1. What is RFID?
RFID is the abbreviation of Radio Frequency Identification, which is radio frequency identification. Often referred to as inductive electronic chips or proximity cards, proximity cards, contactless cards, electronic tags, electronic bar codes, and the like.
A complete RFID system consists of two parts, Reader and Transponder. The principle of operation is that the Reader transmits a certain frequency of infinite wave energy to the Transponder, which is used to drive the Transponder circuit to send the internal ID code. At this time, the Reader receives the ID. Code.
Transponder's speciality is that it is free of battery, contact-free, and free of card, so it is not afraid of dirt, and the chip password is the only one in the world that cannot be copied, with high safety and long life.
The application of RFID is very extensive. At present, typical applications include animal wafers, automobile chip alarms, access control, parking lot control, production line automation, and material management. There are two types of RFID tags: active tags and passive tags.
2. What is RFID technology?
RFID radio frequency identification is a non-contact automatic identification technology. It automatically recognizes target objects and acquires relevant data through radio frequency signals. The identification work can work in various harsh environments without manual intervention. RFID technology recognizes high-speed moving objects and recognizes multiple labels at the same time, making operation quick and easy.
Short-range RF products are not afraid of harsh environments such as oil stains and dust pollution. Bar codes can be replaced in such environments, such as tracking objects on the assembly line of a factory. Long-range RF products are mostly used for transportation, and the recognition distance can reach several tens of meters, such as automatic charging or identification of vehicle identity.
3. Application of RFID technology
a. In the retail industry, the use of bar code technology has enabled tens of thousands of commodity categories, prices, origins, batches, shelves, inventory, sales and other aspects to be managed in an orderly manner;
b. Adopting automatic vehicle identification technology, making road and bridge, parking lots and other toll collection places avoid the phenomenon of vehicle queue clearance, reducing time waste, thus greatly improving transportation efficiency and traffic capacity of transportation facilities;
c. In the automated production line, all aspects of the entire production process are placed under strict monitoring and management;
d. In the harsh environment of dust, pollution, cold, heat, etc., the use of long-range radio frequency identification technology improves the inconvenience of truck drivers having to get off the bus;
e. In the operation management of the bus, the automatic identification system accurately records the arrival time of the vehicles at each station along the line, providing real-time and reliable information for vehicle scheduling and full-time operation management.
4. What benefits will RFID technology bring to enterprise logistics and supply chain management?
Electronic tags are a tool to improve the efficiency and accuracy of recognition, and this technology will completely replace barcodes.
Take Nokia, a well-known mobile phone manufacturer, for example. Nokia is the first to test RFID projects in Finland. It uses a commercial thermal printer to attach a color-coded label to a mobile phone product that is connected to the customer's shipping process system and delivers the information to a secure network server via a smart reading board. In the material procurement process, Nokia's parcels were unloaded in the UK warehouse, and the information was automatically transferred to the Nokia Branch Materials Manager's mobile phone via a barcode reader.
In production companies, such as HP, we are beginning to discover how RFID can help us in the actual manufacturing process. RFID ensures that they use the right components in their manufacturing. Under the company's existing system, HP employees need to scan the in-process products on the production line and then scan the components to determine if they match. After the RFID tag is used, the correctness of the selected components is automatically ensured by verifying the component series code. HP is also actively involved in smart and secure trade channel activities, a project created after 9/11 to ensure the security of cargo containers entering the United States. The project uses active RFID technology to provide real-time visibility into the status, location and security of containers entering the port.
In corporate distribution and retail distribution, RFID has begun to function from the moment the goods leave the warehouse. When the entire vehicle leaves the distribution center, the system scans the goods on the trailer so that the store manager can track every shipment from the store's warehouse information system, knowing which shipments were sent and when they arrived. When the trailer arrives at the store, it takes another scan to see if anything is missing, so that it is no longer necessary to check each trailer and the actual number of goods counted. Once the merchandise is placed on the shelf, when there is a shortage of shelf merchandise, the embedded RFID reader sends a message to the store's back office system, and the goods are replenished as needed, thus avoiding sales losses due to shortage of goods. In addition, the RFID reader can track the sales speed of goods and sell the best and worst products, and has a security anti-theft function. As long as the anti-theft function in the tag is activated, the sensor at the exit of the store can issue an alarm message. At the checkout counter, the anti-theft program will be automatically cancelled. At the checkout counter, the tagged goods will be scanned again and the inventory will be updated. In addition, store customers can directly understand the products they want and immediately get information about the products with labels. In this way, choosing a DVD or CD is very simple, because customers can scan the product in any electronic convenience station in the store and choose to play a video or music clip.
In the past, waiting at the checkout desk for a long time was a headache. In the new store, the RFID tag in the shopping cart tells the store management how many shopping carts are in and out of the store. If the number of shopping carts used in the store increases, more tables are opened to meet the requirements of handling a large number of customers.
RF technology and barcodes are two different technologies that have different applications and sometimes overlap. The biggest difference between the two is that the barcode is "visual technology." The RF tag can be read as long as it is within the scope of the receiver.
What is the difference between RF technology and barcodes? Conceptually, the two are very similar, and the goal is to quickly and accurately confirm the tracking of the target object. The main differences are as follows: the ability to write information or update memory. The memory of the barcode cannot be changed. RF tags are not like barcodes, and their unique identifiers cannot be copied. The role of the tag is not limited to the field of view, because the information is transmitted by radio waves, and the bar code must be within the field of view. Due to the low cost of bar codes and the well-established standard system, which has been spread around the world, it has been generally accepted. In general, RF technology is limited to a limited market share. At present, a variety of bar code control templates are already in use, and there are different standards for radio frequency in accessing information channels.
RF technology and barcodes are two different technologies that have different applications and sometimes overlap. The biggest difference between the two is that the barcode is "visual technology" and the scanner works under human guidance and can only receive barcodes within its field of view. In contrast, radio frequency identification does not require seeing the target. The RF tag can be read as long as it is within the scope of the receiver. The barcode itself has other drawbacks. If the label is scratched, contaminated or dropped, the scanner will not be able to identify the target. The barcode can only identify the producer and the product, and can not identify the specific product. The barcode is the same on all the same product packaging, and it is impossible to identify which products expire first.
At present, in terms of cost, because of the different components, smart labels are much more expensive than barcodes. The cost of barcodes is the cost of barcode paper and ink, while the price of active RF tags with memory chips is more than $2, and the cost of passive RF tags is also At more than $1. However, the price of a tag without a built-in chip is only a few cents, which can be used to make the data information less demanding, and at the same time has the anti-counterfeiting function that the barcode does not have.
Information carrier
Read/write
Reading method confidentiality
Intelligent
Anti-interference ability
life
cost
Bar code
Paper, plastic film, metal surface
small
Read only
CCD or laser beam scanning
difference
no
difference
Shorter
lowest
RFID card
EEPROM
Big
Read/write
Wireless communication
the best
Have
well
longest
Higher
A radio frequency tag is a coded tag that contains a unique identification system for the item. This unique identification system includes the product electronic code EPC, the ubiquitous identification number UCODE, the vehicle identification code VIN, the international security identification number ISIN, and IPv6, and the like.
Among them, the product electronic code (EPC) is a branch of the global product code that identifies targets outside the field of view. The electronic product code is not just a radio wave barcode, it contains a series of data and information, such as origin, date code and other key supply information, which is stored in a small piece of silicon, using tags, readers. Networking with computers allows producers and retailers to keep track of accurate product and inventory information.
RF tags can store data ranging from 512 bytes to 4 megabytes depending on the type of merchant. The data stored in the tag is determined by the application of the system and the corresponding standards. For example, labels can provide product production, transportation, storage, and identify the identity of machines, animals, and individuals. These are similar to the information stored in the barcode. The tag can also be connected to a database to store product inventory number, current location, status, price, lot number information. Correspondingly, the RF tag can directly determine the meaning of the code without reading the database when reading the data.
At present, the price of RF tags varies from 30 cents to 50 dollars depending on the type of label and the application price. In general, smart labels used in high-end products are more than 50 cents, and active labels are more expensive and complicated. The price of sensitive components is above $100.
The purpose of the RF tag is to use a uniform standard of electronic product code to enable the product to be identified in different areas.
Many companies that currently produce RFID products use their own standards, but there is no uniform standard in the world. Several standards for RF cards are now available in ISO 10536, ISO 14443, ISO 15693 and ISO 18OOO. The most widely used are ISO14443 and ISO15693, both of which consist of physical characteristics, RF power and signal interface, initialization and anti-collision, and transmission protocol.
According to different ways, RF cards have the following classifications:
1. According to the power supply mode, it is divided into active card and passive card. Active means that there is a battery in the card to provide power, which has a long working distance, but has a limited life, large volume, high cost, and is not suitable for working in a harsh environment; there is no battery in the passive card, it uses beam power supply technology The received RF energy is converted into a DC power supply to supply power to the card circuit, and its working distance is shorter than that of the active card, but the service life is long and the working environment is not high.
2. According to the carrier frequency, it is divided into low frequency radio frequency card, intermediate frequency radio frequency card and high frequency radio frequency card. The low-frequency RF card mainly has two kinds of 125 kHz and 134.2 kHz. The frequency of the intermediate frequency RF card is mainly 13.56 MHz, and the high frequency RF card is mainly 433 MHz, 915 MHz, 2.45 GHz, 5.8 GHz, and the like. Low frequency systems are mainly used in short-range, low-cost applications such as most access control, campus cards, animal supervision, and cargo tracking. The IF system is used for access control and application systems that need to transmit large amounts of data; the high frequency system is used in applications where long read/write distance and high read/write speed are required, and the antenna beam direction is narrow and the price is high. Application in systems such as highway tolls.
3. According to the different modulation methods, it can be divided into active and passive. Active RF cards use their own RF energy to actively transmit data to the reader; passive RF cards use modulated scatter to transmit data. It must use the carrier of the reader to modulate its own signal. This type of technology is suitable for use in access control or In traffic applications, the reader can ensure that only RF cards within a certain range are activated. In the case of obstacles, with the modulation scattering method, the energy of the reader must come and go through the obstacle twice. The signal transmitted by the active RF card only passes through the obstacle once, so the active RF card is mainly used in obstacle-oriented applications, and the distance is longer (up to 30 meters).
4. According to the working distance, it can be divided into close-coupled card (acting distance less than 1 cm), near-coupling card (acting distance less than 15 cm), loose coupling card (acting distance is about 1 m) and long-distance card (acting distance from 1 m) To 10 meters, or even further).
5. According to the chip, it is divided into read-only card, read-write card and CPU card.
In an RFID system, a signal receiving device is generally called a reader (or a card reader). The basic function of the reader is to provide an interface for data transfer with the tag.
5. What is an RFID antenna?
The type of RF antenna must be chosen such that its impedance matches the free space and ASIC. Directional antennas have less interference from radiated modes and return loss. The access control system can use passive tags with short range of action.
INTRODUCTION In RF devices, when the operating frequency is increased to the microwave region, the matching problem between the antenna and the tag chip becomes more severe. The goal of the antenna is to transmit the most energy into and out of the tag chip. This requires careful design of the antenna and free space and the matching of its associated tag chip. The bands considered in this paper are 435MHz, 2.45 GHz and 5.8 GHz, and are used in retail goods.
The antenna must:
Sufficiently small enough to be attached to the desired item;
Directionality with omnidirectional or hemispherical coverage;
The chip that provides the most likely signal to the tag;
Regardless of the direction of the item, the polarization of the antenna can be matched to the interrogation signal of the card reader;
Robust
Very cheap.
The main considerations when choosing an antenna are:
Type of antenna;
Antenna impedance:
The performance of the RF applied to the item;
RF performance when there are other items around the labelled item.
Possible choices There are two ways to use it: a) Labeled items are placed in the warehouse, have a portable device, may be hand-held, ask for all items, and need them to give information feedback; b) at the door of the warehouse Install the card reader, ask and record the entry and exit. Another major choice is active tags or passive tags [1], [2].
Optional Antennas In the RFID systems used at 435 MHz, 2.45 GHz and 5.8 GHz, there are several optional antennas, see the table below, which focus on the size of the antenna. The gain of such a small antenna is limited, the magnitude of the gain depends on the type of radiation mode, the omnidirectional antenna has a peak gain of 0 to 2 dBi, and the directional antenna gain can reach 6 dBi. The magnitude of the gain affects the range of the antenna. The first three types of antennas in the table below are linearly polarized, but the microstrip antenna can be circularly polarized, and the logarithmic helical antenna is only circularly polarized. Since the directionality of the RFID tag is uncontrollable, the card reader must be circularly polarized. A circularly polarized tag antenna can produce a strong 3dB signal.
Impedance Problem For maximum power transfer, the input impedance of the chip behind the antenna must match the output impedance of the antenna. For decades, the antenna has been designed to match the impedance of 50 or 70 ohms, but it is possible to design the antenna to have other characteristic impedances. For example, a slot antenna can be designed with an impedance of a few hundred ohms. The impedance of a folded dipole can be 20 times the impedance of a standard half-wave dipole. The lead point of the printed patch antenna provides a wide range of impedance (typically 40 to 100 ohms). It is critical to choose the type of antenna so that its impedance can match the input impedance of the tag chip. Another problem is that other objects that are close to the antenna can reduce the return loss of the antenna. For omnidirectional antennas, such as double dipole antennas, this effect is significant. Some actual measurements were made by changing the spacing between the double dipole antenna and a ketchup, showing some changes, see Figures 4 and 5. Other objects have similar effects. In addition, the dielectric constant of the object, rather than the metal, changes the resonant frequency. A plastic bottle of water reduces the minimum return loss frequency by 16%. When the distance between the object and the antenna is less than 62.5mm, the return loss will result in a 3.0 dB insertion loss, while the free-space insertion loss of the antenna is 0.2 dB. The antenna can be designed to match the situation of the approaching object, but the behavior of the antenna varies for different objects and different object distances. It is not feasible for omnidirectional antennas, so antennas with strong directivity are designed and they are not affected by this problem.
Radiation Mode The pattern of the antenna was tested in a non-reflective environment, including various objects that required labeling, and performance was severely degraded when using an omnidirectional antenna. The performance degradation caused by cylindrical metal hearing is the most serious. When it is 50mm away from the antenna, the back-return signal drops by more than 20dB (see Figure 6). When the center distance between the antenna and the object is separated to 100-150 mm, the back-return signal drops by about 10 to 12 dB. A few bottles of water (plastic and glass) were measured at a distance of 100 mm from the antenna. See Figure 7, and the back-return signal was reduced by more than 10 dB. Similar results were obtained by testing in liquids in wax cartons and even on apples.
Effects of local structures When using handheld instruments, a large number of other adjacent objects severely distort the radiation pattern of the reader antenna and tag antenna. This can be calculated for the 2.45 GHz operating frequency, assuming a representative geometry, see Figures 8, 9, 10, which shows a 10 dB reduction in the return signal compared to free space, when the dual antennas are used simultaneously, than expected The mode drops more. Figures 11 and 12 are contour diagrams of the received signal in a cross-sectional plane in front of an antenna showing severe distortion. In a warehouse environment, it is problematic to have one label for an item box, and several labels are attached to one box to ensure that a label is visible at all times. The use of portable systems has several antenna problems. The two antennas of each box are sufficient for the access control device to be detected, so that the influence of the local structure becomes less important because the reader antenna of the access control device is fixed at the entrance and exit of the warehouse and directly points to the tagged object.
The gain from the RFID antenna and the use of active tag chips will affect the system's distance of use. Optimistic consideration, when the radiation intensity of the electromagnetic field meets the relevant standards of the UK, the full-wave rectification under the passive condition of 2.45GHz, the driving voltage is not more than 3 volts, the optimized RFID antenna impedance environment (impedance 200 or 300 ohms), the use distance It is about 1 meter [3]. If the WHO limit [4] is used, it is more suitable for global use, but the distance is reduced by half. These limit the electromagnetic field power of the reader to the tag. The range of action decreases as the frequency increases. If you use active chips, the distance can be 5 to 10 meters.
The omnidirectional antenna should be avoided in the tag, however directional antennas can be used, which have less radiation mode and return loss interference. The antenna type must be chosen such that its impedance matches the free space and ASIC. Using an antenna in a warehouse does not seem to be feasible unless an active tag is used, but in any case, the antenna radiation pattern in the warehouse will be severely distorted. The use of an access control system will be a good choice, and passive tags with short range of action can be used. Of course, the access control system is more expensive than the handheld instrument, but the handheld instrument staff needs to use it to search for items in the warehouse, and the personnel costs are equally expensive. In the access control system, each item box requires only 2 instead of 4 or 6 RFID tags.
6. What is the frequency of RFID tags?
The RF tag and reader need to be modulated to the same frequency to work. LF stands for low frequency radio frequency, around 125KHz, HF stands for high frequency radio frequency, around 13.54MHz, UHF stands for UHF radio frequency, in the range of 850 to 910MHz.
The receiving range of RFID readers is affected by many factors, such as radio frequency, size of the tag, energy of the reader, interference from metal objects, and other RF devices. In general, the effective reception distance of the low frequency passive tag is within one foot, the receiving distance for the high frequency passive tag is about three feet, and the receiving distance for the ultra high frequency tag is ten to twenty feet. For semi-active and active tags that use batteries, the reader can receive signals of three hundred feet or more. For low frequency and high frequency RF, if the tag is the same size as the reader antenna, the receiving distance can be calculated by multiplying the diameter of the antenna by 1.4. This rule applies to diameters within thirty centimeters.
As with the radio we listen to, the RF tag and reader must be modulated to the same frequency to work. LF, HF, UHF correspond to RF at different frequencies. LF stands for low frequency radio frequency, around 125KHz, HF stands for high frequency radio frequency, around 13.54MHz, UHF stands for UHF radio frequency, in the range of 850 to 910MHz.
There are four frequency bands in operation, low frequency (125KHz), high frequency (13.54MHz), ultra high frequency (850-910MFz), microwave (2.45GHz). Each frequency has its characteristics and is used in Different fields, so to use correctly, you must first choose the right frequency.
At present, the same frequency used in different countries is not the same. At present, UHF used in Europe is 868MHz, and in the United States it is 915MHz. Japan does not currently allow UHF to be used in RF technology. The government also limits its impact on other devices by adjusting the power supply to the reader. Some organizations, such as the Global Business Promotion Council, are encouraging governments to lift restrictions. Label and reader manufacturers are also developing systems that can use different frequency systems to avoid these problems.
Different frequencies have different characteristics, so their uses are also diverse. For example, low-frequency tags are cheaper than UHF tags, save energy, and penetrate scrap metal objects. They are best suited for objects with high water content, such as fruits. UHF has a wide range of functions and transmits data quickly, but they are more energy-intensive, have less penetrating power, and do not have too much interference in the work area. They are suitable for monitoring items transported from the harbor to the warehouse.
One problem encountered with RF technology is the reader conflict, where the information received by one reader collides with the information received by another reader, creating an overlap. One way to solve this problem is to use TDMA technology, which is simply that the reader is commanded to receive signals at different times, rather than at the same time, thus ensuring that the readers do not interfere with each other. However, items in the same area will be read twice, so it is necessary to establish a system to avoid this.
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