Infrared thermal imaging refrigeration technology

In order for the thermal imaging system to work properly, the technology of cooling its detector elements to low or deep temperatures is also called cryostat technology. The main tasks of this technology are twofold: first, to form a suitable low-temperature and constant-temperature environment through refrigeration to ensure the normal function of electronic devices or systems that need to work at low temperatures, or to improve the sensitivity of the device; second, to shield or reduce the heat from the Thermal noise caused by the filters, baffles and optical system itself of the imaging system.

The working principle of the refrigerator includes two methods: physical and chemical. Depending on the use occasion and the required refrigeration temperature, different principles can be used to make appropriate refrigerators. Thermal imaging systems mostly use physical methods. There are:

1. Use phase change refrigeration

That is, the refrigeration working substance uses the phase change endothermic effect, such as the refrigeration of liquid nitrogen, liquid hydrogen, etc. using a perfusion Dewar bottle.

2. Refrigeration using the Joule-Thomson effect

That is, when the temperature of the high-pressure gas is lower than its own conversion temperature and passes through a small orifice, the expansion of the gas will cause the temperature to drop. For example, the coke-soup refrigerator is characterized by simple structure, high reliability, light weight, small size, no vibration, no moving parts, low noise, low cost, and fast cooling speed. The cooling time usually only takes 15 to 60 seconds ( Second).

3. Refrigeration using isentropic expansion of gas

That is, when the gas expands isentropically, the piston of the expander outputs mechanical work outwards. After expansion, the internal potential energy of the gas increases, which consumes the internal energy of the gas itself to compensate, resulting in a significant decrease in temperature after expansion. Such as Stirling closed cycle refrigerator, which is characterized by low power consumption, small size and light weight.

4. Refrigeration using the Peltier effect

That is, an N-type semiconductor and a P-type semiconductor are used as a pair. When direct current passes through, one end of the pair generates heat and the other end becomes cold, such as a thermoelectric refrigerator, also known as a semiconductor or thermoelectric refrigerator. The main advantages of pyroelectric detectors are: fully solid-state devices, compact structure, long life; no moving parts, no noise; not affected by the environment; high reliability. The disadvantage is that the coefficient of performance (COP) of the refrigerator is low, the cooling capacity is small, and the efficiency is low.

5. Use heat radiation exchange between objects for cooling

For example, in outer space, the high vacuum and deep low temperature of the outer universe can be used for cooling. Its distinguishing features are no moving parts, long life, low power consumption, and no vibration interference. The disadvantage is that there are requirements for the configuration of the orbit and satellite, and strict environmental requirements. After entering the orbit, it needs a period of heating and deflation before it can work.

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