IR Sensors (Infrared Sensors)

IR ( Infra Red ) Sensors

An IR or Infrared sensor is an electronic instrument that is used to sense motion or any changes of its surroundings by either emitting or detecting infrared radiation. It can also measure heat of an object and detecting motion. Infrared waves are not visible to the human eye. 

In the electromagnetic spectrum, infrared radiation is the region having wavelengths longer than visible light wavelengths, but shorter than microwaves. The infrared region is approximately demarcated from 0.75 to 1000µm. The wavelength region from 0.75 to 3µm is termed as near infrared, the region from 3 to 6µm is termed mid-infrared, and the region higher than 6µm is termed as far infrared.



Infrared technology is found in many of our everyday products. For example, TV has an IR detector for interpreting the signal from the remote control. Key benefits of infrared sensors include low power requirements, simple circuitry, and their portable feature.

Infrared radiation enters through the front of the sensor, known as the 'sensor face'. At the core of a PIR sensor is a solid state sensor or set of sensors, made from piezoelectric materials—materials which generate energy when exposed to heat. 


Types of Infra-Red Sensors

They can be classified into two types:

1.Thermal infrared sensors – These type of sensors use infrared energy as heat. Their photo sensitivity is independent of wavelength. Thermal detectors do not require cooling; however, they have slow response times and low detection capability.

2.Quantum infrared sensors – These type of sensors provide higher detection performance and faster response speed. Their photo sensitivity is dependent on wavelength. Quantum detectors have to be cooled so as to obtain accurate measurements. The only exception is for detectors that are used in the near infrared region.

Working Principle

A typical system for detecting infrared radiation using infrared sensors includes the infrared source such as blackbody radiators, tungsten lamps, and silicon carbide. In case of active IR sensors, the sources are infrared lasers and LEDs of specific IR wavelengths. Next is the transmission medium used for infrared transmission, which includes vacuum, the atmosphere, and optical fibers.

Thirdly, 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 infrared radiation. Likewise, to limit spectral response, band-pass filters are ideal.

Finally, the infrared detector completes the system for detecting infrared radiation. The output from the detector is usually very small, and hence pre-amplifiers coupled with circuitry are added to further process the received signals.


Applications are:

1.Tracking and art history

2.Climatology, meteorology, and astronomy

3.Thermography, communications, and alcohol testing

4.Heating, hyperspectral imaging, and night vision

5.Biological systems, photobiomodulation, and plant health

6.Gas detectors/gas leak detection

7.Water and steel analysis, flame detection

8.Anesthesiology testing and spectroscopy

9.Petroleum exploration and underground solution

10.Rail safety. 




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