Researchers at Intel have demonstrated low-power electronics running on nothing more than power harvested from a normal TV aerial, or an RFID reader if there happens to be one nearby.
The project, presented in this paper at TechOnline (free registration required) describes two projects: the first to draw power from an RFID reader, the second to run an electronic thermometer/hygrometer from electricity harvested from a TV transmitter 4km away.
The shop-bought thermometer apparently consumes around 25uA at 1.5v, this is normally supplied by a single AA battery which was replaced with an energy-harvesting circuit attached to a set-top-style aerial balanced on a balcony and pointed at the KING-TV tower. The tower is 4.1km from the Intel Research Seattle Lab from whose balcony the test was conducted. The researchers report that the device worked perfectly, collecting data and displaying it on an LCD screen.
Even when it's free that's still not a lot of power, but the researchers suggest that an unattended data-logging device or similar might benefit from the technique, or just someone wanting to get some free electricity from the airwaves around us. ®