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1 The RFID System

1.1 What is RFID?

Radio Frequency Identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is a small object that can be attached to or incorporated into a product, animal, or person. RFID tags contain silicon chips and antennas to enable them to receive and respond to radio-frequency queries from an RFID transceiver. Passive tags require no internal power source, whereas active tags require a power source.

1.2 Basics of RFID Tags

RFID tags can be either passive, semi-passive (also known as semi-active), or active.

1.2.1 Passive

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 (IC) in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier signal from the reader. This means that the aerial (antenna) has to be designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. The response of a passive RFID tag is not just an ID number (GUID); the tag chip can contain nonvolatile EEPROM (Electrically Erasable Programmable Read-Only Memory) for storing data. Lack of an onboard power supply means that the device can be quite small: commercially available products exist that can be embedded even under the skin of human beings. Passive RFID tags do not require batteries, and can be much smaller and have an unlimited life span. Because passive tags are cheaper to manufacture and have no battery, the majority of RFID tags in existence are of the passive variety.

1.2.2 Semi-passive

Semi-passive RFID tags are very similar to passive tags except for the addition of a small battery. This battery allows the tag IC to be constantly powered, which removes the need for the aerial to be designed to collect power from the incoming signal. Aerials can therefore be optimized for the backscattering signal. Semi-passive RFID tags are faster in response and therefore stronger in reading ratio compared to passive tags.

1.2.3 Active

Unlike passive and semi-passive RFID tags, active RFID tags (also known as beacons) have their own internal power