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1、The history of RFIDWhether we realize it or not, radio frequency identification (RFID) is an integral part of our life. RFID increases productivity and convenience. RFID is used for hundreds, if not thousands, of applications such as preventing theft of automobiles and merchandise; collecting tolls
2、without stopping; managing traffic; gaining entrance to buildings; automating parking; controlling access of vehicles to gated communities, corporate campuses and airports; dispensing goods; providing ski lift access; tracking library books; buying hamburgers; and the growing opportunity to track a
3、wealth of assets in supply chain management. RFID technologies is also being pressed into service for use in U.S. Homeland Security with applications such as securing border crossings and inter modal container shipments while expediting low-risk activities.RFID is a term coined for short-range radio
4、 technology used to communicate mainly digital information between a stationary location and a movable object or between movable objects. A variety of radio frequencies and techniques are used in RFID systems. RFID is generally characterized by use of simple devices on one end of the link and more c
5、omplex devices on the other end of the link. The simple devices (often called tags or transponders) are small and inexpensive, can be deployed economically in very large numbers, are attached to the objects to be managed, and operate automatically. The more complex devices (often called readers, int
6、errogators, beacons) are more capable and are usually connected to a host computer or network. Radio frequencies from 100 kHz to 10 GHz have been used. The tags are usually built using CMOS circuitry while other technologies can be used such as surface acoustic wave (SAW) devices or tuned resonators
7、. Tags can be powered by a battery or by rectification of the radio signal sent by the reader. Tags can send data to the reader by changing the loading of the tag antenna in a coded manner or by generating, modulating, and transmitting a radio signal. A variety of modulation and coding techniques ha
8、ve been used. RFID systems can be read only (data is transferred only in one direction, from the tag to the reader) or read and write (two-way communication). A typical RFID system can use the principle of modulated backscatter (see Fig. 1). In this type of RFID system, to transfer data from the tag
9、 to the reader, the reader sends an un-modulated signal to the tag. The tag reads its internal memory of stored data and changes the loading on the tag antenna in a coded manner corresponding to the stored data. The signal reflected from the tag is thus modulated with this coded information. This mo
10、dulated signal is received by the reader, demodulated using a homodyne receiver, and decoded and output as digital information that contains the data stored in the tag. To send data from the reader to the tag, the reader amplitude modulates its transmitted radio signal. This modulated signal is rece
11、ived by the tag and detected with a diode. The data can be used to control operation of the tag, or the tag can store the data. A simple diode detector allows the detection circuitry in the tag to be simple and consume little power. Mankinds use and understanding of electricity, magnetism, and elect
12、romagnetic in very early times was limited to his eyesight, observation of electrostatic discharge (dont stand under a large tree during a lightning storm), and the magnetic properties of lodestones. Early applications probably included making light with fire, use of mirrors for signaling, and use o
13、f lodestones for navigation. Scientific understanding progressed very slowly until about the 1600s. From the 1600s to 1800s there was an explosion of observational knowledge of electricity, magnetism, and optics accompanied by a growing base of mathematically related observations. The 1800s marked t
14、he beginning of the fundamental understanding of electromagnetic energy. In 1846, English experimentalist Michael Faraday proposed that both light and radio waves are a form of electromagnetic energy. In 1864, Scottish physicist James Clerk Maxwell published his theory on electromagnetic. In 1887, G
15、erman physicist Heinrich Rudolf Hertz confirmed Maxwells electromagnetic theory and produced and studied electromagnetic waves (radio waves). Hertz is credited as the first to transmit and receive radio waves, and his demonstrations were followed quickly by Aleksandr Popov in Russia. In 1896, Guglie
16、lmo Marconi demonstrated the first successful transmission of radiotelegraphy across the Atlantic, and the world would never be the same. Forward to 20th centuryIn 1906, Ernst F.W. Alexanderson demonstrated the first continuous wave (CW) radio generation and transmission of radio signals. This achievement marks the beginning of modern radio communication, where all aspects of radio waves are controlled. The early 20th century was considered the birth of radar. The work in ra
