RFID tags (by communication) are classified into passive, semi-passive (also known as semi-active) and active three.
Passive tags do not have an internal power supply. Its internal integrated circuit is driven by the received electromagnetic waves, which are emitted by the RFID reader. When the tag receives a signal of sufficient strength, it can send data to the reader. These data include not only the ID number (global unique identification ID), but also data pre-existing in the EEPROM in the tag.
Passive tags have the advantage of being inexpensive, compact, and eliminating the need for a power source. The RFID tags in the market are mainly passive.
In general, the antenna of the passive tag has two tasks. First, the electromagnetic wave emitted by the reader is received to drive the tag IC. Secondly, when the tag returns the signal, the impedance of the antenna needs to be switched to generate 0. With a change of 1. The problem is that if you want the best backhaul efficiency, the antenna impedance must be designed to be "open and short", which will completely reflect the signal and cannot be received by the tag IC. The semi-active tag is to solve this problem. Semi-active is similar to passive, but it has a small battery that can drive the tag IC so that the IC is working. The advantage of this is that the antenna can be used as a return signal without the task of receiving electromagnetic waves. Compared with passive, semi-active has faster response speed and better efficiency.
Unlike passive and semi-passive, the active tag itself has an internal power supply to supply the power required by the internal IC to generate external signals. In general, active tags have a longer read range and a larger memory capacity that can be used to store additional messages sent by the reader.