RFID技术介绍【外文翻译】.doc

1、 0 外文翻译 An Introduction to FID Technology Material Source:IEEE CS and IEEE ComSoc Author: Roy Want In recent years,radio frequency identification technology has moved from obscurity into mainstream applications that help speed the handling of manufactured goods and materials.RFID enables identificat

2、ion from a distance,and unlike earlier bar-code technology,it does so without requiring a line of sight.1 RFID tags support a larger set of unique IDs than bar codes and can incorporate additional data such as manufacturer,product type,and even measure environmental factors such as temperature.Furth

3、ermore,RFID systems can discern many different tags located in the same general area without human assistance. In contrast,consider a supermarket checkout counter,where you must orient each bar-coded item toward a reader before scanning it.So why has it taken over 50 years for this technology to bec

4、ome mainstream?The primary reason is cost.For electronic identification technologies to compete with the rock-bottom pricing of printed symbols,they must either be equally low-cost or provide enough added value for an organization to recover the cost elsewhere.RFID isnt as cheap as traditional label

5、ing technologies,but it does offer added value and is now at a critical price point that could enable its large-scale adoption for managing consumer retail goods. Here I introduce the principles of RFID,discuss its primary technologies and applications,and review the challenges organizations will fa

6、ce in deploying this technology. RFID principles Many types of RFID exist,but at the highest level,we can divide RFID devices into two classes:active and passive.Active tags require a power source theyre either connected to a powered infrastructure or use energy stored in an integrated battery.In th

7、e latter case,a tags lifetime is limited by the stored energy,balanced against the number of read operations the device must undergo.One example of an active tag is the transponder attached to an aircraft that identifies its national origin.Another exa- mple is a LoJack device attached to a car,whic

8、h incorporates cellular technology and a GPS to locate the car if stolen.However,batteries make the cost,size,and lifetime of active tags impractical for the retail trade.Passive RFID is of interest because the tags dont require batteries or maintenance.The tags also have an indefinite operational l

9、ife and are small enough to fit into a practical adhesive label.A passive tag consists of three parts:an antenna,a semiconductor chip attached to the antenna,and some form of encapsulation.The tag reader is responsible for powering and communicating with a tag.The tag antenna captures energy and tra

10、nsfers the tags ID(the tags chip coordinates this process).The encapsulation maintains the tags integrity and protects the antenna and chip from environmental conditions or reagents.The encapsulation could be a small glassvial or a laminar plastic substrate with adhesive on one side to enable easy a

11、ttachment to goods. Two fundamentally different RFID design approaches exist for transferring power from the reader to the tag:magnetic induction and electromagnetic(EM)wave capture.These two designs take advantage of the EM properties associated with an RF antenna the near field and the far field.B

12、oth can transfer enough power to a remote tag to sustain its operation typically between 10 W and 1 mW,depending on the tag type.(For comparison,the nominal power an Intel XScale processor consumes is approximately 500 mW,and an Intel Pentium 4 consumes up to50 W.)Through various modulation techniqu

13、es,near-and far-field-based signals can also transmit and receive data. Near-field RFID Faradays principle of magnetic induction is the basis of near-field coupling between a reader and tag.A reader passes a large alternating current through a reading coil, resulting in an alternating magnetic field

14、 in its locality.If you place a tag that incorporates a smaller coil in this field,an alternating voltage will appear across it.If this voltage is rectified and coupled to a capacitor,a reservoir of charge accumulates,which you can then use to power the tag chip.Tags that use near-field coupling sen

15、d data back to the reader using load modulation.Because any current drawn from the tag coil will give rise to its own small magnetic field which will oppose the readers field the reader coil can detect this as a small increase in current flowing through it.This current is proportional to the load ap

16、plied to the tags coil (hence load modulation).This is the same principle used in power transformers found in most homes today although usually a transformers primary and secondary coil are wound closely together to ensure efficient power transfer. However,as the magnetic field extends beyond the pr

17、imary coil,a secondary coil can still acquire some of the energy at a distance,similar to a reader and a tag.Thus,if the tags electronics applies a load to its own antenna coil and varies it over time,a signal can be encoded as tiny variations in the magnetic field strength representing the tags ID.

18、The reader can then recover this signal by monitoring the change in current through the reader coil.A variety of modulation encodings are possible depending on the number of ID bits required,the data transfer rate,and additional redundancy bits placed in the code to remove errors resulting from nois

19、e in the com- munication channel.Near-field coupling is the most straightforward approach for implementing a passive RFID system.This is why it was the first approach taken and has resulted in many subsequent standards,such as ISO 15693 and 14443,and a variety of proprietary solutions.However,near-f

20、ield communication has some physi- cal limitations.The range for which we can use magnetic induction approximates to c/2f,where c is a constant(the speed of light)and f is the frequency. Thus,as the frequency of operation increases,the distance over which near-field coupling can operate decreases.A

21、further limitation is the energy available for induction as a function of distance from the reader coil.The magnetic field drops off at a factor of 1/r3,where r is the separation of the tag and reader,along a center line perpendicular to the coils plane.So,as applications require more ID bitsas well

22、 as discrimination between multiple tags in the same locality for a fixed read time,each tag requires a higher data rate and thus a higher operating frequency.These design pressures haveled to new passive RFID designs based on far-field communication. 译文 RFID 技术介绍 资料来源 ： IEEE CS and IEEE ComSoc 作者：

23、Roy Want 近 年来，射频识别技术 从不被人所知 到成为 主流应用，加快了对 制成品的处理和材料 的控制。 射频识别技术可远距离识别 ，不像早期条码技术， 需要无阻碍的路径。 RFID 标签支持 ID 地址，比 条形码 有更为大量的设置，且 可以包含更多的数据 ， 如制造商 、 产品类型，甚至衡量环境因素，如温度。此外，射频识别系统可以识别许多位于一般相同地区 且 不同的标记 ， 而无需 额外 人力援助 。 与此相反 ， 试想 在超市收银台柜台前，你必须在扫描前调整每个条码 使之 朝着它的 阅读器。 那么为什么这项 技术会 使用超过 50 年？其中主要的原因是成本问题。由于电子识别技术与

24、谷底价格 印刷符号的竞争，他们必须以同样的低成本，或者提供一个组织 ，用于 从别处来取得足够的附加值 来 收回成本。 RFID 技术不像传统的标记技术那么便宜，但它确实提供附加值 。 现在 国际市场 正处于一个关键价格点，可以通过消费零售商品管理来使其大规模采用。在这里，我将介绍RFID 的原则，讨论其主要技术和应用，审查机构将面临挑战部署这种技术。 RFID 的原则 许多类型的 RFID 存在，但在最高层面上，我们可以将 RFID 技术分为两类设备：主动和被动。主动标签需要一个电源资源，它们是既可连接到通电能源基础设施又可使用储存于一体的综合电池 。在后一种情况下，标签的寿命受限于对储存的能

25、，由设备必须接受的读取操作数量所平衡。其中一个关于主动标签的例子是连接飞机的转发器能够标识国家起源。另一个例子是连接到汽车的 LoJack设备，它能够在汽车被盗时采用蜂窝技术和 GPS 定位汽车。 然而，电池使得主动标签的成本，大小和寿命在零售方面显得不切实际。被动 RFID 更受青睐的原因则是这是标签不需要电池和维护。该标签还具有无限的使用寿命，以及有足够小的身形来适应实际不干胶标签。被动标签由三部分组成：天线，连接天线的半导体芯片和各种形式的封装。 该标记识读者为供电和 与标签之间的沟通负责。标签天线捕捉能源并转移标签的 ID（标签的芯片坐标这个过程）。包封保持标签的完整，保护天线和来自自

26、然环境芯片及试剂。该封装可能是一个小玻璃瓶或是在一侧有着胶粘剂的塑胶层以使其容易附着于货物。 两种根本不同的 RFID 设计方法存在功率的转移 ， 从读者标签 、 磁性感应和电磁（电磁）波捕获。这两个设计利用电磁特性连接一个射频天线 近场和远场的优势。依靠标签的类型都可以足够的电力传输到远程标签以维持其运作特别是介于 10 W 和 1 毫瓦之间的时候 。作为比较，额定功率的英特尔 XScale 处理器消耗约 500 毫 瓦，英特尔奔腾 4 和消耗高达 50W。通过不同的调制技术，依据信号的距离远近还可以发送和接收数据。 RFID 技术：从默默无闻到沃尔玛 自从大规模制造的出现，迅速查明技术有助

27、于加速处理货物和材料。从历史上看，印刷标签以其简单，更具成本效益技术的优势一直是生产主食产业。在20世纪 70年代，通用产品代码的条码介绍帮助自动化和标准化的鉴定过程形成，标签也因此作出了巨大的飞跃。酒吧代码也迅速廉价生产，但他们有很多局限性。 他们需要一个阅读器和标签之间的清晰视线，一种可通过油脂和附近的物体遮蔽的，在阳光下很难阅读或在一些基 板上打印是也困难的东西。 RFID 成为一种替代标签技术，也就在这几十年左右。 英国在二战中采用 RFID 的原则来确定他们的飞机使用的敌我识别系统。在 20 世纪 60 年代，美国洛斯阿拉莫斯国家实验室开展的工作控制。它把 RFID的标签自动雇员证鉴

28、定人，限制进入安全地区，并使它更难伪造证件。小生境域也用在各种应用，如 RFID 识别动物，标签航空公司的行李，为马拉松运动员测时，使玩具互动，防止盗窃，并找到遗失物品。 除去这些应用， RFID 技术仍然相对掩盖了许多年。但现在，三大机构正扩大其大规模采用：沃尔玛，乐购，和美国国防部 。每个都以通过使用 RFID 的价格，以降低运营成本精简库存，销售，订单跟踪来获得更高的竞争力为目的。在结合计算机数据库和库存控制，通过数字化通信网络相连接的横跨全局设置地点方面， RFID 都可以针对个别项目进行处理，任由他们在工厂，仓库，车辆和商店间移动。 近场的 RFID 法拉第的电磁感应原理是近场连接阅

29、读器和标签之间的工作原理。一个阅读器通过阅读线圈传递一个大型的交流电流，并在交替中产生磁场。如果你把一个含有较小线圈的标签，放在这一领域就会产生交流电压。如果把这个电压换个方向，加上一个电容器，负责容量的积累， 那你就可以用它来给标签芯片充电。 标签能够使用近场连接发送数据，使用负载调制使其传回给阅读器。由于任何来自标签线圈电流会产生自己的小磁场，这将干扰阅读器的范围，即使是一股小幅流动经过的信号阅读器也可以检测到。在应用到标签的线圈负载时这个电流成正比（因此负载调制）。 这个原理同样适用于当今在大多数家庭中都能找到的电力变压器，尽管变压器通常是以单圈和双线圈绕密切环绕，以确保有效的电源转移的

30、。然而，由于磁场超越初级线圈延伸，二级线圈仍然能够在一定距离获取相应的能量，这和阅读器与标签之间的关系一样。因此，如果标签的 电子设备适用于负载到自己的天线线圈并能随着时间而变化，一个信号能在细微变化的磁场中编码实力代表标签的ID。该阅读器可以通过这个信号，然后恢复监测中通过阅读器线圈的电流的变化。可能依靠数位 ID 获取的数量，数据传输速率，和在代码中放置的额外的冗余位，各种调制品种编码成为可能，以去除在沟通通道中造成的误差噪音。 ThiNear 场耦合是实施被动式射频辨识系统最简单的方法。这是它作为第一个被采取的方法和在随后成为标准的原因，如 ISO 15693 和 14443，以及各种专有的解决方案。然而，近场通信还是有一些物理限制。我 们可以用磁感应的范围的标准是 c/2f，其中 c 是一个常数（即光速）， f 是频率。因此，随着频率操作的增加，超过近场耦合的距离会相应的减少。进一步的限制是能量的感应可用作为一个来自阅读器线圈的距离函数。磁场脱落在一个 1/r3 因素，其中 r 是分离在标签和读写器以及一个中心，垂直线线圈的平面。因此，当应用需要更多的 ID位以及同时在同一个地方固定的标签阅读时间出现多重歧视时，每个标签要求更高的数据速率，从而产生更高的工作频率。这些设计压力导致以远场沟通为基础的新的被动 RFID 的设计。