RFID Tags: Active, Passive, and Coupling Methods Explained

Inductive Coupling

Propagative Coupling

• Uses a magnetic field, comparable to a transformer where the reader's antenna is the primary winding and the tag's antenna is the secondary winding.
• Relies on the magnetic field to couple information. Works best at close ranges and is simple and rugged.
• Used at lower frequencies where the wavelength is much longer than the distance between the reader and the tag.
• Shorter range than propagative coupling.
• Used in LF (125 kHz to 135 kHz) and HF (13.56 MHz) systems.

• Uses electromagnetic waves, comparable to radio.
• Relies on an electromagnetic wave to couple information.
• Longer range than inductive coupling.
• Used in UHF (860 MHz to 960 MHz) and microwave (2.45 GHz) RFID systems.

Active Tags

Passive Tags

Semi-Active Tags

• On-board power source.
• Active transmitter.
• Additional circuitry (receiver, sensors, microprocessors, ports, etc.). Long range.
• They do not have to wait to be interrogated before transmitting.
• Larger, more expensive, limited battery life, more temperature sensitive.
• Can be triggered by extremely low-level RF signals. Tags transmit a very high-level signal back to the interrogator, giving them very long range.

• No on-board power source.
• Tag does not transmit; it reflects the signal from the reader.
• Powered by the reader’s signal.
• Short range (typically measured in inches). Inexpensive.
• Operating temperature ranges: -25°C to +70°C (-13°F to +158°F).
• Storage temperature: -40°C to 85°C (-40°F to +185°F).

• Also called: Semi-passive, Battery-assisted Passive (BAP).
• On-board power source powers ICs, but not the transmitter.
• Reflects the received signal like a passive tag.
• Often has a greater range than a passive tag, but less than an active tag.
• Larger and more expensive than passive tags, with limited battery life.
• May be more sensitive to temperature extremes.