Radio Frequency Identification RFID (Radio Frequency Identification, RFID), is a kind of automatic identification technology. It communicates bidirectionally and wirelessly via radio in different frequencies, reading or writing recording media (RFID tag or RFID card), to meet the aim of identifying objective and exchanging data, it is considered as one of the most potential information technology in the 21st century.
A complete RFID system is composed by Reader, Tag or called Transponder and software system, the basic working principle of RFID technology is that while the tag goes into the magnetic field, it receives the RF signal from the reader, then sends the product information stored in the chip with the energy achieved by the induced current (Passive Tag), or sends a signal in a specific frequency, (Active Tag) the reader reads and decodes the information, then sends to the central information system for processing.
In communication between the RFID card reader and electronic tag and energy induction methods generally can be divided into, Inductive Coupling (Inductive Coupling) and later to the scattering coupled (Backscatter Coupling) two kinds, generally low-frequency RFID are mostly adopted the first type, while the high frequency mostly adopts the second way.
Depending on the structure and technology used, the reader can be a read or read/write device, which is the information control and processing center of the RFID system. A reader usually consists of a coupling module, a transceiver module, a control module, and an interface unit. Information is exchanged between the reader and the transponder in a semi-duplex communication mode, and the reader provides energy and timing to the passive transponder through the coupling. In practice, it can further realize the management functions of object recognition information collection, processing, and remote transmission through Ethernet or WLAN. The transponder is the information carrier of the RFID system. At present, transponders are mostly composed of coupling elements (coil, microstrip antenna, etc.) and microchips.
RFID technology can be divided into three types according to the power supply mode of its tags, called passive RFID, active RFID, and semi-active RFID.
1. Passive RFID.
Passive RFID is the earliest, most mature, and the most widely used technology. In passive RFID, the RFID tag completes this exchange by receiving an electromagnetic signal from an RFID reader and power itself through its inductive coil. Since no power supply is needed, the passive RFID tag can reach centimeters size or even smaller, while it can be simply structured, low cost, and long service life. However, the effective identification range of passive RFID is usually not long, which is generally used for proximity to middle range identification. Passive RFID mainly works in frequency band 125KHz, 13.56MHz and 900MHz, its typical applications include access card, transportation, and ID card, immobilizer, animal identification, and industrial & logistics.
2. Active RFID.
The rise of active RFID is not long, but it has played an important role in various fields, especially in the electronic toll collection system on the highway. The active RFID tag actively sends signals to the RFID reader through an external power supply and it is relatively big. But it also has a longer transmission distance and higher transmission speed. A typical active RFID tag can communicate with an RFID reader at up to 100 meters distance with up to 1,700 times/second. Active RFID mainly works in higher frequency bands such as 900MHz, 2.45GHz, and 5.8GHz, and has a very strong anti-collision function. The long reading distance and high speed of active RFID make it indispensable in some challenging applications. Crepak is one of active RFID tag manufacturers that can provide very economical active RFID tags to meet different applications.
3. Semi-active RFID.
Passive RFID identification distance is too short while active RFID is big and needs an external power supply. Semi-active RFID is a compromise for this contradiction. Semi-active RFID is also called low-frequency activation trigger technology. Normally, semi-active RFID tags are dormant, only the maintenance of data is powered, so power consumption is small, and can be used for a long time. When the tag enters the range of RFID reader, the reader first activates the tag with a 125KHz low-frequency signal, and then the tag transmits the information through 2.4GHz microwave. Its common application scenario is: in a big range that covered by 2.4GHz signal, multiple 125KHz readers are placed for activation of semi-active RFID tags. This can be used not only for location but also can be applied for data collection.
1. Access control
To identify who, when, and where enters a building or a room and to allow or deny this entry.
2. Logistic&Warehouse management
Logistics&warehouse is one of the most potential application areas of RFID. International logistics giants such as UPS, DHL, and FedEx are actively experimenting with RFID technology, expect to improve their logistic operation and capacity, including goods tracking in the logistics process, automatic data collection, inventory management, ports applications, postal parcels, express, etc. 
There are already many successful cases in taxi management, bus management, railway locomotive identification, etc
4. Personal Identification
RFID technology is widely used in personal identification because of its fast reading and anti-counterfeiting function. Such as electronic passport, ID cards, driving license cards, student CARDS, etc
5. Retail operation management
To identify the inventory visibility of retail products and prevent it is stolen as well as interact with consumers to improve user experience.
RFID has characteristics that are difficult to counterfeit, applications include the anti-counterfeiting of valuables (luxury goods, cigarettes, alcohol, drugs) and tickets.
7. Asset management
It can be applied to the management of all kinds of assets, including valuables, large volume similar goods, and dangerous goods. With tag prices falling, RFID can manage almost everything.
Can be applied to traceability management of fruits, vegetables, meats, and seafood.
9. Track&Trace management
To track objects in the production/operation/circulation process and capture related equipment, personnel, and tool data to enable traceability.
10. Archives management
With the application of RFID technology, archives statistics becomes simple and fast. work. The archives management platform sends an inventory statistic order, the reader can quickly read the content and location information of the archives and returns it to the management platform for comparison. If the archives cannot match, the clerks will use the reader to double-check and update it on the platform.