Therefore, RFID is recognized as one of the most promising 10 technologies in this century. 1. Foreword RFID systems have actually existed and developed for decades, and can be divided into "active" and "passive" according to the power supply status; Working frequency can be divided into low frequency (125KHz~ 135KHz), high frequency (13.56MHz), ultra-high frequency, microwave (2.45GHz, 5.8GHz) and so on. The hardware prices of different RFID systems vary greatly, and the characteristics of the systems themselves are also different, and the maturity of the systems is also different. Many questions, even people in the industry can't easily give clear answers, so users often feel at a loss when choosing RFID technology. Based on my own development and application experience, and referring to relevant application materials and technical data, the author tries to give readers a more comprehensive and objective understanding through this article, hoping to provide some help for users to choose the appropriate RFID system. 2 Brief introduction of the technical characteristics of RFID in different frequency bands 2. 1 low frequency: The frequency bands used range from 10 kHz to 1 mHz, and the common main specifications are 125KHz and 135KHz. Generally, the electronic tags in this frequency band are passive, and power supply and data transmission are carried out through inductive coupling. The biggest advantage of low frequency is that the label is less affected when it is close to metal or liquid objects. At the same time, the low-frequency system is very mature, and the reading and writing equipment is cheap. However, the disadvantage is that the reading distance is short, and multiple tags cannot be read at the same time (anti-collision), and the amount of information is low. General storage capacity is 128 bits to 5 12 bits. Mainly used in access control systems, animal chips, car burglar alarms and toys. Although the low-frequency system is mature and the reading and writing equipment is cheap, because of its low resonance frequency, the tag needs to make a wound inductor with large inductance, and often needs to package the off-chip resonance capacitor, so the tag cost is higher than other frequency bands. 2.2 High frequency: The frequency band used is 1MHz~400MHz, and the common main specification is 13. 156MHz ISM band. The tag in this frequency band is still passive, and the energy supply and data transmission are also carried out through inductive coupling. The biggest application of this frequency band is the well-known contactless smart card. Compared with low frequency, its transmission speed is faster, usually above 100kbps, and it can be used for multi-tag identification (international standards have mature anti-collision mechanisms). The system in this frequency band benefits from the application and popularization of contactless smart cards. The system is relatively mature and the reading and writing equipment is cheap. The products are the most abundant, with storage capacity ranging from 128 bits to more than 8kbytes, and can support high security features, from the simplest write lock to stream encryption, and even integrated encryption coprocessor. Generally used for identification, library management, product management, etc. At present, this frequency band is the only choice for RFID applications with high security requirements. 2.3 UHF: the frequency band 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 very common in this frequency band. The reading distance of passive tags is about 3 ~ 1 0 m, and the transmission rate is fast, which can generally reach about 100kbps. In addition, because the antenna can be manufactured by etching or printing, the cost is relatively low. Because of the long reading distance and fast information transmission rate, it can read and identify a large number of labels at the same time, which is especially suitable for logistics and supply chain management. However, the disadvantages of this frequency band are that the application in metal and liquid articles is not ideal, 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 safety characteristics of this frequency band are general, and it is not suitable for application fields with high safety requirements. 2.4 Microwave: The frequency band used is above 1GHz, and the common specifications are 2.45GHz and 5.8GHz. The characteristics and applications of microwave frequency band are similar to UHF frequency band, and the reading distance is about 2 meters, but it is highly sensitive to the environment. Because its frequency is higher than UHF, the tag size can be made smaller than UHF, but the attenuation of water to this frequency band signal is higher than UHF, and the working distance is also smaller than UHF. Generally used in baggage tracking, cargo management, supply chain management, etc. 2.5 Select the appropriate frequency band 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 choose the appropriate RFID technology. First of all, the cost of RFID system includes hardware cost, software cost and integration cost. Hardware cost includes not only the cost of reader and tag, but also the installation cost. Many times, application and data management software and integration are the main costs of the whole application. If you consider the cost, you must do it according to the overall cost of the system, not just the price of hardware, such as labels. This part of the problem will not be further discussed and analyzed here, but readers need to know and understand it. Below we mainly discuss how to choose the appropriate frequency band from the technical point of view. Secondly, we know that the communication distance of RFID system is very different even in the same frequency band. Because the communication distance usually depends on the antenna design, the output power of the reader, the power consumption of the tag chip, the receiving sensitivity of the reader and so on. It cannot be simply considered that the working distance of a certain frequency band RFID system is greater than that of another frequency band RFID system. Third, although the ideal RFID system has long working distance, high transmission rate and low power consumption. However, this ideal RF system does not exist in reality, and high data transmission rate can only be achieved in a relatively short distance. On the contrary, if we want to increase the communication distance, we need to reduce the data transmission rate. Therefore, if you want to choose RFID technology with long communication distance, you must sacrifice communication speed. The process of choosing a frequency band is usually a compromise process. Fourthly, in addition to communication distance, when we choose a radio frequency system, we usually have to consider factors such as storage 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 longest range (up to 3 to 1 0 meter) and fast communication speed. 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 lock and password protection. Moreover, the electromagnetic wave energy in this frequency band is seriously attenuated in water, which is not suitable for tracking animals (more than 50% of the body is water) and drugs containing liquids. The reading and writing distance of low-frequency and high-frequency systems is small, usually less than one meter. Mature contactless smart cards adopt high frequency band, which can support large storage capacity and complex security algorithms. As mentioned above, due to the requirements of communication speed and security, the working distance of contactless smart cards is generally around 10cm. The high-frequency ISO 15693 specification increases the communication distance by reducing the communication rate, and the working distance can reach more than 1 meter through a large antenna and a high-power reader.