Nokia demonsrates self charging energy harvesting mobile phone

Nokia has started demonstrating a prototype mobile phone that uses energy harvesting technology to recharge itself using only ambient radio waves - emitted from mobile antennas, TV masts and other sources. Current prototypes can scavenge between 3 to 5 mW.

The short-term goal is to get in excess of 20 mW, enough power to keep a phone in standby mode indefinitely without having to recharge it. But this would not be enough to actually use the phone to make or receive a call. So ultimately the hope is to be able to harvest as much as 50 mW which would be sufficient to slowly recharge the battery.

The antenna and the receiver circuit are designed to pick up a wide range of frequencies — from 500MHz to 10GHz — and convert the electromagnetic waves into an electrical current, while the second circuit is designed to feed this current to the battery to recharge it.

The Nokia device will work on the same principles as a crystal radio set or radio frequency identification (RFID) tag: by converting electromagnetic waves into an electrical signal. This requires two passive circuits. The trick is to ensure that these circuits use less power than is being received.

In order to achieve the 50mW threshold, scientists believe that a device would have to collect about 1,000 strong signals from a wide range of frequencies. Nokia believe the technology could reach the market within three to four years.

Intel researchers recently demonstrated a modified RFID circuit that harvested 60 microwatts of power from a TV tower 4.1 km away using a simple UHF TV antenna.

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