passive tag

Passive RFID tags are those that operate without their own power supply and do not have a transmitter. They consist of a microprocessor and a resonant circuit. In addition to pure passive tags, there are also semi-passive tags. These have a small buffer battery for storing volatile data.

In the passive tags, the transmit frequency of the RFID reader corresponds to the resonant frequency of the tag resonant circuit. Passive tag antennas with resonant frequencies of 135 kHz or 13.56 MHz are usually an inductor or loop antenna that is inductively or electromagnetically coupled to the RFID reader.

There are several transmission principles based on the absorption ofRF energy. In RFID transmission, the reader's radio frequency received by the antenna is converted into electrical energy to power the chip. To transmit the information stored in the microprocessor, the oscillating circuit is connected with different capacitances or damped with resistors. This changes the absorption behavior detected by the RFID reader, which corresponds to information transmission.

Passive tags are much smaller and less expensive than active tags, but they are also limited in range, which ranges from a few centimeters to as much as 10 meters, depending on whether the tag is a Close Coupling Integrated Chip Card( CICC), Proximity Integrated Circuit Card ( PICC) or Vicinity Integrated Circuit Cards( VICC).