What are the two parts of RFID?

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What are the two parts of RFID? [Copy link]

Radio frequency identification (RFID) technology is a contactless automatic identification technology. Its basic principle is to use radio frequency signals and their spatial coupling and transmission characteristics to achieve automatic machine recognition of stationary or moving objects to be identified.

The RFID system generally consists of two parts, namely the electronic tag and the reader. The electronic tag and the reader realize the spatial (contactless) coupling of the RF signal through the coupling element. In the coupling channel, according to the timing relationship, the energy transfer and data exchange are realized. There are two types of coupling of RF signals between the reader and the electronic tag.

1) Inductive coupling, which achieves coupling through high-frequency alternating magnetic fields in space, is based on the law of electromagnetic induction.

(2) Electromagnetic backscatter coupling: Radar principle model. The emitted electromagnetic waves are reflected after hitting the target and carry back the target information at the same time. This is based on the spatial propagation law of electromagnetic waves.

Inductive coupling is generally suitable for short-range RFID systems operating at medium and low frequencies. Typical operating frequencies are: 125kHz, 225kHz and 13.56MHz. The identification distance is less than 1m, and the typical range is 10cm to 20cm. Electromagnetic backscatter coupling is generally suitable for long-range RFID systems operating at high frequencies and microwaves. Typical operating frequencies are: 433MHz, 868MHz, 915MHz, 2.45GHz, 5.8GHz. The identification distance is greater than 1m, and the typical range is 3m to 10m.

Electronic tags are also called radio frequency tags, transponders, and data carriers. Electronic tags are attached to the items to be identified and are the real data carriers of the radio frequency identification system. Generally, electronic tags are composed of tag antennas and tag-specific chips.

According to the different power supply methods of electronic tags, they can be divided into active tags and passive tags. Active tags have batteries inside, while passive tags do not.

A reader is also called a reading device. It can be a read/write or read-only device. It is used to automatically retrieve the agreed identification information in the electronic tag in a contactless manner when the object to be identified with an electronic tag passes through its reading range, thereby realizing the function of automatically identifying the object or automatically collecting the identification information of the object.

Surface Acoustic Wave Device Technology

Surface acoustic wave (SAW) is a mechanical wave propagating on the surface of piezoelectric crystal. Its sound speed is only one ten-thousandth of the speed of electromagnetic wave, and the propagation loss is very small. SAW devices are made of interdigital electroacoustic transducers and reflector couplers on piezoelectric substrates using microelectronic process technology. The piezoelectric effect of the substrate material is used to convert the electrical signal into an acoustic signal through the input interdigital transducer (IDT), and the acoustic signal is confined to the surface of the substrate. The output IDT restores the acoustic signal to an electrical signal, realizing the electrical-acoustic-electrical conversion process, completing the electrical signal processing process, and obtaining electronic devices for various purposes. Surface acoustic wave devices manufactured using advanced microelectronic processing technology have the advantages of small size, light weight, high reliability, good consistency, multi-function and flexible design. They have been widely used in communications, televisions, remote control and alarm systems. Multiple surface acoustic wave filters are used in hundreds of millions of mobile phones and televisions. With the rapid development of processing technology, the operating frequency of SAW devices has covered 10MHz~2.5GHz, and they are indispensable key components in the modern information industry.

Working principle of SAW passive electronic tag

SAW passive electronic tags use reflection modulation to transmit electronic tag information to the reader.

SAW tags are composed of an interdigital transducer and several reflectors. The two buses of the transducer are connected to the antenna of the electronic tag. The antenna of the reader periodically sends high-frequency interrogation pulses. Within the receiving range of the electronic tag antenna, the received high-frequency pulses are converted into surface acoustic waves through the interdigital transducers and propagate on the surface of the crystal. The reflector group partially reflects the incident surface wave and returns it to the interdigital transducer, which in turn converts the reflected acoustic pulse string into a high-frequency electrical pulse string. If the reflector group is designed according to a certain specific rule so that its reflected signal represents the specified coding information, then the reflected high-frequency electrical pulse string received by the reader will carry the specific code of the item. Through demodulation and processing, the purpose of automatic identification is achieved.

Due to the low propagation speed of surface acoustic waves, the effective reflected pulse train returns to the reader after a delay of several microseconds. During this delay period, the interfering reflections from the reader's surroundings have attenuated and will not interfere with the effective signal of the surface acoustic wave electronic tag.

SAW Passive Electronic Tags Application

Electronic tags using surface acoustic wave technology began in the late 1980s, and the research on surface acoustic wave tags has become a hot topic in recent years. Surface acoustic wave electronic tags are a new system achievement that applies modern electronics, acoustics, semiconductor planar process technology, radar and signal processing technology. It is another new type of non-contact automatic identification technology that is different from IC chip identification.

Since the SAW device itself works in the radio frequency band, is passive and has strong anti-electromagnetic interference ability, the electronic tag realized by SAW technology has certain unique advantages and is a supplement to the integrated circuit technology. Its main features are:

1. Large and reliable reading range, up to several meters;

2. Can be used on metal and liquid products;

3. The tag chip and antenna are easy to match, and the manufacturing process cost is low;

4. It can not only identify stationary objects, but also high-speed moving objects with a speed of up to 300 km/h;

5. It can be used in harsh environments such as high temperature difference (-100℃～300℃) and strong electromagnetic interference.

The application fields of electronic tag technology are very wide, including logistics management, road and bridge tolls, public transportation, access control, anti-counterfeiting, farm health and safety monitoring and identification, supermarket anti-theft and charging, airline baggage sorting, parcel tracking, factory assembly line control and tracking, equipment and asset management, sports competitions, etc.

SAW tags are also suitable for measuring changes in parameters such as pressure, stress, distortion, acceleration and temperature, such as hot axle positioning of railway infrared axle temperature detection systems, track scales, overload detection systems, automobile tire pressure, etc.

The OIS-W SAW tag produced by Baumer Ident GmbH in Germany and the SOFIS SAW system of Siemens have been successfully used in the automatic toll collection system for vehicles crossing the bridge in Oslo, Norway, and the train station positioning system in Munich, Germany. In the United States, companies such as Identtronix, i-Ray, and RF-SAW also produce commercial SAW electronic tags.