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瞭解RFID

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瞭解RFID

  1. 1. RFID RFID (radio frequency identification) is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency (RF) portion of the electromagnetic spectrum to uniquely identify an object, animal, or person. RFID is coming into increasing use in industry as an alternative to the bar code. The advantage of RFID is that it does not require direct contact or line-of-sight scanning. An RFID system consists of three components: an antenna and transceiver (often combined into one reader) and a transponder (the tag). The antenna uses radio frequency waves to transmit a signal that activates the transponder. When activated, the tag transmits data back to the antenna. The data is used to notify a programmable logic controller that an action should occur. The action could be as simple as raising an access gate or as complicated as interfacing with a database to carry out a monetary transaction. Low-frequency RFID systems (30 KHz to 500 KHz) have short transmission ranges (generally less than six feet). High-frequency RFID systems (850 MHz to 950 MHz and 2.4 GHz to 2.5 GHz) offer longer transmission ranges (more than 90 feet). In general, the higher the frequency, the more expensive the system. RFID is sometimes called dedicated short range communication (DSRC). How Smart Labels Will Work by Kevin Bonsor http://electronics.howstuffworks.com/smart-label.htm Long checkout lines at the grocery store are one of the biggest complaints about the shopping experience. By 2005, these lines could disappear when the ubiquitous Universal Product Code (UPC) bar code is replaced by smart labels, also called radio frequency identification (RFID) tags. RFID tags are intelligent bar codes that can talk to a networked system to track every product that you put in your shopping cart. Photo courtesy Motorola Smart labels like Motorola's BiStatix tags will enable manufacturers to track their products at all times. Imagine going to the grocery store, filling up your cart and walking right out the door. No longer will you have to wait as someone rings up each item in your cart one at at time. Instead, these RFID tags will communicate with an electronic reader that will detect every item in the cart and ring each up almost instantly. The reader will be connected to a large network that will send information on your products to the retailer and product manufacturers.
  2. 2. Your bank will then be notified and the amount of the bill will be deducted from your account. No lines, no waiting. RFID tags, a technology once limited to tracking cattle, will soon be tracking trillions of consumer products worldwide. Manufacturers will know the location of each product they make from the time it's made until it's used and tossed in the recycle bin or trash can. In this edition of How Stuff WILL Work, you'll learn about the types of RFID tags in development and how these smart labels will be tracked through the entire supply chain. Reinventing the Bar Code Almost everything that you buy from retailers has a UPC bar code printed on it. These bar codes help manufacturers and retailers keep track of inventory. They also give valuable information about the quantity of products being bought and, to some extent, by whom the products are being bought. These codes serve as product fingerprints made of machine- readable parallel bars that store binary code. Barcodes, like this one found on a soda can, are found on almost everything we buy. Created in the early 1970s to speed up the check out process, bar codes have a few disadvantages:  In order to keep up with inventories, companies must scan each bar code on every box of a particular product.  Going through the checkout line involves the same process of scanning each bar code on each item.  Bar code is a read-only technology, meaning that it cannot send out any information. Let's look at two types of smart labels that have read and write capabilities, which means that the data stored on these labels can be changed, updated and locked. Inductively Coupled RFID Tags This type of RFID tag has been used for years to track everything from cows and railroad cars to airline baggage and highway tolls. There are three parts to a typical inductively coupled RFID tag:  Silicon microprocessor - These chips vary in size depending on their purpose  Metal coil - Made of copper or aluminum wire that is wound into a circular pattern on the transponder, this coil acts as the tag's antenna. The tag transmits signals to the reader, with read distance determined by the size of the coil antenna. These coil antennas can operate at 13.56 MHz.
  3. 3.  Encapsulating material - glass or polymer material that wraps around the chip and coil Inductive RFID tags are powered by the magnetic field generated by the reader. The tag's antenna picks up the magnetic energy, and the tag communicates with the reader. The tag then modulates the magnetic field in order to retrieve and transmit data back to the reader. Data is transmitted back to the reader, which directs it to the host computer. RFID tags are very expensive on a per-unit basis, costing anywhere from $1 for passive button tags to $200 for battery-powered, read-write tags. The high cost for these tags is due to the silicon, the coil antenna and the process that is needed to wind the coil around the surface of the tag. Capacitively Coupled RFID Tags Capacitively coupled RFID tags have been created in an attempt to lower the cost of radio-tag systems. These tags do away with the metal coil and use a small amount of silicon to perform that same function as a inductively coupled tag. A capacitively coupled tag also has three parts:  Silicon microprocessor - Motorola's BiStatix RFID tags use a silicon chip that is only 3 mm2. These tags can store 96 bits of information, which would allow for trillions of unique numbers that can be assigned to products.  Conductive carbon ink - This special ink acts as the tag's antenna. It is applied to the paper substrate through conventional printing means. (For more information, read How Printable Computers Will Work.)  Paper - The silicon chip is attached to printed carbon-ink electrodes on the back of a paper label, creating a low-cost, disposable tag that can be integrated on conventional product labels. By using conductive ink instead of metal coils, the price of capacitively coupled tags are as low as 50 cents. These tags are also more flexible than the inductively coupled tag. Capacitively coupled tags, like the ones made by Motorola, can be bent, torn or crumpled, and can still relay data to the tag reader. In contrast to the magnetic energy that powers the inductively coupled tag, capacitively coupled tags are powered by electric fields generated by the reader. The disadvantage to this kind of tag is that it has a very limited range. The range of Motorola's BiStatix tags is limited to just about 1 cm (.39 inch). Making the tag cover a larger area of the product packaging will increase the range, but not to the extent that would be ideal for the system that retailers would want. In order for a global system of trillions of talking tags to work, the range needs to be boosted to several feet or more. Intermec has developed RFID tags that meet these needs, but that are too expensive to be cost-effective. Researchers at several companies are looking for ways to create a tag with a range of several feet, but that costs about the same as bar code technology. In order for retailers to implement a widespread RFID tag system, the cost of the tags will have to get down to one
  4. 4. penny (1 cent) per tag. In the next section, you will learn how these tags will be used to create a global system of tags that link to the Internet. Talking Tags When scientists are able to increase the range and lower the price of RFID tags, it will lead to a ubiquitous network of smart packages that track every phase of the supply chain. Store shelves will be full of smart-labeled products that can be tracked from purchase to trash can. The shelves themselves will communicate wirelessly with the network. The tags will be just one component of this large product-tracking network to collect data. The other two pieces to this network will be the readers that communicate directly with these smart labels and the Internet, which will serve as the communications lines for the network. Readers could soon be everywhere, including home appliances and gadgets. In fact, readers could be built directly into the walls during a building's construction becoming a seamless, unseen part of our surroundings. Let's look at a real-world scenario of how this system might work:  On a typical trip to the grocery store, one of the items on your shopping list is milk. The milk containers will have a smart label that stores the milk's expiration date and price. When you pick up the milk from the shelf, the shelf may display that milk container's specific expiration date or the information could be wirelessly sent to your personal digital assistant or cell phone.  The milk and all of the other items you've picked up at the store are automatically tallied as you walk through the doors that have an embedded tag reader. The information from the purchases you've made are sent to your bank, which deducts
  5. 5. the amount of the bill from your account. Product manufacturers know that you've bought their product and the store's computers know exactly how many of each product that need to be reordered.  Once you get home, you put your milk in the refrigerator, which is also equipped with a tag reader. This smart refrigerator is capable of tracking all of your groceries stored in it. It can track the foods you use, how often you restock your refrigerator and can let you know when that milk and other foods spoil.  Products are also tracked when they are thrown into a trash can or recycle bin. At this point, your refrigerator could add milk to your grocery list, or you could program it to order these items automatically. In order for this system to work, each product will have to be given a unique product number. MIT's Auto-ID Center, created a couple of years ago, is working on an Electronic Product Code (EPC) identifier that could replace the UPC. Every smart label could contain 96 bits of information, including the product manufacturer, product name and a 40-bit serial number. Using this system, a smart label would communicate with a network, called the Object Naming Service. This database would retrieve information about a product and then direct information to the manufacturer's computers. The information stored on the smart labels would be written in a Product Markup Language (PML), which is based on the eXtensible Markup Language (XML). PML would allow all computers to communicate with any computer system in a similar way that Web servers read Hyper Text Markup Language (HTML), the common language used to create Web pages. Researchers believe that smart labels could be on your favorite consumer products by 2005. Once the technical challenges are overcome, the only obstacle might be the public's reaction to a network system that can track every thing that they buy and keep in their kitchen cabinets. Lots More Information! Related HowStuffWorks Links • How UPC Bar Codes Work • How Anti-shoplifting Devices Work • How Stuff WILL Work Other Great Links • MIT Auto-ID Center • Motorola BiStatix • Texas Instruments: Tag-It System
  6. 6. • BISTAR • Rafsec • Gemplus Smart Labels • Radio Frequency Tags: An Alternative to Bar Coding • Barcode Server • Uniform Code Council RFID - The Technology and How does it work? In the last section we mentioned many things that you are relevant to an RFID system. In this section we will try to explain all of them. The diagram below explains the basic schematic of all RFID systems. The Tag or Transponder can be either active or passive. It responds to a signal from the Interrogator (reader/writer/antenna) which in turn sends a signal to the Computer. Taking each piece in turn: The Tag comes in a variety of shapes. It is made up from a chip (IC) and an antenna. Depending on your application it may be embedded in glass, or epoxy, or it may be in a label, or a card. See below for a selection of shapes. The tag can be passive, battery assisted, or active. Passive tags get all their power from the signal sent by the interrogator. As well as using this radio wave to carry the data, the tag is able to convert it into power. This means that the tag is only powered when it is in the beam of the interrogator. The tag then uses a technique called backscatter to reply to the interrogator. This does not involve a transmitter on the tag, but is a means of "reflecting" the carrier wave and putting a signal into that reflection.
  7. 7. Battery assisted tags are just like passive tags (they use backscatter) but they have a battery to provide the power to the chip. This provides a big advantage, because the tag is not dependent on the strength of the carrier from the interrogator to provide the power it needs. Now it can use all the power from the battery and so is able to work at a greater distance from the interrogator. Active tags, have not only a battery, but also some form of transmitter on the tag. Now we can really talk about long range. The disadvantage of having a battery is two fold. One, it adds cost to the tag, and two they run out of power eventually. The decision on which one is right for you will depend on your application. The tag is made of an IC and an antenna. The IC will include memory and some form of processing capability. The memory may be read only or read/write, the type selected will depend on the application. The tag talks to the interrogator using what is called the air-interface. This is a specification for how they talk to each other and includes the frequency of the carrier, the bit data rate, the method of encoding and any other parameters that may be needed. ISO 18000 is the standard for the air interface for item management. Also a part of this air interface is what is commonly called the anti-collision protocol (if the tag support it). This is a means of allowing many tags in the field to talk "at the same time". There are several ways of doing this, and each manufacturer has developed their own way of implementing it. Simplistically, consider a first grade teacher talking to his/her class. She says "Call out your name if you are here today". What she hears is 20 (or more) kids all shouting at the same time. So she says, "If your name begins with an A, shout out your name". Maybe she only hears one name now, or maybe she hears several. If she hears several, she refines the command, "If you name begins AA". By telling a child to keep quiet after she is able to record the name, she is now able to collect all the names. Two other terms you may hear are "Reader talks first" (RTF) and "Tag talks first" (TTF). With a RTF system, the tag just sits there, until it hears a request from the interrogator. This means that even though a tag may be illuminated (receiving power) from the interrogator, it does not talk until it is asked a question. With TTF the tag talks as soon as it gets power, or in the case of a battery assisted tag or active tag, it talks for short periods of time, all the time. This gives you a much faster indication of a tag within sight of the interrogator, but it also means that the airwaves have constant traffic. The antenna in a tag is the physical interface for the RF to be received and transmitted. Its construction varies depending on the tag itself and the frequency it operates on. Low frequency tags often use coils of wire, whereas high frequency tags are usually printed with conducting inks. Another form of tag is often called the smart label. This is really a paper (or similar material) label with printing, but also with an RFID tag embedded in it. Examples are shown below (with the antenna structure shown in the corner).
  8. 8. RFID - The Frequencies RFID operates in several frequency bands. The exact frequency is controlled by the Radio Regulatory body in each country. The generic frequencies for RFID are:  125 - 134 kHz  13.56 MHz  UHF (400 – 930 MHz)  2.45 GHz  5.8 GHz Although there are other frequencies used, these are the main ones. In the UHF band, there are two areas of interest. Several frequencies in the 400 MHz band and then the band 860 – 930 MHz Each of the frequency bands have advantages and disadvantages for operation. The lower frequencies 125-134kHz and 13.56MHz work much better near water or humans than do the higher frequency tags. Comparing passive tags, the lower frequencies usually have less range, and they have a slower data transfer rate. The higher frequency ranges have more regulatory controls and differences from country to country. The various bodies that control frequencies include the FCC in the USA and CEPT/ETSI in Europe. Bar Code History At 8:01 a.m. on June 26, 1974, a customer at Marsh's supermarket in Troy, OH, made the first purchase of a product with a bar code, a 10-pack of Wrigley's Juicy Fruit Gum. This began a new era in retail that sped up check-outs and gave companies a more efficient method for inventory control. That pack of gum took its place in American history and is currently on display at the Smithsonian Institute's National Museum of American History. That historical purchase was the culmination of nearly 30 years of research and development. The first system for automatic product coding was patented by Bernard Silver and Norman Woodland, both graduate students at Drexler Institute of Technology. They used a pattern of ink that glowed under ultraviolet light. This system was too expensive and the ink wasn't too stable. The system we use today was unveiled by IBM in 1973, and uses readers designed by NCR.

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