In the early 1940s, the improvement and application of radar gave birth to radio frequency identification (RFID) technology. After a long exploration stage, RFID has played an important role in the fields of public security, manufacturing, logistics management and so on.
Radio frequency identification (RFID) technology is a non-contact automatic identification technology. It automatically identifies the target object and obtains relevant data through spatial coupling (alternating magnetic field or electromagnetic field), so as to achieve the purpose of target identification and data exchange. The identification work does not need manual intervention.
The basic working principle of AFID system can be described through figure 1: the signal to be sent by the reader is encoded and loaded on the carrier signal of a certain frequency, which is sent outward by the antenna. The electronic tag entering the working area of the reader receives the pulse signal. The relevant circuits in the chip in the tag demodulate, decode and decrypt the signal, and then request the command, password, Authority, etc. If it is a read command, the control logic circuit reads relevant information from the memory, encrypts, encodes and modulates it, and then sends it to the reader through the antenna in the electronic tag. The reader demodulates, decodes and decrypts the received signal and sends it to the central processing system for relevant data processing; If it is a write command to modify the information, the internal charge pump will increase the working voltage caused by the control logic, and the contents in eeprqm will be rewritten. If it is judged that the corresponding password and authority are inconsistent, an error message will be returned.
Application scope of RFID system
The era of the international Internet of things is coming. It is reported that RFID technology has been widely used in European and American markets. With the increasing maturity of RFID technology in the Chinese market and the reduction of RFID tag price, RFID electronic tag will replace the traditional one-dimensional bar code and two-dimensional code. If two-dimensional code is the extension of one-dimensional code label, the birth of RFID is a revolution in the label industry. Its application fields are mainly in the following aspects:
1. Logistics management
Logistics is the largest market application space of RFID, which can greatly improve the efficiency of logistics links and provide technical guarantee for the realization of zero inventory. Global retail giant Wal Mart and Germany Metro have vigorously promoted the application of RFID tags, and have realized the use of RFID technology in supermarkets to realize product identification, anti-theft, real-time inventory and product validity control.
2. Food safety
Food safety is a national livelihood event. RFID technology can ensure food safety in an all-round way through the whole process management record of the original food planting or breeding process and the forward tracking and reverse tracing of the links of food circulation.
3. Commodity anti-counterfeiting I
Commodity anti-counterfeiting can ensure the normal market order and consumer reputation, and has a huge market space. RFID anti-counterfeiting technology and wireless communication network can realize the quality inspection of goods at any time and anywhere. At present, it has been used in tobacco and wine. Carry out pilot projects on medicine and other commodities.
4. Applications in other fields
RFID has a very wide range of applications, such as traffic management, military management, security, animal breeding and pet management, library management and other fields.
Preparation technology of RFID tag antenna
The core issues affecting the promotion of RFID are chip technology and cost. As shown in Fig. 2, the main function of RFID chip and antenna is the energy in and out layer, as shown in Fig. 2. Compared with the traditional etching method and winding method, the direct printing method of tag antenna greatly saves the cost.
1. Traditional manufacturing process of tag antenna
① The tag antenna is fabricated by etching
The antenna shall be printed with anti-corrosion film before etching. Firstly, both sides of PET film sheet shall be covered with metal (such as copper, aluminum, etc.); Then, the printing method (screen printing, gravure printing, etc.) or photolithography method is used to print the anti-corrosion ink in the double-sided antenna pattern area of the substrate to protect the line pattern from being dissolved during etching: then etching is carried out, that is, the cured sheet of the printing ink pattern is immersed in the etching solution to dissolve the metal in the non printed anti-corrosion ink layer area; Then, the anti etching ink on the metal layer of the film sheet antenna pattern is removed, and the label antenna is obtained. Alternatively, the photoresist film is pre coated on the surface of the copper-clad substrate by photolithography, and exposed with the corresponding mask. After development and corrosion, the residual photoresist film on the plate is removed to obtain a complete antenna pattern.
② Preparation of tag antenna by winding method
At present. The manufacturing process of RFID tag antenna wound with copper wire is usually carried out by automatic winding machine, that is, the insulating paint is directly wound on the substrate carrier film, and the copper wire with low melting point paint is used as the substrate of RFID tag antenna. Finally, the wire and substrate are mechanically fixed with adhesive. The process flow is shown in Figure 4. This method has high reliability, but the cost is too high for rf19 electronic tag.
2. Label antenna printing process
Based on the disadvantages of environmental pollution, high cost, complex process and long production time in the traditional preparation method of tag antenna, it will be replaced by the new process. Printing RFID tag antenna directly is an environmentally friendly, energy-saving and low-cost manufacturing process. The existing feasible printing methods of RFID tag antenna include screen printing and inkjet printing.
① Preparation of antenna by screen printing
Screen printing is a process of direct printing using template, that is, directly printing on paper-based or plastic film coil with conductive ink. Its general process flow is as follows:
The screen printing of label antenna is to sweep the conductive ink through the screen plate with a scraper from the other side of the screen plate, and the ink passes through the mesh gap of the antenna pattern on the screen plate and is pasted on the printed substrate. During RFID tag antenna printing, because the antenna coils of RFID tags with different working frequencies will correspond to different turns, coil thickness and distance between each turn (for example, HF band uses 13.56MHz chip, which usually requires 6 turns and a thickness of about 20um; UHF band uses 868mhz and 950mhz chips, and the coil section thickness is about 4um), Therefore, the thickness of the printed ink layer, the width of each line and the graphic outline after drying have a strict tolerance range (for example, the error of two overlapping overprint must be within 0.1mm).
The ink layer thickness of screen printing can reach 100um at most, which is several times that of flexographic printing, offset printing and gravure printing, which is very advantageous for printing label antenna with conductive ink. In actual printed circuit production, the thickness of ink layer is generally 8 ~ 12um, and its drying can be completed by UV, IR and hot air.
② Preparation of antenna by inkjet printing
Screen printing saves the cost to a certain extent, but its ink adopts about 70% conductive silver paste with high silver content to obtain an antenna between 15 ~ 20um. It belongs to thick film printing, with high cost, solvent discharge in the printing process and poor ink layer flexibility. The conductive line is prepared by using an inkjet printer. Only according to the pattern designed by the computer system, the conductive ink is sprayed on the substrate by the nozzle of the inkjet printer to form a conductive line. As a non-traditional printing, inkjet printing has attracted extensive attention in antenna manufacturing because of its short manufacturing cycle, no pollution and low cost. Many well-known universities and research institutes at home and abroad have been committed to the research of inkjet conductive ink for a long time and have made remarkable achievements. The scientific research team led by Professor Li Luhai of Beijing Institute of printing has successfully developed inkjet conductive ink with conductive film thickness of about 1um and resistance of about 1 Ω: American kovio company launched FFD prepared with inkjet nano silicon ink in 2008, which has become the first commercial success case of inkjet printing ink; In 2009, Shuntian University of Korea developed a fully printed 1-bit RF tag based on carbon nanotube ink.
There are three ways to make RFID tags by ink-jet printing: ① spray anti-corrosion ink, solder resist ink and character ink on copper clad laminate by ink-jet printing, and obtain the finished product after curing; ② The conductive ink containing nano metal particles is used to spray the circuit pattern directly on the polyester substrate, and the circuit is formed after low-temperature baking and curing: ③ the capacitors, resistors and other electronic devices in RFID tags are manufactured by ink-jet printing with corresponding characteristics. Compared with the traditional printing method. Using inkjet printing can achieve faster production speed, reduce the printing cost, and more importantly, increase its wiring density, so as to improve the quality of finished products.
With its unique advantages, RFID tags are gradually applied in various fields. People are committed to studying and solving the disadvantages of traditional preparation methods. As a new technology of tag antenna, inkjet printing will make RFID technology more widely used by relying on the advantages of low cost, good conductivity, no pollution and easy control of antenna pattern.
Responsible editor: CT