boost battery life by as much as 30 percent.

While systems already exist to harvest power from ambient electromagnetic energy sources (such as radio waves), until now the technology has been limited in size and scope. In this case, because the radio waves are captured at source - almost as soon as the smartphone emits them - they produce a more powerful charging effect that can make a substantial difference to battery life.

When a smartphone looks for a cell tower or Wi-Fi network, it emits signals in all directions at once, so a lot of that power is wasted. This new system uses those redundant radio waves - essentially a high-frequency form of alternating current - by converting them to DC power that can then recharge the battery.

According to the scientists behind the invention, it could be incorporated into a US$100 stick-on skin for smartphones, without any impact on the strength of the data or web connection on the phone itself. Nikola Labs, the spin-off company charged with developing the technology, is running a crowdfunding campaign on Kickstarter in this month to pay for mass production. Potentially, the technology could also be built directly into a smartphone.

"No one can charge a cell phone from the air, but we can reduce power consumption by retrieving some of those lost milliwatts," one of the team, Robert Lee, said in a press release. "Think of it as a battery extender rather than a charger." The phone needs to be transmitting for it to work though - if you're in airplane mode, it won't work.

The team estimates that around 97 percent of cell phone signals never reach a destination and are lost in the ether. Not all of those lost signals can be recovered and converted back into energy, but some of them can, and that could make a significant difference to smartphone battery life in the near future.

The technology has grown out of other work being carried out by Chi-Chih Chen, research associate professor of electrical and computer engineering. His other projects cover antennas that can be embedded into ordinary clothing, and radar technology that's able to detect hidden landmines. We can't wait to see what else is up his sleeve.