An electrical current capable of charging a mobile phone has been created from microwave signals.
A team from Duke University said the technology they had used had been as efficient as using solar panels.
The device they created used metamaterials, which capture various forms of wave energy and convert them for other applications.
In the future, satellite, sound or wi-fi signals could be harvested
Using fibreglass and copper conductors on a circuit board, the researchers converted microwaves into 7.3 volts of electricity.
A USB charger, which is often used to recharge mobile phone batteries and cameras, provides about five volts.