Researchers at the Nokia Research Centre in Cambridge in the UK are working hard on a technology that can harvest small amounts of energy from ambient radio and TV waves. The cell phone would pick up radio wave frequencies as low as 500 megahertz up to 10 gigahertz, which includes television broadcasts, microwave ovens, mobile phones, wireless LAN, bluetooth, GPS, and two-way radios. In theory, two circuits would be capable of receiving and then converting the free energy to an electrical current to charge the battery of a cell phone.
Hopefully, it would be enough energy to keep the phone charged in standby mode; although at first it won’t be enough to charge the phone while in use, or to full battery capacity. Markku Rouvala, one of the researchers who developed the device, says “trick here is to ensure that these circuits use less power than is being received.” So far, their device can collect up to 5 milliwatts of power, and their short term goal is to collect 20 milliwatts of power, which is just enough to keep the phone charged in standby mode. Ultimately, 50 milliwatts of power would be ideal and could help slowly recharge the battery.