RFID, Radio Frequency Identification

Radio Frequency Identification, RFID Related Theory

 RFID (Radio Frequency Identification) technology, that is, radio frequency identification technology, is a non-contact automatic identification technology that began to emerge in the 1990s. Radio frequency identification technology is a method that uses radio frequency signals to achieve spatial coupling (alternating magnetic field or electromagnetic field)

Overview of RFID Technology

 The technology of contactless information transmission and the purpose of identification through the transmitted information. Compared with automatic identification technologies such as bar codes, magnetic stripes, magnetic cards, fingerprints, optical characters, etc., RFID has wireless read / write, strong signal penetration ability, long recognition distance, long service life, good environmental adaptability, and multiple tags at the same time Identification, large information storage capacity and data can be rewritten and other advantages.


From the basic principle of information transmission, RFID technology is based on the transformer coupling model (energy transfer and signal transmission between primary and secondary) in the low frequency band, and the space coupling model based on the radar detection target in the high frequency band (radar emits electromagnetic waves.

After encountering the target, carry the target information back to the radar receiver). In 1948, Harry Stockman's "Communications that Utilize Reflected Power" laid the theoretical foundation for radio frequency identification technology.

Composition and working principle of RFID system

System composition

The general radio frequency identification system is generally composed of three parts: a radio frequency card (transponder), a reader / writer (reader), and an application system (including connection lines.

Radio frequency card: An antenna that carries information about the target item and transmits radio frequency signals between the reader and the electronic tag;


RF transceiver: generates RF signals

Reader: Receive the radio frequency signal returned from the electronic tag, and transmit the decoded data to the host system. In actual design, readers, antennas and transceivers are generally integrated together and are collectively called readers. Therefore, it can also be said that the RFID system is composed of a tag and a reader.

Working principle

The working principle of the RFID system is that in the coupling channel, the reader and the tag realize the spatial coupling of the RF signal through the coupling element, and according to the timing relationship, the data exchange and energy transfer are completed. The basic model of its work is shown in Figure 2- 2 shows,

RFID field

The reader provides working energy to the electronic tag. For passive tags, when the tag leaves the RFID field, the tag is dormant due to no energy activation. When the tag enters the RFID field, the radio frequency wave emitted by the reader activates the tag circuit.

The tag rectifies the radio frequency. The wave is converted into electrical energy and stored in the capacitor in the tag, thereby providing energy for the tag's work and completing the data exchange.

For semi-active tags, the RF field only plays an active role. Active tags are always in an active state, in an active working state, and interact with the radio frequency waves emitted by the reader, and have a long reading distance.


Timing refers to the working order of readers and tags. That is, the reader actively wakes up the tag, and then the tag first reports to the door. For passive tags, it is generally the reader-first format. For simultaneous reading of multiple tags, the reader-first format or the label-first format can be used.

Data communication between the reader

The data communication between the reader and the tag includes the data communication from the reader to the tag and the data communication from the tag to the reader. The data communication from the reader to the tag includes offline data writing and online data writing.

For the data communication process from the tag to the reader, its working methods include the following two tags:

When the tag receives the radio frequency energy of the reader, it is activated and transmits the data information stored in the tag to the reader.

After the tag is activated, it transfers according to the instructions of the reader. Enter the data transmission state or sleep state. In these two working methods, the former belongs to one-way communication, and the latter belongs to half-duplex two-way communication.

In the working process of the radio frequency identification system, energy is always used as the basis to exchange data through a certain timing method. Therefore, there are three event models based on energy supply in the working space channel, an event model for realizing data exchange in a time series manner, and an event model for the purpose of data exchange.

Classification of RFID systems

According to the different functions completed by the RFID system, the RFID system can be roughly divided into four types: EAS system, portable data acquisition system, network system, positioning system.


 EAS technology

ELECTRONIC ARTICLE SURVEILLANCE (EAS) is an RFID technology installed at the doorway that needs to control the entry and exit of items. Typical applications of this technology are stores, libraries, data centers, and other places.

When unauthorized persons illegally remove items from these places, the EAS system will issue a warning. When applying the EAS technology, first attach an EAS label to the item. When the item is normally purchased or legally removed, the EAS tag is deactivated by a certain device at the checkout point, and the item can be removed.

When an item passes through the door equipped with the EAS system, the EAS device can automatically detect the activity of the tag, and the EAS system will issue a warning if the active tag is found. The application of EAS technology can effectively prevent the theft of items, whether it is a large item or a small item.

Radio Frequency Identification

Using EAS technology, items no longer need to be locked in glass cabinets, allowing customers to view and inspect products freely.

This is of great practical significance in the increasingly popular choice today. A typical EAS system generally consists of three parts: 1) an electronic tag attached to a commodity, an electronic sensor.

2) an electronic tag inactivation device so that authorized goods can enter and exit normally

3) a monitor, which causes a certain area of ​​surveillance at the exit space.


The working principle of the EAS system is: in the surveillance area, the transmitter transmits signals to the receiver at a certain frequency. The transmitter and receiver are generally installed at the entrance and exit of retail stores and libraries to form a certain monitoring space.

When a tag with special characteristics enters the area, it will interfere with the signal sent by the transmitter. This interference signal will also be received by the receiver. After the analysis and judgment of the microprocessor, the alarm will be controlled.

EAS can be divided into many types according to the different signals emitted by the transmitter and the different principles of the tag interference to the signal. The latest research direction of EAS technology is the production of labels. People are discussing whether EAS labels can be added to the product during the production or packaging process as a barcode, and become a part of the product.


 Portable data acquisition system

The portable data collection system uses a handheld data collector with an RFID reader to collect the data on the RFID tag. This kind of system has greater flexibility and is suitable for application environments where fixed RFID systems are not suitable.

The handheld reader (data input terminal) can transmit data to the host computer system in real time through radio wave data transmission (RFDC) while reading the data, or it can temporarily store the data in the reader. Transfer data to the host computer system in batches.


 Logistics control system

In the logistics control system, fixedly arranged RFID readers are distributed in a given area, and the readers are directly connected to the data management information system, and the signal transmitter is mobile, generally installed on moving objects and people.

When objects and people flow through the reader, the reader will automatically scan the information on the label and input the data information into the data management information system for storage, analysis, and processing to achieve the purpose of controlling logistics.


 GPS (Geographical Positioning System)

The positioning system is used for positioning in an automated processing system and for operating positioning support for vehicles, ships, etc.

The reader is placed on a moving vehicle, ship, or moving material, semi-finished product, or finished product in an automated assembly line. The signal transmitter is embedded below the surface of the operating environment.

Position identification information is stored on the signal transmitter, and the reader is generally connected to the main information management system in a wireless manner or a wired manner.

RFID standards and technical specifications

The RFID standard system is divided into technical standards and application standards. Technical standards mainly include interface specifications, physical characteristics, reader protocol, coding system, test specifications, application specifications, data management, information security and other standards.

The application standards are mainly divided into animal identification, identification, business, transportation, military and so on.


At present, the commonly used international standards mainly include the ISO / IEC18000 standard (including 7 parts, involving 125KHz, 12.56MHz, 860-960MHz, 2.45GHz and other frequency bands), ISO11784 and ISO1178 for animal identification, and ISO10536 for contactless smart cards , 15693, 14443, ISO10374 for container identification, etc.

At present, there are three well-known organizations that formulate RFID standards internationally: ISO International Organization, EPC global led by the United States, and Ubiquitous ID Center in Japan.

These three organizations have their own goals and development plans for RFID technology application specifications. The following briefly introduces the relevant EPC global international standards.


Electronic Product Code Frequency

The frequency used by the EPC (Electronic Product Code) standard is 13.56MHz and 902-928MHz, which is promoted and proposed by EPC global Inc. The goal of EPC is mainly to promote that each item in life has a unique code, and are connected to form a so-called Internet of Things concept.

Internet of Things EPC

Users can use the Internet of Things EPC code name resolution service ONS (Object Name Service), so that goods using EPC RFID tags can be circulated around the world. In June 2004, EPC global officially announced the world ’s first RFID standard, allowing different companies around the world to have a common standard in using RFID. The five different levels set by EPC Tag are:


1) Class0: Only for reading, simple and passive, only providing read-only labels with the number specified at the factory. The label is written with a set of unchangeable numbers at the factory to provide simple service identification;


2) Class1: write only once, simple passive, available for write once;


3) Class2: Repeated reading and writing, with repeatable reading and writing functions, passive tags;


4) Class3: Semi-passive tag with built-in sensor, repeated reading and writing function, and additional sensor, which can detect temperature! Humidity! Dynamic change etc. and recorded in the tag, built-in battery to increase reading distance;


5) Class4: belongs to the antenna, it is a semi-passive tag, which can actively communicate with other tags, and is still in the process of research and development.

2.5. Current status of RFID development at home and abroad


The prototype of RFID technology can actually be traced back to World War II, when the British army used wireless identification technology to identify the aircraft of both the enemy and us.

Despite its 60-year history, the lack of industry standards has made the commercialization of radio frequency identification technology so long. With the development of science and technology, the civilian use of RFID technology has gradually emerged in the 1990s.


Since the 1990s, many regions and companies have begun to pay attention to the interoperability between these systems, namely the standardization of operating frequency and communication protocols. Only standardization can make RFID's automatic identification technology more widely used.

At the same time, RFID smart cards and smart keys have become popular as means of access control and physical security, trying to replace traditional access control mechanisms.

This kind of smart card called contactless IC has strong data storage and processing capabilities, can be personalized for the holder, and can more flexibly implement the access control strategy.


In the late 1990s, ultra high frequency (UHF) passive RFID tag technology began to appear, providing longer transmission distances and faster transmission speeds.

From this point on, RFID technology is really a real application, such as pallet and packaging tracking in supply chain management, inventory and warehouse management, container management, logistics management, etc. And gradually try to become the data and semantic basis of synthetic enterprise applications (including ERP, SCM, CRM, EAM, B2B, etc.).


From the late 1990s to the present, RFID technology has developed rapidly at home and abroad. TI, Motorola, NXP (formerly Philips Semiconductor Division), Microchip and other world-renowned semiconductor manufacturers have invested in the production of RFID products.

Retail giants such as Wal-Mart, Target, Metro Group and some government agencies, such as the US Department of Defense, have begun to promote RFID applications, and require their suppliers to adopt this technology. At the same time, there have been multiple global RFID standards and technology alliances in standardization disputes, mainly EPCglobal, AIM Global, ISO / IEC, UID, IP-X, etc.

These organizations are trying to achieve a globally unified platform in terms of tag technology, frequency, data standards, transmission and interface protocols, network operation and management, and industry applications.

RFID technology will bring tens of billions of dollars to the global market, followed by huge demand for servers, data storage systems, management software, and computer facilities. As the cost of tags decreases and technology advances, RFID technology will soon gain popularity worldwide.

The popularity of RFID identification technology will inevitably lead to revolutionary changes in various industries such as logistics, retail, manufacturing, transportation, and medical treatment.

As a global electronics manufacturing plant and the third largest trading country, RFID will bring opportunities and new economic growth points for China's development.


In the next 10 years, countless radio frequency tags will fill our lives. All kinds of identification cards / cards, bank cards, air tickets, and various retail products in shopping malls will be affixed with these small RF tags.

Through the radio frequency tag, the RFID device communicates wirelessly and obtains the data of the target object to achieve the purpose of automatic identification.

Typical application of RFID

  • Logistics and supply management
  • Manufacturing and assembly
  • Air baggage handling / Express Parcel Processing
  • Document tracking / library management
  • Animal identity
  • Sports timing
  • Access control / electronic tickets
  • Road automatic toll collection

Summary of this chapter

This chapter mainly introduces the concepts related to RFID and other theoretical knowledge related to RFID. First of all, RFID, as a non-contact automatic identification technology, has many outstanding advantages over the currently widely used barcode technology. Therefore, RFID technology has received widespread attention at home and abroad, and its application prospects are very broad.

Secondly, the composition and working principle of the RFID system and related international standards are introduced, which provides a theoretical basis for the realization of the RFID warehouse management system.

Next, the development status of RFID at home and abroad and the classification of RFID system are introduced. It is pointed out that RFID technology is widely respected by people. After nearly 80 years of exploration and research, many good results have been achieved.

According to the different functions of the RFID system, it can be divided into different types and can be applied to different applications. However, due to its own complexity, there are many technical difficulties that have not been well resolved and the cost is too high. At present, this technology is still not widely used in industrial production and life.

The technical difficulties in RFID software are mainly concentrated in RFID data cleaning algorithms, complex event processing algorithms, data mining, etc. This article is to implement a local complex event processing algorithm to solve the problem of out-of-order data flow.


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