Thermal imaging system is an equipment that collects the radiant energy which an object emits, and changes it to visible light and makes observations using the feature that all objects with over the temperature of absolute zero degrees, emit infrared of the wavelength and intensity corresponding to the temperature. Unlike the current imaging system that observes objects by the presence of visible light or the difference of the intensity of light, thermal imaging system can make observations even during night time when there is no light because it changes the original radiant energy to an image. Moreover, it has started to be developed for military application since 1930 owing to its comparatively satisfactory performance in target detection even in the weather of bad visual sight. Currently it is widely used for industrial and medical application since it started to be used for the sensor of night vision or firing control equipment for military in mid 1970. That is, it is often used for heat loss detection of a building, measurement of storage amount inside a tank, defect check in transmission lines, invader surveillance. Recently it is being applied to circuit monitor and analysis, weather observation by a satellite, firefighting and rescue by the firefighters, medical equipment, and this application range is getting larger. Radiant energy from an object is absorbed by gases or vapor such as CO₂, ozone in the air. Infrared is mainly absorbed in the vapor absorption range of 6.3μm and CO₂ absorption range of 2.7, 15μm. As a result, the infrared in the range of 3~5μm and 8~14μm is hardly absorbed and spreads far in the air.
Thermal imaging system concentrates ‘Far Infrared’ radiant energy mostly in the range of 8~14μm using the feature that an object with normal temperature emits the biggest radiant energy in the range of 10μm and the wavelength range of 8~14μm is superior in air penetration, and reproduces it to visible light by detection and electrical signal process.Therefore, thermal imaging system necessarily requires ‘Far Infrared’ detection sensor.IR detector can be classified into thermal detector and photon detector. In case of thermal detector, the differences between the infrared radiant energies which are projected changes the electric feature of detection element. Thermal detector is classified into thermocouple, bolometer, pyroelectric detector. Thermal detector has the strength that it can be small sized and lightweight because it does not require a cooling device, but it is low in sensitivity and response speed compared with photon detector. However, recently the high efficient bolometer and pyroelectric detector which enables a real-time thermal imaging has been developed owing to the manutacturing progress in MEMS, and now is being applied to small sized and lightweight portable uncooled thermal imager.