First, the nature is different.
As an electromagnetic wave, microwave also has wave-particle duality. The basic properties of microwave usually show three characteristics: penetration, reflection and absorption. For glass, plastic and porcelain, microwaves can almost pass through without being absorbed. For water and food, it absorbs microwaves and heats itself. For metal things, it will reflect microwaves.
We call high-frequency electromagnetic waves with long-distance transmission capability RF. In order to transmit TV signals in the air, it is necessary to modulate video full TV signals into high frequency or RF- RF signals, and each signal occupies one channel, so that multiple TV programs can be transmitted in the air at the same time without causing confusion.
Second, the signals are different.
Microwave signal refers to electromagnetic wave signal with frequency of 300MHz~300GHz. The frequency of microwave is higher than that of ordinary radio waves, which is also commonly known as "UHF electromagnetic waves".
Radio frequency signal is a modulated electric wave with a certain transmission frequency. When the frequency of electromagnetic wave is lower than 100kHz, the electromagnetic wave will be absorbed by the surface and cannot be effectively transmitted. Once the frequency of electromagnetic wave is higher than 100kHz, it can propagate in the air and be reflected by the ionosphere at the outer edge of the atmosphere, forming a long-distance transmission capability.
Extended data:
Classification and application of radio frequency
At present, the working frequency of RFID products is defined as different products that meet different standards in the frequency range of low frequency, high frequency and very high frequency, and RFID products in different frequency bands will have different characteristics. Among them, the sensor has two ways: passive and active.
low frequency
In fact, RFID technology was first widely used and popularized at low frequencies (125kHz to 134kHz). This frequency mainly works by inductive coupling, that is, there is transformer coupling between the reader coil and the inductive coil, and the voltage induced by the alternating magnetic field of the reader in the inductive antenna can be used as the power supply voltage after rectification. The magnetic field area can be well defined, but the field strength drops too fast.
Features:
Generally, the working frequency of inductors working at low frequency is between 120kHz and 134kHz, and the working frequency of Ti is 134.2kHz, and the wavelength of this frequency band is about 2500m；.
1. Generally speaking, except for the influence of metal materials, low frequencies can pass through any material without reducing its reading distance.
2. There are no special licensing restrictions for readers working at low frequencies in the world.
3. Low-frequency products have different packaging forms. A good packaging form is too expensive, but it has a service life of more than 10 years.
4. Although the magnetic field area of this frequency drops rapidly, it can produce a relatively uniform reading and writing area.
5. Compared with RFID products in other frequency bands, the data transmission rate in this frequency band is relatively slow.
6. The price of sensors is more expensive than other frequency bands.
Main applications:
Animal husbandry management system; The application of car anti-theft and keyless door opening system: the application of marathon running system: automatic parking fee collection and vehicle management system; Automatic refueling system application: hotel door lock system application: access control and safety management system.
high frequency
The high frequency (working frequency is 13.56MHz) inductor of this frequency does not need coil winding, and the antenna can be made by etching or printing.
Inductors generally work by load modulation. That is to say, the voltage on the reader antenna is changed by the load resistance on the switching inductor, and the amplitude modulation of the antenna voltage is realized by using the remote inductor. If people control the on-off of the load voltage through data, then these data can be transmitted from the sensor to the reader.
Features:
1. The working frequency is 13.56MHz, and the wavelength of this frequency is about 22m；;
2. Except for metal materials, the wavelength of this frequency can pass through most materials, but it often reduces the reading distance. The sensor needs to keep a certain distance from the metal;
3. This frequency band is recognized all over the world, and there is no special restriction;
4. Sensors are usually in the form of electronic tags;
5. Although the magnetic field area of this frequency drops rapidly, it can produce a relatively uniform reading and writing area;
6. The system has anti-collision characteristics and can read multiple electronic tags at the same time;
7. Some data information can be written into the tag;
8. Data transmission rate is faster than low frequency, and the price is not very expensive.
Main applications:
The application of book management system; Management and use of liquefied gas cylinders; Management and application of clothing production line and logistics system; Three-meter pre-charging system; Management and application of hotel door lock: large-scale conference personnel access system; Fixed assets management system; Management and application of medical logistics system: intelligent shelf management.
Extra high frequency
Very high frequency (VHF system, the working frequency is between 860MHz and 960MHz, and energy is transmitted through electric field. The energy of the electric field does not drop rapidly, but the reading area is not well defined. The reading distance of this frequency band is relatively long, and the passive frequency can reach about 10m. It is mainly realized by capacitive coupling.
Features:
1. In this frequency band, the definitions are different all over the world-the frequency defined in Europe and some Asia is 868MHz, the frequency defined in North America is between 902 MHz and 905MHz, and the recommended frequency band in Japan is between 950 MHz and 956 MHz. The wavelength of this frequency band is about 30cm.
2. At present, the power output of this frequency band is uniformly defined (defined as 4W in the United States and 500mW in Europe).
3.VHF radio waves cannot pass through many substances, especially suspended particulate substances such as water, dust and fog. Compared with high-frequency electronic tags, electronic tags in this frequency band do not need to be separated from metals.
4. The antenna of electronic tag is usually long and tag-shaped. The antenna has linear polarization and circular polarization design to meet the needs of different applications.
5. This frequency band has a good reading distance, but it is difficult to define the reading area.
6. It has a high data transmission rate and can read a large number of electronic tags in a short time.
Main applications:
Management and application in supply chain; Management and application of production line automation; Management and application of air parcels; Management and application of containers; Management and application of railway parcels; Application of logistics management system; Application of large-scale personnel access management.
Active RFID technology
Active RFID technology (2.45GHz, 5.8GHz) Active RFID has the characteristics of low transmission power, long communication distance, large amount of transmitted data, high reliability and good compatibility. Compared with passive RFID, it has obvious technical advantages.
Widely used in expressway toll collection, port freight management, personnel positioning management and other application fields. However, the use of this frequency band has a strong directivity. If there is a metal object in the receiving area, the metal object will refract and reflect the radio frequency of this frequency band, thus affecting the signal reading and writing of the radio frequency receiver.
Baidu encyclopedia-radio frequency
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