"1. Preface
Radio frequency identification (RFID) is a kind of two-way communication between transponder / tag and interrogator / reader by wireless means of magnetic field or electromagnetic field, So as to achieve the purpose of recognition and exchange data. This technology can realize multi-target recognition and moving target recognition; It has the advantages of anti harsh environment, high accuracy, security, flexibility and scalability; It is convenient to realize goods tracking and logistics management through the Internet, so it has attracted extensive attention. Therefore, RFID is recognized as one of the 10 most promising technologies in this century.
In fact, RFID system has existed and developed for decades. From the power supply state, it can be divided into "active" and "passive"; In terms of working frequency, it can be divided into low frequency (125kHz ~ 135KHz), high frequency (13.56MHz), UHF, microwave (2.45GHz, 5.8GHz), etc. The hardware price difference of different RFID systems is huge, and the characteristics of the system itself are also different, and the maturity of the system is also different. Many questions, even industry personnel can not easily give a clear answer, so users often feel at a loss when choosing RFID technology. Combined with my own development and application experience, and referring to the relevant application materials and technical data, the author tries to give readers a more comprehensive and objective understanding through this paper, hoping to provide some help for users in selecting the appropriate frequency RFID system.
2 brief description of RFID technical characteristics of different frequency bands
2.1 low frequency:
The frequency band used ranges from 10 kHz to 1 MHz, and the common main specifications include 125kHz, 135KHz, etc. Generally, the electronic tags in this frequency band are passive, and energy supply and data transmission are carried out through inductive coupling. The biggest advantage of low frequency is that when the label is close to metal or liquid objects, the label is less affected. At the same time, the low frequency system is very mature and the price of reading and writing equipment is low. However, the disadvantages are short reading distance, inability to read multiple tags at the same time (anti conflict) and low amount of information. The general storage capacity is 128 bits to 512 bits. It is mainly used in access control system, animal chip, automobile anti-theft device and toys. Although the low-frequency system is mature and the reading and writing equipment is cheap, due to its low resonant frequency, the label needs to make a winding inductor with large inductance value, and often needs to package the off chip resonant capacitor. On the contrary, the cost of the label is higher than that of other frequency bands.
2.2 high frequency:
The frequency band used ranges from 1MHz to 400MHz, and the common main specification is the ISM band of 13.156mhz. The tags of this frequency band are mainly passive, and energy supply and data transmission are also carried out through inductive coupling. The biggest application in this frequency band is the well-known contactless smart card. Compared with low frequency, its transmission speed is faster, usually more than 100kbps, and multi label identification can be carried out (each international standard has a mature anti-collision mechanism). The system in this frequency band benefits from the application and popularization of contactless smart card. The system is also relatively mature, and the price of reading and writing equipment is low. The products are the most abundant, with storage capacity ranging from 128 bits to more than 8K bytes, and can support high security features, from the simplest write locking to stream encryption, and even encryption coprocessor integration. It is generally used in identity recognition, library management, product management, etc. For RFID applications with high security requirements, this frequency band is the only choice at present.
2.3 ultra high frequency:
The frequency band range used is 400MHz ~ 1GHz, and the common main specifications are 433MHz and 868 ~ 950mhz. This frequency band transmits energy and information through electromagnetic waves. Active and passive applications are common in this frequency band. The reading distance of passive tags is about 3 ~ 10 m, and the transmission rate is fast. Generally, it can also reach about 100 Kbps. Moreover, because the antenna can be manufactured by etching or printing, the cost is relatively low. Because the reading distance is long, the information transmission rate is fast, and a large number of labels can be read and identified at the same time, it is especially suitable for the fields of logistics and supply chain management. However, the disadvantage of this frequency band is that the application in metal and liquid goods is not ideal. At the same time, the system is not mature, the price of reading and writing equipment is very expensive, and the cost of application and maintenance is also very high. In addition, the security characteristics of this frequency band are general, and it is not suitable for applications with high security requirements.
2.4 microwave:
The frequency band used is more than 1GHz, and the common specifications are 2.45GHz and 5.8GHz. The characteristics of microwave band are similar to those of application and UHF band. The reading distance is about 2m, but it is highly sensitive to the environment. Because its frequency is higher than UHF, the size of the tag can be smaller than UHF, but the attenuation of water to the signal in this frequency band is higher than UHF, and the working distance is smaller than UHF.
It is generally used in baggage tracking, item management, supply chain management, etc.
2.5 select the appropriate frequency band RFID technology according to the application
In the previous part, we have briefly introduced the characteristics of RFID technology in each frequency band. In this part, we will focus on how to select the appropriate RFID technology.
First, the cost of an RFID system includes hardware cost, software cost and integration cost. The hardware cost includes not only the cost of readers and labels, but also the installation cost. Many times, application and data management software and integration are the main cost of the whole application. If the cost is considered, it must be based on the overall cost of the system, not limited to hardware, such as the price of labels. Here, we will not further discuss and analyze this part of the problem, but readers need to have an understanding and understanding of it. Next, we mainly discuss how to select the appropriate frequency band from the technical level.
Second, we know that even if the RFID system is in the same frequency band, its communication distance is very different. Because the communication distance usually depends on antenna design, reader output power, tag chip power consumption, reader receiving sensitivity and so on. We can not simply think that the working distance of RFID system in one frequency band is greater than that of RFID system in another frequency band.
Third, although the ideal RFID system is long working distance, high transmission rate and low power consumption. However, in reality, this ideal RF system does not exist, and high data transmission rate can only be realized at a relatively close distance. On the contrary, if we want to improve the communication distance, we need to reduce the data transmission rate. Therefore, if we want to choose RFID technology with long communication distance, we must sacrifice the communication rate. The process of selecting frequency bands is often a compromise process.
Fourth, in addition to considering the communication distance, when we choose an RF system, we usually have to consider factors such as memory capacity and security characteristics. According to these application requirements, the appropriate RFID frequency band and solution can be determined. From the existing solutions, UHF and microwave RFID systems have the largest operating distance (up to 3 to 10 meters) and fast communication rate. However, in order to reduce the power consumption and complexity of the tag chip, complex security mechanisms are not implemented, which are limited to simple security mechanisms such as write locking and password protection. Moreover, the electromagnetic wave energy in this frequency band attenuates seriously in water, so it is not suitable for tracking animals (containing more than 50% water in the body) and drugs containing liquid. The reading and writing distance of low-frequency and high-frequency systems is small, usually no more than one meter. The high frequency band is adopted by the non-contact smart card with mature technology. The non-contact smart card can support large memory capacity and complex security algorithms. As mentioned earlier, due to communication rate and security requirements, the working distance of contactless smart card is generally about 10cm. The iso15693 specification in the high frequency band increases the communication distance by reducing the communication rate. The working distance can reach more than 1m through large-size antenna and high-power reader. The low frequency band has a low carrier frequency, which is more than 100 times lower than the high frequency 13.56MHz, so the communication rate is the lowest, and usually does not support the reading of multiple tags.
3 case analysis
3 。 1. Animal tracking management
Traditionally, animal tracking and management adopts low-frequency radio frequency identification technology, and has international standard coding and spatial signal interface. The corresponding international standards are iso11784 and ISO11785 respectively. Due to the advantages and disadvantages of high-frequency and low-frequency RFID technology, there is also a debate on the frequency band of animal tracking management in the world. The main reasons supporting the adoption of low-frequency technical scheme are:
(1) In fact, there are international norms and compatibility requirements.
(2) If the single antenna solution is adopted, the reading and writing distance of low-frequency system is usually 20% to 30% larger than that of high-frequency system. Because the data rate of the low-frequency system is low, the power consumption of the tag chip can be less than MW.
(3) Although the data transmission rate of low-frequency system is low, the reading efficiency is not low in practical application due to the strength of its signal.
(4) The low frequency system can penetrate animal tissue and is the only frequency choice for implantable electronic tags. The reasons for supporting the high-frequency technology scheme
It mainly includes:
(1) The animal coding method of the international standard iso11784 can be fully realized in the solutions of high frequency and ultra-high frequency bands. There is no difference at the application and system level.
(2) Due to the frequency difference, the low-frequency tag needs to be wound with winding inductance to form the tag antenna, and the cost of making the tag is higher than that of high-frequency tag. For the size of the credit card, the high-frequency label usually only needs to be wound about 3 times, and the low-cost printing process can be adopted. The overall cost of high-frequency tags is lower. This is a recognized fact.
(3) If the implementation is reasonable, the high-frequency system can also obtain a reading and writing distance equivalent to that of the low-frequency system. Moreover, the high-frequency reader can control the action range through the gate antenna, which is conducive to accurate and rapid data acquisition.
(4) The complete anti-collision mechanism can realize multi-target reading quickly and accurately. The efficiency and accuracy are higher than using low-frequency handset for data acquisition.
(5) The use of high frequency has become a global unified standard. The use of high frequency systems will not face compatibility problems all over the world. The editor further supports the adoption of high-frequency technical solutions in the tracking and management of animals such as pigs that do not need to be implanted with RFID. The main reason is based on the cost of the system. The price and profit margin of agricultural products in China are very low. In the tracking management of pigs and other animals, the cost of hardware mainly comes from labels. In order to reduce this part of the cost, high-frequency technology should be adopted. At the same time, considering that pig breeding and other production units usually do not have broadband connection, the electronic label may store not only a label information, but also some relevant data. The common storage space in high-frequency solutions can reach more than 1K bits. Secondly, at present, China's main RFID infrastructure is based on high-frequency technology. The adoption of compatible technology system has advantages in installation cost and reliability. From the aspects of chip, label packaging, reading and writing machines, system integration and so on, China has hundreds of suppliers, which is unmatched by low-frequency technology. In addition, in applications such as pig management, implantable electronic labels are not required, and animal ear labels can be used. Of course, the high-frequency technology scheme used in animal tracking management is different from the traditional high-frequency RF system. It is necessary to carry out R & D work in reducing the impact of the environment on the operating distance and the development of special reading and writing equipment, so that the high-frequency technology can meet the system requirements in terms of operating distance and reliability.
3.2 drug management
Experts still believe that the realization of item level tracking management in the field of consumer goods is still a goal that can be achieved in three to five years. However, it is a reality that relatively high-value drugs use RFID technology to realize single product management. The U.S. Food and Drug Administration (FDA) requires to realize the whole process tracking and management of single drugs in 2007, and realize the whole process management from raw materials to family medicine boxes. For the single product management of drug management, it seems that the use of high-frequency technology has more comprehensive advantages, specifically:
(1) Both high frequency and ultra-high frequency transmit energy and signal through electromagnetic field. Ultra high frequency transmits energy and signal through electric field. The system generally works in the far field. For a single item close to each other, the detuning of the label will cause the missing reading of the label (item). The high-frequency system works in the near-field range (that is, the electromagnetic field is still bound inside the system and no electromagnetic wave is formed to be emitted). The energy and signal are carried out through the magnetic field. The labels inside the system can be accurately identified (of course, the action distance is only within 1m), which has better anti electromagnetic interference, EMI) capability.
(2) Effects of liquids and metals. High frequency signal has less attenuation in water than UHF, which is more suitable for containers containing liquid, and a considerable part of drugs are in liquid form.
(3) Storage capacity: the storage capacity of high-frequency tag can reach 8K bytes, so more information can be stored on the tag to realize a "mobile database" rather than just an electronic number. There is no such a large capacity electronic tag in the current UHF solution.
(4) The high frequency 13.56MHz is an international ISM band, and there is no compatibility problem. So far, not all regions in the world have corresponding RFID tag bands to use. China's UHF band is in the process of formulation.
4 Summary
To sum up, RFID technology in each frequency band has its own characteristics. Even if the RFID system is in the same frequency band, its communication distance is very different. We can not simply think that the working distance of RFID system in one frequency band is greater than that of RFID system in another frequency band. In the actual selection of RF system, we need to consider the overall cost of an RFID system, memory capacity, security characteristics and other factors, and comprehensively select the appropriate RFID frequency band according to these factors.
Responsible editor: CT, read the full text“
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