“Radio Frequency Identification (RFID) is a wireless communication technology that can identify specific targets through radio signals and read and write related data without the need to establish mechanical or optical contact between the identification system and the specific target. The most important advantage of RFID is non-contact identification, which can read labels through snow, fog, ice, paint, grime, and harsh environments where barcodes cannot be used, and read labels extremely fast, less than 100 milliseconds in most cases.
1. What is RFID?
Radio Frequency Identification (RFID) is a wireless communication technology that can identify specific targets through radio signals and read and write related data without the need to establish mechanical or optical contact between the identification system and the specific target. The most important advantage of RFID is non-contact identification, which can read labels through snow, fog, ice, paint, grime, and harsh environments where barcodes cannot be used, and read labels extremely fast, less than 100 milliseconds in most cases.
The advantage of RFID technology is not in monitoring equipment and environmental status, but in “identification”. That is, corresponding processing is performed by actively identifying objects that enter the magnetic field identification range. RFID is not a sensor, it mainly identifies the marker through the unique ID number corresponding to the tag. The sensor is a detection device that can sense the measured information, and can transform the sensed information into electrical signals or other required forms of information output according to certain rules, so as to meet the requirements of information transmission, processing and storage. , Display, recording and control requirements. It is the first link to realize automatic detection and automatic control.
2. Composition and working principle of radio frequency identification system
1. The composition of the radio frequency identification system
The RFID system is mainly composed of three parts: tags, antennas, and readers. In addition, a special application system is also required to deal with the reader identification accordingly.
Figure 1 RFID system by composition
1) Tag: Electronic tag or radio frequency tag, transponder, composed of chip and built-in antenna. A certain format of electronic data is stored in the chip, which is used as the identification information of the item to be identified, and is the data carrier of the radio frequency identification system. The built-in antenna is used for communication with the RF antenna.
2) Reader: A device that reads or reads/writes electronic tag information. The main task is to control the radio frequency module to transmit a read signal to the tag, receive the tag’s response, decode the tag’s object identification information, and associate the object identification information with the tag information. Other relevant information on the label is transmitted to the host for processing.
3) Antenna: The transmitting and receiving device that transmits data between the tag and the reader.
2. The operating principle of the radio frequency identification system
After the electronic tag enters the antenna magnetic field, if it receives a special radio frequency signal sent by the reader, it can send out the product information (passive tag) stored in the chip with the energy obtained by the induced current, or actively send a signal of a certain frequency (active tag), the reader reads and decodes the information, and sends it to the central information system for data processing.
Figure 2 The reader obtains read and write instructions
Figure 3 The reader RF modulator sends the signal to the antenna
Figure 4 Antenna Interrogation Tag
Figure 5 The antenna will return the acquired tag information
In addition, according to the coupling method of the radio frequency signal between the reader and the tag, the communication between them can be divided into inductive coupling and electromagnetic backscattering coupling.
1) Inductive coupling: According to the law of electromagnetic induction, coupling is realized through a high-frequency alternating magnetic field in space. The inductive coupling method is generally suitable for short-range RFID systems operating at medium and low frequencies.
2) Electromagnetic backscatter coupling: According to the spatial propagation law of electromagnetic waves, the emitted electromagnetic waves will be reflected after hitting the target, thereby carrying back the corresponding target information. The electromagnetic backscattering coupling method is generally suitable for long-distance RFID systems working with high frequency and microwave.
Popular understanding, the mode of inductive coupling is mainly used in the low frequency (LF) and intermediate frequency (HF) bands. Because the low frequency RFID system has a longer wavelength and relatively weak energy, it mainly relies on short-range induction to read information. Electromagnetic backscatter coupling is mainly used in high frequency (HF) and ultra-high frequency (UHF) bands, because the wavelength of high frequency is shorter and the energy is higher. Therefore, the reader antenna can radiate electromagnetic waves to the tag, and part of the electromagnetic waves are modulated by the tag and then reflected back to the reader antenna. After decoding, they are sent to the central information system for reception and processing.
Three, radio frequency identification system classification
At present, according to the frequency range used by the RFID system, the RFID system can be divided into four application frequency bands: low frequency, high frequency, ultra-high frequency and microwave.
According to different operating frequencies, RFID tags can be divided into different types such as low frequency (LF), high frequency (HF), ultra high frequency (UHF) and microwave. Among them, RFID tags in the LF and HF frequency bands generally use the principle of electromagnetic coupling (electromagnetic induction), while RFID in the UHF and microwave frequency bands generally use the principle of electromagnetic emission (electromagnetic propagation).
1. Low frequency radio frequency tags
Low-frequency radio frequency tags, referred to as low-frequency tags for short, have an operating frequency range of 30kHz to 300kHz. Typical operating frequencies are 125KHz and 133KHz. Low-frequency tags are generally passive tags, and their working energy is obtained from the radiated near field of the coupling coil of the reader through inductive coupling. When transmitting data between a low-frequency tag and a reader, the low-frequency tag needs to be located in the near-field area radiated by the antenna of the reader. The reading distance of low frequency tags is generally less than 1 meter.
Typical applications: animal identification, container identification, tool identification, electronic locking anti-theft (car key with built-in transponder), etc.
2. High frequency radio frequency tags
The operating frequency of high-frequency radio frequency tags is generally 3MHz to 30MHz. The typical operating frequency is 13.56MHz. The radio frequency tag in this frequency band, because its working principle is exactly the same as that of the low frequency tag, that is, it works in the way of inductive coupling, so it should be classified into the low frequency tag category. But on the other hand, according to the general division of radio frequency, its working frequency band is also called high frequency, so it is often called high frequency tag.
High-frequency tags are generally passive, and their working energy is the same as that of low-frequency tags, and is obtained from the radiated near field of the coupling coil of the reader through inductive (magnetic) coupling. When the tag exchanges data with the reader, the tag must be located in the near-field area radiated by the reader antenna. The reading distance of IF tags is generally less than 1 meter.
Typical applications: electronic ticket, electronic ID card, electronic lock and anti-theft (electronic remote control door lock controller), residential property management, building security system, etc.
3. UHF, microwave radio frequency tags
UHF and microwave radio frequency tags are referred to as microwave radio frequency tags for short, and their typical operating frequencies are 433.92MHz, 862(902)MHz~928MHz, 2.45GHz, and 5.8GHz.
Microwave radio frequency tags can be divided into two categories: active tags and passive tags. When working, the radio frequency tag is located in the far field of the antenna radiation field of the reader, and the coupling method between the tag and the reader is electromagnetic coupling. The reader antenna radiation field provides radio frequency energy to passive tags, and wakes up active tags. The reading distance of the corresponding radio frequency identification system is generally greater than 1m, and the typical case is 4m to 6m, and the maximum can reach more than 10m. Reader antennas are generally directional antennas, and only radio frequency tags within the directional beam range of the reader antenna can be read/written. Due to the increase of the reading distance, it is possible for multiple radio frequency tags to appear in the reading area at the same time in the application, which puts forward the requirement of simultaneous reading of multiple tags.
Typical applications: automatic identification of railway vehicles, container identification, and can also be used in road vehicle identification and automatic toll collection systems.
4. RFID and the Internet of Things
RFID is an important supporting technology for the Internet of Things to perceive the outside world. Sensors can monitor and sense various information, but lack the ability to identify items, while RFID technology has a strong ability to identify items. Therefore, for the development of the Internet of Things, both sensors and RFID are indispensable.
Without the ability of RFID to identify objects, the Internet of Things will not be able to achieve the highest ideal of the Internet of Everything. Without the support of RFID technology, the application scope of the Internet of Things will be greatly limited. But on the other hand, because RFID radio frequency identification technology can only realize the identification of objects within the magnetic field, its reading and writing range is affected by the distance between the reader and the tag. Therefore, improving the sensing capability of the RFID system and expanding the coverage capability of the RFID system are urgent problems to be solved at present. At the same time, considering the long effective distance of the sensor network, the application range of RFID technology can be well expanded. In the future, the integration of RFID and sensor network will be an inevitable direction.
As far as the current development of RFID is concerned, the initial integration of RFID and sensor network applications has been achieved in many industrial industries. The complementary advantages of the two are deepening the application of the Internet of Things. Their mutual integration and system integration will greatly To promote the development of the entire Internet of Things industry, the application prospects are immeasurable.