Communications engineering. A general term describing a system that transmits the identity of an object, a person or an animal wirelessly by using radio waves. An RFID tag consists of a microchip attached to an antenna. Passive RFID tags have no power source whereas an active RFID tag includes usually a battery. An RFID reader is used to retrieve the data stored on an RFID tag. It has one or more antennas that emit radio waves and receive signals back from the RFID tag. RFID systems can operate at low frequency (124 kHz, 125 kHz or 135 kHz), high frequency (13.56 MHz) and ultra-high frequency (860 MHz to 960 MHz).