Radiofrequency identification technology can be divided into three types according to the power supply method of its tags, namely passive RFID, active RFID, and semi-active RFID.
Among the three types of RFID products, passive RFID is the earliest and most mature, and its applications are also the most widespread. In passive RFID, the electronic tag completes the information exchange by accepting the microwave signal transmitted by the radio frequency identification reader and obtaining energy through the electromagnetic induction coil to temporarily supply power to itself. Generally used for close contact recognition. Passive RFID mainly works in the lower frequency bands of 125KHz, 13.56MKHz, etc. Its typical applications include bus cards, second-generation ID cards, cafeteria meal cards, etc.
Active RFID has not been around for a long time, but it has played an indispensable role in various fields, especially in highway electronic toll collection systems. Active RFID is powered by an external power source and actively sends signals to the RFID reader.
Passive RFID itself does not supply power, but the effective identification distance is too short. The active RFID identification distance is long enough, but it requires an external power supply and is relatively large. And semi-active RFID is the product of compromise for this contradiction. Semi-active RFID is also called low-frequency activation triggering technology. Under normal circumstances, semi-active RFID products are in a dormant state and only power the data-holding part of the tag, so the power consumption is small and can be maintained for a long time. After the tag enters the recognition range of the RFID reader, the reader first activates the tag accurately in a small range with a low-frequency signal of 125KHz to enter the working state, and then transmits information to it through a 2.4GHz microwave. That is to say, first use low-frequency signals to accurately locate, and then use high-frequency signals to quickly transmit data. Its usual application scenario is: in a large range covered by a high-frequency signal, multiple low-frequency readers are arranged at different positions for activating semi-active RFID products. This not only completes the positioning but also realizes the collection and transmission of information.