IR Sensor Working

What is IR Sensor

Infrared technology is used in everyday life as well as in industry for a variety of purposes. TVs, for example, use an infrared sensor to decode the signals transmitted by remote control. The main advantages of IR sensors are their low power consumption, simple design, and useful features. IR signals are undetectable to the human eye. In the electromagnetic spectrum, IR radiation can be found in the visible and microwave regions. The wavelengths of these waves typically range from 0.7µm to 5 to 1000 µm. Near-infrared, mid-infrared, and far-infrared are the three regions of the IR spectrum. The wavelength ranges from 0.75 to 3 µm in the near-infrared region, 3 to 6 µm in the mid-infrared region, and more than 6 µm in the far IR region.

what is ir sensor

An infrared sensor is a device that detects infrared radiation in its environment and outputs an electric signal. An infrared sensor can detect movement as well as to measure the heat of an object.

The Infrared Sensor can detect infrared radiation, which is invisible to our eyes. An infrared sensor is a photodiode that is sensitive to infrared light. When infrared light hits the photodiode, the resistances and output voltages change in proportion to the magnitude of the IR light.

Working of an IR sensor

The working principle of an infrared sensor is similar to the object detection sensor. This sensor includes an IR LED & an IR Photodiode, so combining these two can be formed as a photo-coupler otherwise optocoupler. The physics laws used in this sensor are planks radiation, Stephan Boltzmann & Wein's displacement.

  • Planck’s Radiation Law: Any object whose temperature is not equal to absolute zero (0 Kelvin) emits radiation.
  • Stephan Boltzmann Law: The total energy emitted at all wavelengths by a black body is related to the absolute temperature.
  • Wein’s Displacement Law: Objects of different temperature emit spectra that peak at different wavelengths that is inversely proportional to Temperature.

How does an IR sensor work

IR LED is one kind of transmitter that emits IR radiation. This LED has the appearance of a standard LED, and the radiation it emits is not visible to the human eye. An infrared transmitter is used to detect the radiation by infrared receivers. These infrared receivers are available in photodiode form. IR Photodiodes are different from regular photodiodes in that they only detect IR radiation. Different types of infrared receivers exist based on voltage, wavelength, package, and other factors.

When used as an IR transmitter and receiver, the wavelength of the receiver must match that of the transmitter. The transmitter is an infrared LED, and the receiver is an infrared photodiode. The infrared photodiode is activated by the infrared light produced by an infrared LED. The photodiode's resistance and the change in output voltage are proportional to the amount of infrared light obtained. This is the IR sensor’s fundamental working principle.

Once the infrared transmitter generates emission, when it arrives at the object & some of the emission will reflect toward the infrared receiver. The sensor output can be decided by the IR receiver depending on the intensity of the response.

IR Proximity Sensor Working Principle

IR Proximity sensor working principle

The working principle of the IR Proximity sensor is the same as the working principle of the IR sensor as explained above. Infrared light (IR) is based on the principles of optics.
An IR proximity sensor works by applying a voltage to a pair of IR light-emitting diodes (LEDs) which in turn, emit infrared light. This light propagates through the air and once it hits an object it is reflected towards the sensor. If the object is close, the reflected light will be stronger than if the object is further away.

Types of IR Sensors

1. Active IR Sensor

 Active IR sensor

This type of sensor includes both the emitter & the receiver which are also known as transmitter & receiver. In the majority of cases, a laser diode or LED is used as a light source. LEDs are used for non-imaging infrared sensors, while laser diodes are used for imaging infrared sensors.
An infrared sensor works by emitting energy that is detected and received by the detector. To obtain the required data, it is further processed through a signal processor. Reflectance and break beam sensors are the best examples of active infrared sensors.

working priciple of ir sensor

2. Passive IR Sensor

Passive IR Sensor

The passive infrared sensor includes detectors only but they don’t include a transmitter. These sensors make use of a transmitter or an infrared source. This object emits energy, which infrared receivers detect. After that, a signal processor is used to decode the signal and extract the necessary data.

working of passive IR sensor

The best examples of this sensor are pyroelectric detector, bolometer,
thermocouple-thermopile, etc. These sensors are classified into two types thermal IR sensors and quantum IR sensors.

1. Thermal Infrared Sensor

this image shows Thermal Infrared Sensor

These types of sensors are independent of wavelength and they utilize heat-like energy sources. These are slow along with the response time as well as detection time.

2. Quantum Infrared Sensor

Quantum Infrared Sensor

These types of sensors depend on wavelengths and the response time and they have high detection. These kinds of infrared sensors need repeated cooling for exact measurement.

Applications of IR Sensors

IR sensors have found their applications in most of today’s equipment. Following is the list of sensors that are named after their usage.

1. Proximity Sensor
These are used in smartphones to find the distance of objects. They use a principle called Reflective Indirect Incidence. Radiation transmitted by the transmitter is received by the receiver after being reflected from an object. Distance is calculated based on the intensity of radiation received.

2. Item Counter
This uses the direct incidence method to count the items. Constant radiation is maintained between transmitter and receiver. As soon as the object cuts the radiation, the item is detected and the count is increased. The same count is shown on a display system.

3. Burglar Alarm
This is one of the widely and commonly used sensor applications. It is another example of the direct incidence method.
It works similar to the item counter, where the transmitter and receiver are kept on both sides of a door frame. Constant radiation is maintained between transmitter and receiver, whenever an object crosses the path alarm starts.

4. Radiation Thermometers
It is one of the key applications of Infrared sensors. The working of a radiation thermometer depends on temperature and type of object.
These have faster response and easy pattern measurements. They can do measurements without direct contact with an object.

5. Human Body Detection
This method is used in intrusion detection, auto light switches, etc. An intrusion alarm system senses the temperature of the human body.
If the temperature is more than the threshold value, it sets the alarms. It uses an electromagnetic system that is suitable for the human body to protect it from unwanted harmful radiation.

6. Gas Analyzers
Gas Analyzers are used to measure gas density by using the absorption properties of gas in the IR region. Dispersive and Non Dispersive types of gas analyzers are available.

7. Other Applications
IR sensors are also used in IR imaging devices, optical power meters, sorting devices, missile guidance, remote sensing, flame monitors, moisture analyzers, night vision devices, infrared astronomy, rail safety, etc.


We hope the above blog helped you to get started with the IR sensors, working principles, Types of IR sensor, IR proximity sensor, and their applications. Check out our blog on IR Sensor Interfacing with Arduino

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