What is the difference between active, passive, and semi-passive RFID?
Active RFID uses an internal power source (a battery) within the tag to continuously power the tag and its RF communication circuitry. Active RFID allows extremely low-level RF signals to be received by the tag (since the reader/interrogator does not power the tag), and the tag can generate high-level signals back to the reader/interrogator. Active RFID tags are continuously powered, whether in the reader/interrogator field or not, and are normally used when a longer tag read distance is desired. Passive RFID relies on RF energy transferred from the reader/interrogator to the tag to power the tag. Passive RFID tags reflect energy from the reader/interrogator or receive and temporarily store a small amount of energy from the reader/interrogator signal in order to generate the tag response. Passive RFID requires strong RF signals from the reader/interrogator, and the RF signal strength returned from the tag is constrained to very low levels by the limited energy. Passive RFID tags are be
