2. IR temperature sensing
Infrared sensing is based on the fact that the intensity of infrared radiation emitted by a surface depends on its temperature in the first approximation, according to Boltzmann's law. Since the field-of-view of the sensor has to be restricted in a practical mobile application, the sensor also detects a surface which is typically not at the same temperature as the surface to be measured. In idealised conditions, it is possible to calibrate the detector to compensate for this Narcissus effect [7] using an internal compensation circuit that measures the temperature of the sensor element itself. Fig. 1 shows a traditional optomechanical design for IR sensing, where the Narcissus effect can be seen.