Editorial Feature

The Working Principle and Key Applications of Infrared Sensors

Image Credits: Dario Sabljak/shutterstock.com

An infrared sensor is an electronic instrument that is used to sense certain characteristics of its surroundings. It does this by either emitting or detecting infrared radiation. Infrared sensors are also capable of measuring the heat being emitted by an object and detecting motion.

Infrared technology is found not just in industry, but also in every-day life. Televisions, for example, use an infrared detector to interpret the signals sent from a remote control. Passive Infrared sensors are used for motion detection systems, and LDR sensors are used for outdoor lighting systems. The key benefits of infrared sensors include their low power requirements, their simple circuitry and their portable features.

Infrared Radiation Theory

Infrared waves are not visible to the human eye. In the electromagnetic spectrum, infrared radiation can be found between the visible and microwave regions. The infrared waves typically have wavelengths between 0.75 and 1000µm.

The infrared spectrum can be split into near IR, mid IR and far IR. The wavelength region from 0.75 to 3µm is known as the near infrared region. The region between 3 and 6µm is known as the mid-infrared region, and infrared radiation which has a wavelength greater higher than 6µm is known as far infrared.

The Foundations of Infrared Science

The theory of infrared spectroscopy had been around since F.W. Herschel discovered infrared light in 1800. Herschel conducted an experiment using a prism to refract light from the sun and was able to detect the presence of infrared radiation beyond the red part of the visible spectrum using a thermometer to measure an increase in temperature.

The Types of Infrared Sensors

Infrared sensors can be active or passive and they can be split into two main types:

  • Thermal infrared sensors – use infrared energy as heat. Their photosensitivity is independent of the wavelength being detected. Thermal detectors do not require cooling but do have slow response times and low detection capabilities. Read more about Thermal Infrared Sensors here.
  • Quantum infrared sensors – provide higher detection performance and faster response speed. Their photosensitivity is dependent on wavelength. Quantum detectors have to be cooled in order to obtain accurate measurements.

The Working Principle of Infrared Sensors

The physics behind infrared sensors is governed by three laws:

  1. Planck’s radiation law: Every object at a temperature T not equal to 0 K emits radiation
  2. Stephan Boltzmann Law: The total energy emitted at all wavelengths by a black body is related to the absolute temperature
  3. Wein’s Displacement Law: Objects of different temperature emit spectra that peak at different wavelengths

All objects which have a temperature greater than absolute zero (0 Kelvin) possess thermal energy and are sources of infrared radiation as a result.

Sources of infrared radiation include blackbody radiators, tungsten lamps, and silicon carbide. Infrared sensors typically use infrared lasers and LEDs with specific infrared wavelengths as sources.

Image Credit: Dario Sabljak/Shutterstock.com

A transmission medium is required for infrared transmission, which can be comprised of either a vacuum, the atmosphere, or an optical fiber.

Optical components such as optical lenses made from quartz, CaF2, Ge and Si, polyethylene Fresnel lenses, and Al or Au mirrors are used to converge or focus the infrared radiation. In order to limit spectral response, band-pass filters can be used.

Next, infrared detectors are used to detect the radiation which has been focused. The output from the detector is usually very small and hence pre-amplifiers coupled with circuitry are required to further process the received signals.

The Key Applications of Infrared Technology

Night Vision Devices

Infrared technology is implemented in night vision equipment if there is not enough visible light available to see unaided. Night vision devices convert ambient photons of light into electrons and then amplify them using a chemical and electrical process before finally converting them back into visible light. Read more about infrared technology in night vision devices here.

Infrared Astronomy

Infrared astronomy is a field of astronomy that studies astronomical objects that are visible in infrared radiation. By using telescopes and solid-state detectors, astronomers are able to observe objects in the universe which are impossible to detect using light in the visible range of the electromagnetic spectrum.

Image Credit: Procy/Shutterstock.com

Infrared observatories have been set up in space such as the Spitzer Space Telescope and the Herschel Space Observatory have been set up in space. The observatories are not affected by the absorption of infrared light by water vapor in the Earth's atmosphere.

Infrared Tracking

Infrared tracking, also known as infrared homing, is a missile guidance system that operates using the infrared electromagnetic radiation emitted from a target to track it. These missile systems are often known as 'heat-seekers' as infrared is radiated strongly by hot bodies such as people, vehicles, and aircraft.

Art History and Restoration

Infrared reflectography is used by art historians in order to reveal hidden layers in paintings. This reflectography technique is useful in helping to decide whether a painting is an original version or a copy and whether it has been altered by restoration work.

Hyperspectral Imaging

Hyperspectral imaging accumulates and processes information from across the electromagnetic spectrum and can be used to track nanoparticles inside large living organisms.

Other Key Application Areas

Other key application areas that use infrared sensors include:

  • Climatology
  • Meteorology
  • Photobiomodulation
  • Gas detectors
  • Water analysis
  • Anesthesiology testing
  • Petroleum exploration
  • Rail safety

Sources and Further Reading

This article was updated on the 24th July, 2018.

Alexander Chilton

Written by

Alexander Chilton

Alexander has a BSc in Physics from the University of Sheffield. After graduating, he spent two years working in Sheffield for a large UK-based law firm, before relocating back to the North West and joining the editorial team at AZoNetwork. Alexander is particularly interested in the history and philosophy of science, as well as science communication. Outside of work, Alexander can often be found at gigs, record shopping or watching Crewe Alexandra trying to avoid relegation to League Two.


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  1. mukesh rajendran mukesh rajendran India says:

    can IR sensor be used for human tracking?

  2. Gido Edae Gido Edae Ethiopia says:

    being I am a MSc graduate students I need to  get a reference book for the application of infra red, UV/Vis

  3. thaslima parveen thaslima parveen India says:

    am biomedical student final year i have some  project idea about analyze blood glucose using mid-infrared laser.its get success or not.please reply tome i am very confuse about it.

  4. Janees Khan Janees Khan Hong Kong S.A.R. says:

    interesting knowledge.

  5. Raja . Raja . India says:

    Now my question is infrared sensor how to detect human body.please reply me

    • Mohammed Hoq Mohammed Hoq Australia says:

      you can use thermal camera or get the human photo and apply AI to know the human shape

  6. anu choudhary anu choudhary India says:

    This Infrared Sensor Adaptable to ambient light, have a pair of infrared emitting and receiving tubes, transmitting tubes emit infrared frequency, when the direction of an obstacle is detected, the infrared reflected is received by the reception tube. After a comparator circuit processing, the green light is on, but the signal output interface,output digital signal,you can adjust the detection distance knob potentiometer, the effective distance range of 2cm to 30cm, the working voltage of 3.3V to 5V. Detection range of the sensor can be obtained by adjusting potentiometer, with little interference, easy to assemble, easy to use features, can be widely used in robot obstacle avoidance, avoidance car, line count, and black and white line tracking and many other occasions. When the module detects an obstacle in front of the signal, the green indicator lights on the board level, while the OUT port sustained low signal output, the module detects the distance 2cm to 30cm, detection angle 35 degree, the distance can detect potential is adjusted clockwise adjustment potentiometer, detects the distance increases; counterclockwise adjustment potentiometer, reducing detection distance.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoSensors.com.

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