Signal pyroelectric element

For practical purposes, the very small signals generated by pyroelectric elements must be amplified. The most widely used first stage consists of a field effect transistor (FET) which responds to electric potential rather than to charge. In this case, it is advantageous for the material to have a low permittivity to match the low input capacitance of the FET. Therefore the compositions with high... 

Various workers have developed models relating the thermal and electrical properties of a pyroelectric element [2] yielding an expression for voltage responsivity (amplitude of signal per unit input power) ... 

It can be shown from Figure 11 and Equation 1 that the rise time of the signal will be controlled by the RC time constant of the circuit loading the pyroelectric current generator. The simplest case is where the heat flow into the pyroelectric is one dimensional as shown in Figure 12. Then the signal across the parallel load resistor of the pyroelect-ic element is... 

The electrical impedance of a pyroelectric detector is almost that of a pure capacitance. Hence an output signal only appears when the input radiation is changing. For maximum output the rate of change of the input radiation should be comparable with the electrical (RC) time constant of the element. Figure 3.10 is the equivalent electrical circuit of a pyroelectric detector (Putley [3.11, 51J). Assume that the element receives radiation over an area A normal to the polar axis of the material and that this produces a modulated temperature rise (3.4). 

Pyroelectric currents are proportional to the time derivative of the temperature and, in case of infrared (IR) detectors, to the changes of IR radiation. In order to assess stationary IR sources as well, a chopper is used to modulate the IR radiation. Signals thus exhibit a well-defined angular chopping frequency a>. The smallest detectable temperature change is limited to the terr5>erature fluctuation of the detector system, the electronics or the intrinsic noise current jn of the p)Toelectric element, given here for a thin film by the expression... 

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