In general, RFID systems consist of five components, including transmitters, receivers, microprocessors, antennas, and tags. Transmitters, receivers, and microprocessors are often packaged together and collectively referred to as readers, so the industry often divides RFID systems into readers, antennas, and tags. These three components are generally Can be produced by different manufacturers. RFID comes from radar technology, so its working principle is very similar to radar. First, the reader sends an electronic signal through the antenna. After the tag receives the signal, it transmits the internally stored identification information. The reader then receives and recognizes the information sent back by the tag through the antenna. Finally, the reader sends the recognition result to the host. The architecture is shown in the figure.
Between the electronic tag and the reader, a coupling element is used to achieve spatial (non-contact) coupling of the RF signal. Within the coupling channel, energy transfer and data exchange are realized according to the timing relationship. There are two types of RF signal coupling between the reader and the electronic standard: one is the inductive coupling, the transformer model, the coupling is achieved through the spatial high-frequency alternating magnetic field, the theoretical basis is the law of electromagnetic induction, and the other is the electromagnetic response. Scatter coupling, radar model, the electromagnetic wave that launches and hits the target to reflect, carry back target information at the same time, the theoretical basis is the propagation characteristic of electromagnetic wave in space.
ReaderThe reader is the most important and complex component of an RFID system. Because its up-selling mode is generally an initiative to ask the tag for identification information, it is sometimes referred to as an interrogator. Figure 2.10 shows several different appearances of readers. The reader is connected to the host through a standard network port, an RS232 serial port, or a USB interface. On the other hand, the reader communicates with the RFID tag through the antenna. Sometimes for convenience, readers and antennas as well as smart terminals can be integrated into a mobile handheld reader.
antennaThe antenna is connected to the reader for transmitting RF signals between the tag and the reader. The reader can be connected to one or more antennas, but only one antenna can be activated each time it is used. The shape and size of the antenna will vary with the operating frequency and function. The operating frequency of the RFID system ranges from low frequency to microwaves, which is very wide, which makes the matching problem between the antenna and the tag chip complicated.
Label 1. ConceptAn RFID tag is composed of a coupling element, a chip, and a micro antenna. Each tag has a unique electronic code and is attached to the object to identify the target object. After the tag enters the scanning field of the reader, it receives the radio signal from the reader and sends out the electronic code (passive tag) stored in the chip with the energy obtained by the inductive current, or actively transmits the signal with a certain frequency (active tag). .
The principle of RFID tags is similar to the bar code, but it also has the following advantages compared to it:
1) Small size and various shapes. The RFID tag is not limited in size and shape for reading and does not need to match the fixed size and print quality of the paper for reading accuracy.
2) Environmental resistance. Barcodes are easily contaminated and affect identification, but RFID has strong anti-pollution properties for water, oil and other substances. In addition, RFID tags can be read even in dark environments.
3) Reusable. The tag has a read/write function, and the electronic data can be repeatedly covered so that it can be recycled and reused.
4) Strong penetration. Labels can also be penetratively communicated when wrapped in non-metallic or non-transparent materials such as paper, wood, and plastic.
5) Data Security. The data in the tag guarantees the accuracy of the data sent by the tag through the cyclic redundancy check force method.
2. Data storageThe tag uses three methods for data storage: Electrically Erasable Programmable Read-Only Memory (EEPROM), Ferroelectric Random Access Memory (FRAM), and Static Random Access Memory (SRAM). General radio frequency identification system uses EEPR0M. The disadvantage of this method is that the power consumption in the writing process is very high, and the service life is generally 100000 times. There are also manufacturers using FRAM. The FRAM write power consumption is 1/100 of the EEPROM, and the write time is 1/1000 of the EEPROM. FRAM is a non-volatile memory. However, FRAM has not been widely used due to production problems. SRAM can write data quickly and is suitable for microwave systems, but SRAM needs auxiliary battery uninterrupted power supply to save data.
3. classificationTags can be divided into three types depending on whether they are built-in power supplies: passive tags, active tags, and semi-active tags.
(1) Passive tags
Passive tags are also called passive tags because they do not have a power supply inside. An integrated circuit inside the passive tag drives the electromagnetic wave emitted by the reader and sends data to the reader. The communication frequency of the passive tag may be high frequency (HF) or ultra high frequency (UHF). The first generation of passive tags uses high-frequency communications, and its communication band is 13.56 MHz. The communication distance is short and can only reach about 1m at the longest, which is mainly used for access control and non-contact payment. The second generation of passive tags uses ultra-high frequency communications, and its communication band is 860-960 MHz. The communication distance is longer, up to 3 to 5m, and multi-tag recognition is supported, ie the reader can accurately identify multiple tags at the same time. So far, the second generation of passive tags is also the most widely used RFID standard, mainly used in industrial automation, asset management, cargo monitoring, personal identification and access control.
(2) Active tags
Active tags are also called active tags because they carry power inside the tags. Power devices and their associated circuitry determine that active tags are larger and more expensive than passive tags. However, the active label communication distance is farther, up to a hundred meters away. Active tags have two operating modes. One is the active mode. In this mode, the tags are actively broadcast to the periphery, even if there are no readers; the other is the wake-up mode, in order to save power and Reduce RF signal noise. The first one is in a low power sleep state. When the reader recognizes, it needs to broadcast a wake-up command first. Only when the tag receives the wake-up command will it start broadcasting its own code. This low-power wake-up mode can often enable the life of active tags for several years, such as RFCode active tags can be used for more than 7 years.
(3) Semi-active label
The semi-active label combines all the advantages of both passive and active labels. It carries internal batteries and provides power for the internal calculation of the label. This tag can carry sensors that can be used to detect environmental parameters such as temperature, humidity, mobility, and so on. Unlike active tags, their communication does not require batteries to provide energy, but rather uses electromagnetic waves emitted by the reader like passive tags to take communication energy.
car key cover,key holder for keychain,key fob cover,key fob protector,accessories
Dongguan Metalwork Technology Co., LTD. , https://www.dgdiecastpro.com