RFID tags can be passive, active or battery-driven passive. An active tag has an on-board battery and periodically transmits its ID signal. A small battery is there on the board of a battery-assisted passive. It is activated in the presence of the RFID reader. A passive tag has no battery so it is cheaper and smaller.
The tag uses the radio energy supplied by the reader. To run a passive tag, it must be illuminated with a power level. It is approximately a thousand times stronger compared to signal transmission. You may search for RFID chip timing Edmond Oklahoma on the Internet to retrieve more information on this regard.