Temp. and voltage compensated electret sensor - has sensing circuit connected to two conductive layers for specified compensation

摘要

The sensor has an electret layer of polarised material with both piezoelectric and pyroelectric properties. The layer generates electrostatic charges of opposite polarity on its surfaces under the effect of temperature and voltage variations. One side of the electret layer is in close planar contact with a conductive layer. A second electret layer of the same properties is arranged parallel to the first layer and has also a second conductive layer. A third conductive layer is sandwiched between the other sides of the two electret layers. An electronic sensing circuit (10) is connected to at least two conductive layers in such manner that, when the electret layers are exposed to identical temperature changes and opposite voltage changes, the circuit picks up the electrostatic charges, while not responding to electrostatic charges due to the other change of the two states.