What is an IR sensor?

Fundamentals
All but the very coldest objects emit electromagnetic radiation in the form of heat that can be detected by infrared sensors. (Getty Images)

An infrared (IR) sensor is an electronic device that measures and detects infrared radiation in its surrounding environment. Infrared radiation was accidentally discovered by an astronomer named William Herchel in 1800. While measuring the temperature of each color of light (separated by a prism), he noticed that the temperature just beyond the red light was highest. IR is invisible to the human eye, as its wavelength is longer than that of visible light (though it is still on the same electromagnetic spectrum). Anything that emits heat (everything that has a temperature above around five degrees Kelvin) gives off infrared radiation.

There are two types of infrared sensors: active and passive. Active infrared sensors both emit and detect infrared radiation. Active IR sensors have two parts: a light emitting diode (LED) and a receiver. When an object comes close to the sensor, the infrared light from the LED reflects off of the object and is detected by the receiver. Active IR sensors act as proximity sensors, and they are commonly used in obstacle detection systems (such as in robots).

PIR Sensor Diagram.
PIR Sensor Diagram. Source: ResearchGate

Passive infrared (PIR) sensors only detect infrared radiation and do not emit it from an LED. Passive infrared sensors are comprised of:

Free Newsletter

Like this article? Subscribe to FierceSensors!

The sensors industry is constantly changing as innovation runs the market’s trends. FierceSensors subscribers rely on our suite of newsletters as their must-read source for the latest news, developments and analysis impacting their world. Register today to get sensors news and updates delivered right to your inbox.
  • Two strips of pyroelectric material (a pyroelectric sensor)
  • An infrared filter (that blocks out all other wavelengths of light)
  • A fresnel lens (which collects light from many angles into a single point)
  • A housing unit (to protect the sensor from other environmental variables, such as humidity)

PIR sensors are most commonly used in motion-based detection, such as in-home security systems. When a moving object that generates infrared radiation enters the sensing range of the detector, the difference in IR levels between the two pyroelectric elements is measured. The sensor then sends an electronic signal to an embedded computer, which in turn triggers an alarm.

Suggested Articles

Cepton Technologies, Inc., a 3D lidar solutions provider, has announced a partnership with ThinkReps, a physical security manufacturers' representative.

Binghamton University researchers have found a way to improve the performance of tiny sensors that could improve the design for microphones and other tiny…

SiC can make medical devices more perceptive, it can make electronics more energy-efficient, and it can help sensors perform in higher temperatures.