How does an RFID system work?

The system consists of a tag, which is made up of a microchip with a coiled antenna, and an interrogator or reader with an antenna. The reader sends out electromagnetic waves that form a magnetic field when they "couple" with the antenna on the RFID tag. A passive RFID tag draws power from this magnetic field and uses it to power the microchip�s circuits. The chip then modulates the waves that the tag sends back to the reader and the reader converts the new waves into digital data.

Why is RFID better than using bar codes?

RFID is not necessarily "better" than bar codes. The two are different technologies and have different applications, which sometimes overlap. The big difference between the two is bar codes are line-of-sight technology. That is, a scanner has to "see" the bar code to read it, which means people usually have to orient the bar code towards a scanner for it to be read. Radio frequency identification, by contrast, doesn�t require line of sight. RFID tags can be read as long as they are within range of a reader. Bar codes have other shortcomings as well. If a label is ripped, soiled or falls off, there is no way to scan the item. And standard bar codes identify only the manufacturer and product, not the unique item. The bar code on one milk carton is the same as every other, making it impossible to identify which one might pass its expiration date first.

Will RFID replace bar codes?

Probably not. Bar codes are inexpensive and effective for certain tasks. It is likely that RFID and bar codes will coexist for many years.

Is RFID new?

RFID is a proven technology that's been around since the Second World War. Up to now, it's been too expensive and too limited to be practical for many commercial applications. But if tags can be made cheaply enough, they can solve many of the problems associated with bar codes. Radio waves travel through most non-metallic materials, so they can be embedded in packaging or encased in protective plastic for weather-proofing and greater durability. And tags have microchips that can store a unique serial number for every product manufactured around the world.

If RFID has been around so long and is so great, why aren�t all companies using it?

Many companies have invested in RFID systems to get the advantages they offer. These investments are usually made in closed-loop systems � that is, when a company is tracking goods that never leave its own control. That�s because all existing RFID systems use proprietary technology, which means that if company A puts an RFID tag on a product, it can�t be read by Company B unless they both use the same RFID system from the same vendor. But most companies don�t have closed-loop systems, and many of the benefits of tracking items come from tracking them as they move from one company to another and even one country to another.

Is the lack of standards the only thing that has prevented RFID from being more widely used? Another problem is cost. RFID readers typically cost $1,000 or more. Companies would need thousands of readers to cover all their factories, warehouses and stores. RFID tags are also fairly expensive � 50 cents or more � which makes them impractical for identifying millions of items that cost only a few dollars (see below).

How much do RFID tags costs?

They can cost as little as 30 cents or as much as $50 depending on the type of tag and the application. Generally speaking, finished smart labels that can be applied top products typically cost 50 cents or more. Active tags � those with a battery � can cost far more. And if you bundle in a sophisticated sensor, the cost can rise to more than $100.

What is the difference between low-, high-, and ultra-high frequencies?

Just as your radio tunes in to different frequency to hear different channels, RFID tags and readers have to be tuned to the same frequency to communicate. RFID systems use many different frequencies, but generally the most common are low- (around 125 KHz), high- (13.56 MHz) and ultra-high frequency, or UHF (850-900 MHz). Microwave (2.45 GHz) is also used in some applications. Radio waves behave differently at different frequency, so you have to choose the right frequency for the right application.

How do I know which frequency is right for my application?

Different frequencies have different characteristics that make them more useful for different applications. For instance, low-frequency tags are cheaper than ultra high frequency (UHF) tags, use less power and are better able to penetrate non-metallic substances. They are ideal for scanning objects with high-water content, such as fruit, at close range. UHF frequencies typically offer better range and can transfer data faster. But they use more power and are less likely to pass through materials. And because they tend to be more "directed," they require a clear path between the tag and reader. UHF tags might be better for scanning boxes of goods as they pass through a bay door into a warehouse. It is probably best to work with a consultant, integrator or vendor that can help you choose the right frequency for your application.

Do all countries use the same frequencies?

No. Europe uses 868 MHz for UHF and the U.S. uses 915 MHz. Japan currently does not allow any use of the UHF spectrum for RFID. Government�s also regulate the power of the readers to limit interference with other devices. Some groups, such as the Global Commerce Initiative, are trying to encourage governments to agree on frequencies and output. Tag and reader makers are also trying to develop systems that can work at more than one frequency, to get around the problem.

What�s the difference between passive and active tags?

Active RFID tags have a battery, which is used to run the microchip's circuitry and to broadcast a signal to a reader (the way a cell phone transmits signals to a base station). Passive tags have no battery. Instead, they draw power from the reader, which sends out electromagnetic waves that induce a current in the tag's antenna. Semi-passive tags use a battery to run the chip's circuitry, but communicate by drawing power from the reader. Active and semi-passive tags are useful for tracking high-value goods that need to be scanned over long ranges, such as railway cars on a track, but they cost a dollar or more, making them too expensive to put on low-cost items. The Auto-ID Center is focusing on passive tags, which cost under a dollar today. Their read range isn't as far - less than ten feet vs. 100 feet or more for active tags - but they are far less expensive than active tags and require no maintenance.

How much information can the tag store?

It depends on the vendor and the application, but typically a tag would carry no more than 2KB of data � enough to store some basic information about the item it is on.

What�s the difference between read-only and read/write tags?

Chips in RF tags can be read-write or read-only. With read-write chips, you can add information to the tag or write over existing information when the tag is within range of a reader, or interrogator. Read-write tags are useful in some specialized applications, but since they are more expensive than read-only chips, they are impractical for tracking inexpensive items. Some read-only microchips have information stored on them during the manufacturing process. The information on such chips can never been changed. A more flexible option is to use something called electrically erasable programmable read-only memory, or EEPROM. With EEPROM, the data can be overwritten using a special electronic process.

What is reader collision?

One problem encountered with RFID is the signal from one reader can interfere with the signal from another where coverage overlaps. This is called reader collision. One way to avoid the problem is to use a technique called time division multiple access, or TDMA. In simple terms, the readers are instructed to read at different times, rather than both trying to read at the same time. This ensures that they don't interfere with each other. But it means any RFID tag in an area where two readers overlap will be read twice. So the system has to be set up so that if one reader reads a tag another reader does not read it again.

What is tag collision? Another problem readers have is reading a lot of chips in the same field. Tag collision occurs when more than one chip reflects back a signal at the same time, confusing the reader. Different vendors have developed different systems for having the tags respond to the reader one at a time. Since they can be read in milliseconds, it appears that all the tags are being read simultaneously.

What is the read range for a typical RFID tag? The read range of passive tags depends on many factors: the frequency of operation, the power of the reader, interference from metal objects or other RF devices. In general, low-frequency tags are read from a foot or less. High frequency tags are read from about three feet and UHF tags are read from 10 to 20 feet. Where longer ranges are needed, such as for tracking railway cars, active tags use batteries to boost read ranges to 300 feet or more.

Are there any standards for RFID?

Yes. International standards have been adopted for some very specific applications, such as tracking animals. Many other standards initiatives are under way. The most interesting efforts involve GTag, which is promoted by EAN and UCC as a way to communicate with UHF tags; ISO 18000-6, which is an international effort that forms the foundation for the GTag standard; and the Auto-ID Center�s electronic product code. The EPC and the technology surrounding it is not a standard in any formal way, but the Auto-ID Center hopes that it will be widely adopted and become the de facto standard.

Who are the leading RFID vendors? There are many different RFID vendors with different areas of expertise. We have compiled a director of vendors around the world. Click on Find a Vendor in the left-hand navigation bar to locate the type of vendor you are looking for.

What are some of the most common applications for RFID? RFID is used for everything from tracking cows and pets to triggering equipment down oil wells. It may sound trite, but the applications are limited only by people�s imagination. The most common applications are tracking goods in the supply chain, tracking assets, tracking parts moving to a manufacturing production line, security (including controlling access to buildings and networks) and paymant systems that let customers pay for items without using cash.

What are intelligent software agents and how do they fit into RFID? Software agents are basically autonomous applications that automate decision making by establishing a set of rules. For instance, if X happens, do Y. They are important to RFID because humans will be overwhelmed by the amount of data coming from RFID tags and the speed at which it comes (real-time in many cases). So agents will likely be used to automate routine decisions and alert employees when a situation requires their attention. SAP and a company called BiosGroup are working on an automated replenishment system in which software agents would make decisions when trends indicate a product will be out of stock.

What is "energy harvesting"?

Most passive RFID tags simply reflect back waves from the reader. Energy harvesting is a technique in which energy from the reader is gathered by the tagged, stored momentarily and transmitted back at a different frequency. This method may improve the performance of passive RFID tags dramatically.

Source: RFID Journal