An infrared sensor, IR sensor, detects infrared light (IR). Such a sensor consists of a temperature-sensitive pyrosensor made of lead sulfide or lithium tantalate(LiTaO3), which reacts to temperature changes and generates an electrical voltage. This effect of pyroelectricity occurs only in pyroelectric crystals.
In terms of construction, IR detectors consist of a metallic housing in which the temperature-sensitive sensor crystals are located, which generate a voltage when the temperature changes. To limit the sensitive wavelength range, the sensor crystals are covered with an infrared filter. The voltage emitted by the sensor elements is amplified in an amplifier element, for example a field-effect transistor, and is then available for further processing.
IR sensors have their highest spectral sensitivity in the wavelength range of about 1 µm and 20 µm. Depending on the application, a filter glass is used to filter out certain wavelengths. For passive infrared motion detectors( PIR), it is the mid-infrared range between 7 µm and 15 µm. One can also select the wavelength by choosing the pyrotechnic crystals.
Photodiodes operating in infrared light, in combination with infrared filters and lens systems such as Selfoc lenses or Fresnel lenses, can also detect different thermal radiation over longer distances. This allows objects with different temperatures to be distinguished.
There are already organic infrared sensors used as photodiode arrays as infrared image sensors in machine vision. The treated infrared sensors can only detect the total IR radiation of a body, but not the distribution of temperature differences. This spatial temperature resolution can be captured by infrared sensor arrays. On such an array, which can be concentrated on one chip, many infrared sensors are arranged, which independently detect the temperature and create a thermal image from it. Infrared sensors are used in pyrometers and thermal imaging cameras for thermography.