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A Closer Look at IR Sensor: Types and Applications

IR circuits have been stunning users for many years. It is because of their features that render great results for the fine performance of the tech devices. IR tech is a great asset for wireless devices and remote-controlled machines.

The technology uses different regions of the electromagnetic spectrum that includes three parts. The common parts of the spectrum include near, mid, and far IR regions.

Now, one interesting thing here is that the wavelengths of these three regions are different from each other. Also, know this there are different use cases for these individual regions. For instance, near IR is useful for fiber optic applications and sensing devices. You can rely on the mid-IR for the heat-sensing devices.

The far IR is highly efficient for thermal imaging gadgets.  It’s time to see how you can define an IR sensor in simple terminology!

What is IR Sensor?

The IR sensor means an Infrared sensor. It is an integral component used in electronics and has some remarkable features. There are some major roles of IR sensors which include emitting and detecting infrared radiation. You can even use IR sensors for tracking and motion-detecting tools and radars.

The functioning of an IR sensor is somewhat similar to human vision, as humans can differentiate between objects and detect them as well. Now, there are different types of regular IR sensors. If you want to only detect infrared radiation, then use a PIR sensor. PIR means passive infrared sensor.

However, regular IR sensors are reliable for thermal imaging and such radiations that are beyond detection with normal human vision. There is a special IR LED that is present in this sensor that performs as an emitter. There is a photodiode that plays its part as a detector. When infrared light comes in contact with the photodiode, it will cause the voltage and resistance to change as compared to the amount of IR light. 

Working Principle of IR Sensor

ir sensor circuit
ir sensor circuit

IR sensors, like all the other types of sensors, follow a definite phenomenon for working. The basic principle of function for IR sensors is important to understand to review how they perform in variable conditions. 

  • For the sake of simplification, you can divide an IR sensor into two parts. One is the emitter (transmitter), and the other is the receiver.
  • The emitter is basically an IR LED.
  • The receiver is an IR photodiode.
  • You can call these two parts a photo-coupler or an opt coupler.
  • Now, the photodiode we are talking about here is extremely sensitive to light that comes from the IR LED.
  • This light eventually influences the voltage and resistance of the photodiode as well. 
  • In case when the light is indirect, you can position the IR light after the photodiode.
  • You can also place the photodiodes beside each other and keep them after the sensor itself. 
  • There is a solid structure that helps to reflect the light to the photodiodes and is present between diodes. 

Laws observed by IR SensorsIR sensors cannot work efficiently without the following laws of Physics. We are going to see the science behind these laws and will try to establish their relationship with the IR sensors as well:

  • Planck’s Radiation Law: This law states that no object’s temperature can be equal to 0.
  • Stephan Boltzmann Law: It states that the energy that wavelength produces with the help of a black body directly relates to the temperature.
  • Wein’s Displacement Law: This law states that different objects produce different spectrums of light, and their wavelengths are also different. These have an inverse relation with the temperature. 


Different Types of IR Sensors

The types of IR sensors vary as per the applications. Therefore, it is important to note how these perform for different applications. We have listed the following types of sensors in this regard:

1. Active IR Sensor

  • Such a sensor contains both an emitter and a receiver. The source for this sensor would be a laser diode, or you can also rely on a LED for this.
  • Some sensors are not reliable for detecting IR light, and for these, it is reliable to use a LED instead of a laser diode.
  • You can trust an IR sensor for detecting radiation energy. 
  • After this, the sensor will process this through a signal processor for gathering the critical data. 
  • Some common examples of active IR sensors would be break beam sensors and reflectance.

2. Passive Infrared Sensor

  • These sensors are useful for IR transmitters and sources.
  • The targeted object will produce the energy so that the sensor can detect the energy with the help of its IR receivers.
  • It also contains a signal processor for processing the signals to collect the requisite data. 
  • Now, for the examples of PIR sensors, we have a bolometer, Thermocouple- thermopile, and a pyro-electric detector. 

3. PIR sensors Types:

Now, in the further sections, we are going to decipher both the abovementioned sub-types of PIR sensors for you!

4. Thermal Infrared Sensor

Such a sensor does not have a default wavelength for working. These sensors use such resources that offer an incredible amount of heat. Due to this reason, these are reliable for thermal detection as well. However, you might get disappointed with the slow response time of these sensors. Sometimes it also takes much time for detection. 

5. Quantum Infrared Sensor

These sensors work on different wavelengths later and give relevant results as well. These are also much more reliable in terms of response time. Their detection time is also more than the thermal PIR sensors. However, you need to frequently cool them down to get accurate results since overheating can create a negative impact on the output data. 

6. IR Sensor Circuit


One of the major applications of an IR sensor is the obstacle detection. You need some components to build such a circuit. Don’t worry; you don’t have to run errands for the construction. The components are:

  • A photodiode
  • An IR LED
  • An operational amplifier
  • A potentiometer
  • A regular LED

Now that you have your components ready let’s see the individual roles of these parts below:

  • The IR LED is for emitting infrared light
  • The role of the photodiode is to detect this IR light
  • The OP-AMP is for acting as a comparator 
  • A potentiometer will help in changing the output data as per your needs

Its time to have a look at the mutual interaction of these components for this application:

  • The IR LED will produce light that will interact with the photodiode, which will reduce the resistance of the photodiode.
  • After this, the OP-AMP will give one of its inputs for the threshold value that later would be easy for the potentiometer to adjust.
  • Other inputs of the OP-AMP need resistors in a series arrangement of the photodiode for the adjustment.
  • When the radiation interacting with the photodiode will maximize, it will reduce the voltage throughout the series resistors. 
  • Now, remember this: If you will increase the voltage and it exceeds the threshold voltage, it will increase the output value as well.
  • When the circuit passes this value to the regular LED, it will start flickering.
  • A potentiometer will help in fixing a certain threshold value based on the application and its requirements. 

7. Direct Incidence in IR sensor circuits

You know that we used two parts (an IR receiver and IR LED) in this circuit which are the backbone for its functioning. Direct incidence happens when you position the IR LED in front of the IR receiver while working on the circuit’s arrangement. 

End Result: It is clear that the IR receiver will gather the entire radiation of the IR LED. It means in case of a drop in the arrangement, the emission will be prevented from going toward the receiver in two ways. It will either reproduce the radiation or absorb it for this purpose.




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