OPTIMIZATION OF A PYROELECTRIC DETECTOR

Pyroelectrics are the subclass of thermal detectors. These can detect pulses of electromagnetic radiation in the range between ultraviolet and terahertz. The principle of operation is to generate electrical charges in response to the heat flux pulsed or permanent being chopped. Pyroelectric detectors are used in many fields. The widest applications are flame and motion detectors. These detectors are not designed to be applied to instrumentation. However, gas analyzers, optical pyrometers, optical radiometers, electrically calibrated radiometers, or the like, are related to the instruments. Each application requires that a detector to be used, be optimized. At least, three major criteria for thermal detectors of optimization, have been postulated [1]:  maximum thermal isolation;  minimum thickness of the sensor element;  maximum area of the sensor element. The three criteria should be considered in details. The first criterion meets the requirement that the sensitive element should be used in vacuum, with thermal losses occuring due to radiation. In this case, a thermal contact between the sensitive element and a mounting should be minimal. In practice, pyroelectric detectors as vacuum sensors are not widely produced. A problem is that the detector may collect air, moisture, dust, or other contaminants that may result in bad. For example, if the sensitive element of an open detector is observed with a microscope, one can see some parts of dust attracted by the former. These parts of dust are, at least, one more source of noise. Moisture decreases the electrical resistance of the high-ohm circuit. Air and other contaminants absorb the infrared radiation that results in false measurement [2]. In order to avoid said problems, pyroelectric detectors are filled with gas preferably optically transparent in infrared. Such a gas is found to be nitrogen [1]. This gas relates to a group of inertia gases. Other gases from the group can be used as well [3]. As a result, it is hardly possible to meet the first criterion. The second criterion is limited with mechanical performance. Also, it is not possible to provide the thickness of a crystal close to some layers of molecules, probably, theoretically, due to the pyroelectric effect itself may have a strange behavior. Besides, the thinner the crystal, the higher the electrical capacitance which is not always desirable. As a result, to meet the second criterion is pretty hard. The third criterion is limited with manufacturing feasibility. It is hard enough to manufacture a single crystal of a large area. Another problem is to make the domains be uniform. This problem seems to be major and is near-impossible to control. As a result, the third criterion is not assumed to be met. The three criteria are postulated to provide the highest output. The latter is observed at a special moment of time, hereinafter called max t , that depends on time constants. The time constants determine the transient process of a detector. However, it has been noted that the detector absorbs the energy of electromagnetic radiation pulsed, or being chopped. It is clear that when the pulse width, so-called pulse t , equals max t , the out-