RFID技术外文文献(共7页)

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1、精选优质文档-倾情为你奉上外文文献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

2、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 m

3、illimeter 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

4、 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 electro-magnetic field which i

5、nduces a current 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. On

6、ce activated 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

7、the reading unit. 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 th

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

9、cesWe distinguish 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.

10、Because of the 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 t

11、hey do not depend 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 t

12、he number of 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 ene

13、rgy from the 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 us

14、e the energy 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

15、to 5 years.2. 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

16、for most applications, 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 frequ

17、encies used for 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

18、from 3-6 meters 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 ran

19、ge. UHF tags 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 l

20、icense exempt 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

21、 number of standards. 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

22、 around RFID 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 re

23、trieval of a 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

24、 scanned. In 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 da

25、tabase and if 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 si

26、nce they are 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

27、 backend also 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

28、 LF, HF, and 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 backlogg

29、ed patents US 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

30、影响最大。在标签的中心可看见的是芯片。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

31、标签供电。它所建立的场将产生连续波,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

32、。它有许多优点:由于芯片在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

33、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。 高频标签有更高的传输速率和更广的范围，成本也比低频标签高。该类标签中最常见的是智能标签，工作于13.56赫兹。超高频标签是所有标签中工作范围最广的，其范围可从

34、被动标签的3-6米到主动标签的30米。此外传送速率也很高,这使得可在很短时间识别单标签。此功能在标记高速度运动实体的位置时是很重要的，但在识别范围内只保持很短的一段时间。超高频标签也比其他任何标签都贵，受流体和金属的影响也是最严重的。这些特性在超高频自动收费系统中得到了极大应用。它的典型频率是868 MHz(欧洲),915兆赫(美国),950兆赫(日本)和2.45兆赫。LF和HF标签频率无限制，全球通用。但UHF标签的频率标准不同，各国分别都有认证标准。3.标准标签的应用范围广泛并且由于矛盾的目的(如低成本和安全)，这就可能需要很多不同种类的标签。这体现在标准的数量上。一个短期的RFID标准名

35、单如下:国际标准11784,年国际标准11785、国际标准14223,国际标准10536、国际标准14443,国际标准15693、国际标准18000。 注意该列表并不是完全的。由于RFID技术不是直接与互联网有关的，所以是否有可用的RFC这并不奇怪。最近围绕RFID技术的炒作，导致了专利爆炸。目前，已经发行的RFID相关专利超过了1800个（从1976年至2001年），积压了超过5700个描述RFID系统或应用程序的专利。4 .RFID系统一个RFID阅读器和一些标签一般来说是没用的。检索序列号不向用户提供大量的信息，也无助于保持生产链中的项目跟踪。真正的动力来自于RFID的后端存储额外的结合

36、信息，如产品的描述和一定的标签被扫描时。在一般的RFID系统结构如图2所示。射频识别读取机扫描标签,提出后台的信息。后台一般包括一个数据库和一个非常明确的应用接口。当后台接收新信息时,根据是否需要执行一些相关领域的计算来决定增加数据库。应用程序检索后台数据。在许多情况下,阅读器都配有应用程序。例如超市的结帐点(注:给的例子是使用条码代替RFID电子标签,因为它们更常见,然而如果标签被使用,这个系统也会产生同样效果) 。当阅读器扫描条码时，应用程序使用派生标识符查找当前价格。此外，后端也提供合格产品的折扣信息。如果数量低于一定的阈值，后端也减少了那种产品的数量，并通知经理。该节描述RFID标签一般是如何工作的, 存在的类型和区别。RFID标签通常使用的三个频率段LF、HF、和UHF，也解释了被动,半被动和主动标签的不同点并对优缺点进行了比较。本节总结了不同的标准并显示了业界在发行和积压此类专利的极大兴趣美国专利局专心-专注-专业