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RFID Electronic Tag Application
Mar 15, 2019

Radio Frequency Idenficaon (RFID) is a non-contact automatic identification technology that automatically recognizes target objects and acquires relevant data through radio frequency signals. The identification work can be performed in various harsh environments without manual intervention. UHF RFID technology is used to identify high-speed moving objects and to identify multiple tags at the same time. UHF RFID identification has non-directionality, can be identified in batch, long life, non-rewriteable, pollution-resistant, etc., and can use RFID storage area to write important information.

RFID electronic tag application and technology tutorial

First, the frequency standard of RFID

Frequency license

The operating frequency of the RF system is one of the most basic technical parameters of the RFID system. The choice of operating frequency largely determines the application range, technical feasibility and system cost of electronic tags.

The RFID system is, in the final analysis, a radio propagation system that must occupy a certain spatial communication channel. In the spatial communication channel, the intelligence of the radio frequency signal is expressed in the form of electromagnetic coupling or electromagnetic reflection. Therefore, the performance of the radio frequency identification system is inevitably affected by the spatial transmission characteristics of the electromagnetic wave.

In people's daily lives, electromagnetic waves are everywhere, such as aircraft navigation, radio broadcasting, military applications, and so on. China is managed by the National Radio Management Committee (referred to as the No. Committee). Therefore, the production and use of radio products must be approved by the state.

Second, the frequency division

Since applications in many fields require the system to operate within a certain frequency range, the frequency needs to be segmented. In recent years, segmentation of the spectrum has been carried out several times, the most commonly used by the Institute of Electrical and Electronics Engineers (IEEE), which states that radio frequency identification systems are part of the radio application and therefore their use cannot interfere with other For the normal operation of the system, the frequency range used by the ISM is usually the local radio communication band. Therefore, in general, the frequency band used by the radio frequency is the ISM band.

The most important operating frequency of the RFID system is 0-135k, and the ISM frequency is 6.78MHZ\13.56MHZ\27.125MHZ\40.68MHZ\433.92MHZ\869.0MHZ\915MHZ\2.45GHZ\5.8GHZ and 24.125GHZ.

Below we mainly introduce the frequency bands 869MHZ and 915MHZ.

At present, the global UHF RFID system operates at frequencies between 860 and 960. This is because RFID systems will be used all over the world. However, there is no common frequency that can be applied to a radio frequency identification system in the world. The specific provisions of the aspects are also different. Therefore, frequency issues are an important issue for RFID systems. The frequency problem mainly includes the range of operating frequency, the size of the transmitting power, the frequency modulation technology, and the channel width.

The frequency band is 869MHz, allowing short-distance use, such as postal, conference, etc. The bands 888-889 and 902-928 are widely used by radio frequency identification systems. In addition, the frequency bands in which the next adjacent frequency band is occupied by D-network telephones and cordless telephones are uniformly planned and allocated by the International Telecommunication Union (ITU). The ITU divides the world into three regions, which are respectively Region 1 (Europe and Africa), Region 2 (Americas), Region 3 (Oceania and Asia).

The characteristics of UHF RFID tags are as follows:

1. Ultra-high frequency electronic tags transmit energy through an electric field. The energy of the electric field drops not very fast, but the read area is not well defined. The reading distance of this band is relatively long, and the passive can reach about 10m, mainly through capacitive coupling for energy exchange and data transmission.

2. The electric wave in the ultra-high frequency band cannot pass many materials, especially suspended particles such as water, dust and fog.

3. The antenna of the electronic tag is generally strip and label. The antenna is available in both linear and circular polarization to meet the needs of the application.

4. This band has a good read range, but it is difficult to define the read area. 5. It has a high transmission rate and can read a large number of electronic tags in a short time.

Third, UHF RFID electronic tag composition

The electronic tag can be divided into two parts, namely the chip of the electronic tag and the antenna of the tag. The antenna function is the electromagnetic wave emitted by the mobile phone reader into the space and the energy emitted by the chip itself is transmitted by electromagnetic waves; the function of the chip is to adjust, decode and other signals received by the tag, and the electronic tag needs to be returned. The signals are encoded, modulated, and the like.

1, the chip

The UHF electronic tag chip is the core part of the electronic tag, and its functions include tag information storage, tag reception signal processing, and tag transmission signal processing.

According to the function and structure characteristics, the chip is divided into three modules: RF, analog front end, digital control and storage unit. The system structure diagram is as follows:

Key technologies and frequency band division of UHF electronic tags

A, RF front end

In addition to providing a transmission interface for the reader and the digital module of the electronic tag, a power supply for the digital circuit is also provided.

B, analog front end

The ultra-high-profile electronic tag analog front end is located between the RF front-end and the back-end digital circuit, and mainly includes:

1. The chip provides a stable voltage

2. Detect the signal from the RF input to obtain the signal required for the digital baseband.

3. The digital baseband provides a power-on reset signal.

4. Provide a stable bias current for the chip.

5. Bit digital baseband provides stable clock signal and so on.

C, digital control module

The digital control module is composed of a PPM decoding module, a command processing module, a CRC module, a main state machine, an encoding module, an anti-collision control, a mapping module, a general-purpose register, a special register, and an EEPROM interface, and its main function is to process data after simulating the debit. Responsible for communication with the moon and communicate with the EEPROM as needed. Based on the consideration of reducing hardware overhead and design complexity, the timing control of the digital part is implemented by a state machine.

2, the antenna

The antenna is a structure having a function of mutually translating a guided wave and a free space wave. It exists in a three-dimensional world consisting of beam range, solid curvature and solid angle. The radio signal power output by the radio design is transmitted to the antenna through the feeder, and is radiated by the antenna in the form of electromagnetic waves. After the electromagnetic wave arrives at the receiving location, it is received by the antenna and sent to the radio receiver through the feeder. There is no radio communication without an antenna.

In UHF electronic tags, the antenna area dominates, ie the tag area is mainly determined by its antenna area. However, the physical size of the antenna is limited by the wavelength of the electromagnetic wave of its working frequency. The electromagnetic wave has a wavelength of 30 cm at ultra high frequency. Compared with the application of the electronic tag, this size is not too large, so the size of the actual electronic tag antenna design will be smaller than this. Dimensions, generally sized to 5-10 cm, are generally referred to as small antennas.

Generally, in the UHF application frequency band, the most commonly used dipole antenna (also known as a symmetric vibrator antenna). The dipole antenna is composed of a straight line of the same thickness and equal length at both ends, and the signal is fed from the two end points in the middle, and a certain current distribution is generated on the arms of the dipole, and various current distributions are generated. The electromagnetic field is excited in the space around the antenna. Dipole antennas can also be classified into four types, namely a half-wave dipole antenna, a two-wire folded dipole antenna, a three-wire folded even ring antenna, and a double dipole antenna. As shown below.

Key technologies and frequency band division of UHF electronic tags

Fourth, the packaging of UHF electronic tags

Package classification

From the material:

1. paper label; 2 plastic label; 3 glass label

From shape:

1. credit card label; 2, linear label; 3, round label; 4, watch type label; 5 other shapes

Package processing

The packaging process mainly includes three main processes, namely, antenna substrate fabrication, Inlay fabrication (primary packaging), coating of insulating film on the substrate, and punching (secondary packaging).

1. The fabrication of the antenna substrate currently mainly includes two methods, one is a conventional etching process, and the other is realized by a screen printing process. The etching process is to process the aluminum foil and the film into an aluminum composite material, and then form a new composite material by printing a color anticorrosive agent, and process it into an antenna-shaped composite material substrate through an etching production equipment. This process is actually a molding process for an antenna composite. In the process of printing ultra-high frequency electronic labels, conductive inks are mainly used to print RFID antennas to replace metal foil antennas or corrosion methods.

2. Inlay production (primary packaging) refers to the process of making the Inlay with the substrate and chip with the antenna through the dispensing method. The packaging of the ultra-high frequency electronic label is mainly reflected in the interconnection of the antenna substrate and the chip. The suitable packaging method is Flip Chip technology, which has the characteristics of high performance, low cost, miniaturization and high reliability. To adapt to the flexible substrate material, the flip-chip bonding material should be realized by conductive adhesive. Interconnection with antenna pads.

3. The substrate is coated with an insulating film and punched (secondary package). UHF electronic tags are categorized into three categories, namely traditional labels (stickers), injection molding and cards.

4. The traditional self-adhesive self-adhesive electronic label uses a label composite device to complete the packaging process. The label consists of a layer, a chip circuit layer, a glue layer, and a bottom layer. The surface layer can be made of various materials such as paper, PP, PET, etc., and the cold gel is applied to the Inlay layer by using a coating device, and the plastic backing paper is formed to form a circuit-protected label. , then brushing the glue, combined with the release paper, forming a roll of self-adhesive electronic label, and then undergoing a process such as die cutting to form a single self-adhesive electronic label;

5. Injection molding and PVC cards are similar to the traditional card-making process, that is, applying varnish on the surface of the roll of Inlay, and combining with the printed upper and lower primers to form a large finished label card, and then through printing, Lamination, punching, etc. form a label card that conforms to the ISO7810 card standard size, and can also be processed into a form of the opposite sex as needed.

Five, UHF RFID tag technical parameters

1. The energy requirement of the tag: the energy requirement of the tag refers to the range of energy required to activate the tag chip circuit;

2. Label transmission rate: The rate at which the tag feeds back the data carried by the reader and the rate at which the data command is received from the reader.

3. Tag read/write speed: determined by the time of reader recognition and writing, usually in milliseconds

4. The capacity of the tag: generally up to 1024 bytes of data.

5. The package form of the tag: depending on the shape of the tag antenna

Sixth, electronic label application field

Application areas include: management and application in the supply chain, management and application of production line automation, management and application of air parcels, container management and application, management and application of railway parcels, and application of logistics management.

Seven, the standard of UHF RFID tags

1. ISO/IEC 18000-6 defines the UHF physical layer and communication protocol; the air interface defines Type A and Type B; supports read and write operations.

2. EPCglobal defines the structure of the electronic article code and the UHF air interface and communication protocols, such as class0, Class1Gen1, ClassGen2.

3. UbiquitousID, a Japanese organization that defines the structure and communication management protocol for UID encoding.