Basic components of an RFID system
Chip tags consist of a microchip and a coupling element - an antenna. Most tags are only activated when they are within the interrogation zone of the interrogator; outside they "sleep". Chip tags can be both read-only (programmed during manufacture) or, at higher complexity and cost, read-write, or both. Chip tags contain memory. The size of the tag depends on the size of the antenna, which increases with range of tag and decreases with frequency.
Depending on the application and technology used, some interrogators not only read, but also remotely write to, the tags. For the majority of low cost tags (tags without batteries), the power to activate the tag microchip is supplied by the reader through the tag antenna when the tag is in the interrogation zone of the reader, as is the timing pulse - these are known as passive tags.