Radio frequency identification (RFID) is used for describing technologies that make use of radio waves in order to identify people and objects automatically. There are multiple ways of identification, the most popular one being storing a unique serial number on a microchip with an antenna. The antenna and microchip are collectively known as RFID tag or transponder. The antenna transmits identification information from the microchip to a specific reader. The reader then converts that message into digital information which can be forwarded to computers.
In RFID detection systems, the reader or interrogator sends out multiple electromagnetic waves that create a field from which the passive circuits of a microchip in an RFID tag draw power and modulate the waves. Just like a radio needs to be tuned to different frequencies for listening to different channels, RFID transponders and interrogators must be tuned to one specific frequency for establishing communication between them. The most common frequencies used by them include low (125 KHz), high (13.56 MHz) and ultra high (850 to 900 MHz). Microwave frequency of 2.45 GHz is used as well in a few applications. Varied frequencies have varied characteristics which make them even more useful for various applications. For example, low frequency tags use limited power and can pass through non-metallic substances better. They are appropriate to scan objects having a high water content, like fruits, at a close range. Ultra high frequencies can send data more quickly and provide better range. However, they require more power and cannot penetrate materials. Since they are more directed, they need a conspicuous path between the interrogator and transponder. They are ideal for scanning boxes when they are passing through the door of a warehouse.
RFID tags can be active, semi-passive or passive, the former ones having a battery used for running the circuitry of the microchip and broadcasting signal to an interrogator. Semi-passive ones have a battery, but draw power from the electromagnetic field created by the interrogator. Semi-passive and active tags are of great significance when it comes to tracking expensive goods which must be scanned over long ranges. A tag can generally carry not more than 2 kilobytes of data which is quite sufficient for storing some fundamental information about the article it is attached to. Nowadays, companies are starting to favour the ‘license plate’, a simple tag that can hold just a 96-bit serial number.