At the recent 2010 International Consumer Electronics Show (CES), RCA introduced the Airnergy Charger which they claim is able to convert the energy in WiFi signals into electricity to power small devices. RCA demonstrated at CES that the Airnergy Charger was able to charge a BlackBerry from 30% to full charge in around 90 minutes using only ambient WiFi signals at the show for power.
The pocket sized Airnergy Charger has an internal battery for electricity storage. Power can be extracted from WiFi signals as the charger is carried around, or it can be left near a WiFi router at night to collect and store power for use the next day. Although this device would be a boon to the energy harvesting industry, some detractors suggest that the device would not generate a useful amount of power unless placed in the immediate vicinity of a high power broadcast.
RCA aims to produce a battery with WiFi harvesting technology but in the meantime they say the USB Airnergy Charger will be available later this year for US$40.
Parasitic use of WiFi signals has already been employed by so-called WiFi Real Time Locating Systems RTLS ("Second Generation Active RFID") as detailed in the IDTechEx report Real Time Locating Systems 2009-2019 . Here principles such as Received Signal Strength Indication RSSI from several WiFi nodes are used in conjuction with radio mapping to permit the tag to be located in 3D. However, the tag always contains a battery because the WiFi emissions are inadequate for the necessary data processing and transmission of derived information.
Image source TechCat
For more read : Energy Harvesting and Storage for Electronic Devices 2009-2019