Remote sensors need no wires or batteries

Siemens researchers have developed a form of remote sensor which needs no wiring or power supply. Instead, the sensor draws its energy from piezoelectric or pyroelectric materials that generate a voltage when they are stressed or undergo a change in temperature.

In the new sensors, which are still at the laboratory stage, these voltages are fed to a spark gap. When the voltage exceeds a threshold value, a discharge occurs across the gap, generating a high-frequency signal from which the sensor draws its energy. This powers the measuring element - a surface acoustic wave (SAW) sensor - which imprints a unique identification code and the measured data on the high-frequency signal. This is then transmitted via an antenna.

The signal can be picked up and decoded by a receiver up to 20m way from the sensor. The developers hope to extend this range to more than 100m. They foresee many applications for the "event driven" sensing technology in industry, commerce and the home.

For example, the sensors could act at light switches, activating a receiver installed in a lamp. Signals from many sensors around a plant or building could be picked up and acted upon by a central receiver. Siemens says that "a significant amount of development work remains to be done" on the new sensors.