RFID Tags & Applications

What is an RFID tag?

The RFID tag is a microchip with an antenna in a compact package. The Tag can be attached to the object to be tracked through Radiofrequency. The Tag’s antenna picks up the signals from the RFID reader and then returns the signal usually with some additional data like the unique serial number. The RFID tags are too small so that it can be incorporated into any objects. Some Tags require battery while most of them do not need battery power and read at short distances using the electromagnetic induction. The Tag contains stored data that can be sent to several meters through the radio waves. The Tag does not need a line of sight with the reader and can be incorporated in moving objects also.

3 Types of RFID systems involving different types of tags:

There are three configurations for the RFID system.

1. Passive Reader Active Tag or PRAT – It has a passive reader that only receives the signals from an Active Tag. The range of the system can be many feet.
2. Active Reader Passive Tag or ARPT – It uses an Active reader and a Passive Tag. The Active Reader transmits signals to the Passive Tag and receives the signals from the Tag.
3. Battery Assisted Passive Tag or BAP- It also functions like a Passive Tag, but there is the battery to power the tag to send signals to the reader.

6 Types of Tags:

There are different types of Tags like Passive Tags, Active Tags, battery-operated Tags, etc.

• Passive Tags – It is the cheaper version using no battery. The Tag uses radio energy transmitting from the reader. So the Reader must be close to the tag to transfer energy to power the Tag. Since the tags have a unique serial number, the reader can recognize them individually.
• Active Tags– These have an onboard battery and periodically transmits ID signals to the reader.
• Battery Assisted Passive or BAP– These Tags have a small battery on board and will be activated in the presence of signals from the reader.
• Read-only Tags – These have a unique factory assigned serial number used as the key for the database.
• Read/ Write Tags – These can write object-specific data give by the system user.

Field programmable Tags– These can write once but read many times. Black tags can be written with an electronic product code by the user.

RFID Tag is an important part of the system in which the data is stored in the volatile memory. The Tag has two parts namely a Transmitter and a Receiver. The Tag contains an integrated circuit for storing and processing the information and the circuit for modulating and demodulating the radio signals. Circuits to receive power from the reader signal are also present in Tags without battery. An antenna is present in all tags for receiving and transmitting the signals. The Tag receives the encoded radio signals from the reader. When the Tag receives the information from the reader, it responds to it with its identification data. It may be the unique serial number or other information like stock number, date of manufacturing, etc.

The Electronic Product Code or EPC is a kind of data stored in the Tag. This is written in the Tag using an RFID printer and the data contains 96 bits. The first 8 bits represent the Header for the identification of the protocol version. The next 28 bits represent the organization that manages the data in the Tag. The next 24 bits represent the object class and the last 36 bits show the unique serial number of the Tag.

Interfacing a tag to an RFID reader

The Reader may be fixed or movable. Fixed readers create a zone for the interrogation with the Tags fixed in the objects. This zone is tightly controlled within the range of the reader. The fixed reader identifies the movement of the Tags into and out of the zone. Mobile readers are handheld devices or fixed in moving vehicles.

The interrogation between the Tag and the Reader is done in different ways depending on the radio frequency band used by the Tag. Some Tags use near field in which Low and High-frequency radio waves are used. In this condition, the tag and the Reader will be closely coupled through radio frequencies. The Tag is capable of modulating the signals of the reader by changing its electrical load. Through changing the load between the lower and higher loads, the Tag can produce a change that can be detected by the reader. Tags using UHF and Higher frequencies require a different approach. Here the Tag is more than one radio length away from the reader and backscatters the signal.

An application involving RFID tags – RFID based billing System

Customers at popular shopping malls have the bad experience of standing in a long queue for getting their bills paid. This project is about developing an RFID based device to help ease the situation. Customers spend a lot of time in selecting products one after another and while reaching the counter they expect to be billed immediately which is practically impossible in a busy counter. A customer at the entrance is given a trolley built-in with an RFID reader with an LCD display. While picking up any product which would have a specific RFID tag attached to the product group would display the name, quantity, and price and then add to the cart. Simultaneously it will send the data to the counter over wireless. The RFID reader is directly connected to the network which sends information on the tags to the centralized system and the bank is accordingly notified and the transactions take place accordingly.

Thus by the time the customer reaches the counter his billing is almost ready and he can be disposed of by just physically matching the goods and collecting the payment. This system is a great improvement over the traditional method of tracking and checking the bar code on each product.  It also eliminates the counter person’s wrong entry that often happens for unwary customers who pay for some item that they never had taken.