RFID (Radio Frequency Identification) is a wireless technology that is used to identify things. It typically involves three components: a tag, a reader, and a computer system.

Sometimes referred to as a transponder, the tag consists of a microchip and a radio antenna. The chip in the tag contains information about the item that it is either attached to or that it is embedded in. The tag transmits that information to the reader using radio signals.

The reader, also called an interrogator, is a device that is designed to pick up those radio signals and deliver the information they contain to the computer system. The computer system can use the information in a variety of ways, depending on what it is set up to do – for example, it might be to track inventory or give a person access to an office building. It may be connected to databases that contain more information linked to the item and, in some cases, to the person using it

There are two main types of Tags :-

1 .Passive

2. Active

Passive RFID Tags

Passive RFID tags have no internal power supply. The minute electrical current induced in the
antenna by the incoming radio frequency signal provides just enough power for the CMOS
integrated circuit in the tag to power up and transmit a response. The lack of an onboard
power supply means that the device can be quite small: commercially available products exist that can be embedded in a sticker, or under the skin.

Active RFID Tags

Unlike passive RFID tags, active RFID tags have their own internal power source which is used to power any ICs that generate the outgoing signal. Active tags are typically much more reliable (e.g. fewer errors) than passive tags due to the ability for active tags to conduct a "session" with a reader .Active tags, due to their onboard power supply, also transmit at higher power levels than
passive tags, allowing them to be more effective in "RF challenged" environments like water (including humans/cattle, which are mostly water), metal (shipping containers, vehicles), or at longer distances.Many active tags have practical ranges of hundreds of meters, and a battery life of up to 10 years. Some active RFID tags include sensors such as temperature logging which have been used in concrete maturity monitoring or to monitor the temperature of perishable goods.Oher sensors that have been married with active RFID include humidity, shock/vibration, light, radiation, temperature and atmospherics like ethylene.

Active tags typically have much longer range (approximately 300 feet) and larger memories than passive tags, as well as the ability to store additional information sent by the transceiver. The United States Department of Defense has successfully used active tags to reduce logistics costs and improve supply chain visibility for more than 15 years. At present, the smallest active tags are about the size of a coin and sell for a few dollars.

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