Electronic Design

Tag It!

From the feed lot to the parking lot, is this the year for RFID?

RFID, or radio-frequency identification, is a short-range wireless technology. It goes beyond bar coding to mark, identify, and track everything from products to people.

RFID uses electronic tags or smart labels to electronically store a unique identifying number instead of a printed bar code. Each tag consists of a single chip with an EEPROM containing the ID number and a radio transceiver or transponder. A popular tag format is a chip mounted on a plastic sheet that contains an antenna in the form of a small loop (Fig. 1).

Unlike bar codes, readers don't need a line-of-sight (LOS) scan. Furthermore, reading can be automated because orientation of the labeled device isn't an issue. Reading or scan time thus becomes much faster. In addition, automatic reading cuts costs and human reading errors, especially in supply-chain applications. It's also possible to write to an RFID tag and change its code or content. Another huge time-saving benefit is the ability to scan or read multiple items concurrently.

The other major piece of the RFID system is the reader. Also called an interrogator, this higher-power transceiver (usually 1 W or so) uses a larger antenna to interrogate the tag. Passive tags receive the RF signal from the reader. Then they rectify and filter the signal into a dc that powers up the transponder circuits, which in turn transmit the tag's ID code back to the reader. Working with a computer, the reader recognizes and/or records the tag info and takes the appropriate action, depending upon the application. Most readers are fixed in place, but handheld readers are available, too.

To read a passive tag, the distance between the reader and the tag must be relatively close (Fig. 2). A typical range is several inches. But this varies with the frequency of operation as well as the antenna size, and it can range from a few centimeters to about 20 ft. This short range is within what wireless engineers call the near field. The near-field range extends up to about one wavelength (λ) from the transmitting antenna, where λ = 300/fMHz in meters. The far field is beyond one wavelength.

Most wireless systems use the far field, in which the radio wave breaks away from the antenna and becomes a self-supporting electromagnetic wave. The electric and magnetic fields regenerate one another along the way according to Maxwell's equations. The near field is essentially the magnetic field produced by the reader's antenna.

RFID uses transformer theory in the near field. The interrogator antenna is the primary winding of the transformer, while the tag antenna is the secondary. Signal strength at the tag is proportional to the cube of the distance (r) from the reader, or 1/r3. The larger the tag antenna, the larger the signal and the greater the range. Typical tag antenna sizes range from less than an inch to 4 or 5 in.

RFID uses the Federal Communication Commission's unlicensed industrial-scientific-medical (ISM) frequency assignments. The most popular frequencies are 125 kHz, 13.56 MHz, 915 MHz, and 2.4 GHz. The original tags used the lower frequencies, but the most popular today is 13.56 MHz. The UHF frequency of 915 MHz is growing in use because it provides a longer reading range and is the key operating frequency of the new Gen 2 standard.

Backscatter modulation, the most common modulation scheme, is a form of amplitude shift keying (ASK). When the reader is turned on, the tag powers up and begins to transmit its ID data. The binary pulses modify the impedance of the tag's antenna, which in turn causes an amplitude shift in the reader signal. The process loads and unloads the secondary winding to reflect an impedance back into the primary. The result is an AM wave with a very low percentage of modulation. The actual amplitude shift on a 100-V p-p carrier may only be several hundred millivolts peak-to-peak or less, depending on the range. This signal is peak-detected and reshaped into a serial data signal. Manchester coding typically is used to make clock recovery reliable.

High-speed data rates aren't a major requirement in most applications. Speeds from a few kilobits per second to several hundred bits per second are typical. The higher the operating frequency, the higher the potential data rate. When reading physically close multiple tags, higher speed is necessary.

RFID tags use EEPROM memory. The manufacturer usually programs it, but users can buy programmers to program the data themselves. The smallest memories are only 64 or 96 bits, though memories up to several kilobits are available. Greater memory sizes consume more power. They also provide less for transmission back to the reader and have shorter reading distances. Readers can reprogram some tags as well. Write distance is usually about one half the read distance or less.

Newer tags feature anticollision resolution, as multiple tags powered up simultaneously interfere with one another. Many available schemes prevent such collisions. One uses a time-division multiplexed arrangement, assigning each tag a time slot in which to transmit. Others use an access scheme, where a tag waits a random time before transmitting. Anticollision is a must in applications where multiple items will appear within the reader's antenna field. Otherwise, you'll wind up with read errors or no usable data.

While passive tags are the most widely used, active tags also are available. Active tags have a battery to boost the transmit power back to the reader, so they have a longer read range. Such tags use thin button batteries, which make the tag bulkier and much more expensive. An active 433-MHz tag features a read range to 300 ft.

Finally, tag cost is a huge issue. Passive tags have dropped in cost over the years from a few dollars each to as low as 25 cents in large quantities. Lower prices are the key to wider usage.

Cost-wise, the holy grail is a 5-cent tag. At this stage, RFID tags can begin to replace the lowly printed bar code on a wider scale. Many in the industry wonder if that will ever happen.

Does RFID spell the demise of bar codes? No way, say most people in the industry. Bar-code labels always will be cheaper than electronic tags, and the need for them will never subside. Bar-code reading systems have been in place for decades, and virtually every product uses one. Even as RFID tags evolve to increase reading distance and lower price, there still will be items whose price better fits a printed code. Expect many years of coexistence between RFID and bar codes.

Like most wireless technologies, standards rule RFID. In the beginning, most systems were proprietary to the company making the products. But in an effort to increase RFID usage, interoperability between products and systems was inevitable. Now dozens of related standards have entered the fray.

First, don't forget that the FCC regulates every wireless device. Because RFID products use the ISM unlicensed bands, tags and readers must meet the FCC's regulations. These are found in the U.S. Code of Federal Regulations (CFR), Tile 47, Part 15. If you don't have a copy, you should. Look it up on the FCC's Web site at www.fcc.gov.

The American National Standards Institute (ANSI) was one of the first organizations to get into the RFID standards business. To learn more, start with ANSI's standard 256.

The International Organization of Standardization/International Electrotechnical Commission (ISO/IEC) in Geneva also has many RFID standards. Key standards related to the most widely used 13.56-MHz tags are 14443 and 15691/15692/15693. A UHF standard is designated 18000. Lower-frequency tags are defined by the 10536 standard. Different versions exist.

EPCGlobal, an international organization, regulates the electronic product code industry and sets standards. First-generation standards are designated class 0 (read-only) and class 1 (one-time programmable, or OTP). Most recent of these, the Gen 2 UHF tag and reader standards were developed under the guidance of over 60 worldwide companies seeking an international standard. The standard has been ratified, and many companies will soon offer products. In fact, a few are already out there.

The Gen 2 standard specifies operation in the 868- to 956-MHz range with ASK backscatter modulation. It includes a 96-bit code plus a 16-bit cyclic redundancy check (CRC), and it can read at a range of up to 25 ft. Its very high 640-kbit/s data rate will allow read rates of up to 1500 tags per second. EPCGlobal submitted the standard to ISO/IEC for full standard status. Also, it will initiate a testing and certification procedure to ensure the interoperability of Gen 2 products.

With prices dropping fast, RFID is finding its way into more everyday-type applications. Right now, the greatest use of RFID involves security and access. Toll-road access and automatic payment are common around the world. The E-ZPass system is deployed across the U.S. Many companies and government agencies use RFID in ID badges for building access. Other tags are used to enter parking lots and other restricted or for-pay facilities.

Many cars and trucks these days use a special RFID tag key that's encoded to work only with the ignition key lock on that car. Inserting the key causes a reader in the steering column to power up and read the key. If the key provides the right code, the car starts. Otherwise, the system immobilizes the vehicle.

Asset management and tracking is another growing use. Large valuable and high-ticket items like capital equipment are candidates for tags, so that companies and other organizations can track their property. Libraries are adopting RFID to make inventory faster and easier and to produce automated book checkout and missing-book detection. Even animal tracking is in the RFID mix: Farmers and ranchers have adopted the technology big time, and it's playing a major role in the mad cow disease problem.

The greatest application will be supply-chain management. Retailers like Walmart have already adopted RFID, but its use is only in the early stages. Right now, tags can be found on pallets, crates, and cartons instead of individual products. Individual tagging will come next as prices decline further. Some large consumer goods manufacturers like Gillette and Proctor & Gamble are experimenting with and rolling out RFID.

RFID is invaluable in inventory control. As costs decline, look for grocery stores and other retail operations to adopt it. One of the biggest users of RFID is the military thanks to a Department of Defense mandate. The military uses it for asset tracking as well as logistics worldwide. RFID helps to locate those MREs that were sent last month. They even use mobile robots with readers to monitor critical or dangerous items.

Transportation is another big potential user. Shipping and handling will be accelerated and simplified with RFID. Airline baggage, shipping companies, and containers on large ships all will benefit.

Manufacturing is yet another market. Bar codes have been used for years in manufacturing. Yet RFID can play a larger role in automation, materials handling, production sequencing, and work-in-progress monitoring. The ability to write to a tag lets manufacturers keep track of an item's status as it's processed in the manufacturing sequence.

Medical applications are growing, too. Patients receive RFID wristbands when they enter the hospital. This helps doctors and nurses ensure patients get the right treatment and medicine. Using portable readers that wirelessly connect to the hospital network, doctors and other staff can update records and specify treatments. These wristbands can reduce medical errors, simplify billing, and otherwise perform duties that may involve life or death decisions.

In the pharmaceutical industry, companies want to better track their products because they are expensive and sometimes dangerous or even illegal. By tagging pills and other medicines, companies can prevent counterfeiting, dilution, or falsely labeled products.

A growing use of RFID can be seen in the automatic-payment arena. The ultimate application would be the automatic reading of a full grocery basket and automatic billing and payment. The ExxonMobil SpeedPass, which has been around for years, lets drivers automatically pay for gasoline.

Finally, the U.S. government will begin integrating an RFID chip in all new passports starting this year. Other countries are adding them as well for automating entry to foreign locations. This could help solve immigration and terrorist problems. Eventually, you may even see RFID in your driver's license.

Expect more widespread use of RFID as costs tumble. Tags will sport built-in sensors that will detect temperature, pressure, acceleration, proximity, and even bio or chemical hazards. The U.S. government has mandated tire-pressure sensors in all vehicles by 2008, and these systems will use RFID. Also, look for location-based tagging systems where readers will have built-in GPS capability to transmit the actual location of a read item. With RFID tag pricing dropping so low, look for manufacturers to simply build in an RFID chip as routinely as they now mark products with bar codes.

EM Microelectronic has made RFID parts since 1989. While the company is readying a Gen 2 product, its older traditional tags and accessories continue to find applications.

The EM Microelectronic EM4569 125-kHz tag is optimized for animal identification (Fig. 3). It has a larger antenna. In the ear-tag format, the read range has been extended to 1 m— that's a great distance at 125 kHz. The tag complies with ISO 11784/5.

The EM4223 is a UHF tag that meets IDO 18000-6a standards. It operates in the 868- to 2400-MHz range, matching the regulations in the country of use. The 15-ft read-range tag also has anticollision capability. On top of that, it features an Application Family Identifier in a segment of memory to aid in tracking and identifying items and to distinguish between different pallets or other large packages with multiple tagged items.

While most RFID suppliers will announce products for the new Gen 2 standard, Impinj Inc. announced some of the first available chips and systems. Impinj's GrandPrix solution comprises the company's new Speedway reader platform and the Monza tag chips. The Monza tag chips, which operate in the 900-MHz band, have an 8-m read range and 6-m write range. The system permits 640-kbit/s backscatter modulation that delivers a read rate of greater than 1500 tags per second and a write rate of 15 tags per second up to 30 ft away.

Maxwell Corp. of America's Heliport RFID system targets the pharmaceutical and laboratory markets. It's designed to help automate the clinical trial and drug development process. The goal is to improve quality control, eliminate counterfeiting, improve consumer safety, and meet regulatory compliance.

These 13.56-MHz tags also feature an on-chip antenna coil. This greatly reduces the tag size, making it possible to attach the tag to very small items like test tubes, specimen bottles, vials, and prescription drug containers. The tags contain read/write memory with a data capacity from 128 bytes up to 4 kbytes. Encryption and authentication also are included. The tags work with a reader that features a read range of about 5 mm, which further helps security (Fig. 4). Engineering sample demo kits are available now for $1500.

The MLX90121 RFID transceiver from Melexis suits access control readers, portable data terminals, contactless payment terminals, and smart label printers (Fig. 5). Using ASK backscatter modulation at 10%, the 13.56-MHz chip has Manchester encoding, a 212-kbit/s data rate, and a 16-bit CRC. Eventually, it will be upgraded to 424 kbits/s and 1.6 Mbits/s, speeds supported by the ISO/IEC 14443A/B and 15693 standards. It's housed in a standard SSOP20 package and comes in 0°C to 70°C and ­40°C to 85°C versions.

A really neat new product is the MPR7000 PCMCIA Type II reader card, which plugs into a PCMCIA slot on a laptop. It's the latest in WJ Communications' line of reader products. It operates in the 902- to 928-MHz band and has an output power of 1 W. The antenna is built in, but it comes with MMCX coax connectors for external antennas. The reader fully complies with the EPCGlobal Class 0 (read), Class 1 (read and program), and Class 0+ (read and program) standards. It can be upgraded to meet the new Gen 2 standard with a firmware addition.

WJ also offers its MPR readers' dynamic link library to the public on an open-source basis. It includes sufficient code call examples and documentation so designers can rapidly develop custom reader control software.

Philips Semiconductors has had a huge presence in RFID since 1989. It makes the chips that populate other manufacturers' tags and readers. Philips' recently announced EPCGlobal UHF Gen 2 chip, an addition to the UCODE family of UHF chips, meets the forthcoming ISO 18000-6c standard. It uses an anticollision algorithm and can deliver up to 1600 reads per second under U.S. regulations and up to 600 reads per second under European regulations.

The UCODE EPC G2 chip is scheduled for mass production in the third quarter of 2005. Target price is $0.09. Philips also is a major supplier of proximity chips for use in smart cards. Called the MIFARE series, this line conforms to the ISO 14443 13.56-MHz standard.

Finally, Texas Instruments is another company that has bandied about the RFID realm for a long time. Bill Allen, director of the Strategic Alliance of TI, says the company has been doing RFID for 15 years. It got into the business with 125-kHz cattle ID tags and toll-collection systems. Many car manufacturers use TI's antitheft key tags. In fact, TI offers a huge line of chips, tags, readers, and accessories for almost any application. Soon the company will announce Gen 2 products.

When implementing an RFID system, the biggest challenge involves the data that it collects. The problem can be solved via middleware. It is software that helps designers sort out and use the data with existing applications software packages from companies like Oracle and SAP.

One example of middleware, Dat-Link from Acsis Inc., runs on a server and contains drivers for most RFID readers. It collects the data and stores, filters, aggregates, and normalizes it. It then links to the applications software, where the real work is done.

According to Steve Brown, executive vice president of Marketing and Business Development at Acsis, middleware like this can help make an RFID system function on a real-time basis by making critical tracking data available almost immediately. Such middleware is a key part of the RFID systems design process.

See "RFID FAQs," Drill Deeper 1027, at www.elecdesign.com for answers to key questions about designing and implementing an RFID system.

Acsis Inc.

American National Standards Institute

EM Microelectronic


Federal Communications Commission

Impinj Inc.


Maxwell Corporation of America
[email protected]

Melexis Semiconductor

Philips Semiconductors

Texas Instruments

WJ Communications Inc.

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