radio-frequency identification

Radio-frequency identification moves data between a tag and a reader without direct contact or line of sight. A tag contains a small integrated circuit and an antenna; when a reader transmits a radio signal at a specific frequency, the tag wakes up, processes the command, and transmits back its stored information. The reader decodes this response and passes it to a host system. Frequencies vary by application and region: 125 kHz for low-frequency animal tracking, 13.56 MHz for high-frequency access cards and merchandise, and 860-960 MHz for ultra-high-frequency supply chain work.

Tags fall into two main types: passive tags contain no battery and harvest power from the reader's signal, typically operating within 1 to 10 meters depending on frequency and antenna design; active tags carry their own power source and transmit stronger signals, reaching 100 meters or more. A third category, semi-passive, uses onboard power only to run sensors, not to transmit. Passive tags cost pennies per unit and suit high-volume applications like retail inventory and toll collection. Active tags cost dollars and appear in fleet management, container tracking, and asset monitoring where range and reliability matter more than unit cost.

Memory and encoding challenges

Passive tags typically store 64 to 256 bits of data; high-frequency tags may hold 4 kilobytes or more. The tag's memory usually contains an electronic product code (EPC), which references product data in a backend database, not the full product record itself. Writing to a tag during manufacturing takes microseconds per byte, but the process is sensitive to antenna design and component tolerance. Read range depends critically on antenna orientation, metal presence, and moisture in the environment. Radio waves scatter unpredictably around conductors, so reading tags on steel shipping containers or in the presence of water demands careful reader placement and sometimes multiple antennas.

Collision and interference are persistent problems. When many tags occupy the same reading zone, their responses collide. Modern systems use anti-collision protocols (algorithms that force tags to transmit one at a time) and spread-spectrum techniques to reduce mutual interference. Regulatory limits on transmission power, set by bodies like the FCC and ETSI, cap how hard a reader can transmit and thus constrain read range. In densely tagged environments such as warehouses or distribution centers, installers must balance coverage with cost and electrical load.

The term radio-frequency identification emerged in the 1970s but refers to work done from the 1940s onward. Military radar operators noticed that some aircraft returned stronger signals than expected, a phenomenon later exploited for identification. The acronym RFID took hold in supply chain and retail circles by the 1990s, as costs fell and reading speeds improved. Today it competes with and complements barcode scanning in logistics, coexists with magnetic strips in access control, and serves specialized roles in livestock tracking, library management, and industrial asset visibility.