RFID UHF Tag Applications

Radio Frequency Idenficaon, RFID for short, is a non-contact automatic identification technology, which automatically identifies the target object and obtains relevant data through radio frequency signals, identification work without human intervention, and can work in a variety of harsh environments. The use of ultra-high frequency RFID (UHF RFID) technology can identify high-speed movement of objects, and can simultaneously identify multiple tags. UHF RFID identification has no direction, can be batch identification, long life, can not be rewritten, pollution-resistant characteristics, and can use the RFID storage area to write important information.

I. RFID frequency standards
The working frequency of the radio frequency system is one of the most basic technical parameters of the radio frequency identification technology system. The choice of the working frequency determines to a large extent the application scope of the electronic label, the technical feasibility and the system cost high and low.
The radio frequency recognition system in the final analysis is a kind of radio propagation system, it must occupy the certain space communication channel. In the space communication channel, the radio frequency signal intelligence to the electromagnetic coupling or the electromagnetic reflection form manifests, therefore, the radio frequency recognition system performance will certainly be affected by the electromagnetic wave space transmission characteristic.
In people's daily life, electromagnetic waves are ubiquitous, such as the navigation of aircraft, radio broadcasting, military applications and so on. China is under the unified management of the State Radio Administration Commission (SARAC). Therefore, the production and use of radio products must be licensed by the state.

II. Frequency division
As many applications in the field require systems to operate within a certain frequency range, segmentation of frequencies is required. In recent years, the segmentation of the frequency spectrum has been carried out several times, among them, the most commonly used is the Institute of Electrical and Electronics Engineers (IEEE) established, stipulates: the radio frequency identification system belongs to the application of radio, therefore, its use cannot interfere with the normal work of other systems, ISM use the frequency range is usually local radio communication band, therefore, usually, the radio frequency use of the frequency band is ISM frequency band.

The radio frequency recognition system most main working frequency is 0-135k,ISM frequency 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 ultra high frequency radio frequency recognition system working frequency in 860-960 between, this is because the radio frequency recognition system will apply in the world, however in the global cannot find a radio frequency recognition system can apply the common frequency, the world each country to the frequency aspect specific regulation also varies. Therefore, the frequency issue is an important issue for the radio frequency identification system. The frequency issue mainly includes the range of the working frequency, the size of the transmitting power, the frequency modulation technology, the channel width and so on.

The frequency band 869MHz, allows the short distance use, such as postal, conference and so on. The frequency bands 888-889 and 902-928 are widely used by radio frequency identification systems. In addition, the sub-adjacent frequency band is occupied by D-Internet phone and cordless phone global frequency band by the International Telecommunication Union (ITU) for unified planning and allocation, the ITU divided the world into 3 large areas, they are region 1 (Europe and Africa region), region 2 (America region), region 3 (Oceania and Asia region).

The characteristics of UHF RFID tags are as follows.
1. UHF tags transmit energy through an electric field. The energy of the electric field does not fall very quickly, but the reading area is not very well defined, the frequency band reading distance is relatively far, passive up to about 10m, mainly through the capacitive coupling of the way to exchange energy and data transmission.
2.The radio waves of the UHF band cannot pass through many materials, especially water, dust, fog and other suspended particulate matter.
3. The antenna of the electronic tag is generally long and tag-like. The antenna has linear and circularly polarized two designs to meet the corresponding application requirements.
4. The band has a good reading distance, but it is difficult to define the reading area.
5. There is a high transmission rate, in a very short period of time, can read a large number of RFID tags.

Three, UHF RFID tag composition
The rfid tag can be divided into two parts, namely the chip of the electronic tag and the antenna of the tag. The function of the antenna is the electromagnetic wave that the mobile phone reader emits into space and the energy that the chip itself emits in the way of electromagnetic wave; the function of the chip is to regulate the signal received by the tag, decode and other kinds of processing, and the electronic tag needs to return to the signal for encoding, modulation and other kinds of processing.

1、Chip
UHF label chip is the core part of the electronic label, its role includes label information storage, label receiving signal processing and label transmitting signal processing.

The chip is divided into RF, analog front-end, digital control, storage unit three modules according to the function and structure characteristics, the system structure diagram is as follows.
UHF electronic label key technology and frequency band division
A, RF front-end
In addition to providing the transmission interface between the reader and the digital module of the electronic tag, it also provides the power supply of the digital circuit.
B、Analog front end
The analog front-end of the UHF tag is between the RF front-end and the back-end digital circuit, which mainly includes.

1. chip to provide a stable voltage
2. the signal obtained from the RF input for wave detection, to obtain the signal required for the digital baseband.
3. providing a power-on reset signal to the digital baseband
4. provide the stable bias current of the chip
5. bit digital baseband to provide stable clock signal, etc.

C. Digital Control Module
The digital control module consists of a PPM decoding module, command processing module, CRC module, main state machine, coding module, anti-collision control, mapping module, general purpose registers, special registers and EEPROM interface. Its main function is to process the data after the analogue debit, responsible for communication with the moon burst and to communicate with the EEPROM as required. Based on the consideration of reducing hardware overhead and design complexity, the timing control of the digital part is all implemented using a state machine.

2、Antenna
An antenna is a structure that has the function of transferring guided waves to each other and to free space waves. It exists in a three-dimensional world composed of beam range, three-dimensional radian and three-dimensional angle. The radio design outputs RF signal power, which is delivered to the antenna via a feeder line, which is radiated by the antenna in the form of electromagnetic waves. Once the electromagnetic waves reach the receiving location, they are received down by the antenna and sent to the radio receiver via the feed line. Without antenna there is no radio communication.

In the UHF tag, the antenna area dominates, i.e. the tag area depends mainly on its antenna area. However, the physical size of the antenna is limited by its operating frequency electromagnetic wave wavelength, in the UHF under the electromagnetic wave wavelength of 30cm, relative to the application of electronic tags, this size is not too large, so the actual electronic tag antenna design size will be smaller than this size, general size design to 5-10cm, this antenna is generally known as a small antenna.

Generally in the UHF application band, the most commonly used is the dipole antenna (also known as symmetrical oscillator antenna). Among them, the dipole antenna by the two ends of the same thickness and equal length of straight wire line into a straight line, the signal from the middle of the two endpoints into, in the dipole of the two arms of the current distribution, all kinds of current distribution in the space around the antenna to excite the electromagnetic field. The dipole antenna can also be divided into four types, namely half-wave dipole antenna, two-line folded dipole antenna, three-line folded dipole antenna and double dipole antenna. The diagram below.

The key technology and frequency band division of UHF electronic label

Four, the UHF electronic label packaging
Classification of packaging

From material.
1. paper label; 2. plastic label; 3. glass label
From the shape.
1. credit card labels; 2. linear labels; 3. round labels; 4. watch-type labels; 5 other shapes

Processing of the package
The packaging process consists of three main processes, namely the production of the antenna substrate, the production of Inlay (primary packaging) and the coating of insulating film on the substrate and punching (secondary packaging).

1. the antenna substrate production currently includes two main ways, one is the traditional etching process, the other is through the screen printing process to achieve. The etching process involves processing aluminium foil and film into an aluminium composite, then forming a new composite by printing a coloured anti-corrosion agent, which is processed into an antenna-shaped composite substrate by etching production equipment. This process is actually an antenna composite forming process. Today's UHF label printing process, conductive ink is mainly used to print RFID antennas to replace the traditional pressure foil method or etching method to produce metal antennas.

2. Inlay production (a package) refers to the antenna with the substrate and chip through the way of glue into the process of Inlay, UHF electronic tag packaging link is mainly reflected in the antenna substrate and chip interconnection, the most suitable packaging for the inverted chip technology (Flip Chip), which has high performance, low cost, miniaturization, high reliability characteristics, in order to adapt to Flexible substrate material, the bonding material of the flip chip should be used to realize the interconnection of the chip and antenna pads.

3. the base plate has to be coated with insulating film, punching (secondary packaging). UHF electronic labels are divided into three categories from the form, namely, the traditional label class (self-adhesive), injection molding and card class. 4.

4. traditional self-adhesive electronic labels with label composite equipment to complete the packaging process. The label consists of a layer, chip line layer, adhesive layer and bottom layer. The surface layer can be made of paper, PP, PET and other materials to produce the surface of the product, the application of coating equipment will be coated with cold gel to Inlay layer, plus the plastic material backing paper, the formation of a circuit with the protection of the label, and then brush on the adhesive, and the combination of release paper, the formation of a roll of self-adhesive electronic labels, and then after die-cutting and other processes, the formation of a single self-adhesive electronic labels;

5. injection molding class and PVC cards and the traditional card making process is similar, that is, in the roll of Inlay surface coated with varnish, through the combination with the printed upper and lower backing, the formation of a large sheet of finished label card, and then through the printing, lamination, punching, etc. to form the ISO7810 card standard size of the label card, but also according to the need to process into heterosexual and other forms.

V. Technical parameters of UHF RFID tags
1. the energy requirements of the tag: the energy requirements of the tag refers to the range of energy required to activate the tag chip circuit;
2. the transmission rate of the tag: the transmission rate of the data carried by the tag back to the reader and the rate of accepting the write data command from the reader.
3. the read-write speed of the label: is read-write recognition and write time decision, generally for millisecond level
4. the capacity of the label: generally can reach 1024Byte of data volume.
5. The package form of the label: depends on the shape of the label antenna

Ⅵ, electronic label application areas
Application areas mainly include: management and application in the supply chain, management and application of production line automation, management and application of air parcels, management and application of containers, management and application of railway parcels, application of logistics management, etc.

VII. Standards for UHF RFID tags
1. ISO/IEC18000-6 defines the physical layer of UHF and the protocol of communication; the air interface defines the two parts of TypeA and TypeB; it supports readable and writable operation.
2. EPCglobal defines the structure of the electronic article code and the air interface of UHF and the protocol of communication, such as class0, class1Gen1, classGen2. 3.
3. UbiquitousID, a Japanese organisation, defines the structure of the UID code and the communication management protocol.