Researchers at the Eindhoven University of Technology in the Netherlands have created what they call the tiniest temperature sensor that is powered by the same wireless network it uses to communicate data. The sensor measures 2 square millimeters and needs no physical connection to send data. The current version of the sensor has a range of 2.5 centimeters but this is something to be improved in future versions.
The sensor contains an antenna that captures the energy from the router. The sensor stores that energy and, once there is enough, the sensor switches on, measures the temperature and sends a signal to the router. This signal has a slightly distinctive frequency, depending on the temperature measured. The router can deduce the temperature from this distinctive frequency.
The world’s tiniest temperature sensor is powered by radio waves – [Link]