RFID

Radio-frequency identification, or RFID, is a technology that uses electromagnetic fields to automatically identify and track a tag attached to an object, made up of a small radio transponder tag, a reader and a transmitter; when the reader sends out an interrogating radio pulse, the tag responds by transmitting a stored identifying number back to it, without requiring line of sight between the two. RFID's roots trace back to a 1945 covert listening device built by Leon Theremin for the Soviet Union that passively retransmitted radio waves, but the American engineer Mario Cardullo's patent, granted on January 23, 1973, for a passive radio transponder with memory, is considered the first true ancestor of the modern technology, and further demonstrations followed in 1973 at Los Alamos National Laboratory using the modulated-backscatter technique still used in most UHF and microwave RFID tags today. Passive tags draw their power directly from the reader's own radio signal, while active, battery-powered tags can transmit over much greater distances, and because RFID tags can be read through packaging and containers rather than requiring a direct line of sight, the technology became widely used for tracking inventory and shipments in warehouses and supply chains.