What is the difference between active and passive RFID?

Radio-frequency identification (RFID) tags are used to track and identify personnel (including implanted RFID) and inventory/assets in warehouses, work-in-process (WIP) in manufacturing plants, animals in laboratories, on farms or in the wild and to provide access control and for automatic toll collection for vehicles in consumer as well as government applications. The RFID tag is a transponder that is read and decoded by an RF reader. For inventory and WIP in harsh environments or non-line of sight (LOS) operations, RFID is an alternative to a bar-code system.

The tags can be active or passive. Active tags have on-board batteries and larger data capacities approaching 1 Mb. Decision making ability is included in some varieties with the addition of a microcontroller. Active tags are further classified as either transponders or beacons. Passive tags obtain their operating power from RF energy transmitted from an antenna and, as a result, have limited data capacities, typically 1 to 128 bits. There is also a classification called semi-passive RFID. This type uses an internal power source to monitor environmental conditions but requires RF energy from a reader/interrogator similar to passive tags to provide a tag response.

Image source: SICK USA

RFID systems operate in both low, high-frequency and ultra-high frequency (UHF) ranges. Low-frequency systems typically operate in the frequency range of 100 kHz to 1.5 MHz and also have lower data transfer rates. They are cost effective in access control and asset tracking applications and are commonly used for employee badges, door and gate access control.  Ultra-high frequency systems operate in the spread spectrum range of 900 MHz to 2.4 GHz and have higher data transfer rates. High frequency systems cost more than low frequency systems, but they can operate at distances up to 100 feet (30 meters) or more. They are used for identification, access control and transaction processes. In between high frequency RFID operates around 13.56 MHz and provides a higher security format than low frequency versions. They are common in credit cards and employee badges for access control.