Radio frequency identification technology is a non-contact automatic identification technology. It is a short-distance wireless communication system composed of electronic tags (Tag / Transponder), reader / writer (Interrogator) and middleware (Middle-Ware). The tag in RFID is a combination of RFID tag chip and tag antenna. The tags are divided into active tags and passive tags according to their working modes. The active tag itself carries the battery to provide the energy required for the reader to communicate: the passive tag uses inductive coupling or backscattering working mode, that is, the electromagnetic field or electromagnetic wave emitted from the reader through the tag antenna obtains energy to activate the chip, and Adjust the matching degree of the RFID tag chip and the tag antenna, and feed back the information stored in the tag chip to the reader. therefore. The impedance of the RFID tag antenna must be conjugately matched with the input impedance of the tag chip, so that the tag chip can maximize the electromagnetic energy emitted by the RFID reader. In addition, the design of the tag antenna must also consider the application of the electronic tag, such as the tag antenna applied on the surface of metal objects and the tag antenna applied on the surface of ordinary objects. There are great differences in the structure and selection of the antenna. A tag antenna suitable for a variety of chips, low cost, and multiple uses is one of the key technologies for radio frequency identification that has been widely popularized in China.
Radio frequency identification system and antenna classification
For the radio frequency identification system using passive tags, there are two working modes according to the working frequency band. One is inductive coupling (Induc. TIve Coupling) T operation mode, this mode is also called near field operation mode, it is mainly suitable for low frequency and high frequency RFID systems: the other is backscattering (Backscattering) 32 operation Mode, this mode is also called far-field T-operation mode, which is mainly applicable to UHF and microwave RFID systems.
The inductive coupling mode mainly means that both the reader antenna and the tag antenna adopt a coil form. When the reader is reading the tag, it emits an unmodulated signal. After the electronic tag antenna in the near field of the reader antenna receives the signal and activates the tag chip, the tag chip controls the current in the tag antenna according to the globally unique identification number (ID) stored internally. The magnitude of this current further enhances or reduces the magnetic field emitted by the reader antenna. At this time, the near-field component of the reader exhibits a modulated characteristic, and the internal circuit of the reader detects the modulation amount generated by the tag from 0 to demodulate and obtain the tag information.
In the backscattering T mode, electromagnetic waves are used between the reader and the electronic tag to transmit information. When the reader recognizes the tag, it first emits unmodulated electromagnetic waves. At this time, the electronic tag antenna located in the far field receives the electromagnetic wave signal and generates an induced voltage on the antenna. The internal circuit of the electronic tag rectifies this induced voltage And zoom in to activate the tag chip. After the tag chip is activated, the impedance of the tag chip is changed with its own global unique identification number. When the impedance matching between the electronic tag chip and the tag chip is good, the signal is basically not reflected, while the impedance matching is not good. The signal will be almost completely reflected. In this way, the amplitude of the reflected signal changes, which is similar to the amplitude modulation of the reflected signal. The reader recognizes the identification number of the electronic tag and recognizes it by receiving the modulated reflection signal. Such antennas mainly include microstrip antennas, planar dipole antennas and loop antennas. Figure 2 is the UHF electronic tag antenna that we developed to work in a variety of identification environments.
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