Wednesday, January 5, 2011
【 Weak current College 】 electromagnetic spectrum (3 】
Keywords: electromagnetic wave spectrum
Time: location: user: label type: operating frequency: standard: implementation of the company: solution providers: hardware providers:
【 Summary 】 electromagnetic spectrum (3)
Because RFID system generated and radiation of electromagnetic waves, which are reasonably classified as a class of radio equipment, RFID systems work does not cause interference to other radio services or weakened. In particular, shall ensure RFID systems will not cause interference with radio and television broadcasting, mobile radio services (police, security services, business and industry), shipping and aviation radio services and mobile phone, etc.
Radio frequency identification system operating frequency selection, take into account other radio service, not service cause interference and influence. It is usually only used for industrial, scientific and medical (ISM — Industrial-Scientific-Medical) application and reserved frequency range. These frequency ranges in the world is unification of, as shown in Figure 1. Following on the ISM frequency range of each frequency band individually to a simple introduction.
In addition to the ISM frequency, in the entire 135kHz following frequency range is also available (in the North and South America and in Japan: < 400kHz), because here you can use a large magnetic field work, especially suitable for inductive coupling with radio frequency identification system.
On radio frequency identification system, the most important frequency is 0 ~ 135kHz, and ISM frequency 6.78MHz, 13.56MHz, 27.125MHz, 40.68MHz, 433.92MHz, 869.0MHz, 915.0MHz (in Europe do not use), as well as 24.125GHz 2.45GMHz, 5.8GHz. First, the frequency range 9 ~ 135KHz
The scope of the following without 135KHz as industrial, scientific, medical (ISM) frequency range reserved, so is the extensive use of other radio services. According to the band of the electromagnetic wave propagation in occupies the frequency range of radio services can be quite small technical costs continuously achieve the radius of 1000 km distance wireless communication. The frequency range of a typical radio service is the aviation and maritime navigation and radio services (LORAN C, OMEGA remote navigation system, DECCA Navigator System), timing signals and frequency standard service and military radio service. Therefore, people in Central Europe with frequency 77.5kHz can receive United States Mainflingen transmitting station time signal. One use of this frequency of radio frequency identification systems will make the reader around hundreds of meters in all radio clock are disabled.
In order to prevent such conflicts, the future European electric induction radio system license Ordinance 220ZV122, in between 70 to 119kHz provides a monument, does not allow the RFID system usage. 2. frequency range 6.78MHz
Frequency range 6.765 ~ 6.795MHz belonging to short-wave frequencies. According to the frequency of electromagnetic wave propagation characteristics, the days of only a very small distance, up to several hundred kilometres. At night, Transcontinental Media. The frequency range of the users are different categories of radio service, for example, radio broadcasting services, weather radio services and aeronautical radio services, and news, etc.
This frequency range has assigned by the International Telecommunication Union as ISM band, and will increasingly be using radio frequency identification system. III. frequency range 13.56MHz
Frequency range 13.553 ~ 13.567MHz is in the Middle-wavelength range. According to the band propagation characteristics of electromagnetic wave allowing contact circadian transcontinental. The frequency range of the users are different categories of radio services, such as news agencies and Telecommunications Agency).
In this frequency range, with the exception of inductance RFID system, other ISM use remote control systems, distance control system,a radio and pagers. 4. frequency range 27.125MHz
Frequency range 26.565 ~ 27.405MHz throughout Europe and the United States, Canada allocated to civil radio use. Allows transmitting power up to 4W unregistered and without charge of radio equipment for private users in the far distance of the 30km radio communication.
Between 26.565 ~ 27.405MHz ISM-band between approximately in civilian radio radio bands. In addition to inductively coupled radio frequency identification system, in the frequency range of ISM applications include: electrical apparatus (medical), high-frequency welding equipment (industrial), remote-control model and paging devices.
During the installation of industrial 27MHz RFID system, special attention should be paid to any possible in the vicinity of high-frequency welding device. High frequency welding device produces very high field strength, would seriously interfere with the work on the same frequency of the radio frequency identification system, in the planning of hospital 27MHz RFID system (for example access system), you should pay special attention to the possible existence of electrothermal treatment instrument. 5. frequency range 40.680MHz
Frequency range 40.660 ~ 40.700MHz in VHF band lower-end. Electromagnetic propagation is limited to surface waves, buildings and other obstructions caused by the attenuation is not obvious. Adjacent to the ISM-band frequency range is moved to commercial radio system (forestry management, Freeway Management) and TV broadcasting (VHF-band).
In the frequency range of the main application is ISM: telemetry and remote control. There are currently no RFID systems work in the band, they belong to this type of system does not apply in the bands. In this range of inductively coupled radio frequency identification systems can be achieved forDistance obviously less than all of the lower frequency range, and in the frequency range of wavelengths is certainly not suitable for 7.5m build small and inexpensive backscatter transponder. 6. frequency range 433.920MHz
Frequency range 430.050 ~ 440.000MHz worldwide distribution to the amateur radio service. Radio amateurs using this frequency range for language and data transmission as well as a radio relay station or household space satellite communications.
In the UHF frequency range, wave propagation approximate the light waves. Experience building or other obstructions, the obvious decay and reflection of electromagnetic wave incident.
With the working methods and the transmitting power, the radio amateurs using system can meet the 30 and 300 km/h. The use of space satellites can also be connected throughout the world.
ISM-band 433.050 ~ 434.790MHz roughly in the middle of the amateur radio bands, has a lot to be occupied various ISM applications. In addition to the backscatter of the RFID system, there are also small telephone, telemetry transmitter (including those whose household applications such as wireless outdoor thermometer), wireless headphones, unregistered short-range low power wireless walkie-talkie, no key access system (car central locking device with a handheld transmitter) and many other applications are filled with this band. Unfortunately, in this band, a wide range of ISM application extraordinary mutual interference. 7. frequency range 869.0MHz
Since late 1997, frequency range 868 ~ 870MHz in Europe allows short-range devices, therefore, the European Conference of postal and telecommunications of the 43 Member States can also be used for radio frequency identification system.
Some far eastern countries are also considering Sprint device allows the use of this frequency range. 8. frequency range 915.0MHz
The frequency range in Europe also did not provide the ISM applications. In Europe (United States and Australia), frequency range 889MHz and 902 888 ~ ~ 928MHz has available, and inverse scattering using radio frequency identification system. And the adjacent frequency rangeis pressed CT1 + and CT2 standard production of D-network telephone cordless phone use. 9. frequency range 2.45GHz
ISM frequency range 2.400 ~ 2.4835GHz and amateur radio enthusiasts and radiolocation services using the frequency range partially overlap. This UHF and high propagation characteristics of SHF is subject of light. Buildings and obstructions is a good reflector, the electromagnetic waves during the transfer process attenuation.
As the frequency range of a typical application of the ISM, in addition to the backscatter radio frequency identification systems, mainly: telemetry transmitter as well as PC's wireless network PC LAN system. 10. frequency range 5.8GHz
ISM frequency range 5.725 ~ 5.875GHz and amateur radio enthusiasts and radiolocation services using the frequency range partially overlap.
The frequency range of typical applications are: for ISM door opening and closing (in store or department store) or non-touch toilet flushing mobile sensors and backscatter radio frequency identification system. 11. frequency range 24.125GHz
ISM frequency range 24.00 ~ 24.25GHz and amateur radio enthusiasts and radiolocation services, as well as Earth resources satellite service using the frequency range partially overlap.
In this frequency range, mainly using mobile signal sensor, also using the transfer data radio system redirect. There is currently no RFID systems work in this band. 12. working band RFID system
Radio frequency identification system working band as shown in table 1. Not all table 1 frequencies in the radio frequency identification has been widely used, mainly uses for RFID frequencies in order to have the following four: 13.56 ± .007 MHz, 13 MHz, 915 ± 2450 ± 50 MHz, 5800 ± 75 MHz.
The primary information source for references:
 jianglin. Summary of radio wave propagation and spectrum utilization. Beijing: defense industry press, 1974
 Liu Yang Wang Yu-Min. automatic train identification system principles andapplications-Beijing: China railway Publishing House, 2003