Microwave Tech - Principle of Radio Frequency PCB Identification (RFID) Technology

To enhance the understanding of the technology of Chinese engineers, this paper carefully introduced the Radio Frequency PCB Identification (RFID) technology principle, classification, standards, and related applications.Compared with traditional information card and IC card technology, radio frequency identification (RFID) technology has its unique features such as non-contact, fast reading speed, and no wear, and has made rapid progress in recent years.

RFID technology uses the radio frequency form to carry out non-contact two-way numerical transmission between the reader and the radio frequency card to achieve the goal of identification and numerical exchange. Compared with the traditional bar code, information card, an IC card, the RF card has non-contact, fast reading speed, no wear, not affected by the background, long life, easy to use the unique place and has the conflict prevention function, can simultaneously handle multiple cards. Overseas, rf discrimination technology has been widely used in industrial semi-automation, economic activity semi-automation, traffic control management, and many other fields.

System composition and working principle

The most basic radio frequency identification (RFID) technology system consists of three parts:

1. Tag (radio frequency card): Consists of coupling elements and chips. The Tag includes a built-in receiving antenna for communication with the Radio Frequency PCB receiving antenna.

2. Reader: A device that reads (and writes to) label information on a reader card.

3. Receiving antenna: Transmit rf signals between the tag and the reader.

Some systems also through the RS232 or RS485 interface of the reader and external computer (host system of the upper computer) cosigned, numerical exchange.

The basic office process of the system is: the reader sends a certain frequency of radio frequency signal through the transmitting and receiving antenna. When the radio frequency identification card enters the transmitting and receiving antenna office area, the induced current is generated, and the system antenna captures can carrier signal from the RF card. The radiofrequency card sends its coding and other information to the receiving antenna through the built-in card. The system antenna collects the carrier signal sent from the RF card, which is transmitted to the viewer through the receiver antenna regulator. The viewer demodulates and decodes the captured signal and then sends it to the background main system for relevant disposal. The main system calculates the legitimacy of the card according to the law of thinking, makes the corresponding disposal and choke according to different Settings, and sends out command signals to choke the action of the actuator.

radio frequency identification (RFID) technology

In the coupling form (inductor-electromagnetic), communication process (FDX, HDX, SEQ), from the rf card to the reader of the numerical transmission method (load modulation, backscattering, high harmonic) and frequency range, different non-contact transmission methods have fundamental differences, but all the readers in the functional principle, All the readers can be simplified into two basic plates: high-frequency interface and choke unit. The high-frequency interface contains a transmitter and a receiver, its functions include: initiation of high frequency transmitting power to start working radio frequency card and supply + ray; The transmitting signal is modulated to transmit the value to the RF card; Capture and demodulate the high-frequency signal from the rf card. The hf interface of different RF PCB discrimination systems is supposed to be slightly different.

The functions of the choke unit of the reader include: communicating with the application system software and executing the instructions sent by the application system software; The communication process of strangling and RF card (master-slave principle); Signal codec. For a particular system, there are anti-collision algorithms, encryption, and decryption of the values to be passed between the rf card and the reader, as well as authentication between the RF card and the reader and other ancillary functions.

The read/write distance of the rf discrimination system is a key parameter. Until now, long-distance RFID systems have been expensive because of the difficulty of finding ways to increase the read/write distance. The influencing factors of RF card read-write distance cover the receiving antenna office frequency, the RF output power of the reader, viewer confiscate the acuity degree, power consumption of the radio frequency card, receiving antenna and the Q value of the resonant circuit, receiving antenna direction, RF card reader and decoupling is appropriate, and RF card itself can strand and send information can strand, etc. In most score systems, the read distance is different from the write distance. The write distance is about 40 to 80 percent of the read distance.

Rf card standards and classification

According to different forms, there are the following categories of radio frequency card :

1. According to the power supply form, it is divided into the active card and the passive card. Active refers to the card has dry battery supply power, its utility distance is far, but the life of limited, large size, high cost, and uncomfortable to work in a despicable background; Passive card irrelevant battery, it uses the beam power supply technology will be collected to the radio frequency energy yaryards into DC power supply for the card power supply internal circuit power supply, its utility distance is the relatively short active card, but the life of a long and office background requirements are not high.

2. There are low-frequency, IF, and high-frequency RF cards based on the carrier frequency. There are two types of low-frequency RF cards: 125kHz and 134.2khz. The frequency of intermediate frequency RF cards is mainly 13.56mhz. The frequency of high-frequency RF cards is mainly 433MHz, 915MHz, 2.45ghz, and 5.8ghz. A Low-frequency system is mainly used in short-range, low-cost applications, such as most of the door guard choke, campus card, animal surveillance management, cargo tracking, etc. The intermediate frequency system is used for the guard and control of the door and the application system which needs to transmit the number of numbers. The high-frequency system is applied to occasions requiring long read/write distance and high read/write speed. The receiving antenna beam direction is narrow and the price is high. It is used in train monitoring, expressway toll collection, and other systems.

3. According to the different modulation forms can be divided into active and inactive. Active radio frequency card with its own radio frequency wisp actively send out the value to the reader; The non-active RF card uses the modulated scattering form to transmit the value, it must use the reader carrier to modulate its signal, this technology is suitable for the door guard or traffic applications because the reader can ensure that only a certain range of rf card. In the event of a stumbling block, with the modulated scattering form, the reader's ability ray must come and go over the stumbling block twice. The active form of the card only sends a signal over the stumbling block once, because the active form of the official card is mainly used in applications where the stumbling block is present, at a greater distance (up to 30 meters).

4. According to the utility distance, it can be divided into tightly coupled cards (utility distance less than 1 cm), near-coupled cards (utility distance less than 15 cm), loosely coupled cards (utility distance about 1 m), and long-distance cards (utility distance from 1 m to 10 m, or even farther).

5. Read-only cards, read-write cards, and CPU cards.

So far, many enterprises that produce RFID products think it is appropriate to use their standards, but there is no unified international standard. So far, several standards available for RF PCB cards are ISO10536, ISO14443, ISO15693, and ISO18OOO. The most widely used are ISO14443 and ISO15693. These two standards are composed of four parts: physical special properties, radio frequency identification (RFID) technology power and signal interface, initialization and anti-collision, and transmission protocol.