Infrared Sensors and Their Uses
An infrared sensor is an electronic device used to sense characteristics of its surroundings, either by emitting or detecting infrared radiation. Infrared sensors are also able to measure the heat of an object and detect motion. Infrared technology is found throughout many industries as well as every-day life. For example, TVs use infrared to receive signals from the remote. Infrared sensors have many benefits, the primary of those being their low power requirements, simple circuitry, and portable features.
Infrared sensors can be active or passive, and can be divided into two main groups: acuator thermal and quantum. Thermal infrared sensors use infrared energy as heat and their photosensitivity is not linked to the wavelength being detected. Thermal infrared sensors do not require cooling but tend to have slower response times and lower detection capabilities. Quantum infrared sensors offer higher detection performance and faster response speed, but their photosensitivity is dependent on wavelength and they must be cooled to provide accurate measurements.
The working principle of infrared sensors is based on three laws: Planck’s radiation law, which states that every object at a temperature not equal to 0 Kelvin emits radiation, Stephan Boltzmann Law, which states that the total energy emitted at all wavelengths by a black body is the absolute temperature, and Wein’s displacement Law, which states that objects of different temperature emit spectra that peak at different wavelengths. All objects with a temperature above absolute zero (0 Kelvin) have thermal energy and are therefore sources of infrared radiation. Common sources include blackbody radiators, tungsten lamps, and silicon carbide. Infrared sensors commonly use infrared lasers and LEDs with specific infrared wavelengths as sources.
A transmission is necessary for infrared transmission. This can be a vacuum, the atmosphere, or an optical fiber. Optical components, such as lenses made from quartz, polyethylene, and other materials are used to converge or focus the infrared radiation. Finally, infrared detectors detect the focused radiation. As the detector output is commonly very small, pre-amplifiers coupled with circuitry are required to further process the signals.
Infrared technology has a broad range of applications, among which are night vision, infrared tracking, hyperspectral imaging, and even art restoration. In night vision devices, infrared technology is used when there is not enough visible light to otherwise see. Night vision devices take ambient photons of light, convert them into electrons, amplify them through an electrical process, and ultimately convert them back into visible light. Infrared tracking, or homing, is a missile guidance system that tracks a target by using the infrared electromagnetic radiation it emits. Systems of this type are commonly referred to as ‘heat-seeking,’ as infrared radiation is given off by hot bodies such as people, vehicles, and aircraft.
Hyperspectral imaging is a process that accumulates and processes light from all over the electromagnetic spectrum. It can be used to track nanoparticles inside large living organisms. Finally, infrared technology can even be used in art restoration where it can reveal hidden layers in paintings. This is helpful in deciphering whether a piece of art is original or a copy, and whether or not it has been altered from its original form.
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