What is RFID

Radio frequency identification or RFID is a technology which is working on the radio frequency of radio waves. This technology is used to automatically identifying the object or tracking the objects. Now, here this object could be anything the objects could be books in a library or it could be any item which we purchase from the shopping mall or it could be the inventory in the warehouse or maybe it could be your own car. And not only the objects but it can be used for tracking the animals as well as the birds. So in this RFID Technology, the RFID tag is used to get attached to the object which we want to track.

The RFID reader is continuously sending radio waves. So whenever the object is in the range of the reader then the RFID tag transmits its feedback signal to the reader. It is very similar to the technology which is used in a barcode.  But in the case of a barcode, the object and the scanner should be in the line of sight. As This RFID technology is not a line of sight technology, so as far as this object is within the range of the reader, the object is able to identify the reader and it is able to send the feedback single back to the reader.  Using this RFID Technology we can track even multiple objects at the same time.

RFID System 

RFID System

RFID  system contains two components. RFID reader and the RFID tag. RFID tags are coming in many forms. It could be a active tag, passive  tag or semi passive tag.

Passive tag:

Do not have their own power  supply. So this passive tag relies on the radio waves which is coming from the rfid reader for the source of energy.

Semi passive tag:

They have their own  power supply. But for transmitting the feedback signal back to the rfid reader they rely on the signal which is coming from the rfid reader.

Active tag:

They have their own power supply. But for transmitting the signal back to the reader  also they are relying on their own power supply.

So, as this passive tag do not have their  own power supply the range is less compared to the active and semi passive tags.

What’s inside RFID System

RFID Reader

The RFID readers comes in many size and shapes. It could be your handheld reader or it could  be as large as the size of the door which we normally see inside the shopping malls. RFID reader mainly consists of three components.

First component of the RFID  reader is RF signal generator. This signal generator generates radio wave which are transmitted  using the antenna. Also to receive the feedback signal which is coming from the tag, the RFID  reader have a receiver or a signal detector. And to process the information which is being  sent by the RFID tag, RFID reader have microcontroller. Many times this RFID  reader is directly connected to the computer.



RFID tags are a type of tracking system that identifies items using barcodes. Radio frequency technology is used in RFID tags. These radio waves carry information from the rfid tag to a rfid reader, which then sends it to an RFID computer program. RFID tags are commonly used to track items, but they can also be used to track cars, dogs, and even Alzheimer’s patients. An RFID tag is also known as RFID chip. Most of the tags, which are being used today are passive tags. Because these passive tags are quite cheaper compared to the active tags as well as they do not require any power source, so they are quite compact. These passive tags come in many forms. The passive tag could be either size of a key chain or it could be the size of a credit card or maybe it could be in a form of a label.

What are the basic components inside the RFID Tag


The first component that you see inside RFID tag is a transponder. Which receives the radio waves which are coming from the reader and send the feedback signal back to the reader. As the passive tags do not have their own supply so they rely on the radio waves which are coming from the reader. They used to get the energy from the radio waves which are coming from The reader. Using the rectifier circuit the energy that is coming from the radio waves is stored across the capacitor. And this energy is used as a supply for the controller as well as the memory element inside is RFID tag.

Frequency of Operation

Let us see the different frequencies at which the RFID tags are operated. So, mainly RFID  tags are operated at 3 frequencies. The low-frequency range, the high-frequency range and the Ultra high-frequency range. The frequency range or frequency of operation varies from country to country. But majority of the countries follow these frequencies for the operation of the RFID tags. As the low-frequency signals can travel very short distance, the range of RFID tags which is using this low-frequency range is up to 10 cm. The high-frequency radio waves can travel up to 1 Meter. While the Ultra High-Frequency radio waves can travel up to 10 to 15 Meters.

The RFID system is mainly operated in three frequency bands.

1) LF: Low-Frequency band

2) HF: High-Frequency band

3) UHF: Ultra High-Frequency band

Working Principle of the RFID System

Now, this working principle also depends upon the frequency of operation. So, for the low frequency and the high-frequency operation, the working principle is based on the inductive coupling. While in case of a Ultra high frequency RFID tags, the working principle is based on the electromagnetic coupling.


First of all, let’s see the working principle of the low frequency and high frequency RFID tags. As mentioned earlier, the RFID reader continuously sends radio waves with a particular frequency this radio waves which is being sent by this RFID reader serves 3 purposes. First it induces the enough power into the passive tag. Second, it provide the synchronization clock  for the passive tag. Third, it acts as a career for the data which is coming back from the RFID tag. These are the basic 3 purpose which is being served by the radio waves that is sent by this RFID reader. In case of a low frequency and high frequency operation as a RFID reader and tag are very close to each other, the working principle is based on the inductive coupling. So, the field which is generated by this RFID reader get couple with the antenna of a RFID tag. And because of this mutual coupling, the voltage will get induce across the coil of RFID tag. Now the some portion of this voltage  is getting rectified and used as a power supply for the controller as well as the memory elements. 

Now, as the RFID reader is sending a radio waves of a particular frequency, so the voltage  that is induced across the coil is also of a particular frequency. This induced voltage is also used to derive the synchronization clock for the controller. Now suppose if we connect a load of the coil, then current will start flowing through this load and if we change the impedance of this load then the current that is flowing through this load will also get  changed. So now suppose if we switch on and off this load and the current will also get switched  on and off. This switching of current or rate of change of current also generates a voltage  in a RFID reader. So this switching on and off the load is known as the load modulation.

Now suppose, if we switch on and off this load according to the data that is stored inside this RFID tag, then that data can be read by the RFID reader in the form of a voltage. In this way using this load modulation we are changing the voltage that is generated across the RFID reader coil. And in this way, we are generating modulation on carrier frequency.  Also, low frequency and high-frequency RFID tags, using this load modulation technique are sending the data back to the RFID reader.

Ultra high frequency : FAR FIELD COUPLING

In case of a Ultra high frequency, as a distance  between the reader and the tag is up to few meters, so the coupling between the reader  and the coil will be the Far field coupling. This RFID reader continuously sending the radio waves of a particular frequency towards the tag, and in response, this tag is sending  a weak signal to the RFID reader. Now this weak signal which is being sent back to the RFID reader  is known as the back scattered signal. And the intensity of this back scattered signal depends  upon the load matching across the coil.

If the load is matched exactly, then the intensity of the backscattered signal will be more. But if the load is not matched exactly then the intensity of this backscattered signal will be less. So, in this way, by changing the condition of a  load we can change the intensity of this backscattered signal. And if we change the condition of a load according to the data that is being stored across this RFID tag, then that data can be sent back to the RFID reader.

In this way, the RFID reader is able to sense that data. Now in case of a powerful coupling, as the distance between the RFID reader and Tag is few meters the initial signal which is being sent by The Reader should be strong so that the backscattered signal can be retrieved by this RFID reader. In far-field coupling, the signal is sent back to the RFID reader using this backscattered modulation technique.

Applications of the RFID Technology 

RFID is used in a wide range of applications, and many of the applications we have already  discussed. Listed below are few applications in which the RFID system is used.

  1. Institutions: Library, hospital, schools and colleges
  2. Transportation and Logistics
  3. Access Control
  4. Sports
  5. Animal Tracking