Listen to this articlePassive RIFD transponders receive their required operating energy completely via the energy field of the RFID reader. Data is also transmitted bidirectionally via this field.
Active RFID transponders have their own built-in operating energy source.
Semi-passive RFID transponders obtain their operating energy which is required via the energy field of the RFID reader, but an operating energy source is integrated which is required to generate the HF signal.
The RFID system is described based on the resonance principle on contactless magnetic coupling which is inductive. The RFID systems are separated by an air gap interface that consists of a reader with L1 as an antenna coil and L2 as a transponder with an antenna coil.
The reader is an interrogator or a reader which in the simplest case consists of an HF module with an electronic circuit and a resonant circuit whereby antenna coil L1 is an induction coil that can be arranged outside the housing.
Source:- Elektroauto