Detailed RFID core technology Radio frequency tags are tags that contain codes that uniquely identify the item. This unique identification system includes product electronic code EPC, ubiquitous identification number UCODE, vehicle identification code VIN, international securities identification number ISIN, and IPv6. RF Reader In the RFID system, the signal receiving device is generally called a reader (or card reader). The basic function of the reader is to provide an interface for data transmission with the tag. RF card Optional antennas are used in RFID systems with frequencies of 435 MHz, 2.45 GHz and 5.8 GHz. There are several types of optional antennas, as shown in the table below. They focus on the antenna size. The gain of such a small antenna is limited. The size of the gain depends on the type of radiation pattern. The omnidirectional antenna has a peak gain of 0 to 2dBi; the gain of the directional antenna can reach 6dBi. The size of the gain affects the range of the antenna. The first three types of antennas in the table below are linearly polarized, but microstrip antennas can make circular polarizations, and logarithmic spiral antennas are only circularly polarized. Since the directionality of RFID tags is uncontrollable, the card reader must be circularly polarized. A circularly polarized tag antenna can generate a signal of 3dB or more. Impedance issues For maximum power transmission, the input impedance of the chip behind the antenna must match the output impedance of the antenna. For decades, antennas have been designed to match the impedance of 50 or 70 ohms, but it is possible to design antennas with other characteristic impedances. For example, a slot antenna can be designed with an impedance of several hundred ohms. The impedance of a folded dipole can be 20 times the impedance of a standard half-wave dipole. The extraction point of the printed patch antenna can provide a wide range of impedance (usually 40 to 100 ohms). It is critical to choose the type of antenna so that its impedance can match the input impedance of the tag chip. Another problem is that other objects close to the antenna can reduce the return loss of the antenna. For omnidirectional antennas, such as dual dipole antennas, this effect is significant. A plastic bottle of water reduces the minimum return loss frequency by 16%. When the distance between the object and the antenna is less than 62.5mm, the return loss will cause a 3.0 dB insertion loss, while the free space insertion loss of the antenna is only 0.2dB. The antenna can be designed to match the situation of approaching an object, but the behavior of the antenna is different for different objects and different object distances. It is not feasible for omnidirectional antennas, so designing antennas with strong directivity will not be affected by this problem. Influence of local structure When using hand-held instruments, a large number of other nearby objects severely distort the radiation patterns of the reader antenna and tag antenna. This can be calculated for the working frequency of 2.45GHz, assuming a representative geometric shape, in the use environment of the warehouse, there will be a problem with an item box having a label, and several labels are attached to a box to ensure that there is one The label is visible. There are several antenna problems with the use of portable systems. Two antennas per box are adequate for access control device detection, so that the influence of the local structure becomes less important because the antenna of the card reader of the access control device is fixed at the entrance of the warehouse and points directly to the labeled object. Distance In summary, omnidirectional antennas should be avoided in tags. However, directional antennas can be used, which have less interference from radiation patterns and return loss. The choice of antenna type must match its impedance with free space and ASIC. The use of antennas in a warehouse seems infeasible unless active tags are used, but in any case, the antenna radiation pattern in the warehouse will be severely distorted. The use of an access control system will be a good choice, and passive tags with short range can be used. Of course, the access control system is more expensive than the handheld instrument, but the staff of the handheld instrument needs to use it to search the warehouse, and the personnel cost is also expensive. In the access control system, each item box only needs 2 instead of 4 or 6 RFID tags. Wire To Board Connectors,Electronic Connector,Connectors For Flat Cables,Underwater Sealing Connector Zooke Connectors Co., Ltd. , https://www.zooke.com
Among them, the product electronic code (EPC) is a branch of the global product code, which can identify targets outside the field of vision. Electronic product code is not just a radio wave barcode, it contains a series of data and information, such as origin, date code and other key supply information, these information are stored in a small silicon chip, using tags, reader Networked with computers, producers and retailers can learn accurate product and inventory information at any time.
The radio frequency tag can store data ranging from 512 bytes to 4 trillion, depending on the type of business. The data stored in the label is determined by the application of the system and the corresponding standards. For example, labels can provide information about the production, transportation, and storage of products, and can also identify the identity of machines, animals, and individuals. These are similar to the information stored in the barcode. The tag can also be connected to a database to store product inventory number, current location, status, selling price, lot number information. Correspondingly, the radio frequency tag can directly determine the meaning of the code without referring to the database when reading the data.
At present, the price of radio frequency tags varies from 30 cents to 50 dollars depending on the type of tag and application. In general, smart tags used in high-end products are more than 50 cents, and active tags are much more expensive and complicated. The price of sensitive components is above $ 100.
The purpose of the radio frequency tag is to use a unified standard electronic product code, so that the product can be identified in different fields.
At present, many companies that produce RFID products adopt their own standards, but there is no uniform standard in the world. At present, several standards available for RF cards are ISO10536, ISO14443, ISO15693 and ISO18OOO. The most widely used are ISO14443 and ISO15693, which are composed of four parts: physical characteristics, RF power and signal interface, initialization and anti-collision, and transmission protocol.
According to different methods, RF cards are classified as follows:
1. According to the power supply mode, it is divided into active cards and passive cards. Active means that there is a battery in the card to provide power, and its action distance is far, but the life is limited, the volume is large, the cost is high, and it is not suitable for working in harsh environments; there is no battery in the passive card, which uses beam power supply technology to The received radio frequency energy is converted into a DC power supply to supply power to the circuit inside the card. Its working distance is shorter than that of the active card, but it has a long life and does not require high working environment.
2. According to the carrier frequency, it is divided into low frequency radio frequency card, intermediate frequency radio frequency card and high frequency radio frequency card. There are two main types of low-frequency radio frequency cards: 125kHz and 134.2kHz, the frequency of intermediate frequency radio frequency cards is 13.56MHz, and the frequency of high frequency radio frequency cards is 433MHz, 915MHz, 2.45GHz, and 5.8GHz. Low-frequency systems are mainly used in short-range, low-cost applications, such as most access control, campus cards, animal supervision, cargo tracking, etc. The mid-frequency system is used for access control and application systems that need to transmit large amounts of data; the high-frequency system is used in applications that require long read and write distances and high read and write speeds. The antenna beam direction is narrow and the price is high. In train monitoring, Used in expressway tolling and other systems.
3. According to the modulation method, you can get Mou Huang? Sha Zhi? Fu? Jiao Huan? Jian V Fu? Pay your condolences? Mi Miao Na Na's phoenix ?? y⑺ fade? Smile? Mourning ã„Š Coat Rosemeal ⑸ 浞 Ground Pepper⑸ 涫? è© ?? 匦 è‚œ? Enumerating female and female brains? ꞬBlowing the spectrum about the dry male lotus cattle? Beautiful intercropping feces suspected to be confused ?? A; class = bluekey href = "http: //" target = "_ blank"> Transport applications, because the reader can ensure that only the radio frequency card within a certain range is activated. In the case of obstacles, with the modulation scattering method, the energy of the reader must come and go through the obstacle twice. The signal transmitted by the active mode RF card only passes through the obstacle once, so the active mode RF card is mainly used in applications with obstacles, and the distance is farther (up to 30 meters).
4. According to the action distance, it can be divided into densely coupled cards (action distance less than 1 cm), near-coupling cards (action distance less than 15 cm), sparsely coupled cards (action distance about 1 meter) and long-distance cards (action distance from 1 meter To 10 meters or even further).
5. According to the chip, it is divided into read-only card, read-write card and CPU card.
RF antenna
Introduction In RF devices, when the operating frequency is increased to the microwave region, the matching problem between the antenna and the tag chip becomes more severe. The goal of the antenna is to transmit the maximum energy into and out of the tag chip. This requires careful design of the antenna and the matching of the free space and the connected tag chip. The frequency bands considered in this article are 435MHz, 2.45 GHz and 5.8 GHz, used in retail products.
The antenna must:
Small enough so that it can be attached to the required items;
Directionality covered by omnidirectional or hemisphere;
Provide the largest possible signal to the chip of the tag;
Regardless of the direction of the item, the polarization of the antenna can match the query signal of the card reader;
Robust;
Very cheap.
The main considerations when choosing an antenna are:
Type of antenna;
Antenna impedance:
RF performance applied to articles;
RF performance when there are other items surrounding the labeled item.
Possible options There are two ways of use: 1) The tagged items are placed in the warehouse, there is a portable device, which may be handheld, ask all the items, and need them to give feedback information; 2) At the door of the warehouse Install the card reader configuration, inquire and record the entry and exit items. There is also a main choice whether to be active tags or passive tags [1], [2].
The radiation mode tested the antenna mode in a non-reflective environment, including various objects that need to be labeled, and the performance is seriously degraded when using the omnidirectional antenna. The performance degradation caused by the cylindrical metal hearing is the most serious. When it is 50mm away from the antenna, the return signal drop is greater than 20dB. When the distance between the antenna and the center of the object is separated to 100-150mm, the return signal drops by about 10 to 12dB. At a distance of 100mm from the antenna, several bottles of water (plastic and glass) were measured.
The gain of the RFID antenna and whether an active tag chip is used will affect the distance of the system. Consider optimistically, when the radiation intensity of the electromagnetic field meets the relevant standards of the UK, in the passive case of 2.45GHz, full-wave rectification, the driving voltage is not more than 3 volts, the optimized RFID antenna impedance environment (impedance 200 or 300 ohms), the use distance It is about 1 meter [3]. If you use the WHO restriction [4], it is more suitable for global use, but the range is reduced by half. These limit the electromagnetic field power from the reader to the tag. The range of action decreases with increasing frequency. If the active chip is used, the working distance can reach 5 to 10 meters.