RFID技术外文文献

1、外文文献Current RFID TechnologyThis section describes 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

2、(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

3、 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

4、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 electro-magnetic field which induces a curr

5、ent into the tags 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

6、the tag receives commands 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 electro-magnetic field, instead it uses back scattering to modulate (reflect/absorb) the field sent by the reading u

7、nit. Because most fluids absorb electro-magnetic fields and most metal reflect those fields the reading of tags in presence of those materials is complicated.During a reading cycle, the reader has to continuously power the tag. The created field is called continuous wave, and because the strength of

8、 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 on side-channels which are located directly below and above the frequency of the continuous wave.1. Energy SourcesWe disting

9、uish 3 types of RFID tags in relation to power or energy: Passive, Semi-passive, Active Passive tags do not have an internal power source, and they therefore rely on the power induced by the reader. This means that the reader has to keep up its field until the transaction is completed. Because of th

10、e lack of a battery, these tags are the smallest and cheapest tags available; however it also restricts its reading range to a range between 2mm and a few meters. As an added benefit those tags are also suitable to be produced by printing. Furthermore their lifespan is unlimited since they do not de

11、pend on an internal power source.The second type of tags is semi-passive tags. Those tags have an internal power source that keeps the micro chip powered at all times. There are many advantages: Because the chip is always powered it can respond faster tore quests, therefore increasing the number of

12、tags that can be queried per second which is important to some applications. Furthermore, since the antenna is not required for collecting power it can be optimized for back scattering and therefore increasing the reading range. And last but not least, since the tag does not use any energy from the

13、field the back scattered signal is stronger, increasing the range even further. Because of the last two reasons, a semi-active tag has usually a range larger than a passive tag.The third type of tags is active tags. Like semi-active tags they contain an internal power source but they use the energy

14、supplied for both, to power the micro chip and to generate a signal on the antenna. Active tags that send signals without being queried are called beacons. An active tags range can be tens of meters, making it ideal for locating objects or serving as landmark points. The lifetime is up to 5 years.2.

15、 Frequency BandsRFID tags fall into three regions in respect to frequency: Low frequency (LF, 30- 500kHz), High frequency (HF.10-15MHz), Ultra high frequency (UHF, 850- 950MHz, 2.4-2.5GHz, 5.8GHz)Low frequency tags are cheaper than any of the higher frequency tags. They are fast enough for most appl

16、ications, however for larger amounts of data the time a tag has to stay in a readers range will increase. Another advantage is that low frequency tags are least affected by the presence of fluids or metal. The disadvantage of such tags is their short reading range. The most common frequencies used f

17、or low frequency tags are 125-134.2 kHz and 140-148.5 kHz.High frequency tags have higher transmission rates and ranges but also cost more than LF tags. Smart tags are the most common member of this group and they work at 13.56MHz. UHF tags have the highest range of all tags. It ranges from 3-6 mete

18、rs for passive tags and 30+ meters for active tags. In addition the transmission rate is also very high, which allows to read a single tag in a very short time. This feature is important where tagged entities are moving with a high speed and remain only for a short time in a readers range. UHF tags

19、are also more expensive than any other tag and are severely affected by fluids and metal. Those properties make UHF mostly useful in automated toll collection systems. Typical frequencies are 868MHz (Europe), 915MHz (USA), 950MHz (Japan), and 2.45GHz.Frequencies for LF and HF tags are license exempt

20、 and can be used worldwide; however frequencies for UHF tags differ from country to country and require a permit.3. StandardsThe wide range of possible applications requires many different types of tags, often with conflicting goals (e.g. low cost vs. security). That is reflected in the number of st

21、andards. A short list of RFID standards follows: ISO11784, ISO11785, ISO14223, ISO10536, ISO14443, ISO15693, ISO18000. Note that this list is not exhaustive. Since the RFID technology is not directly Internet related it is not surprising that there are no RFCs available. There cent hype around RFID

22、technology has resulted in an explosion in patents. Currently there are over 1800 RFID related patents issued (from 1976 to 2001) and over 5700 patents describing RFID systems or applications are backlogged.4. RFID SystemsA RFID reader and a few tags are in general of little use. The retrieval of a

23、serial number does not provide much information to the user nor does it help to keep track of items in a production chain. The real power of RFID comes in combination with a backend that stores additional information such as descriptions for products and where and when a certain tag was scanned. In

24、general a RFID system has a structure as depicted in figure 2. RFID readers scan tags, and then forward the information to the backend. The backend in general consists of a database and a well defined application interface. When the backend receives new information, it adds it to the database and if

25、 needed performs some computation on related fields. The application retrieves data from the backend. In many cases, the application is collocated with the reader itself. An example is the checkout point in a supermarket (Note that the given example uses barcodes instead of RFID tags since they are

26、more common; however, the system would behave in exactly the same way if tags were used). When the reader scans the barcode, the application uses the derived identifier to look up the current price. In addition, the backend also provides discount information for qualifying products. The backend also

27、 decreases the number of available products of that kind and notifies the manager if the amount falls below a certain threshold.This section describes how RFID tags work in general, what types of tags exist and how they differ. The three frequency ranges that RFID tags typically use are LF, HF, and

28、UHF. Also the difference between passive, semi-passive, and active tags was explained and their advantages and disadvantages were compared. The section concluded by looking at different standards and showed the great interest of the industry by counting the number of issued and backlogged patents US

29、 Patent Office.翻译：当前的RFID技术该节描述的是RFID标签由哪些部分组成、工作原理和确实存在的标签类型，关注标签的供电方式和使用频率范围。这部分也总结了一些重要的标准。RFID应答器的一般组成:微芯片、天线、线圈和电池(仅适用于有源标签)。芯片的大小主要取决于天线，它的规模和形式的取决于标签的使用频率，也取决于它的使用面积。它的大小范围可从不到一毫米的植入体大到一本关于集装箱物流的书。除了微型芯片,有些标签也附有可重写内存，这样标签就可储存更新阅读周期之间的或新的数据，如序号。如图1所示的RFID标签。天线清晰可见。正如前面所说的，天线对标签大小的影响最大。在标签的中心可看

30、见的是芯片。因为这是一个无源标签所以无内部的能源。RFID标签工作原理是如下:阅读单元产生电磁场引导电流流进标签的天线。该电流用以给芯片提供能源。在无源标签中该电流还为冷凝器充电，以保证芯片的不间断供电。在有源标签中电池取代了冷凝器。有源和无源标签的区别是短期内的信息阐释。一旦被激活的标签收到阅读的命令它就可以发送序列号或所要求的信息。总的来说,标签没有足够的能量来创造自己的电磁场, 相反它可以采用反向散射调制（反映/吸收）来产生由阅读单元发射的电磁场。由于大多数流体吸收电磁场和大多数金属反射这些场，故可使用的标签阅读材料是复杂的在一次循环解读中, 阅读器不得不持续给标签供电。它所建立的场将产

31、生连续波,因为磁场的强度随距离的平方而减少，故阅读器必须有一个相当大的能源。该场迅速响应标签给的任何指示, 因此标签位于正下方的侧渠道可以响应上述连续波的频率。1.能源我们辨别三种不同的RFID电子标签的能量或能源：被动、半被动和主动。被动式标签没有内部电源,因此它们的能量来源于阅读器。这意味着阅读器必须保持磁场直到转换完成。由于没有电池,故这些都是可用的最小和最便宜的标签。但它的阅读范围可从2毫米和几米。这些标签的另一个好处是适用于印刷生产。此外，因为它不依赖于内部电源，所以它们的寿命是无限的。第二种类型是半被动式标签。这些标签都有内部电源可在任何时候都给微芯片供电。它有许多优点:由于芯片在

32、持续带电的情况下反应迅速,因此可以增加每秒查询的标签数量，这是非常重要的应用。此外,由于天线不需要收集能量，故可以优化用以反向散射和回归来增加阅读范围。最后但并非不重要，因为标签不使用任何磁场能量所以反向散射的信号越强，阅读范围更广。由于最后两个原因，半被动标签通常比被动标签应用范围更广泛。第三种类型是主动式标签。类似于半主动标签，它的内部也有能源但它的能源用于两个方面：给微芯片供电和使天线产生信号。主动式标签发送信号而不被质疑,这被称为信标。主动标签可查询的范围是几十公尺,从而使其适宜于定位对象或理想标志点。寿命长达5年的。2.频带RFID电子标签按照频率分为三个部分:低频(LF,30-500千赫)、高频 (HF、10-15兆赫)、超高频 (UHF),（850-950兆赫,2.4-2.5兆赫,5.8兆赫)。低频标签比任何高频率的标签都便宜。对于大多数应用程序来讲,它们的响应速度很快。 但是，留在阅读器的大量标记数据的时间范围将增加。另一个优点是低频标签由于流体的存在或金属的存在而受到的影响最小。这类标签的缺点是它们识别范围很短。最常见的低频标签频率是125-134.2千赫和140-148.5千赫。 高