2. Pyroelectric sensors

Figure 2.4.3 Principle of pyroelectricity

These sensors work on the principle of pyroelectricity , which states that a crystal material such as Lithium tantalite generates charge in response to heat flow . In presence of an electric field, when such a crystal material heats up, its electrical dipoles line up as shown in figure 2.4.3. This is called as polarization. On cooling, the material retains its polarization. In absence of electric field, when this polarized material is subjected to infra red irradiation, its polarization reduces. This phenomenon is the measure of detection of movement of an object.