How electronic price tags work

Electronic tags are a non-contact automatic identification technology that uses radio frequency signals to identify target objects and obtain related data.

The identification work does not require human intervention. As a wireless version of barcodes, RFID technology has waterproof, antimagnetic, and High temperature resistance, long service life, large reading distance, data on the label can be encrypted, storage data capacity is larger, storage information can be changed freely and other advantages. The encoding method, storage and read-write method of electronic tags are different from traditional tags (such as barcodes) or manual tags. The storage of electronic tag codes is stored in a read-only or read-write format on the integrated circuit; especially the read-write method, The electronic tag is realized by wireless electronic transmission. The outstanding technical characteristics of RFID electronic tags are: it can identify a single very specific object, instead of only one type of object like a bar code; it can read multiple objects at the same time, and the bar code can only be read one by one; storage; The amount of information is very large; using radio frequency, data can be read through external materials, and bar codes must rely on laser or infrared to read information on the surface of the material medium.

(1) Tag. It is composed of coupling elements and chips. Each tag has a unique electronic code. The high-capacity electronic tag has a user-writeable storage space and is attached to an object to identify the target object.

(2) Reader. A handheld or fixed device that reads (and sometimes writes to) tag information.

(3) Antenna. Pass the radio frequency signal between the tag and the reader.The basic working principle of RFID technology is not complicated. After the tag enters the magnetic field emitted by the reader, it receives the radio frequency signal from the reader, and uses the energy obtained by the induced current to send out the product information (PassiveTag, passive tag or passive tag) stored in the chip, or actively send a certain frequency The signal (ActiveTag, active tag or active tag); after the reader reads and decodes the information, it is sent to the information processing center of the system for relevant data processing.

Electronic tags can be divided into three types: integrated circuit curing type, on-site wired rewriting type, and on-site wireless rewriting type according to the different injection methods of internally stored information; according to the technical means of reading electronic tag data, they can be divided into three categories: There are three types of broadcast transmission type, frequency multiplication type and reflection modulation type; according to the different energy supply methods (battery power supply), radio frequency identification technology can be divided into three types: active, passive and semi-active. The generally popular classification method of RFID is, according to the different working frequency (unit: Hz), it is divided into 4 kinds of low frequency (LF), high frequency (HF), ultra high frequency (UHF) and microwave frequency band (MW).

(1) Low/high frequency systems generally have a working frequency of<30MHz. Typical working frequencies are 125kHz, 225kHz, 13.56MHz (non-contact IC card-working frequency of radio frequency card), etc. Radio frequency identification systems based on these frequency points generally have corresponding international standards. Their basic characteristics are: the cost of electronic tags is lower, the amount of data stored in the tags is less, and the reading distance is short (passive conditions, the typical reading distance is 10cm), the shape of the electronic tag is diverse (card-shaped, ring-shaped, button-shaped, pen-shaped), and the directivity of the reading antenna is not strong.

(2) UHF/microwave systems generally have a working frequency> 400MHz, and typical working frequency bands are 915MHz, 2450MHz, 5800MHz, etc. The system also has many international standards to support these frequency bands. The basic features are: high cost of electronic tags and readers, large amount of data stored in tags, long reading distance (up to several meters to ten meters), and adaptability to objects High-speed motion performance is good, the shape is generally card-shaped, and the reading antenna and electronic tag antenna have strong directivity.

(3) There is a battery inside the active electronic tag, which generally has a long reading distance. The disadvantage is that the battery has a limited lifespan (3-10 years); there is no battery in the passive electronic tag. After receiving the microwave signal from the reader (probe device), it converts part of the microwave energy into direct current for its own work. Generally, maintenance-free can be achieved. Compared with the active system, the passive system has a slight limitation in the reading distance and the speed of adapting to the movement of the object.

(4) The information in the integrated solidified electronic tag is generally injected in the ROM process mode during the production of integrated circuits, and the stored information is immutable; the field wired rewrite electronic tag generally writes the information stored in the electronic tag into it In the internal E2 storage area, a dedicated programmer or writer is required for rewriting, and it must be powered during the rewriting process; the on-site wireless rewriting electronic tag is generally suitable for active electronic tags, with specific rewriting instructions, and the electronic tags The saved information is also located in the E2 storage area. In general, the time required to rewrite the electronic tag data is much longer than the time required to read the electronic tag data. Generally, the time required for rewriting is in the order of seconds, and the reading time is in the order of milliseconds.

(5) Broadcast transmission type radio frequency identification system. The electronic tag must work in an active way and broadcast its stored identification information in real time. The reader is equivalent to a receiver that only receives but does not send. The disadvantage of this system is: because the electronic tag has to continuously transmit information to the outside, it wastes electricity and causes electromagnetic pollution to the environment, and the security and confidentiality of the system is poor. It is difficult to realize the double-frequency radio frequency identification system. In general, the reader sends out a radio frequency query signal, and the signal carrier frequency returned by the electronic tag is a multiplier of the radio frequency sent by the reader. This working mode provides convenience for the reader to receive and process echo signals. However, for passive electronic tags, when the electronic tag converts the received radio frequency energy of the reader into a double-frequency echo carrier frequency, its energy conversion efficiency is low. Improving conversion efficiency requires higher microwave skills, which means higher electronic tag costs. At the same time, the work of this kind of system must occupy two working frequency points, and it is generally difficult to obtain the product application license of the Radio Frequency Management Committee.

(6) The realization of reflection modulation radio frequency identification system is mainly to solve the problem of sending and receiving at the same frequency. When the system is working, the reader sends out a microwave inquiry (energy) signal, and the electronic tag (passive) rectifies part of the received microwave inquiry energy signal into direct current for the circuit in the electronic tag to work, and the other part of the microwave energy signal is stored in the electronic tag The data information is modulated (ASK) and reflected back to the reader. After the reader receives the reflected amplitude modulation signal, it decodes the identifying data information stored in the electronic tag. During the working process of the system, the reader sends out the microwave signal and receives the reflected amplitude modulation signal at the same time. The strength of the reflected signal is much weaker than that of the transmitted signal. Therefore, the difficulty in technical implementation lies in co-frequency reception.

Electronic tag coupling is to use different methods to transmit different signals.

The working distance between the radio frequency tag and the reader in the radio frequency identification system is an important issue in the application of the radio frequency identification system. Normally, this working distance is defined as the distance between the radio frequency tag and the reader to reliably exchange data. The range of radio frequency identification system is a comprehensive index, which is closely related to the matching situation of radio frequency tags and readers. According to the distance of the radio frequency identification system, the coupling between the radio frequency tag antenna and the reader antenna can be divided into three categories.

(1) Closely coupled system. The typical operating distance of the system ranges from 0 to 1cm. In practical applications, it is usually necessary to insert the radio frequency tag into the reader or place it on the surface of the reader antenna. The close coupling system uses the inductive coupling (closed magnetic circuit) between the radio frequency tag and the reader antenna reactive near-field area to form a contactless spatial information transmission radio frequency channel. The working frequency of the tightly coupled system is generally limited to any frequency below 30MHz. Since the electromagnetic leakage of the close coupling method is small and the energy obtained by the coupling is large, it is suitable for application systems (such as electronic door locks) that require high safety and have no requirements for operating distance.

(2) Telecoupling system. The typical operating distance of the telecoupling system can reach lm. The telecoupling system can be subdivided into two types: the near-coupled system (typical working distance is 15cm) and sparsely coupled system (typical working distance is lm). The typical operating frequency of the remote coupling system is 13.56MHz, and there are also some other frequencies, such as 6.75MHz, 27.125MHz and so on. The main difference between the telecoupling system and the tight coupling system is that the power of the inductive coupling is different, which makes the coupling distance different. Remote coupling systems are still the mainstream of low-cost radio frequency identification systems.

(3) Long-distance system. The typical operating distance of the long-distance system is 1～10m, and individual systems have a longer operating distance. All long-distance systems use the electromagnetic coupling (electromagnetic wave emission and reflection) between the radio frequency tag and the reader antenna to radiate the far field area to form a contactless spatial information transmission radio frequency channel. The typical working frequency of the long-distance system is 915MHz, 2.45GHz, 5.8GHz, in addition, there are some other frequencies, such as 433MHz and so on. The radio frequency tags of the long-distance system are divided into passive radio frequency tags (without batteries) and semi-passive radio frequency tags (with batteries) according to whether they contain batteries. In general, the range of the radio frequency tag containing the battery is longer than that of the radio frequency tag without the battery. The battery in the semi-passive radio frequency tag does not provide energy for the data transmission between the radio frequency tag and the reader, but only provides energy for the radio frequency tag chip to serve for reading and storing data. The long-distance system generally adopts the reflection modulation work mode to realize the data transmission from the radio frequency tag to the reader/writer. Long-distance systems generally have typical directivity, and the cost of radio frequency tags and readers is still at a relatively high level. From a technical point of view, a long-distance system that meets the following characteristics is an ideal RFID system: RFID tags are passive and can be read and written wirelessly; RFID tags and readers support multi-tag reading and writing; suitable for identification of high-speed moving objects (The object moving speed is greater than 80kin/h); long distance (read and write distance is greater than 5-10m); low cost (which can meet the requirements of one-time use).