Radio frequency identification technology can be divided into three categories based on the power supply mode of its tags, namely passive RFID, active RFID, and semi-active RFID.
1. Passive RFID.
Among the three types of RFID products, passive RFID is the earliest and the most mature, and its application is also the most extensive. In passive RFID, the electronic tag completes the information exchange by receiving the microwave signal transmitted from the radio frequency identification reader and obtaining energy through the electromagnetic induction coil to power itself for a short time. Because the power supply system is omitted, the volume of the passive RFID product can reach the order of centimeters or even smaller, and its own structure is simple, the cost is low, the failure rate is low, and the service life is long. But as a price, the effective recognition distance of passive RFID is usually short, and it is generally used for close-range 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, canteen meal cards, etc.
2. Active RFID.
Active RFID has not been around for a long time, but it has played an indispensable role in various fields, especially in the electronic non-stop toll collection system of highways. Active RFID is powered by an external power source and actively sends signals to the radio frequency identification reader. Its volume is relatively large. But it also has a longer transmission distance and higher transmission speed. A typical active RFID tag can establish contact with a radio frequency identification reader from a hundred meters away, and the read rate can reach 1,700 read/sec. Active RFID mainly works in higher frequency bands such as 900MHz, 2.45GHz, 5.8GHz, and has the function of identifying multiple tags at the same time. The long-distance and high efficiency of active RFID make it indispensable in some radio frequency identification applications that require high performance and a large range.
3. Semi-active RFID.
Passive RFID itself does not supply power, but the effective identification distance is too short. Active RFID has a long enough recognition distance, but requires an external power source and is relatively large. The semi-active RFID is the product of compromise for this contradiction. Semi-active RFID is also called low-frequency activation trigger technology. Under normal circumstances, semi-active RFID products are in a dormant state and only supply power to the part of the tag that holds the data, so the power consumption is small and can be maintained for a long time. When the tag enters the recognition range of the RFID reader, the reader first activates the tag in a small range with a 125KHz low-frequency signal to make it enter the working state, and then transmits information to it through 2.4GHz microwave. In other words, first use low-frequency signals for precise positioning, and then use high-frequency signals to quickly transmit data. Its general application scenario is: in a large range covered by a high-frequency signal, multiple low-frequency readers are placed in different positions to activate semi-active RFID products. This not only completes the positioning, but also realizes the collection and transmission of information.
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