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How to choose frequency for RFID TAG?

Radio frequency identification (hereinafter referred to as RFID) is a method of storing data on an electronic data carrier (such as an integrated circuit), and transponder / tag and interrogator / Interrogator / Reader Two-way communication between readers to achieve the purpose of identification and exchange of data Emerging technology This technology can realize multi-target recognition and moving target recognition; it has the resistance to harsh environments, high accuracy, security, flexibility and Scalability and many other advantages; it is easy to implement article tracking and logistics management through the Internet, so it has attracted widespread attention. Therefore, RFID is recognized as one of the 10 most promising technologies in this century.

RFID systems have been in existence and developed for decades. From the perspective of power supply, they can be divided into two categories: "active" and "passive." From the operating frequency, they can be divided into low frequency (125KHz ~ 135KHz) High frequency (13.56MHz), ultra high frequency, microwave (2.45GHz, 5.8GHz) and several other categories. The hardware price difference of different RFID systems is huge, and the characteristics of the system are also different, and the maturity of the system is also different. Many questions, even those in the industry, cannot easily give a clear answer, so users often feel confused when choosing radio frequency identification technology. The author combines his own development and application experience, while referring to relevant application materials and technical data, and tries to give readers a more comprehensive and objective understanding through this article, hoping to provide users with the choice of a suitable frequency RFID system Some help.

Which frequency is suitable for RFID system

2 Brief description of RFID technology characteristics in different frequency bands

2.1 Low Frequency:

The frequency band used is from 10 K Hz to 1 M H z, and the common main specifications are 125KHz, 135KHz, etc. Generally, electronic tags in this frequency band are passive, and energy supply and data transmission are performed through inductive coupling. The biggest advantage of low frequency is that the tag is less affected when the tag is close to metal or liquid items. At the same time, the low frequency system is very mature and the price of reading and writing equipment is low. However, the shortcomings are short reading distance, unable to read multiple tags at the same time (anti-collision), and low information volume. The general storage capacity is 128 to 512 bits. Mainly used in access control systems, animal chips, car alarms and toys. Although the low-frequency system is mature and the reading and writing equipment is low in price, because of its low resonance frequency, the tag needs to make a winding inductor with a large inductance value, and often it is necessary to package the off-chip resonance capacitor. The cost of the tag is higher than other frequency bands.

2.2 High Frequency:

The frequency band used is from 1MHz to 400MHz, and the common main specification is the ISM band of 13.156MHz. The tags in this frequency band are mainly passive, and also provide energy supply and data transmission through inductive coupling. The largest application in this band is the contactless smart card as we know it. Compared with low frequency, its transmission speed is faster, usually above 100kbps, and multi-tag identification can be performed (each international standard has a mature anti-collision mechanism). The system in this frequency band benefits from the application and popularization of contactless smart cards. The system is also relatively mature, and the price of reading and writing equipment is low. The products are the most abundant, with storage capacities ranging from 128 bits to over 8K bytes, and can support high security features, from the simplest write lock, to stream encryption, and even encryption coprocessors are integrated. Generally used in identification, library management, product management, etc. RFID applications with high security requirements are currently the only choice for this frequency band.

2.3 Ultra High Frequency:

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 common in this frequency band. Passive tag reading distances are about 3 to 10 m. The transmission rate is fast, and can generally reach about 100 kbps. Moreover, the antenna can be manufactured by etching or printing, so the cost relatively low. Because the reading distance is long, the information transmission rate is fast, and the large number of tags can be read and identified at the same time, it is especially suitable for areas such as logistics and supply chain management. However, the shortcomings of this frequency band are that the application on metal and liquid items is less ideal and the system is not mature. The price of reading and writing equipment is very expensive, and the cost of application and maintenance is also high. In addition, the frequency band has general security characteristics, which is not suitable for applications with high security requirements.

2.4 Microwave:

The frequency band used is above 1GHz, and common specifications are 2.45GHz and 5.8GHz. The characteristics of the microwave frequency band are similar to the application and the ultra-high frequency band. The reading distance is about 2 meters, but the sensitivity to the environment is high. Because its frequency is higher than UHF, the size of the tag can be made smaller than UHF, but the attenuation of water in this frequency band is higher than UHF, and the working distance is also smaller than UHF.

Generally used in baggage tracking, item management, supply chain management, etc.

2.5 Choosing the right frequency identification technology for the application

First, the cost of an RFID system includes hardware costs, software costs, and integration costs. The hardware cost includes not only the cost of the reader and the tag, but also the installation cost. Many times, application and data management software and integration are the main costs of the entire application. If you consider the cost, you must do it according to the overall cost of the system, not just hardware, such as the price of tags. Here, we do not discuss and analyze this part of the problem further, but the reader needs to have an understanding and understanding of this. Below we mainly discuss from a technical perspective, how to choose the appropriate frequency band.

Secondly, we know that even the RFID systems in the same frequency band have very different communication distances. Because the communication distance usually depends on the antenna design, reader output power, tag chip power consumption and reader sensitivity. We cannot simply think that the working distance of a radio frequency identification system in one frequency band is greater than that of another radio frequency identification system.

Third, although the ideal RFID system is long working distance, high transmission rate and low power consumption. However, in an actual situation, such an ideal radio frequency system does not exist, and a high data transmission rate can only be achieved at a relatively short distance. Conversely, if you want to increase the communication distance, you need to reduce the data transmission rate. Therefore, if we want to use radio frequency identification technology with long communication distance, we must sacrifice the communication rate. The process of selecting a frequency band is often a compromise process.

Fourth, in addition to considering the communication distance, when we choose an RF system, we usually also need to consider factors such as memory capacity and security features. Based on these application requirements, it is possible to determine suitable RFID frequency bands and solutions. Judging from the existing solutions, UHF and microwave radio frequency identification systems have the largest operating distance (can reach 3 to 10 meters) and have fast communication rates, but in order to reduce the power consumption and complexity of the tag chip , Does not implement complex security mechanisms, and is 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, so it is not suitable for tracking animals (more than 50% of water in the body), medicines containing liquids, etc. Low-frequency and high-frequency systems have shorter read and write distances, usually no more than one meter. The high-frequency band is adopted by contactless smart cards with mature technology. Contactless smart cards can support large memory capacity and complex security algorithms. As mentioned earlier, due to the communication speed and security requirements, the working distance of contactless smart cards is generally around 10cm. The ISO15693 specification in the high-frequency band increases the communication distance by reducing the communication rate. With a large antenna and a high-power reader, the working distance can reach more than 1 meter. The low-frequency band has the lowest carrier frequency and is more than 100 times lower than the high-frequency 13.56MHz. Therefore, the communication rate is the lowest, and multi-tag reading is usually not supported.

Animal tracking management

Animal tracking and management have traditionally adopted radio frequency identification technology in the low frequency band, and have international normative coding and space signal interfaces. The corresponding international norms are ISO11784 and ISO11785. Due to the advantages and disadvantages of high-frequency and low-frequency radio frequency identification technology, there is also an international debate about the frequency bands for animal tracking management. The main reasons for supporting the use of low-frequency technology solutions are:

(1) International standards and compatibility requirements in fact.

(2) If a single antenna solution is used, the read-write distance of low-frequency systems is usually 20% to 30% greater than that of high-frequency systems. Because the data rate of the low-frequency system is low, the power consumption of the tag chip can be less than microwatts.

(3) Although the data transmission rate of the low-frequency system is low, in view of its signal strength, the reading efficiency is not low in practical applications.

(4) The low-frequency system can penetrate animal tissues and is the only frequency choice for implanted electronic tags. Reasons to support high-frequency technology solutions

There are:

(1) The international standard ISO11784 animal coding method can be completely implemented in the high-frequency and ultra-high-frequency band solutions. There does not appear to be a difference at the application and system level.

(2) Due to the frequency difference, low-frequency tags need to be wound with a winding inductor to form a tag antenna, and the cost of making tags is higher than high-frequency tags. For credit card-sized sizes, high-frequency tags usually only need to be wound for about 3 turns, and low-cost printing processes can be used. The overall cost of HF tags is lower. This is an accepted fact.

(3) If the implementation is reasonable, the high-frequency system can also achieve a read-write distance equivalent to that of the low-frequency system. In addition, the high-frequency reader can control the range through a gate antenna, which is conducive to accurate and fast data acquisition.

(4) A complete anti-collision mechanism can realize multi-target reading quickly and accurately. Both efficiency and accuracy are higher than data acquisition with a low frequency handset.

(5) The use of high-frequency frequencies has become a globally unified specification, and high-frequency systems will not face compatibility issues around the world. The editors even support the use of high-frequency technical solutions in animal tracking management, such as pigs, which do not require RFID. The main reason is based on system cost considerations. China's agricultural product prices and profit margins are very low. The consumption cost of hardware in animal tracking management such as pigs mainly comes from labels. To reduce this part of the cost, high-frequency technology should be used. At the same time, considering that production units such as pig breeding usually do not have a broadband connection electronic label, it may not only store a label information, but also some related 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 use of compatible technology systems has advantages in terms of installation cost and reliability. From the perspective of chips, tag packaging, reading and writing equipment, and system integration, China has hundreds of suppliers, which is unmatched by low-frequency technology. In addition, in applications such as pig management, implanted electronic tags are not required, and animal ear tags can be used. Of course, the use of high-frequency technology solutions in animal tracking management is different from traditional high-frequency RF systems. It is necessary to carry out research and development in terms of reducing the impact of the environment on the operating distance and the development of special reading and writing equipment, so that high-frequency technology Meet system requirements in terms of operating distance and reliability.

3.2 Drug Management

Experts still believe that achieving item-level tracking management in the field of consumer goods is still a goal that may take 3-5 years to achieve. However, the relatively high value drugs using RFID technology to achieve single product management is already a reality. The United States Food and Drug Administration (FDA) requires that the entire process of drug product tracking and management be implemented in 2007 to achieve full management from raw materials to household medicine cabinets. 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 signals through the electromagnetic field. Ultra high frequency transmits energy and signals through the electric field. The system generally works in the far field. , Detuning of the label will cause the label (item) to miss reading. The high-frequency system works in the near-field range (that is, the electromagnetic field is still trapped inside the system, and no electromagnetic waves are emitted). The energy and signals are carried out through the magnetic field. The tags inside the system can be accurately identified. (Of course, the working distance is only within 1 meter), it has better ability to resist electromagnetic interference (ElectromagneTIcInterference, EMI).

(2) the influence of liquids and metals. High-frequency signals have less attenuation in water than ultra-high frequencies, and are more suitable for use in containers containing liquids, and a considerable portion of pharmaceuticals are in liquid form.

(3) Storage capacity. The storage capacity of high-frequency tags can reach 8K bytes, so more information can be stored on the tags to implement a "mobile database" rather than just an electronic number. There is no such large-capacity electronic tag in current UHF solutions.

(4) The high-frequency 13.56MHz is an internationally-used ISM band, and there is no compatibility issue. And so far, not all regions in the world have corresponding RFID tag frequency bands available. China's UHF frequency band is in the process of formulation.


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