This article takes you to understand RFID radio frequency identification system

RFID radio frequency identification technology

The full English name of RFID is Radio Frequency Identification, radio frequency identification, also known as electronic label, radio frequency identification, inductive electronic chip, proximity card, proximity card, non-contact card, electronic barcode.

RFID radio frequency identification is a non-contact automatic identification technology, which automatically recognizes the target object and obtains relevant data through radio frequency signals. The identification work does not require manual intervention and can work in various harsh environments.

RFID technology can identify high-speed moving objects and can identify multiple tags at the same time, which is fast and convenient. Short-distance radio frequency products are not afraid of harsh environments such as oil stains and dust pollution. They can replace barcodes in such environments, such as tracking objects on the assembly line of a factory. Long-distance radio frequency products are mostly used in traffic, and the identification distance can reach tens of meters, such as automatic toll collection or vehicle identification.

RFID system architecture

A typical RFID system is mainly composed of four parts: reader, electronic tag, RFID middleware and application system software. Generally, we refer to middleware and application software as application system.

RFID system structure

In the actual RFID solution, the RFID system contains some basic components. The components are divided into hardware components and software components.

From the perspective of functional realization, the RFID system can be divided into two parts: the edge system and the software system. The edge system mainly completes information perception and belongs to the hardware component part; the software system completes the information processing and application; the communication facility is responsible for the entire RFID system Information transfer.

Basic composition of RFID system

1. Electronic label

Electronic Tag (Electronic Tag), also known as transponder or Smart Label, is a miniature wireless transceiver device, mainly composed of built-in antenna and chip.

2. Reader

The reader is a device that captures and processes RFID tag data. It can be a separate individual or it can be embedded in other systems. The reader is also one of the important components of the RFID system. Because it can write data to the RFID tag, it is called a reader.

The hardware part of the reader is usually composed of transceivers, microprocessors, memories, external sensors/actuators, alarm input/output interfaces, communication interfaces and power supplies.

Schematic diagram of reader composition

3. Controller

The controller is the command center for the reader chip to work in an orderly manner. Its main functions are:

Communicate with application system software; execute action instructions sent from application system software; control the communication process with tags; encode and decode baseband signals; implement anti-collision algorithms; encrypt data transmitted between readers and tags And decryption; perform identity authentication between the reader and the electronic tag; control the keyboard, display device and other external devices.

Among them, the most important is the control operation of the reader chip.

4. Reader antenna

An antenna is a device that receives or radiates the front-end radio frequency signal power in the form of electromagnetic waves. It is an interface device between the circuit and the space and is used to convert the energy of the guided wave and the free space wave. In the RFID system, antennas are divided into two categories: electronic tag antennas and reader-writer antennas, which are responsible for receiving energy and transmitting energy respectively.

The characteristics of the RFID system reader antenna are:

Small enough to be affixed to the required items; omnidirectional or hemispherical coverage directionality; able to provide the largest possible signal to the tag chip; no matter what direction the item is, the polarization of the antenna can be interrogated by the card reader The signals are matched; robust; cheap.

The main factors that should be considered when choosing a reader antenna are:

The type of antenna; the impedance of the antenna; the performance of the RF applied to the article; the performance of the RF when there are other articles surrounding the labeled article.

5. Communication facilities

Communication facilities provide secure communication connections for the management of different RFID systems and are an important part of the RFID system. Communication facilities include wired or wireless networks and serial communication interfaces that connect readers or controllers with computers. The wireless network can be a personal area network (PAN) (such as Bluetooth technology), a local area network (such as 802.11x, WiFi), or a wide area network (such as GPRS, 3G technology) or a satellite communication network (such as a synchronous orbit satellite L-band RFID system) .

Basic principles of RFID system

1. Basic principles

From the perspective of communication and energy induction methods between the electronic tag and the reader, the system can generally be divided into two categories, namely, inductive coupling (Inductive Coupling) systems and electromagnetic backscatter coupling (Backscatter Coupling) systems. Inductive coupling realizes coupling through space high-frequency alternating magnetic field, which is based on the law of electromagnetic induction; electromagnetic backscatter coupling, that is, the principle model of radar, the emitted electromagnetic wave is reflected when it hits the target, and the target information is carried back at the same time, based on electromagnetic wave The law of space propagation.

2. Inductively coupled RFID system

The inductive coupling method of RFID corresponds to the ISO/IEC 14443 protocol. Inductively coupled electronic tags consist of an electronic data carrier, usually composed of a single microchip and a large area coil used as an antenna.

The electronic tags of the inductive coupling mode almost all work passively, and all the energy required for the operation of the microchip in the tag is provided by the induced electromagnetic energy sent by the reader. The high-frequency strong electromagnetic field is generated by the antenna coil of the reader, and passes through the cross section of the coil and the surrounding space of the coil, so that the nearby electronic tags produce electromagnetic induction.

Working principle diagram of inductive coupling RFID system

3. Electromagnetic backscatter RFID system

(1) Backscatter modulation

Radar technology provides a theoretical and application basis for backscatter coupling of RFID. When an electromagnetic wave encounters a space target, part of its energy is absorbed by the target, and the other part is scattered in various directions with different intensities. Among the scattered energy, a small part is reflected back to the transmitting antenna and received by the antenna (so the transmitting antenna is also a receiving antenna), and the received signal is amplified and processed to obtain relevant information about the target.

When electromagnetic waves are emitted from the antenna to the surrounding space, they will encounter different targets. Part of the electromagnetic wave energy (free space attenuation) that reaches the target is absorbed by the target, and the other part is scattered in various directions with different intensities. Part of the reflected energy will eventually return to the transmitting antenna, which is called an echo. In radar technology, this reflected wave can be used to measure the distance and orientation of a target.

For the RFID system, electromagnetic backscatter coupling can be used to use electromagnetic wave reflection to complete the data transmission from the electronic tag to the reader. This working mode is mainly used in 915MHz, 2.45GNz or higher frequency systems.

(2) RFID backscatter coupling method

The frequency of electromagnetic waves reflected by a target is determined by the reflection cross section. The size of the reflection cross section is related to a series of parameters, such as the size, shape and material of the target, the wavelength and polarization direction of electromagnetic waves, etc. Since the reflection performance of the target usually increases with the increase of the frequency, the RFID backscatter coupling method adopts UHF and UHF, and the distance between the transponder and the reader is greater than 1 m. The reader, transponder (electronic tag) and antenna constitute a transceiver communication system.

Principle of RFID backscatter coupling method

4. The recognition principle of surface acoustic wave tags

(1) Surface acoustic wave device

Surface Acoustic Wave (SAW) devices are based on piezoelectric effect and low-speed acoustic waves related to surface elasticity. SAW devices are small in size, light in weight, high in operating frequency, and relatively wide in bandwidth, and can use the same planar processing technology as integrated circuit technology, simple manufacturing, high reproducibility and design flexibility.

Surface acoustic wave devices have a wide range of applications, such as filters in communication equipment. In RFID applications, the operating frequency of surface acoustic wave transponders is currently mainly 2.45 GHz.

Basic structure of surface acoustic wave transponder

(2) Principle of surface acoustic wave RFID

The SAW tag consists of an interdigital transducer and several reflectors. The two buses of the transducer are connected to the antenna of the electronic tag. The antenna of the reader periodically sends high-frequency interrogation pulses. Within the receiving range of the electronic tag antenna, the received high-frequency pulses are converted into surface acoustic waves by the interdigital transducer and propagate on the crystal surface. The reflector component partially reflects the incident surface wave and returns to the interdigital transducer, which in turn converts the reflected pulse train into a high-frequency electric pulse train. Due to the low propagation rate of surface acoustic waves, the effective reflected pulse train returns to the reader after a subtle delay time.

Propagation of surface acoustic waves

(3) The key technology of surface acoustic wave RFID system

Cooperating application of tag encoding capacity and range of transponder and reader

Since the items attached to the label and the use environment are very different, the packaging structure has its own characteristics, and they must meet the following requirements.

Ensure that the piezoelectric chip can withstand external environmental stress and its changes during the working life, without causing performance degradation. At least it can't affect or rarely affect the high-frequency electromagnetic wave receiving effect of the tag antenna. The method of fixing to the object to be identified is simple, firmly attached, and does not obviously damage the object. Beautiful appearance, harmonious for the object to be identified, and meet the requirements of safety and environmental protection.

(4) Advantages of surface acoustic wave RFID

As the SAW device itself works in the radio frequency band, is passive and has strong anti-electromagnetic interference capability, the electronic tag implemented by SAW technology has certain unique advantages and is a supplement to integrated circuit (IC) technology.

The main features of surface acoustic wave RFID are:

The reading range is large and reliable, up to several meters; it can be used on metal and liquid products; the matching of the tag chip and the antenna is simple, and the production process cost is low; not only can identify stationary objects, but also can identify the speed of 300km/h High-speed moving objects. It can be used in harsh environments such as high temperature difference (-100℃～300℃) and strong electromagnetic interference.

Advantages and disadvantages of RFID technology

1. Advantages:

RFID chips and RFID readers are highly resistant to substances such as water, oil, and chemicals. The reading of information is not limited by the size and shape of the chip, and there is no need to match the fixed size and printing quality of the paper for reading accuracy. Moreover, RFID tags are developing in miniaturization and various forms to be applied to different products . RFID technology recognition is more accurate than traditional smart chips, and the recognition distance is more flexible. It can read through and without barriers. RFID chip tags can repeatedly add, modify, and delete internally stored data to facilitate the update of information. The internal data content is protected by a password, so that the content is not easily forged and altered. The data capacity of RFID chips is very large, and with the development of technology, the capacity is still increasing.

2. Disadvantages:

The technology is not mature enough. RFID technology has been in existence for a relatively short period of time and is not very mature in technology. Due to the retro-reflective characteristics of UHF RFID electronic tags, it is difficult to apply them to commodities such as metals and liquids. high cost. Compared with ordinary barcode labels, the price of RFID electronic tags is higher, which is dozens of times that of ordinary barcode labels. If they are used in large quantities, the cost will be too high, which greatly reduces the enthusiasm of the market to use RFID technology. Security is not strong enough. The security problems faced by RFID technology are mainly manifested in the illegal reading and malicious tampering of RFID electronic tag information. Technical standards are not uniform. RFID technology has not yet formed a unified standard, and multiple standards coexist in the market, resulting in incompatibility of RFID tags of products of different enterprises, which in turn causes confusion in the application of RFID technology to a certain extent.

The development status and prospects of RFID technology

With the continuous reduction of the cost of RFID equipment, the gradual unification of standards, the in-depth and extensive application of digital information technology in various industries, and the expansion of scale application industries, RFID technology will have a broader development prospect and its potential value will be brought into play , RFID technology industry will gradually grow and mature.

1. The development history of radio frequency identification

RFID technology was born during World War II and was first used by the British Emperor *air* to identify its own fighters and allied fighters. In order to identify the returning aircraft, the United Kingdom equipped a radio transceiver on the Allied aircraft. Then, when the interrogator on the control tower transmits an interrogation signal to the returning aircraft, the transceiver on the aircraft receives this signal. Send a signal back to the interrogator, and the interrogator can identify friend or foe based on the received return signal. This is the first recorded RFID identification friend or foe system and the first practical application of RFID.

Since then, RFID technology has also been applied to wildlife tracking, highway toll systems and other fields. Since the 1990s, with the rapid development of integrated circuit manufacturing and information technology, RFID technology has become more mature and its cost has become lower and lower, which has gradually attracted people's attention.

2. Development prospects of radio frequency identification

RFID radio frequency identification technology has gradually developed into an independent interdisciplinary professional field. RFID radio frequency identification technology integrates a large number of technologies from completely different professional fields (for example, high frequency technology, electromagnetic compatibility technology, semiconductor technology, data protection and cryptography technology, telecommunications technology, manufacturing technology, etc.).

In the past ten years, RFID radio frequency identification technology has developed rapidly, and has gradually been widely used in many traceability and anti-counterfeiting applications such as industrial automation, commercial automation, and transportation control management. With technological progress, the types of products based on RFID radio frequency identification technology will become more and more abundant, and the application will become more and more extensive. It is expected that in the next few years, RFID radio frequency identification technology will continue to maintain a momentum of rapid development.

In general, the current development of RFID radio frequency identification technology tends to be standardized, low cost, low error rate, high security, and low power consumption.

Standardized industry standards and related product standards are not yet unified, and electronic tags have not yet formally formed a unified international standard (including various frequency bands) so far. Low cost At present, the lowest price of an electronic tag in the United States is about 20 cents. Such a price cannot be applied to certain low-value single items. Only when the unit price of an electronic tag drops below 10 cents can it be applied on a large scale. Goods in full boxes and packages. Low error rate Although the individual technology of RFID electronic tags has become mature, the overall product technology is not mature enough, and there is still a high error rate (the rate of RFID misreading is sometimes as high as 20%). In integrated applications Also need to overcome a lot of technical problems. High security The currently widely used passive RFID system does not have a very reliable security mechanism and cannot keep data confidential. RFID data is also vulnerable to attacks, mainly because of the RFID chip itself and the process of reading or writing data. Both are easily exploited by hackers.

Application fields of RFID technology

Access control: personnel entry prohibition, monitoring and management, animal monitoring: animal husbandry management, pet identification, wild animal ecological tracking Transportation: highway toll system logistics management: air transportation luggage identification, inventory, logistics and transportation management automatic control: cars, Classification of home appliances and electronics, management of assembly production lines. Medical applications: hospital medical record systems, instrumentation and equipment management. Material management and control: automated inventory of factory materials and control system quality tracking: finished product quality tracking, feedback and resource recovery: pallets, recyclable containers Anti-theft management applications: anti-theft management in supermarkets, libraries or bookstores, anti-counterfeiting*: counterfeit and anti-counterfeiting of brand-name tobacco, alcohol, and valuables. Waste treatment: garbage recycling, waste management and control system combined ticket: smart storage for multiple purposes Cards, all-in-one cards and other dangerous goods: ordnance* sticks, detonators* drug control

RFID will build a bridge between the virtual world and the physical world. It is foreseeable that in the near future, RFID technology will not only be widely adopted in all walks of life, but eventually RFID technology will be integrated with pervasive computing technology and have a profound impact on human society.