Radio-frequency identification (RFID) technology involves the use of electromagnetic or electrostatic coupling in the RF portion of the electromagnetic spectrum to uniquely identify an object, animal or person. It has established itself in a wide range of markets including livestock identification and automated vehicle identification because of its ability to track moving objects. The technology has also become a primary component of automated data collection, identification and analysis systems worldwide.
The RFID device serves the same purpose as a bar code or a magnetic strip on the back of a credit card or ATM card; it provides a unique identifier for that object. And, just as a bar code or magnetic strip must be scanned to get the information, the RFID device must be scanned to retrieve the identifying information.
Low-frequency (30-500 kHz) RFID systems have a short transmission range (generally less than 1.8 metres). High-frequency (850-950 MHz and 2.4-2.5 GHz) RFID systems offer a longer transmission range (more than 27 metres). In general, the higher the frequency, the more expensive the system. RFID is sometimes called dedicated short-range communication.
Architecture
An RFID system consists of three components:
1) A transceiver with a decoder to interpret the data(often combined into the reader)
2) A transponder - the RFID tag - that has been programmed with information.
3) A scanning antenna
- RFID reader : RFID reader is the device used to transmit and receive information from the RFID tag. It is also referred to as an ‘interrogator.’ It includes sensors that read the RFID tags in the vicinity. The reader is used to communicate with the tags that may pass within range. The RFID reader will normally be located in a fixed position. Dependent upon the application and the format of the system and the RFID reader data may also be written to the RFID tag.
- RFID tag: RFID tags may also be called RFID transponders and are typically located on items that are mobile. They are small and generally cheap so that they can be attached to low cost (or high cost) items that need to have information associated with them. They are also generally considered as being disposable. The RFID tag contains data that is relayed to the reader, and in some systems it may also be possible to update the data within the tag to indicate that the tag and hence the item has undergone a specific stage in a process, etc.
- Scanning antenna puts out radio-frequency signals in a relatively short range.
The RF radiation does two things:
- It provides a means of communicating with the transponder (the RFID tag)
- It provides the RFID tag with the energy to communicate (in the case of passive RFID tags)
WORKING
An integrated circuit sends a digital signal to a transceiver which generates a radio frequency signal that is transmitted by a dipole antenna.
The electric field of the propagating signal gives rise to a potential difference across the tag's dipole antenna which causes current to flow into the capacitor. The resulting charge is trapped there by the diode.
The voltage across the capacitor turns on the tag's integrated circuit which sends out its unique identifier code as a series of digital high and low voltage levels corresponding to 1's and 0's. The signal moves to the transistor.
The transistor gets turned on or off by the highs and lows of the digital signal alternatively causing the antenna to reflect back radio frequency energy from the reader.
The variation in the amplitude of the reflected signal corresponding to the tag identifier code is called as backscatter modulation.
The reader transceiver detects the reflected signals and converts them into a digital signal that is relayed to the integrated circuit where the tag's unique identifier is determined.
Applications
RFID systems can be used in a variety of ways. There are many RFID applications which have gained popularity over the past years:
- Store product identification - RFID technology can be used within shops and stores as a form of alert for goods that have / have not been paid for.
- Asset tracking - RFID systems can monitor when RFID tags pass given points and in this way track the assets.
- Airline baggage identification - airlines need to monitor where baggage is and route it to the required destination. RFID tags can be attached to the bags to automate baggage routing.
- Parts identification - Data can be written to an RFID tags defining the identity of a part. This can then be used within a manufacturing, stock holding or other process to identify and locate parts.
- Production control - when items are manufactured they pass through many stages. RFID tags can be attached to items. These can be updated each time the item passes through a stage in production. This will enable the manufacturing system to track all items and know what stage they are at, and any other information such as test failures, etc.
- Employee access control - many companies today require intelligent access control systems. RFID technology is able to provide control as well as tracking, noting when cards pass particular access points, etc.
- Supply chain control - with manufacturing working to much tighter timescales with items such as Just-In-Time techniques being involved tracking of the items in a supply chain becomes more critical. RFID tags can be added to items to enable this to be undertaken accurately and more quickly.
- Vehicle tracking - RFID technologycan be used to determine when vehicles have passed particular points and in this way their location can be approximately determined.
- Livestock identification - RFID tags can be injected into animals, under the skin and this enables accurate determination of which animal is which so that injections, etc can be given to the correct animal.
RFID TAG
RFID tag, usually known as transponder, acts as a transmitter as well as a receiver in the RFID system. The three basic components of the RFID tag are an antenna, a microchip (memory) and the encapsulating material. In a typical system, tags are attached to objects. Each tag has a certain amount of internal memory (EEPROM) in which it stores information about the object, such as its unique ID (serial) number, or in some cases more details including manufacture date and product composition.
TYPES OF TAG
- Read-only tag
In the read-only tag, the microchip or memory is written only once, during manufacturing process. The information, along with the serial number on the read-only tag, can never be changed.
- Read-write tag
In the read-write tag, only the serial number is written during manufacturing process. The remaining blocks can be re-written by the user.
Tag classes
One of the main ways of categorising RFID tags is by their capability to read and write data. This leads to the following four classes:
Class 0 (read-only, factory-programmed). These are the simplest type of tags, where the data, which is usually a simple ID number (EPC), is written only once into the tag during manufacture. The memory is then disabled from any further updates. Class 0 is also used to define a category of tags called electronic article surveillance or anti-theft devices, which have no ID and announce their presence only when passing through an antenna field.
Class 1 (write-once read-only, factory- or user-programmed). In this case, the tag is manufactured with no data written into the memory. Data can then either be written by the tag manufacturer or by the user one time. Following this no further writes are allowed and the tag can only be read. Tags of this type usually act as simple identifiers.
Class 2 (read-write). These are the most flexible type of tags, where users have access to read and write data into the tag’s memory. They are typically used as data loggers and therefore contain larger memory space than what is needed for just a simple ID number.
Class 3 (read-write with on-board sensors). These tags contain on-board sensors for recording parameters like temperature, pressure and motion by writing into the tag’s memory. As sensor readings must be taken in the absence of a reader, the tags are either semi-passive or active.
Class 4 (read-write with integrated transmitters). These are like miniature radio devices which can communicate with other tags and devices without the presence of a reader. This means that they are completely active with their own battery power source.
Communication protocol
The communication process between the reader and tag is managed and controlled by one of several protocols, such as the ISO 15693 and ISO 18000-3 for HF, or the ISO 18000-6 and EPC 18000-6 for UHF. Basically, when the reader is switched on, it starts emitting a signal at the selected frequency band (typically 860-915 MHz for UHF or 13.56 MHz for HF). Any corresponding tag in the vicinity of the reader will detect the signal and use the energy from it to wake up and supply operating power to its internal circuits. Once the tag has encoded the signal as valid, it replies to the reader, and indicates its presence by modulating (affecting) the reader field. The number of tags that can be identified depends on the frequency and protocol used, and can typically range from 50 tags/s for HF to 200 tags/s for UHF. Once a tag is selected, the reader is able to perform a number of operations such as reading the tags.
Pros
1. RFID tags are rugged and robust and can work in harsh temperatures and environment. The RFID system works at a remarkably high speed, even in adverse conditions.
2. RFID tags are available in different shapes, sizes, types and materials. The information on the read-only tag cannot be altered or duplicated. Read-write tags can be used repeatedly. The RFID tags are always read without any error.
3. Direct physical contact between the tags and the reader is not required. RF technology is used for communication.
4. Multiple RFID tags can be read at the same time. The RFID tags can be read in a bulk of ten to 100 tags at a time. Reading of the tags is automatic and involves no labour.
5. RFID systems can identify and track unique items, unlike the bar code system which identifies only the manufacturer and the product type.
6. The entire RFID system is very reliable, which allows the use of RFID tags for security purpose.
7. The storage capacity of the RFID tags is greater than of any other automatic identification and tracking system.
Cons
1. The RFID system is costly compared to other automatic identification systems. The cost can increase further if the RFID system is designed for a specific application.
2. Size and weight of the tags is more as compared to barcode system. The electronic components like antenna, memory and other parts of the tags make them bulky.
3. Although the tags work in harsh environments, the signals from certain types of tags get affected when they come in close contact with certain metals or liquids. Reading such tags becomes difficult and sometimes the data read is erroneous.
4. There is no way in which damaged tags can be tracked and replaced with tags that are intact.
5. Although the tags do not require line-of-sight communication, they can be read within a specified range only.
- Newer innovations in the RFID industry include active, semi-active and passive RFID tags. These tags can store up to 2 kilobytes of data and are composed of a micro-chip, antenna and, in the case of active and semi-passive tags, a battery. The tag’s components are enclosed within plastic, silicon or sometimes glass.
Category:
