Fifth, the basic principle of radio frequency tag reading and writing equipment Under normal circumstances, radio frequency tag reading and writing equipment should be designed according to the read and write requirements of radio frequency tags and application requirements. With the development of radio frequency identification technology, radio frequency tag reading and writing equipment has also formed some typical system implementation modes. The focus of this chapter is also to introduce the implementation principle of this reader/writer. The reader/writer is corresponding to the radio frequency tag reading/writing device. The reader/writer transmits the command to the radio frequency tag through the spatial channel between the reading device and the radio frequency tag. The radio frequency tag makes the necessary response after receiving the command from the reader/writer. This realizes radio frequency identification. In addition, in radio frequency identification application system, under normal circumstances, contactless collection of radio frequency tag data realized by a reader/writer or tag information written by a reader/writer into a radio frequency tag is to be returned in an application system or from Application system, this forms the interface API (Application Program Interface) between the radio frequency tag reading and writing device and the application system program. Under normal circumstances, the reader/writer is required to be able to receive commands from the application system, and respond according to the commands of the application system or the agreed protocol (returning the collected tag data, etc.). VI. RF Antennas in Smart Tags The type of RF antenna must be chosen so that its impedance matches the free space and ASIC. Directional antennas have less radiation patterns and return loss interference. The access control system can use short-range passive tags. In an RF device, the matching between the antenna and the tag chip becomes more severe when the operating frequency is increased to the microwave region. The goal of the antenna is to transmit maximum energy into and out of the tag chip. This requires careful design of the antenna and the free space and the matching of its attached tag chips. The frequency bands considered are 435 MHz, 2.45 GHz and 5.8 GHz for use in retail merchandise. 1, the antenna must: (1) It is small enough to be attached to the required items; (2) There is directionality of omnidirectional or hemispherical coverage; (3) Providing the largest possible signal to the tag's chip; (4) Regardless of the direction of the object, the polarization of the antenna can match the reader's interrogation signal; (5) Robust; (6) Very cheap. (7) The main considerations when choosing an antenna are: a. The type of antenna ; c. The performance of the RF applied to the item; d. RF performance when there are other items around labeled items. 2. Possible choices There are two ways of using this: 1) The tagged item is placed in a warehouse, there is a portable device, may be handheld, asks for all items, and they are required to give information feedback information; 2) Install a reader at the door of the warehouse Set up, ask and record entries and exits. Another major choice is active tags or passive tags. 3, optional antenna In the RFID system with 435 MHz, 2.45 GHz and 5.8 GHz frequencies, there are several types of optional antennas. See the table below. They focus on the size of the antenna. The gain of such a small antenna is limited, the magnitude of the gain depends on the type of radiation mode, the omnidirectional antenna has a peak gain of 0 to 2 dBi, and the directional antenna has a gain of 6 dBi. The gain size affects the antenna's range of action. The first three types of antennas in the table below are linearly polarized, but a microstrip antenna can make a circularly polarized, logarithmic spiral antenna only circularly polarized. Since the directionality of the RFID tag is not controllable, the card reader must be circularly polarized. A circularly polarized tag antenna can generate a strong signal of 3dB. 4, impedance problems For maximum power transmission, the input impedance of the chip after the antenna must match the output impedance of the antenna. The antenna is designed to match the impedance of 50 or 70 ohms, but the antenna may be designed to have 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 that of a standard half-wave dipole. The lead-out point of the printed patch antenna can provide a wide range of impedance (usually 40 to 100 ohms). The type of antenna is selected so that its impedance can be matched with 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 double dipole antennas, this effect is significant. Changing the spacing between the dipole antenna and a ketchup did some actual measurements, showing some changes, and other objects had similar effects. In addition, the dielectric constant of the object, not the metal, changes the resonant frequency. 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 result in a 3.0dB insertion loss, while the free space insertion loss of the antenna is only 0.2dB. The antenna can be designed to match the proximity of the object, but the behavior of the antenna varies for different objects and different object distances. It is not feasible for omnidirectional antennas, so designing directional antennas is not affected by this problem. 5, radiation mode The mode of the antenna was tested in a non-reflective environment, including various objects that need to be labeled, and the performance was severely degraded when using omnidirectional antennas. The performance degradation caused by cylindrical metal hearing is the most serious. When it is 50mm away from the antenna, the back-to-back signal drops by more than 20dB. When the distance between the antenna and the center of the object is 100 to 150 mm, the back-to-back signal drops by about 10 to 12 dB. At a distance of 100 mm from the antenna, several bottles of water (plastic and glass) were measured and the back-return signal was reduced by more than 10 dB. Experiments on wax carton liquids and even apples have yielded similar results. 6, distance The gain of the RFID antenna and whether or not to use an active tag chip will affect the system's usage distance. Optimistic considerations, when the radiant intensity of the electromagnetic field complies with relevant UK standards, in the passive case of 2.45 GHz, the full-wave rectification, the driving voltage is not greater than 3 volts, the optimized RFID antenna impedance environment (impedance 200 or 300 ohm), use distance About 1 meter [3]. If the WHO limit [4] is used, it is more suitable for global use, but the effect distance is reduced by half. These limit the electromagnetic field power of the reader to the tag. The effect distance decreases as the frequency increases. If you use an active chip, you can reach a distance of 5 to 10 meters. Seven, bar code and electronic tag comparison Name Information Carrier Information Quantity Read/Write Read Method Confidentiality Intelligent Anti-jamming Capability Life Cost Barcode Paper, Plastic Film, Metal Surface Small Read-only CCD or Laser Beam Scan Difference No Shorter Minimum Minimum RFID Tag EEPROM Large Read/Write Wireless communication is best to have a very good longest Eight, electronic label diagram
Radio frequency tag reading and writing equipment is one of the two important components of RFID systems (tags and readers). According to the features of the specific functions, there are some other popular names such as: Reader, Interrogator, Communicator, Scanner, and Reader. And Writer), a programmer, a reading device, a portable readout device, an AEI device (automatic equipment identification device), and the like.
b. Antenna impedance:
Source: Shenzhen Xinxing Printing Technology Development Co., Ltd. Liu Zhihua
RFID Technology and Screen Printing (II)