(via Renesas Electronics)
The ambient air is saturated with a multitude of broadcasted energy from television signals, WiFi, Cell Phones, and a slew of other sources. Why not use it.
Renesas Electronics has build and demonstrated ultra low power communication system that use other radio waves as a power source. The system is a near field wireless technology, only broadcasting up to 1m, that uses the popular Bluetooth and wireless LAN standards. Energy absorption comes from the onboard LC resonant circuit, that they call the sensor node. In a test 10μW electricity was harvested at about 30cm from a 250mW source in the frequency range of 1.9 - 2.4GHz.
Data transmission from the sensor node to the mobile device that needs to read it, also goes through the same LC resonant circuit used for harvesting. When the LC circuit is on, the ambient radio waves are absorbed and communication to the mobile device is improved, the mobile device interprets that the sensor node is sending a logic 0. When the LC resonant circuit is off the communication to the mobile device is worse, and this is interpreted by the mobile device as a logic 1. In other words data is send from the sensor node by with absorbing or reflecting radio waves, or a logic 0 or 1 respectively. Using WiFi, the maximum data rate demonstrated was between 2.25K-5.5k.
For example, a temperature sensor could be placed on a human being, take a measurement and send the signal to a mobile device within 1m without the need for a battery quite easily with this method. Medical and consumer advertising is the immediate vision of use for the company. More testing needs to be done as well as talks with customers about applications, but Renesas Electronics says that commercial use could be seen within the next three years.