5.5.6 Common Applications

5.5.6.1 Burglar Alarms

Change in temperature of detector against the ambient temperature when an intruder comes in the vicinity of the alarm leads to a voltage which can be used to trigger an alarm. To avoid the effects due to thermal expansion, one needs to use a reference identical material to counter these extraneous effects. Such detectors can sense the objects' presence up to about 100 m.

5.5.6.2 Infrared or Thermal Imaging

Just like we use visible light to make a photograph, infrared (IR) radiation emitted by objects at different temperatures is focused onto a sensitive plate to create thermal image of the object.
The atmospheric window typically used in IR imaging is from 8 to 14 μm and co-incidentally the power radiated from a black body at 300K peaks around 10 μm making it a perfect match.

The pyroelectric elements used in the devices are typically square plates with sides about a mm long and thicknesses around 30 μm. Because entire scenes are focused onto the plates in thermal imaging, they have to be larger, typically squares of side about 1 cm; the thicknesses are the same as for the simpler devices.

A typical photograph generated from IR imaging looks like this:

Here is a simple explanation of how IT imaging using pyroelectrics works.

A special lens focuses the infrared light emitted by all of the objects in view.
The focused light is scanned by a phased array of pyroelectric elements which create a very detailed temperature pattern called a thermogram. It only takes about one-thirtieth of a second for the detector array to obtain to create a thermogram. This information is obtained from several thousand points in the field of view of the detector array.

This thermogram is translated into electrical signals which are sent to a signal-processing unit which then translates the information from the elements into data for the display.
The signal-processing unit sends the information to the display, where it appears as various colors depending on the intensity of the infrared emission. The combination of all the signals from all of the elements creates the image.

5.5.6.3 Pollutant Control

The reduction of pollution and greenhouse gases has become a major priority for our country as we progress. This requires us to monitor the levels of pollution. We can use pyroelectric materials for these purposes as well.

Pyroelectrics being excellent detectors of IR radiation, can easily detect the level of IR radiation which passes through a gas sample. Since each gas has a characteristic wavelength which it absorbs, we can measure it easily.