Seeker Types
The three main materials used in the infrared sensor are lead(II) sulfide (PbS), indium antimonide (InSb) and mercury cadmium telluride (HgCdTe). Older sensors tend to use PbS, newer sensors tend to use InSb or HgCdTe. All perform better when cooled, as they are both more sensitive and able to detect cooler objects.
Early infrared seekers were most effective in detecting infrared radiation with shorter wavelengths, such as the 4.2 micrometre emissions of the carbon dioxide efflux of a jet engine. Such seekers, which are most sensitive to the 3 to 5 micrometre range, are now called single-color seekers. Modern infrared seekers also operate in the 8 to 13 micrometer wavelength range, which is absorbed least by the atmosphere. Such seekers are called two-color systems. Two-color seekers are harder to defeat with countermeasures such as flares.
Read more about this topic: Infrared Homing
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