Introduction to RFID technology
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As we all know, the Olympic Games is currently the largest comprehensive sports event in the world, integrating sports competitions, leisure, communication, play, shopping and other commercial activities. Therefore, the Olympic venues hosting this event will certainly accept a large audience, athletes, Managers, service personnel, etc., and the identity of the crowd is extremely complex and is constantly moving.
How to verify that the ticket and documents held by the personnel are valid? How to track and query people in time to enter the designated area? How do you warn and guide people to leave quickly when they enter or ban illegally? How to check the crowding degree of a certain area in real time? The use of RFID electronic ticket management system will achieve the purpose of efficient and quality management.
The RFID electronic ticket is a new type of ticket that embeds the smart chip into the medium such as paper tickets for quick ticket checking/checking and real-time accurate positioning tracking and query management for the ticket holder. The 2008 Beijing Olympic Games will use electronic tickets based on RFID chip technology to vividly reflect the profound connotation of "Science and Technology Olympics" and "Humanistic Olympics".
The author has compiled RFID related materials for your reference.
1. What is RFID?
RFID is Radio Frequency
Abbreviation for Identification, ie radio frequency identification. Often referred to as inductive electronic chips or proximity cards, proximity cards, contactless cards, electronic labels, electronic barcodes, and the like. a complete RFID system consists of Reader and Transponder are composed of two parts. The principle of action is Reader.
The radio wave energy of a specific frequency is transmitted to the Transponder to drive the Transponder circuit to send the internal ID code, and the Reader receives the ID Code.
Transponder's speciality is that it is free of battery, contact-free, and free of card, so it is not afraid of dirt, and the chip password is the only one in the world that cannot be copied, with high safety and long life.
RFID is sometimes referred to as an electronic volume label or a radio frequency label. Through this non-contact automatic identification technology, as a wireless version of the barcode, the application is very extensive, such as animal chips, access control, parking lot control, production line automation, material management, and the like. The tags can store data ranging from 512 bytes to 4 megabytes depending on the type of merchant. The data stored in the label is determined by the application of the system and the corresponding standards. For example, a volume label can provide product production, transportation, storage, and identify the identity of machines, animals, and individuals. The volume label can also be connected to a database to store information about the product stock number, current location, status, selling price, and batch number. Correspondingly, the RF tag can directly determine the meaning of the code without reading the database when reading the data.
The figure below shows the internal structure of the electronic tag: chip + antenna
The most basic RFID system consists of three parts.
Tag: consists of a coupling component and a chip, each tag has a unique electronic code attached to the object to identify the target object;
Reader: A device that reads (and sometimes writes) the label information, which can be designed as a handheld or fixed type;
Antenna: Transmits RF signals between the tag and the reader.
The following figure shows the composition of the RFID system.
The RFID system contains at least two parts, an electronic volume label and a reader. The electronic label is the data carrier of the RFID system, and the electronic label consists of a label antenna and a label-specific chip. According to the different electronic coil power supply methods, the electronic label can be divided into active electronic labels (Active Tag), passive electronic tag (Passive tag) and semi-passive electronic tag (Semi-passive Tag). The active electronic tag contains a battery, the passive radio tag does not have a built-in battery, and the semi-passive tag partially relies on the battery.
The electronic label can be divided into low frequency electronic label, high frequency electronic label, ultra high frequency electronic label and microwave electronic label according to the frequency. Depending on the package type, it can be divided into credit card labels, linear labels, paper labels, glass tube labels, round labels, and special-purpose labels.
The RFID reader (reader/writer) wirelessly communicates with the RFID electronic tag through the antenna, and can read or write the tag identification code and the memory data. A typical reader includes a high frequency module (transmitter and receiver), a control unit, and a reader antenna.
2. RFID development history
RFID directly inherits the concept of radar. In 1948, Harry Stokeman's "Communication with Reflected Power" laid the theoretical foundation for RFID.
From 1941 to 1950, the improvement and application of radar gave birth to RFID technology. In 1948, the theoretical basis of RFID technology was laid.
From 1951 to 1970, the theory of RFID technology was developed and some application attempts were started.
From 1971 to 1980, RFID technology and product development were in a period of great development. Various RFID technology tests were accelerated, and some of the earliest RFID applications appeared.
From 1981 to 1990, RFID technology and products entered the commercial application stage, and applications of various scales appeared.
From 1991 to 2000, RFID technology standardization issues have been increasingly valued, RFID products have been widely adopted, and RFID products have gradually become a part of people's lives.
From 2001 to the present, standardization issues are increasingly valued by people, and RFID products are more abundant, active electronic tags,
Both passive electronic label and semi-passive electronic label have been developed, the cost of electronic labeling has been continuously reduced, and the scale application industry has expanded.
RFID technology and applications are also developing rapidly in China. In June 2006, the White Paper on China's Radio Frequency Identification (RFID) Technology Policy, jointly prepared by more than 10 ministries and commissions including the Ministry of Science and Technology and the Ministry of Information Industry, was announced. This white paper gives an approximate timetable for the development of Chinese standards: during the incubation period (2006-2008), according to the national RFID standard system framework, the corresponding technical standards and application standards are formulated; in the growth period (2007-2012), basic Formed a Chinese RFID standard system.
3. How RFID works
The basic model of the RFID system is shown below.
The space tag (contactless) coupling between the electronic tag and the reader is realized by the coupling component, and in the coupling channel, energy transfer and data exchange are realized according to the timing relationship.
There are two types of coupling of RF signals that occur between the reader and the electronic tag.
(1) Inductive coupling. The transformer model is coupled by a spatial high-frequency alternating magnetic field, based on the law of electromagnetic induction, as shown in the following figure.
(2) Electromagnetic backscatter coupling: The radar principle model, the electromagnetic wave emitted, hits the target and reflects, and carries back the target information, based on the spatial propagation law of the electromagnetic wave.
Electromagnetic backscatter coupling type RFID reader (above)
As with the radio principle, the RF tag and reader are also modulated to the same frequency to operate. LF, HF,
UHF corresponds to RF at different frequencies. LF stands for low frequency radio frequency, around 125KHz, HF stands for high frequency radio frequency, around 13.54MHz, UHF stands for UHF radio frequency, in the range of 850 to 910MHz, there is 2.4G microwave reader.
The inductive coupling method is generally suitable for short-range radio frequency identification systems operating at medium and low frequencies. The electromagnetic backscatter coupling method is generally suitable for long-range radio frequency identification systems operating at high frequencies and microwaves.
The RFID frequencies used in different countries are also different. Europe's UHF is 868MHz, while the US is 915MHz. Japan does not currently allow UHF to be used in RF technology. Governments have also limited the impact of readers on other devices by adjusting the power of readers. Some organizations, such as the Global Business Facilitation Council, are encouraging governments to remove restrictions, and label and reader manufacturers are also developing systems that can use different frequency systems to avoid these problems.
4. RFID reader anti-collision principle
One difficulty with RFID technology is that multiple tags are read simultaneously. In order to achieve this function, the technology adopted in communication is "anti-collision". Reading multiple tags at the same time is often the case where RFID is far superior to bar codes, but if there is no "anti-collision" function, the RFID system can only read and write one tag. In this case, if there are more than two tags in the readable range at the same time, it will cause a reading error.
Even an RFID system with "anti-collision" functionality does not actually read the contents of all tags at the same time. In the case where a plurality of tags are detected at the same time, the function of retrieving the signal and preventing the collision starts to operate. In order to perform the search, the search condition is first determined. For example, the operational steps of the ALOHA-type anti-collision function applied in the RFID system of the 13.56 MHz band are as follows.
1) First, the reader specifies the specific number of bits (about 1 to 4 bits) of the electronic volume label memory as the number of batches.
2) The electronic volume label discretizes the timing of the response according to the number of times. For example, in the case of a two-digit number batch "00, 01, 10, 11", the reader will respond to these four possibilities one by one at different timings.
3) If there is only one electronic tag at the same time in each time, the normal data of the electronic tag can be obtained. After the information is read, the reader sends a sleep command (Sleep/Mute) that does not respond to the electronic tag for a certain period of time to make it sleep, avoiding the response again.
4) If it is responded to by several electronic tags at the same time in each time, it is judged as "conflict". In this case, the number of times recorded by the other two digits in the memory is repeated, and the processing from 2) above is repeated.
5) After all the electronic labels have been responded, the reader sends them a wake-up command (Wake Up) to complete the reading of all electronic labels.
In such an RFID system equipped with an "anti-collision" function, in order to read only one label, the number of adjustments is repeatedly read and retrieved in batches. Therefore, in the case of a single-time reading with a certain number of tags, all the tags are read at the same speed, the more the number of tags read at one time, the time required to complete the reading is simpler than the simple calculation The longer it takes.
Achieving "anti-collision" is an essential condition for RFID to replace barcodes in the logistics field. For example, in a supermarket, goods are placed in a shopping cart for pricing. In order to achieve this pricing method, the "anti-collision" function must be complete. An RFID system with an "anti-collision" function is more expensive than a system that does not have such a function. When an individual user is making an RFID system, there is no need to select an anti-collision reader if there is no need to carry out multiple IDs at the same time.

