Frequency band characteristics and main application areas in RFID systems

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Frequency band characteristics and main application areas in RFID systems [Copy link]

1. Concepts of several frequency bands/points in RFID systems The receiving range of RFID readers is affected by many factors, such as radio frequency, size and shape of tags, energy of readers, interference from metal objects, and other radio frequency devices. In general, the effective receiving distance of low-frequency passive tags is within one foot, the receiving distance of high-frequency passive tags is about three feet, and the receiving distance of ultra-high frequency tags is ten to twenty feet. For semi-active and active tags using batteries, readers can receive signals from three hundred feet or even farther. For low-frequency and high-frequency radio frequency, if the size of the tag and reader antenna is the same, the receiving distance can be calculated by multiplying the diameter of the antenna by 1.4. This rule applies to diameters within thirty centimeters. Just like the radio we listen to, radio frequency tags and readers must be modulated to the same frequency to work. LF, HF, and UHF correspond to radio frequencies of different frequencies. LF stands for low-frequency radio frequency , which is around 125KHz, HF stands for high-frequency radio frequency, which is around 13.54MHz, and UHF stands for ultra-high-frequency radio frequency, which is within the range of 850 to 910MHz. There are 4 bands of frequencies in operation, low frequency (125KHz), high frequency (13.54MHz), ultra-high frequency (850-910MFz), and microwave (2.45GHz). Each frequency has its own characteristics and is used in different fields, so to use it correctly, you must first choose the right frequency. At present, different countries use different frequencies. Currently, the ultra-high frequency used in Europe is 868MHz, and the United States is 915MHz. Japan currently does not allow the use of ultra-high frequency in radio frequency technology. The government also limits its impact on other devices by adjusting the power supply of the reader. Some organizations such as the Global Business Promotion Council are encouraging the government to lift restrictions. Tag and reader manufacturers are also developing systems that can use different frequencies to avoid these problems. Different frequencies have different characteristics, so their uses are also varied. For example, low-frequency tags are cheaper than ultra-high frequency tags, save energy, and have strong penetration of scrap metal objects. They are most suitable for objects with a high water content, such as fruits. UHF has a wide range and fast data transmission speed, but it consumes more energy and has weaker penetration. There should not be too much interference in the operating area, so it is suitable for monitoring items shipped from the seaport to the warehouse. One problem encountered by radio frequency technology is reader conflict, that is, the information received by one reader conflicts with the information received by another reader, resulting in overlap. One way to solve this is to use TDMA technology. In simple terms, the readers are commanded to receive signals at different times instead of at the same time, so that the readers will not interfere with each other . However, items in the same area will be read twice, so a corresponding system must be established to avoid this situation. Antenna is a device that receives or radiates the radio frequency signal power of a radio transceiver in the form of electromagnetic waves. Antennas can be divided into long wave, short wave, ultra short wave and microwave antennas according to the working frequency band; they can be divided into omnidirectional antennas, directional antennas, etc. according to the directionality; they can be divided into linear antennas, planar antennas, etc. according to the shape. In the RFID system, antennas are divided into two types: tag antennas and reader antennas . The current RFID system is mainly concentrated in LF, HF (13.56MHz), UHF and microwave bands. The principle and design of antennas are fundamentally different in LF, HF and UHF bands. In essence, since there is no electromagnetic wave propagation in the near field of LF and HF band systems, the antenna problem is mainly concentrated in UHF and microwave bands. For tags, the operating frequency of tags refers to the carrier frequency when the tags are working. According to the different energy supply methods, RFID tags can be divided into passive tags, semi-active tags and active tags. The energy of the chip in semi-active tags and active tags is provided by the battery attached to the electronic tags, and active tags can actively send out radio frequency signals. According to the different operating frequencies, RFID tags can be divided into low frequency (LF), high frequency (HF), ultra-high frequency (UHF) and microwave . The working principles of RFID in different frequency bands are different. RFID electronic tags in LF and HF bands generally adopt the principle of electromagnetic coupling, while RFID in UHF and microwave bands generally adopts the principle of electromagnetic emission . There is no doubt that the operating frequency of RFID tags is one of its most important characteristics. The operating frequency of RFID tags not only determines the working principle of the RFID system (inductive coupling or electromagnetic coupling ) and the recognition distance, but also determines the difficulty of implementing RFID tags and readers and the cost of equipment. RFID tags working in different frequency bands or frequency points have different characteristics. The frequency bands or frequency points occupied by RFID applications are internationally recognized, that is, they are located in the ISM band. Typical operating frequencies are: 125kHz, 133kHz, 13.56MHz, 27.12MHz, 433MHz, 902~928MHz, 2.45GHz, 5.8GHz, etc. From the application concept, the operating frequency of the RFID tag is also the operating frequency of the RFID system. For an RFID system, its frequency band concept refers to the frequency range of the tag signal that the reader sends, receives and reads through the antenna. But from the application concept, the operating frequency of the RFID tag is also the operating frequency of the RFID system, which is one of its most important characteristics. So what are the corresponding standards and main application fields for the three main frequency bands of the RFID system ? 2 Typical application frequencies, standards and application fields of tags in each frequency band 2.1 Low-frequency band RFID tags Low-frequency band RFID tags, referred to as low-frequency tags, have an operating frequency range of 30kHz ~ 300kHz. Typical operating frequencies are: 125KHz, 133KHz. Low-frequency tags are generally passive tags , and their working energy is obtained from the radiation near field of the reader coupling coil through inductive coupling. When transmitting data between low-frequency tags and readers, the low-frequency tags must be located in the near field area radiated by the reader antenna. The reading distance of low-frequency tags is generally less than 1 meter. Typical applications of low-frequency tags include: animal identification, container identification, tool identification, electronic locking anti-theft (car keys with built-in transponders), etc. International standards include: ISO11784/11785 (for animal identification), ISO18000-2 (125-135 kHz). Low-frequency tags have a variety of appearances. The appearance of low-frequency tags used for animal identification includes : collar type, ear tag type, injection type, pill type, etc. Typical animals include cattle, pigeons, etc. The main advantages of low-frequency tags are: the tag chip generally adopts ordinary CMOS technology, which is power-saving and cheap; the operating frequency is not subject to radio frequency regulation; it can penetrate water, organic tissue, wood, etc.; it is very suitable for short-range, low-speed, and data-intensive identification applications (for example, animal identification). The disadvantages of low-frequency tags are mainly reflected in: the tag stores less data; it is only suitable for low-speed, short-range identification applications; compared with high-frequency tags: the tag antenna has more turns and the cost is higher; 2.2 Medium and high-frequency band RF tags The working frequency of medium and high frequency band RFID tags is generally 3MHz ~ 30MHz. The typical working frequency is: 13.56MHz. From the perspective of RFID application, the working principle of RFID tags in this frequency band is exactly the same as that of low frequency tags, that is, they work by inductive coupling, so they should be classified as low frequency tags. On the other hand, according to the general classification of radio frequency, its working frequency band is also called high frequency, so it is often called high frequency tag. Given that the RFID tags in this frequency band may be the largest type of RFID tags in practical applications, as long as we understand high and low as a relative concept, there will be no confusion in understanding. For the sake of convenience, we call it medium frequency RFID tag. Medium frequency tags generally use passive design. Their working energy is obtained from the radiation near field of the reader coupling coil through inductive (magnetic) coupling like low frequency tags. 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 medium frequency tags is generally less than 1 meter. Since medium frequency tags can be easily made into card shape, typical applications include: electronic tickets, electronic ID cards, electronic locking and anti-theft (electronic remote control door lock controller), etc. Relevant international standards include: ISO14443, ISO15693, ISO18000-3 (13.56MHz), etc. The basic characteristics of the medium frequency standard are similar to those of the low frequency standard. Due to its increased operating frequency, a higher data transmission rate can be selected. The antenna design of the RFID tag is relatively simple, and the tag is generally made into a standard card shape. 2.3 UHF and microwave tags RFID tags in the ultra-high frequency and microwave frequency bands are referred to as microwave RFID tags. Their typical operating frequencies are: 433.92MHz, 862(902)~928MHz, 2.45GHz, and 5.8GHz. Microwave RFID tags can be divided into two categories: active tags and passive tags. When working, the RFID tag is located in the far field of the reader antenna radiation field, and the coupling mode between the tag and the reader is electromagnetic coupling . The reader antenna radiation field provides RF energy to the passive tag to wake up the active tag. The reading distance of the corresponding RFID system is generally greater than 1m, typically 4~6m, and can reach more than 10m at most . The reader antenna is generally a directional antenna, and only the RFID tag within the directional beam range of the reader antenna can be read/written. Due to the increase in reading distance, it is possible that multiple RFID tags will appear in the reading area at the same time in the application, which puts forward the demand for simultaneous reading of multiple tags, and then this demand has developed into a trend. At present, advanced RFID systems all regard the problem of multi-tag reading as an important feature of the system. At the current technical level, the relatively successful products of passive microwave RFID tags are relatively concentrated in the 902~928MHz working frequency band. 2.45GHz and 5.8GHz RFID systems are mostly semi-passive microwave RFID tag products. Semi-passive tags are generally powered by button batteries and have a long reading distance. The typical characteristics of microwave RFID tags are mainly concentrated in whether they are passive, wireless reading and writing distance, whether they support multi-tag reading and writing, whether they are suitable for high-speed identification applications, the transmission power tolerance of the reader , and the price of RFID tags and readers. The reading distance of a typical microwave radio frequency tag is 3~5m, and some products can reach 10m or more. For wirelessly writable radio frequency tags , the writing distance is usually smaller than the reading distance, because writing requires more energy. The data storage capacity of microwave radio frequency tags is generally limited to 2Kbits. A larger storage capacity does not seem to make much sense. From the perspective of technology and application, microwave radio frequency tags are not suitable as a carrier of large amounts of data. Their main function is to identify items and complete the contactless identification process. Typical data capacity indicators include: 1Kbits, 128Bits, 64Bits , etc. The capacity of the product electronic code EPC formulated by the Auto-ID Center is: 90Bits. Typical applications of microwave radio frequency tags include: mobile vehicle identification, electronic ID card, warehousing and logistics applications, electronic locking and anti-theft (electronic remote control door lock controller), etc. Relevant international standards include: ISO10374, ISO18000-4 (2.45GHz), -5 (5.8GHz), -6 (860-930 MHz), -7 (433.92 MHz), ANSI NCITS256-1999, etc. 3 Summary The communication standard of radio frequency tags is the basis for the design of tag chips. At present, the international communication standards related to RFID are mainly: ISO/IEC 18000 standard (including 7 parts, involving 125KHz, 13.56MHz, 433MHz, 860-960MHz, 2.45GHz and other frequency bands), ISO11785 (low frequency), ISO/IEC 14443 standard (13.56MHz), ISO/IEC 15693 standard (13.56MHz), EPC standard (including Class0, Class1 and GEN2 protocols, involving HF and UHF frequency bands), DSRC standard (European ETC standard, including 5.8GHz). At present, the international standards of electronic tag chips have shown a trend of integration. The ISO/IEC 15693 standard has become a part of the ISO18000-3 standard, and the EPC GEN2 standard has also started to transform to the ISO18000-6 Part C standard. At present, the more commonly used frequency bands are 13.56MHz, 860－960MHz, 2.45GHz, etc. Different frequency bands have different characteristics, so the application fields are also different. Short-range RFID systems mainly use LF and HF bands such as 125KHz and 13.56MHz, and the technology is the most mature; long-range RFID systems mainly use UHF bands such as 433MHz, 860MHz-960MHz , and microwave bands such as 2.45GHz and 5.8GHz. At present, most of them are still under testing and have not been widely used. The working distance of passive microwave RFID tags can exceed 1 meter, and the working distance of passive UHF RFID tags can reach more than 5 meters. China's technology in the design of RFID tag chips in the LF and HF frequency bands is relatively mature, and the design technology in the HF frequency band is close to the international advanced level. It has independently developed RFID chips that meet the ISO14443 Type A, Type B and ISO15693 standards, and has been successfully applied to projects such as transportation cards and China's second-generation ID cards. Access control system 13.56MHz. In the microwave frequency band (2.45GHz and 5.8GHz), some of them are used in non-stop highway toll collection projects in China.