rfid技術(shù)外文文獻(xiàn)翻譯-其他專(zhuān)業(yè)-展示頁(yè)
2025-01-31 06:50本頁(yè)面
【正文】 out of which parts RFID tags consist of, how they work in principle, and what types of tags do exist. It focuses on how tags are powered and what frequency ranges is used. The section concludes by covering a few important standards. RFID transponders (tags) consist in general of: Micro chip, Antenna, Case, Battery (for active tags only) The size of the chip depends mostly on the Antenna. Its size and form is dependent on the frequency the tag is using. The size of a tag also depends on its area of use. It can range from less than a millimeter for implants to the size of a book in container logistic. In addition to the micro chip, some tags also have rewritable memory attached where the tag can store updates between reading cycles or new data like serial numbers. A RFID tag is shown in figure 1. The antenna is clearly visible. As said before the antenna has the largest impact of the size of the tag. The microchip is visible in the center of the tag, and since this is a passive tag it does not have an internal power source In principle an RFID tag works as follows: the reading unit generates an electromagic field which induces a current into the tag39。s antenna. The current is used to power the chip. In passive tags the current also charges a condenser which assures uninterrupted power for the chip. In active tags a battery replaces the condenser. The difference between active and passive tags is explained shortly. Once activated the tag receives mands from the reading unit and replies by sending its serial number or the requested information. In general the tag does not have enough energy to create its own electromagic field, instead it uses back scattering to modulate (reflect/absorb) the field sent by the reading unit. Because most fluids absorb electromagic fields and most metal reflect those fields the reading of tags in presence of those materials is plicated. During a reading cycle, the reader has to continuously power the tag. The created field is called continuous wave, and because the strength of the field decreases with the square of the distance the readers have to use a rather large power. That field overpowers any response a tag could give, so therefore tags reply
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