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RFID(Radio Frequency Identification) is one of the many technologies grouped under the term Automatic Identification like bar code,optical character recognition , magnetic inks, , touch mem-ory, voice recognition, smart cards, biometrics etc. The RFID technology is a means of gathering data about a certain item without the need of touch-ing or seeing the data carrier, through the use of inductive coupling or electromagnetic waves. The data carrier is a microchip attached to an antenna and the antenna enabling the chip to transmit information to a reader within a given range, which can then forward the information to a host computer. The important feature enabling RFID for tracking objects is its capability to provide unique identification.

TYPES OF TAGS AND READERS
1)Passive
-obtains operating power from the reader
- Here, the reader sends electromagnetic waves that induce current in the tagâ„¢s antenna, the tag reflects the RF signal transmitted and adds information by modulating the reflected signal

2)Semi-passive
-uses a battery to maintain memory in the tag and modulate reflected signal.

3)Active
-powered by an internal battery, used to run the microchipâ„¢s cir-cuitry and to broadcast a signal to the reader

classification based on tag's memory type[/b]
Read-only
-the memory is read onla an data is static.

Read-write
-can be as well read as written into and data can be dynamically altered.

[u]classification based on method of wireless signal used for communication between the tag and reader
1)Induction-Close proximity electromagnetic, or inductive coupling”near field
2)Propagation-Propagating electromagnetic waves”far field
- Operate in the UHF and microwaves frequency bands


Advantages of RFID:
-Tag detection not requiring human intervention reduces employment costs and eliminates hu-man errors from data collection
-RFID tags have a longer read range
-An RFID tag can store large amounts of data additionally to a unique identifier,
-Tags are less sensitive to adverse conditions
-Many tags can be read simultaneously

Limitations:
Standardization:There are no standards concerning communication protocols, signal modulation types, data transmission rates, data encoding and frames, and collision handling algorithms.

Collision:Attempting to read several tags at a time may result in signal collision and to data loss.

Frequency: Choice of frequency depends on many factors like,
Transmission mode, Behavior of tagged goods and environment, International standards in frequency allocation,

Possible virus attacks:Studies have exposed the potential vulnerability of current RFID software if used together with a backend database.

APPLICATIONS
1)Instance or class identification: For providing this service, usually, a data-base is maintained in the background to provide or receive the additional information needed. examples in manufacturing demonstrate the benefits of RFID, such as with identifying individual car bodies in customized automotive pro-duction, tracking of manufacturing,architec-tural construction processes etc.

2)Location identification
If a given reader is assigned to a known location, it is possible to track the current place of a given uniquely identifiable item. postal services and many logistics companies have already integrated such RFID-based features into their tracking services .The RFID tags to be read for localization can be either attached to containers or items, or they can identify the transporting vehicle itself.

3)Transfer of further data
Along with the identificaton data, auxiliary data are read or written which usually contains information which would be difficult im-practical or impossible to obtain from a remote or pre-recorded database, or measurement results.

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