RFID Technology

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Seeral types.

Most fascinating is active unpowered. Absorbs RF from interrogate signal, rectifies carrier, uses to power low-power circuitry. Circuit encodes response and transmits code back to interrogator.

Another type does carry battery or some other power, which provides a smarter function- can send more information than simple ID code, or has a longer range than interrogator-powered versions.

Another version is just a passive reflector with a binary function- it either passively reflects, triggering response, or just sits there and does not respond at all. Since these devices do not actually send an ID number, some do not consider them RFID. These are types found in anti-theft devices.