Sensor above absolute 0 ℃ temperature can produce thermal radiation, and temperature of the thermal radiation of objects below 1725 c concentration in the infrared region of the spectrum, so all natural body radiates infrared heat. Due to its physical and chemical properties of any objects and different temperature of the infrared radiation of different wavelengths and distance are not the same, usually divided into three bands.
Near-infrared wavelength range 0.75~3 μ m
Mid-IR wavelength range 3~25 μ m
Far-infrared wavelength range 25~1000 μ m
Infrared light wavelengths of radiation the human body 3~50 μ m, 8~14 μ m, 46% peak wavelength of 9.5 µ m.