Passive tags have no internal power supply. Its internal integrated circuits are driven by received electromagnetic waves, which are emitted by RFID readers. When the tag receives a sufficiently strong signal, it can send data to the reader. These data include not only the ID number (globally unique identification ID), but also data that pre-exist in the EEPROM within the tag.
Because passive tags are inexpensive and compact, there is no need for a power supply. The RFID tag in the market is mainly passive.
In general, the passive tag antenna has two tasks. The first is to receive the electromagnetic wave emitted by the reader to drive the tag IC; the second is to use the impedance of the antenna to switch when the tag returns the signal to generate 0. With 1 changes. The problem is that if you want the best return efficiency, the antenna impedance must be designed to be "open and short circuit," which in turn will cause the signal to completely reflect and not be received by the tag IC. The semi-active tag is to solve this problem. The semi-active type is similar to the passive type, but it has a small battery. The power can just drive the tag IC and make the IC work. This has the advantage that the antenna can be used as a return signal without the task of receiving electromagnetic waves. Compared with passive, semi-active has a faster reaction speed and better efficiency.
Different from passive and semi-active, the active tag itself has an internal power supply for supplying power required by the internal IC to generate external signals. In general, the active tag has a longer read distance and a larger memory capacity can be used to store some additional information sent by the reader.