इस ब्लॉग्स को सृजन करने में आप सभी से सादर सुझाव आमंत्रित हैं , कृपया अपने सुझाव और प्रविष्टियाँ प्रेषित करे , इसका संपूर्ण कार्य क्षेत्र विश्व ज्ञान समुदाय हैं , जो सभी प्रतियोगियों के कॅरिअर निर्माण महत्त्वपूर्ण योगदान देगा ,आप अपने सुझाव इस मेल पत्ते पर भेज सकते हैं - chandrashekhar.malav@yahoo.com
RFID tags can also be quite large. The semipassive RFID tag used in the Fast-
Lane and E-ZPass electronic toll collection systems is the size of a paperback
book and includes an antenna and a five-year battery. The battery gives the system
a longer read range and also makes reads more reliable—at least until the
battery dies. In practice, the instrumented toll crossings have a large light that
flashes green if the tag is read successfully, red if no tag is detected, and amber
or yellow if the tag cannot be read properly. When the light flashes amber, the
driver is supposed to call the program’s administrator and arrange to have the
tag sent in for service.
RFID tags can be promiscuous, in which case they will communicate with any
reader. Alternatively, they can be secure, requiring that the reader provide a
password or other kind of authentication credential before the tags respond.
The vast majority of RFID tags that have been deployed are promiscuous. Not
only are these tags cheaper, but the systems also are much easier to manage.
Systems that employ passwords or encryption codes require that the codes be
distributed in advance and properly controlled. This is an exceedingly difficult
management problem.
The simplest RFID chips contain only a serial number—think of this as a 64-
bit or 96-bit block of read-only storage. Although the serial number can be
burned into the chip by the manufacturer, it is also common for the chips to be
programmed in the field by the end user. Some chips will accept only a single
serial number, while other chips allow the serial number to be changed after it
is burned in. More sophisticated RFID chips can contain read-write memory
that can be programmed by a reader. Chips can also have sensors, an example
of which is an air pressure sensor to monitor the inflation of a tire. The chips
might store the results of the sensor in a piece of read-write memory or simply
report the sensor’s reading to the RFID reader. Chips can also have a selfdestruct,
or “kill” feature. This is a special code that, when received by the chip,
causes the chip to no longer respond to commands. For financial applications,
the full capabilities of smart cards have been combined with the wireless protocols
and passive powering used in RFID. The result is a class of high-capability
RFID tags also called contactless smart cards.
RFID tags can interfere with each other. When multiple tags are present in a
reader’s field, the reader may be unable to decipher the signals from the tags.
For many applications, such as raising the gate in a parking lot, this is not a
problem. The systems are optimized so that only one tag is within range at a
time. However, for other applications, reading multiple tags at once is essential.
For these applications, the tags need to support either an anticollision protocol
or, more commonly, a singulation protocol. A singulation protocol allows a
reader to determine that multiple tags are visible and to iterate through the
tags, getting them to take turns responding so that each may be read without
interference from the others.
Electronic Product Code (EPC) tags are a special kind of tag that follows the
EPC standard developed by the MIT Auto-ID Center and is now managed by
the trade organization EPCglobal. Sanjay Sarma, cofounder of the Auto-ID
Center, discusses the history of the EPC standard in Chapter 3.
EPCglobal has defined a series of RFID tag “classes” and “generations” of
RFID devices (see Tables 2.1 and 2.2).
Table 2.1 EPC RFID Classes
EPC Device Class Definition Programming
Class 0 “Read only” passive tags Programmed by the
manufacturer
Class 1 “Write-once, read-many”
passive tags
Programmed by the customer;
cannot be reprogrammed
Class 2 Rewritable passive tags
Reprogrammable
Class 3 Semipassive tags
Class 4 Active tags
Class 5 Readers
Table 2.2 EPC RFID Chip Generations
Feature Generation 1 Generation 2
Frequency 860–930MHz 860–960MHz
Memory capacity 64 or 96 bits 96–256 bits
Field-programmability Yes Yes
Reprogrammability Class 0—read only
Class 1—write once/ready
many
NA
Other features NA Faster and more reliable
reads than Generation 1
Better compliance with
other global standards
Readers
The RFID reader sends a pulse of radio energy to the tag and listens for the
tag’s response. The tag detects this energy and sends back a response that contains
the tag’s serial number and possibly other information as well.
In simple RFID systems, the reader’s pulse of energy functioned as an on-off
switch; in more sophisticated systems, the reader’s RF signal can contain commands
to the tag, instructions to read or write memory that the tag contains,
and even passwords.
Historically, RFID readers were designed to read only a particular kind of tag,
but so-called multimode readers that can read many different kinds of tags are
becoming increasingly popular.
RFID readers are usually on, continually transmitting radio energy and awaiting
any tags that enter their field of operation. However, for some applications,
this is unnecessary and could be undesirable in battery-powered devices that
need to conserve energy. Thus, it is possible to configure an RFID reader so
that it sends the radio pulse only in response to an external event. For example,
most electronic toll collection systems have the reader constantly powered up
so that every passing car will be recorded. On the other hand, RFID scanners
used in veterinarian’s offices are frequently equipped with triggers and power
up the only when the trigger is pulled.
Like the tags themselves, RFID readers come in many sizes. The largest readers
might consist of a desktop personal computer with a special card and multiple
antennas connected to the card through shielded cable. Such a reader
would typically have a network connection as well so that it could report tags
that it reads to other computers. The smallest readers are the size of a postage
stamp and are designed to be embedded in mobile telephones.
Antennas and Radio
The RFID physical layer consists of the actual radios and antennas used to couple
the reader to the tag so that information can be transferred between the two.
Radio energy is measured by two fundamental characteristics: the frequencies at
which it oscillates and the strength or power of those oscillations. Commercial
FM broadcast stations in the United States transmit with energy at a frequency
between 88MHz and 108MHz, or 1 million isolations per second. The AM
spectrum, by contrast, transmits at 500,000 to 1,500,000 oscillations per second,
or between 500KHz and 1500KHz. Microwave ovens cook with RF
energy that vibrates 2.4 billion times each second, which is 2.4GHz.
Most RFID systems use the so-called unlicensed spectrum, which is a specific
part of the spectrum set aside for use without a radio license. Popular bands
are the low-frequency (LF) band at 125–134.2KHz, the high-frequency band
at 13.56MHz, the ultrahigh-frequency (UHF) band at 915MHz (in North
America; varies in other regions), and the industrial, scientific, and medical
(ISM) band at 2.4GHz.
The names of the LF, HF, and UHF bands reflect the history of radio’s development:
Radio systems first transmitted at the lower frequencies and moved to
the higher frequencies only as technology advanced. For this reason, lowerfrequency
radio gear was traditionally cheaper than equipment that operated at
higher frequencies. Today, however, the difference in radio prices more often
reflects market sizes, the cost of patents and other licenses, and the result of
subsidies or cross-marketing agreements from equipment manufacturers.
Radio energy moves in waves, and each radio wave has not only a frequency but
also a wavelength. The wavelength is like the distance between two wave crests
on the ocean. With radio energy, the wavelength of a radio wave multiplied by
its frequency is equal to the speed of light: 3 × 108 meters per second (roughly
equal to 186,000 miles per second). The size of waves for each of the unlicensed
bands is presented in Table 2.3.
Building proximity cards, automobile immobilizer chips, and implantable RFID
ampoules tend to operate in the LF band. The FDA has adopted the HF band for
RFID systems used for prescription drugs. The EPC system operates in the HF
and UHF bands, although early deployments are favoring the UHF band.
When analyzing the energy that is radiated from an antenna, electrical engineers
divide the field into two parts: the near field, which is the part of radiation
that is within a small number of wavelengths of the antenna, and the far field,
which is the energy that is radiated beyond the near field. Because the wavelength
of LF and HF devices tends to be much larger than the ranges at which
RFID systems typically operate, these systems operate in the near field, while
UFH and ISM systems operate in the far field.
As with most radio systems, the larger the antenna on the reader and the tag,
the better an RFID system will work because large antennas are generally more
efficient at transmitting and receiving radio power than are small antennas.
Thus, a large antenna on the reader means that more power can be sent to the
RFID tag and more of the tag’s emitted energy can be collected and analyzed. A
large antenna on the tag means that more of the power can be collected and
used to power the chip. Likewise, a large antenna on the chip means that more
power can be transmitted back to the reader.
The Network
Most RFID tags transmit a number and nothing more. So what does a typical
reader do with a typical 96-bit number like 79,228,162,514,264,337,593,
543,950,335?6 In most cases, the reader sends it to a computer.
What the computer does with the RFID code depends on the application.
With an access-control system, the computer might look to see if the RFID
number is present on a list of numbers that’s allowed access to a particular door
or location. If the number is present, the computer might energize a solenoid
that would unlock the door. In the case of the Mobil Speedpass system, the tag’s
serial number and its response to the random challenge that was generated by
the reader are sent over Mobil’s payment network. If the challenge response
matches the token, Mobil’s computers approve the user of the customer’s
credit-card number to complete the transaction.
With the EPC, the serial number will be sent to a network of computers that
make up the Object Name Service (ONS), a large distributed database that will
track a variety of pieces of information about objects that have been assigned
EPC codes. The database consists of both central “root” servers and distributed
servers at each company that creates products labeled with EPC tags.
Given any EPC code, the root servers would tell a computer which company’s
servers to go to, and then the company’s servers would explain what the EPC
code means. The overall design of the ONS is similar to that of another distributed
database, the Domain Name System (DNS), which maps Internet hostnames
to Internet Protocol (IP) addresses. In fact, VeriSign, the company that
has the contract to run the global DNS, was also awarded the contract by EPCglobal
to run the ONS.7
6. This number is actually 296–1, the largest number that can be represented with an unsigned
96-bit integer.
7. “VeriSign to Run EPC Directory,” RFID Journal, January 13, 2004. www.rfidjournal
.com/article/articleview/735/1/1.
Here’s how it might work. A computer at Wal-Mart that receives an EPC code
would send that code to one of the ONS root servers and learn that the particular
code space is operated by a manager at Gillette. The computer might then
query the ONS server operated by Gillette and learn that the code is for a box
of Mach3 razors, which was manufactured on a particular date and is authorized
for sale in the United States.
Coupling, Range, and Penetration
As mentioned previously, active and passive RFID systems have very different
reading ranges. With batteries and high-gain antennas, active RFID systems
have ranges roughly equivalent to those of any other system operating under
the rules for unlicensed radio systems. In the United States, for example, an
unlicensed system can transmit with up to 1 watt of power; under these conditions,
a signal can be received over a mile if directional antennas are used and
there are no obstructions.
Coupling
While it is possible to build RFID systems such that both the tag and reader
contain a radio transmitter and a radio receiver, this method of operation is
ideal only for active systems attempting to communicate over the longest distances.
Because placing and powering a transmitter on the tag is an expensive
proposition, passive tag systems are usually chosen for applications that are
extremely sensitive to the cost of the tag. Either the passive tag will have to
have some form of energy storage, for example a capacitor, to provide power
when the reader stops transmitting and starts receiving or the reader must
always transmit, meaning the tag has to reply on a different frequency.
Instead, passive RFID systems typically couple the transmitter to the receiver
with either load modulation or backscatter, depending on whether the tags are
operating in the near or far field of the reader, respectively.
In the near field, a tag couples with a reader via electromagnetic inductance.
The antennas of both the reader and the tag are formed as coils, using many
turns of small gauge wire. The current in the reader’s coil creates a magnetic
field. This field, in turn, induces a current in the coil of the tag. A transformer
works by the same principle, and in essence the coils of the reader and tag
together form a transformer. The reader communicates with the tag by modulating
a carrier wave, which it does by varying the amplitude, phase, or frequency
of the carrier, depending on the design of the RFID system in question.
This modulation can be directly detected as current changes in the coil of the
tag. The tag communicates with the reader by varying how much it loads its
antenna. This in turn affects the voltage across the reader’s antenna. By switching
the load on and off rapidly, the tag can establish its own carrier frequency
(really a subcarrier) that the tag can in turn modulate to communicate its reply.
Tags that operate in the far field (UHF and ISM bands) couple with their readers
using backscatter. Backscatter results when an electromagnetic wave hits a
surface and some of energy of that wave is reflected back to the transmitter, and
it is one of the fundamental physics behind RADAR. The amount of energy
reflected depends on how well the surface resonates with the frequency of the
electromagnetic wave. RFID tags that use backscatter to reply to their readers
have antennas that are designed to resonate well with the carrier put out by the
reader. The tag can throw a switch that changes the resonant properties of its
antenna so that it reflects poorly instead, thus creating a pattern in its backscatter
that is detected at the reader. The return communication is encoded in the
backscatter pattern.
There is a third, less common type of coupling between reader and tag: electrostatic
coupling. With electrostatic coupling, the reader and tag antennas are
charged plates. Adding electrons to the plate on the reader will push electrons
off the plate onto the tag, and vice versa. The plate area determines range with
electrostatic coupling. An advantage to electrostatic coupled systems is that the
antenna patches can be printed with conductive ink, making their design very
flexible and inexpensive.
Reading Range of Passive RFID Systems
Passive systems operate under far more limiting circumstances. To be read, a
passive RFID tag must be provided with sufficient power to both run the electronics
and generate a return signal that the reader can detect. Thus, the read
range of a passive system depends on
Pr: The reader transmitter power (typically 1 watt)
Sr: The reader receiver sensitivity (typically –80dBm or 10–11 watts)
Gr: The reader antenna gain (typically 6dBi)
Gt: The tag antenna gain (1dBi is an omnidirectional antenna)
Pt: The tag’s power requirement (typically 100 microwatts or –10dBm)
Et: The tag modulator efficiency (typically –20dB)8
A system can be limited either by the power available to power the tag or by the
reader’s ability to detect the tag’s transmissions. Since the goal of RFID systems
8. This example was presented by Matthew Reynolds of ThingMagic at the MIT Privacy Workshop
in November 2003.
is to make the chips as cheap as possible, lots of money can be invested into
readers to make them very sensitive. Thus, a well-designed RFID system will
be limited by the power available to the tag.
The power available to the tag, Pt, is given by the formula:
Pt = Pr × Gr × Gt × λ
(4π)2 d2
Where λ is the wavelength of the radio waves used by the system.
Crunching the numbers for a 915MHz system, dmax = 5.8 meters. In other
words, 19.4 feet is the greatest distance that a typical EPC tag can be read by a
reader with the parameters given previously. On the other hand, if someone
could build a tag that could be powered with only 1 microwatt—100 times better
than is possible today—dmax would increase to 194 meters. However, the
return signal would have energy of –99dBm because the RFID tag would be
transmitting its limited amount of power in all directions. A signal at –99dBm is
on the edge of what can be detected with even the best amplifier and radio available
today. (The noise power in 50 ohms at 500KHz is –109dBm; with a practical
receiver that has an NF of 3dB, the power of noise is raised to –106dBm.
Distinguishing a –99dBm signal from a –106dBm noise floor requires a
receiver that has a signal-to-noise ratio of just 7dB.)
One way to improve the reading range of such a system is to use a larger
antenna that can collect more power from the tag. For example, a proximity
card system manufactured by Indala (www.indala.com) has a read range of
eight inches with the company’s lowest-cost reader, but that range jumps to
24 inches with the company’s more expensive reader that has a larger antenna
and more expensive electronics. Researchers at the MIT Computer Science
and Artificial Intelligence Laboratory (CSAIL) have created a one-of-a-kind
reader with a very large antenna that can read cards more than four feet away.
Although greater reading ranges are theoretically possible, background noise
and other real-world factors make it difficult to construct readers with significantly
longer range.
Penetration, Screening, and Shielding
The calculations in the previous section assume that both the RFID reader
and the tag are in a vacuum. This is rarely the case, of course. Most tags are
read through the air, but sometimes there is intervening material, such as
water, plastics, cans, or people. As with all radio signals, the range of an RFID
system is dramatically affected by the environment through which the radio
signals travel.
Two of the most potent barriers for radio signals in the HF and UHF regions
of the spectrum are water and metal, and they can profound impacts on RFID
in typical operations. For example, cardboard is normally transparent to radio
waves. But if a cardboard box picks up moisture, the water in the cardboard will
attenuate the radio signal from an RFID reader, perhaps to the point that the
RFID tag inside the box will not receive enough power to send back a response.
Metal blocks radio waves, so there’s no hope of reading a tag inside a can. What
about a tag that’s on a can? The answer depends on where the reader is in relationship
to the tag and the can, how far away the tag is from the can, and even
what kind of antenna is built into the tag. In some cases, the can will block the
radio waves, but in other cases, the can will focus the waves and make it easier
to read the tag. This is especially a possibility if several cans are packed tightly
together, as might be the case on a supermarket shelf.
Another phenomenon to be considered is dielectric coupling. Dielectric coupling
can take place between antennas and dielectric materials like cardboard
or, in some cases, the human body. Using this coupling will result in detuning
the antenna, which will make the antenna less efficient and, consequently, will
decrease read range. This is why some proximity cards can be read if they are in
a wallet but can’t be read if that wallet is in a person’s pocket. In other cases,
two proximity cards placed next to each other can cause mutual interference
because of this kind of coupling.
If the intention is to shield an RFID tag against an RFID reader, it is quite
easy to do. A single layer of aluminum foil is sufficient to shield most lowpower
RF devices. For RFID, aluminum needs to be only 27 microns thick,
according to Matthew Reynolds at ThingMagic (www.thingmagic.com), to
effectively shield a tag. And just 1mm of dilute salt water (also a conductor)
provides similar protection.
All of this math and physics have caused some interesting reflections by journalists.
In Wired News, for instance, Mark Baard wrote this technically accurate
lead for his article about the MIT RFID Privacy Workshop:
You may need to read the following sentence twice: Aluminum foil
hats will block the signals emitted by the radio tags that will replace
bar-code labels on consumer goods.
That is, of course, if you place your tin-foil hat between the radio
tag and the device trying to read its signal.9
RFID Applications
In this section, we look at a few specific applications of RFID technology that
have been deployed and see how the technical underpinnings of the technology
have a direct impact on the applications.
Supply Chain Visibility and Inventory
Management
The largest use of RFID anticipated within the next ten years is in tags to track the
movement of consumer product goods from the manufacturer to the point of sale.
The international manufacture and movement of goods is a huge business.
Many items sold in the United States are actually manufactured in China,
loaded into containers, sent by truck to a port, and then shipped on a freighter
to a port in the United States. Once in the country, the containers are sent to
distribution points where they are unloaded, repackaged onto trucks, and sent
to stores such as Wal-Mart, where their contents are unloaded, put on store
shelves, and sold to consumers.
At least, that’s the way that the process is supposed to work. In practice, many
things can go wrong. For example, boxes that are supposed to be loaded into
one container can be accidentally loaded into another one and sent to the
wrong customer. Product can be lost in port for days—or weeks—or sent to the
wrong distribution center. Boxes can be lost in distribution centers or, even
worse, sent to a store and then misplaced in a storage room. As a result, a product
could be out of stock on the store shelves, which means that a customer
who wants to buy a particular razor or battery won’t be able to do so. The number
and cost of lost sales can add up.
Equally troublesome for companies like Gillette are product counterfeiting and
product diversion. This problem starts in China, where a look-alike product can
be manufactured in “bandit” factories. (Sometimes a bandit factory is authorized
to make genuine goods but creates extra product that it doesn’t report to the U.S.
company.) Legitimate product with packaging in Chinese and designed to be sold
9. Baard, M. “Is RFID Technology Easy to Foil?” Wired News, November 18, 2003.
in Hong Kong or Taiwan at a low price can be sent to New York and sold on the
so-called gray market in which the intermediaries reap big profits and the American
consumers get their razors or batteries at a lower price, but the brand owner
misses out on the higher profits that are supposed to result from U.S. sales. And
sometimes there is just out-and-out theft: Cases of product disappear out of
“sealed” containers or “fall off” the back of trucks.
Finally there is shoplifting, increasingly an activity of organized gangs who
empty stores of dozens or hundreds of packages of razors or batteries at a clip.
Sometimes insiders facilitate shoplifting and receive a commission or cut from
the perpetrators. Shoplifting causes many problems, of which the actual theft is
just one. Consumers who see shoplifting taking place feel uncomfortable and
may not return to the store. Shoplifting also results in out-of-stock conditions
that are not detected by the store’s inventory management system because the
items were never actually sold.
It is into this supply chain that RFID is likely to make the largest impact over the
next decade. If every package of razors or batteries manufactured in China had its
own embedded and individually serialized RFID tag, it would be possible to track
it as it moves through the entire supply chain. RFID readers at the factory would
verify that the cases left the factory and got onto the truck. RFID readers built
into the shipping container would verify that the products left the truck and were
put in the container. RFID readers in the U.S. port could verify that every package
coming into the country contained product that was both legitimate and
licensed for sale in the United States. Readers at the distribution center would
record the arrival of every package and note which packages went to which
stores. In those stores, RFID readers would be on every shelf. They would keep
track of which product was in the back rooms and which was on the store shelves.
RFID readers on store shelves would give stores a degree of visibility that today
can only be dreamed of. For starters, they would pick up when product was
mis-shelved—perhaps when a consumer picked up a box of razors, had a
change of heart, and put it down on another shelf a few minutes later. The tags
could detect “out-of-stock” conditions caused by theft. It would even be possible
to have the system generate an alert when there is a suspicious removal of
product, such as the simultaneous removal of 12 razor packages, and put a
notation on the surveillance video.
Once this RFID infrastructure is deployed, it could be used for additional purposes.
For example, a special light-sensing RFID tag might detect if the container
was opened between the times that it left a port in China and arrived at a
port in San Francisco; such containers could be subject to extra scrutiny by the
Department of Homeland Security or simply rejected out of hand. The Customs
Service, meanwhile, could automatically impound and destroy any products that
garfinkel.book Page 28 Thursday, June 2, 2005 11:56 PM
UNDERSTANDING RFID
TECHNOLOGY
Introduction
his chapter presents a technical introduction to the RFID, the Electronic
Product Code (EPC), and the Object Name Service (ONS). It then looks at
two specific RFID applications that have been fielded over the past ten years.
RFID Technology
Most histories of RFID trace the technology back to the radio-based identification
system used by Allied bombers during World War II. Because bombers
could be shot down by German anti-aircraft artillery, they had a strong incentive
to fly bombing missions at night because planes were harder for gunners
on the ground to target and shoot down. Of course, the Germans also took
advantage of the cover that darkness provided. Early Identification Friend or
Foe (IFF) systems made it possible for Allied fighters and anti-aircraft systems
to distinguish their own returning bombers from aircraft sent by the enemy.
These systems, and their descendants today, send coded identification signals
by radio: An aircraft that sends the correct signal is deemed to be a friend, and
the rest are foe. Thus, radio frequency identification was born.
1. Henry Holtzman is a research scientist at the MIT Media Laboratory and the founder of
Presto Technologies.
Shortly after the war, an engineer named Harry Stockman realized that it is
possible to power a mobile transmitter completely from the strength of a
received radio signal. His published paper “Communication by Means of
Reflected Power” in the Proceedings of the IRE2 introduced the concept of passive
RFID systems.
Work on RFID systems as we know them began in earnest in the 1970s. In
1972, Kriofsky and Kaplan filed a patent application for an “inductively coupled
transmitter-responder arrangement.”3 This system used separate coils for
receiving power and transmitting the return signal. In 1979, Beigel filed a new
application for an “identification device” that combined the two antennas;
many consider his application by to be the landmark RFID application because
it emphasized the potentially small size of RFID devices.4
In the 1970s, a group of scientists at the Lawrence Livermore Laboratory
(LLL) realized that a handheld receiver stimulated by RF power could send
back a coded radio signal. Such a system could be connected to a simple computer
and used to control access to a secure facility. They developed this system
for controlling access to sensitive materials at nuclear weapons sites.
Today we would call this Livermore system an example of security through
obscurity: What made the system secure was that nobody else had a radio capable
of receiving the stimulating radio signal and sending back the properly
coded response. But at the time it was one of the most secure access control
systems available. The scientists left LLL a few years later and created their
own company to commercialize the technology. This system ultimately became
one of the first building entry systems based on proximity technology and the
first commercial use of RFID.
The Elements of an RFID System
RFID systems fundamentally consist of four elements: the RFID tags themselves,
the RFID readers, the antennas and choice of radio characteristics, and
the computer network (if any) that is used to connect the readers.5
2. Harry Stockman, “Communication by Means of Reflected Power,” Proceedings of the IRE,
pp. 1196–1204, October 1948.
3. Kriofsky, T.A., Kaplan, L.M.: 1975. U.S. Patent No. 3859624
4. Beigel, M. 1982. U.S. Patent No. 4333072
5. Much of the information in this chapter draws on technical information presented in Finkenzeller,
K. RFID-Handbook, Second Edition, Wiley & Sons, Ltd., April 2003. Translated from the
third German edition by Wadding, R. www.rfid-handbook.de/english/index.html.
RFID Tags
The tag is the basic building block of RFID. Each tag consists of an antenna
and a small silicon chip that contains a radio receiver, a radio modulator for
sending a response back to the reader, control logic, some amount of memory,
and a power system. The power system can be completely powered by the
incoming RF signal, in which case the tag is known as a passive tag. Alternatively,
the tag’s power system can have a battery, in which case the tag is known
as an active tag.
The primary advantages of active tags are their reading range and reliability.
With the proper antenna on the reader and the tag, a 915MHz tag can be read
from a distance of 100 feet or more. The tags also tend to be more reliable
because they do not need a continuous radio signal to power their electronics.
Passive tags, on the other hand, can be much smaller and cheaper than active
ones because they don’t have batteries. Another advantage is their longer shelf
life: Whereas an active tag’s batteries may last only a few years, a passive tag
could in principle be read many decades after the chip was manufactured.
Between the active and the passive tags are the semi-passive tags. These tags have a
battery, like active tags, but still use the reader’s power to transmit a message back
to the RFID reader using a technique known as backscatter. These tags thus have
the read reliability of an active tag but the read range of a passive tag. They also
have a longer shelf life than a tag that is fully active.
Tags come in all shapes and sizes. The smallest tag that has ever been produced
is the Hitachi mu-chip, which is less than 0.4mm on a side. Designed to be
embedded in a piece of paper and used for tracking documents printed in an
office environment, the mu-chip can be read only at a distance of a few centimeters.
Of course, the mu-chip is a passive tag. With a larger antenna it could
have a significantly longer reading range, but that would defeat its purpose.
Other small tags are the implantable tags the size of a grain of rice manufactured
by VeriChip. Like the mu-chip, these passive tags have a very limited
reading range; their intended application is to give machine-readable serial
numbers to people. The company says that the chips can be used to authenticate
people in high-security environments—unlike passwords, the implanted
chips can’t be easily shared—and in hospitals, where staff occasionally mix up
patients and give them the wrong treatments. Implantable chips might also
work to identify wandering Alzheimer’s patients who go out without any identification
or cognizance of their location or destination. We’ll come back to the
topic of implantable chips later in this chapter.
Lane and E-ZPass electronic toll collection systems is the size of a paperback
book and includes an antenna and a five-year battery. The battery gives the system
a longer read range and also makes reads more reliable—at least until the
battery dies. In practice, the instrumented toll crossings have a large light that
flashes green if the tag is read successfully, red if no tag is detected, and amber
or yellow if the tag cannot be read properly. When the light flashes amber, the
driver is supposed to call the program’s administrator and arrange to have the
tag sent in for service.
RFID tags can be promiscuous, in which case they will communicate with any
reader. Alternatively, they can be secure, requiring that the reader provide a
password or other kind of authentication credential before the tags respond.
The vast majority of RFID tags that have been deployed are promiscuous. Not
only are these tags cheaper, but the systems also are much easier to manage.
Systems that employ passwords or encryption codes require that the codes be
distributed in advance and properly controlled. This is an exceedingly difficult
management problem.
The simplest RFID chips contain only a serial number—think of this as a 64-
bit or 96-bit block of read-only storage. Although the serial number can be
burned into the chip by the manufacturer, it is also common for the chips to be
programmed in the field by the end user. Some chips will accept only a single
serial number, while other chips allow the serial number to be changed after it
is burned in. More sophisticated RFID chips can contain read-write memory
that can be programmed by a reader. Chips can also have sensors, an example
of which is an air pressure sensor to monitor the inflation of a tire. The chips
might store the results of the sensor in a piece of read-write memory or simply
report the sensor’s reading to the RFID reader. Chips can also have a selfdestruct,
or “kill” feature. This is a special code that, when received by the chip,
causes the chip to no longer respond to commands. For financial applications,
the full capabilities of smart cards have been combined with the wireless protocols
and passive powering used in RFID. The result is a class of high-capability
RFID tags also called contactless smart cards.
RFID tags can interfere with each other. When multiple tags are present in a
reader’s field, the reader may be unable to decipher the signals from the tags.
For many applications, such as raising the gate in a parking lot, this is not a
problem. The systems are optimized so that only one tag is within range at a
time. However, for other applications, reading multiple tags at once is essential.
For these applications, the tags need to support either an anticollision protocol
or, more commonly, a singulation protocol. A singulation protocol allows a
reader to determine that multiple tags are visible and to iterate through the
tags, getting them to take turns responding so that each may be read without
interference from the others.
Electronic Product Code (EPC) tags are a special kind of tag that follows the
EPC standard developed by the MIT Auto-ID Center and is now managed by
the trade organization EPCglobal. Sanjay Sarma, cofounder of the Auto-ID
Center, discusses the history of the EPC standard in Chapter 3.
EPCglobal has defined a series of RFID tag “classes” and “generations” of
RFID devices (see Tables 2.1 and 2.2).
Table 2.1 EPC RFID Classes
EPC Device Class Definition Programming
Class 0 “Read only” passive tags Programmed by the
manufacturer
Class 1 “Write-once, read-many”
passive tags
Programmed by the customer;
cannot be reprogrammed
Class 2 Rewritable passive tags
Reprogrammable
Class 3 Semipassive tags
Class 4 Active tags
Class 5 Readers
Table 2.2 EPC RFID Chip Generations
Feature Generation 1 Generation 2
Frequency 860–930MHz 860–960MHz
Memory capacity 64 or 96 bits 96–256 bits
Field-programmability Yes Yes
Reprogrammability Class 0—read only
Class 1—write once/ready
many
NA
Other features NA Faster and more reliable
reads than Generation 1
Better compliance with
other global standards
Readers
The RFID reader sends a pulse of radio energy to the tag and listens for the
tag’s response. The tag detects this energy and sends back a response that contains
the tag’s serial number and possibly other information as well.
In simple RFID systems, the reader’s pulse of energy functioned as an on-off
switch; in more sophisticated systems, the reader’s RF signal can contain commands
to the tag, instructions to read or write memory that the tag contains,
and even passwords.
Historically, RFID readers were designed to read only a particular kind of tag,
but so-called multimode readers that can read many different kinds of tags are
becoming increasingly popular.
RFID readers are usually on, continually transmitting radio energy and awaiting
any tags that enter their field of operation. However, for some applications,
this is unnecessary and could be undesirable in battery-powered devices that
need to conserve energy. Thus, it is possible to configure an RFID reader so
that it sends the radio pulse only in response to an external event. For example,
most electronic toll collection systems have the reader constantly powered up
so that every passing car will be recorded. On the other hand, RFID scanners
used in veterinarian’s offices are frequently equipped with triggers and power
up the only when the trigger is pulled.
Like the tags themselves, RFID readers come in many sizes. The largest readers
might consist of a desktop personal computer with a special card and multiple
antennas connected to the card through shielded cable. Such a reader
would typically have a network connection as well so that it could report tags
that it reads to other computers. The smallest readers are the size of a postage
stamp and are designed to be embedded in mobile telephones.
Antennas and Radio
The RFID physical layer consists of the actual radios and antennas used to couple
the reader to the tag so that information can be transferred between the two.
Radio energy is measured by two fundamental characteristics: the frequencies at
which it oscillates and the strength or power of those oscillations. Commercial
FM broadcast stations in the United States transmit with energy at a frequency
between 88MHz and 108MHz, or 1 million isolations per second. The AM
spectrum, by contrast, transmits at 500,000 to 1,500,000 oscillations per second,
or between 500KHz and 1500KHz. Microwave ovens cook with RF
energy that vibrates 2.4 billion times each second, which is 2.4GHz.
Most RFID systems use the so-called unlicensed spectrum, which is a specific
part of the spectrum set aside for use without a radio license. Popular bands
are the low-frequency (LF) band at 125–134.2KHz, the high-frequency band
at 13.56MHz, the ultrahigh-frequency (UHF) band at 915MHz (in North
America; varies in other regions), and the industrial, scientific, and medical
(ISM) band at 2.4GHz.
The names of the LF, HF, and UHF bands reflect the history of radio’s development:
Radio systems first transmitted at the lower frequencies and moved to
the higher frequencies only as technology advanced. For this reason, lowerfrequency
radio gear was traditionally cheaper than equipment that operated at
higher frequencies. Today, however, the difference in radio prices more often
reflects market sizes, the cost of patents and other licenses, and the result of
subsidies or cross-marketing agreements from equipment manufacturers.
Radio energy moves in waves, and each radio wave has not only a frequency but
also a wavelength. The wavelength is like the distance between two wave crests
on the ocean. With radio energy, the wavelength of a radio wave multiplied by
its frequency is equal to the speed of light: 3 × 108 meters per second (roughly
equal to 186,000 miles per second). The size of waves for each of the unlicensed
bands is presented in Table 2.3.
Building proximity cards, automobile immobilizer chips, and implantable RFID
ampoules tend to operate in the LF band. The FDA has adopted the HF band for
RFID systems used for prescription drugs. The EPC system operates in the HF
and UHF bands, although early deployments are favoring the UHF band.
When analyzing the energy that is radiated from an antenna, electrical engineers
divide the field into two parts: the near field, which is the part of radiation
that is within a small number of wavelengths of the antenna, and the far field,
which is the energy that is radiated beyond the near field. Because the wavelength
of LF and HF devices tends to be much larger than the ranges at which
RFID systems typically operate, these systems operate in the near field, while
UFH and ISM systems operate in the far field.
As with most radio systems, the larger the antenna on the reader and the tag,
the better an RFID system will work because large antennas are generally more
efficient at transmitting and receiving radio power than are small antennas.
Thus, a large antenna on the reader means that more power can be sent to the
RFID tag and more of the tag’s emitted energy can be collected and analyzed. A
large antenna on the tag means that more of the power can be collected and
used to power the chip. Likewise, a large antenna on the chip means that more
power can be transmitted back to the reader.
The Network
Most RFID tags transmit a number and nothing more. So what does a typical
reader do with a typical 96-bit number like 79,228,162,514,264,337,593,
543,950,335?6 In most cases, the reader sends it to a computer.
What the computer does with the RFID code depends on the application.
With an access-control system, the computer might look to see if the RFID
number is present on a list of numbers that’s allowed access to a particular door
or location. If the number is present, the computer might energize a solenoid
that would unlock the door. In the case of the Mobil Speedpass system, the tag’s
serial number and its response to the random challenge that was generated by
the reader are sent over Mobil’s payment network. If the challenge response
matches the token, Mobil’s computers approve the user of the customer’s
credit-card number to complete the transaction.
With the EPC, the serial number will be sent to a network of computers that
make up the Object Name Service (ONS), a large distributed database that will
track a variety of pieces of information about objects that have been assigned
EPC codes. The database consists of both central “root” servers and distributed
servers at each company that creates products labeled with EPC tags.
Given any EPC code, the root servers would tell a computer which company’s
servers to go to, and then the company’s servers would explain what the EPC
code means. The overall design of the ONS is similar to that of another distributed
database, the Domain Name System (DNS), which maps Internet hostnames
to Internet Protocol (IP) addresses. In fact, VeriSign, the company that
has the contract to run the global DNS, was also awarded the contract by EPCglobal
to run the ONS.7
6. This number is actually 296–1, the largest number that can be represented with an unsigned
96-bit integer.
7. “VeriSign to Run EPC Directory,” RFID Journal, January 13, 2004. www.rfidjournal
.com/article/articleview/735/1/1.
Here’s how it might work. A computer at Wal-Mart that receives an EPC code
would send that code to one of the ONS root servers and learn that the particular
code space is operated by a manager at Gillette. The computer might then
query the ONS server operated by Gillette and learn that the code is for a box
of Mach3 razors, which was manufactured on a particular date and is authorized
for sale in the United States.
Coupling, Range, and Penetration
As mentioned previously, active and passive RFID systems have very different
reading ranges. With batteries and high-gain antennas, active RFID systems
have ranges roughly equivalent to those of any other system operating under
the rules for unlicensed radio systems. In the United States, for example, an
unlicensed system can transmit with up to 1 watt of power; under these conditions,
a signal can be received over a mile if directional antennas are used and
there are no obstructions.
Coupling
While it is possible to build RFID systems such that both the tag and reader
contain a radio transmitter and a radio receiver, this method of operation is
ideal only for active systems attempting to communicate over the longest distances.
Because placing and powering a transmitter on the tag is an expensive
proposition, passive tag systems are usually chosen for applications that are
extremely sensitive to the cost of the tag. Either the passive tag will have to
have some form of energy storage, for example a capacitor, to provide power
when the reader stops transmitting and starts receiving or the reader must
always transmit, meaning the tag has to reply on a different frequency.
Instead, passive RFID systems typically couple the transmitter to the receiver
with either load modulation or backscatter, depending on whether the tags are
operating in the near or far field of the reader, respectively.
In the near field, a tag couples with a reader via electromagnetic inductance.
The antennas of both the reader and the tag are formed as coils, using many
turns of small gauge wire. The current in the reader’s coil creates a magnetic
field. This field, in turn, induces a current in the coil of the tag. A transformer
works by the same principle, and in essence the coils of the reader and tag
together form a transformer. The reader communicates with the tag by modulating
a carrier wave, which it does by varying the amplitude, phase, or frequency
of the carrier, depending on the design of the RFID system in question.
This modulation can be directly detected as current changes in the coil of the
tag. The tag communicates with the reader by varying how much it loads its
antenna. This in turn affects the voltage across the reader’s antenna. By switching
the load on and off rapidly, the tag can establish its own carrier frequency
(really a subcarrier) that the tag can in turn modulate to communicate its reply.
Tags that operate in the far field (UHF and ISM bands) couple with their readers
using backscatter. Backscatter results when an electromagnetic wave hits a
surface and some of energy of that wave is reflected back to the transmitter, and
it is one of the fundamental physics behind RADAR. The amount of energy
reflected depends on how well the surface resonates with the frequency of the
electromagnetic wave. RFID tags that use backscatter to reply to their readers
have antennas that are designed to resonate well with the carrier put out by the
reader. The tag can throw a switch that changes the resonant properties of its
antenna so that it reflects poorly instead, thus creating a pattern in its backscatter
that is detected at the reader. The return communication is encoded in the
backscatter pattern.
There is a third, less common type of coupling between reader and tag: electrostatic
coupling. With electrostatic coupling, the reader and tag antennas are
charged plates. Adding electrons to the plate on the reader will push electrons
off the plate onto the tag, and vice versa. The plate area determines range with
electrostatic coupling. An advantage to electrostatic coupled systems is that the
antenna patches can be printed with conductive ink, making their design very
flexible and inexpensive.
Reading Range of Passive RFID Systems
Passive systems operate under far more limiting circumstances. To be read, a
passive RFID tag must be provided with sufficient power to both run the electronics
and generate a return signal that the reader can detect. Thus, the read
range of a passive system depends on
Pr: The reader transmitter power (typically 1 watt)
Sr: The reader receiver sensitivity (typically –80dBm or 10–11 watts)
Gr: The reader antenna gain (typically 6dBi)
Gt: The tag antenna gain (1dBi is an omnidirectional antenna)
Pt: The tag’s power requirement (typically 100 microwatts or –10dBm)
Et: The tag modulator efficiency (typically –20dB)8
A system can be limited either by the power available to power the tag or by the
reader’s ability to detect the tag’s transmissions. Since the goal of RFID systems
8. This example was presented by Matthew Reynolds of ThingMagic at the MIT Privacy Workshop
in November 2003.
is to make the chips as cheap as possible, lots of money can be invested into
readers to make them very sensitive. Thus, a well-designed RFID system will
be limited by the power available to the tag.
The power available to the tag, Pt, is given by the formula:
Pt = Pr × Gr × Gt × λ
(4π)2 d2
Where λ is the wavelength of the radio waves used by the system.
Crunching the numbers for a 915MHz system, dmax = 5.8 meters. In other
words, 19.4 feet is the greatest distance that a typical EPC tag can be read by a
reader with the parameters given previously. On the other hand, if someone
could build a tag that could be powered with only 1 microwatt—100 times better
than is possible today—dmax would increase to 194 meters. However, the
return signal would have energy of –99dBm because the RFID tag would be
transmitting its limited amount of power in all directions. A signal at –99dBm is
on the edge of what can be detected with even the best amplifier and radio available
today. (The noise power in 50 ohms at 500KHz is –109dBm; with a practical
receiver that has an NF of 3dB, the power of noise is raised to –106dBm.
Distinguishing a –99dBm signal from a –106dBm noise floor requires a
receiver that has a signal-to-noise ratio of just 7dB.)
One way to improve the reading range of such a system is to use a larger
antenna that can collect more power from the tag. For example, a proximity
card system manufactured by Indala (www.indala.com) has a read range of
eight inches with the company’s lowest-cost reader, but that range jumps to
24 inches with the company’s more expensive reader that has a larger antenna
and more expensive electronics. Researchers at the MIT Computer Science
and Artificial Intelligence Laboratory (CSAIL) have created a one-of-a-kind
reader with a very large antenna that can read cards more than four feet away.
Although greater reading ranges are theoretically possible, background noise
and other real-world factors make it difficult to construct readers with significantly
longer range.
Penetration, Screening, and Shielding
The calculations in the previous section assume that both the RFID reader
and the tag are in a vacuum. This is rarely the case, of course. Most tags are
read through the air, but sometimes there is intervening material, such as
water, plastics, cans, or people. As with all radio signals, the range of an RFID
system is dramatically affected by the environment through which the radio
signals travel.
Two of the most potent barriers for radio signals in the HF and UHF regions
of the spectrum are water and metal, and they can profound impacts on RFID
in typical operations. For example, cardboard is normally transparent to radio
waves. But if a cardboard box picks up moisture, the water in the cardboard will
attenuate the radio signal from an RFID reader, perhaps to the point that the
RFID tag inside the box will not receive enough power to send back a response.
Metal blocks radio waves, so there’s no hope of reading a tag inside a can. What
about a tag that’s on a can? The answer depends on where the reader is in relationship
to the tag and the can, how far away the tag is from the can, and even
what kind of antenna is built into the tag. In some cases, the can will block the
radio waves, but in other cases, the can will focus the waves and make it easier
to read the tag. This is especially a possibility if several cans are packed tightly
together, as might be the case on a supermarket shelf.
Another phenomenon to be considered is dielectric coupling. Dielectric coupling
can take place between antennas and dielectric materials like cardboard
or, in some cases, the human body. Using this coupling will result in detuning
the antenna, which will make the antenna less efficient and, consequently, will
decrease read range. This is why some proximity cards can be read if they are in
a wallet but can’t be read if that wallet is in a person’s pocket. In other cases,
two proximity cards placed next to each other can cause mutual interference
because of this kind of coupling.
If the intention is to shield an RFID tag against an RFID reader, it is quite
easy to do. A single layer of aluminum foil is sufficient to shield most lowpower
RF devices. For RFID, aluminum needs to be only 27 microns thick,
according to Matthew Reynolds at ThingMagic (www.thingmagic.com), to
effectively shield a tag. And just 1mm of dilute salt water (also a conductor)
provides similar protection.
All of this math and physics have caused some interesting reflections by journalists.
In Wired News, for instance, Mark Baard wrote this technically accurate
lead for his article about the MIT RFID Privacy Workshop:
You may need to read the following sentence twice: Aluminum foil
hats will block the signals emitted by the radio tags that will replace
bar-code labels on consumer goods.
That is, of course, if you place your tin-foil hat between the radio
tag and the device trying to read its signal.9
RFID Applications
In this section, we look at a few specific applications of RFID technology that
have been deployed and see how the technical underpinnings of the technology
have a direct impact on the applications.
Supply Chain Visibility and Inventory
Management
The largest use of RFID anticipated within the next ten years is in tags to track the
movement of consumer product goods from the manufacturer to the point of sale.
The international manufacture and movement of goods is a huge business.
Many items sold in the United States are actually manufactured in China,
loaded into containers, sent by truck to a port, and then shipped on a freighter
to a port in the United States. Once in the country, the containers are sent to
distribution points where they are unloaded, repackaged onto trucks, and sent
to stores such as Wal-Mart, where their contents are unloaded, put on store
shelves, and sold to consumers.
At least, that’s the way that the process is supposed to work. In practice, many
things can go wrong. For example, boxes that are supposed to be loaded into
one container can be accidentally loaded into another one and sent to the
wrong customer. Product can be lost in port for days—or weeks—or sent to the
wrong distribution center. Boxes can be lost in distribution centers or, even
worse, sent to a store and then misplaced in a storage room. As a result, a product
could be out of stock on the store shelves, which means that a customer
who wants to buy a particular razor or battery won’t be able to do so. The number
and cost of lost sales can add up.
Equally troublesome for companies like Gillette are product counterfeiting and
product diversion. This problem starts in China, where a look-alike product can
be manufactured in “bandit” factories. (Sometimes a bandit factory is authorized
to make genuine goods but creates extra product that it doesn’t report to the U.S.
company.) Legitimate product with packaging in Chinese and designed to be sold
9. Baard, M. “Is RFID Technology Easy to Foil?” Wired News, November 18, 2003.
in Hong Kong or Taiwan at a low price can be sent to New York and sold on the
so-called gray market in which the intermediaries reap big profits and the American
consumers get their razors or batteries at a lower price, but the brand owner
misses out on the higher profits that are supposed to result from U.S. sales. And
sometimes there is just out-and-out theft: Cases of product disappear out of
“sealed” containers or “fall off” the back of trucks.
Finally there is shoplifting, increasingly an activity of organized gangs who
empty stores of dozens or hundreds of packages of razors or batteries at a clip.
Sometimes insiders facilitate shoplifting and receive a commission or cut from
the perpetrators. Shoplifting causes many problems, of which the actual theft is
just one. Consumers who see shoplifting taking place feel uncomfortable and
may not return to the store. Shoplifting also results in out-of-stock conditions
that are not detected by the store’s inventory management system because the
items were never actually sold.
It is into this supply chain that RFID is likely to make the largest impact over the
next decade. If every package of razors or batteries manufactured in China had its
own embedded and individually serialized RFID tag, it would be possible to track
it as it moves through the entire supply chain. RFID readers at the factory would
verify that the cases left the factory and got onto the truck. RFID readers built
into the shipping container would verify that the products left the truck and were
put in the container. RFID readers in the U.S. port could verify that every package
coming into the country contained product that was both legitimate and
licensed for sale in the United States. Readers at the distribution center would
record the arrival of every package and note which packages went to which
stores. In those stores, RFID readers would be on every shelf. They would keep
track of which product was in the back rooms and which was on the store shelves.
RFID readers on store shelves would give stores a degree of visibility that today
can only be dreamed of. For starters, they would pick up when product was
mis-shelved—perhaps when a consumer picked up a box of razors, had a
change of heart, and put it down on another shelf a few minutes later. The tags
could detect “out-of-stock” conditions caused by theft. It would even be possible
to have the system generate an alert when there is a suspicious removal of
product, such as the simultaneous removal of 12 razor packages, and put a
notation on the surveillance video.
Once this RFID infrastructure is deployed, it could be used for additional purposes.
For example, a special light-sensing RFID tag might detect if the container
was opened between the times that it left a port in China and arrived at a
port in San Francisco; such containers could be subject to extra scrutiny by the
Department of Homeland Security or simply rejected out of hand. The Customs
Service, meanwhile, could automatically impound and destroy any products that
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RFID
did not have RFID serial numbers from an approved list of “genuine merchandise”
or any products that had been manufactured for another market.
In theory, RFID is great. When a product is made, the tags can be applied in a
way that they can’t be removed. (Checkpoint, for example, has developed a
series of RFID tags that are on the back of designer clothing labels.) RFID lets
a retailer see what’s inside a pallet or carton without actually opening it. RFID
eliminates counterfeiting. RFID eliminates the problems that result when people
mistype product numbers or mis-scan optical barcodes. Lost shipments can
be automatically tracked or traced. In addition, companies can get better visibility
into their operations by simply adding more RFID readers: A reader on a
forklift, for instance, would make it possible to figure out precisely how many
packages per hour a forklift operator is moving and would probably make it
possible to pinpoint specifically which forklift operator was responsible for
skewering an expensive case of HP printers. (Assuming, of course, that the
forklift operator’s union consented to this degree of worker monitoring.)
That’s the theory. In practice, those trying to deploy RFID into the supply
chain have discovered many problems. As we’ll see in later chapters, although
it’s possible to read 75 or more tags per second, it has been remarkably difficult
to design systems that can read 100% of the cases on a pallet, let alone all of the
individual cartons inside a case. Metal and water inside the packaging add to
the difficulty of reading. Readers sometimes interfere with each other. One of
the greatest problems has been the cost of the tags themselves; the tags could
even cost more money than they would possibly save.
There are other problems, as well. Most organizations deploying RFID assume
that serial numbers on tags can’t be counterfeit (they can) and that they can’t be
read by competitors (they can). So U.S. Customs needs more than a read-only
list of all the valid RFID tags allowed to enter the country: It also needs to cross
items off the list when they come into the country. A read-write database system
is dramatically more difficult to operate than one that is read-only. As for
the competitive intelligence problem, it’s one that is addressed in Chapter 18,
Would Macy’s Scan Gimbels?: Competitive Intelligence and RFID, so we
won’t dwell on it here. Suffice it to say that there are a lot of opportunities for
competitors to snoop on each other. As evidenced by Appendix F, Realizing the
Mandate: RFID at Wal-Mart, many organizations haven’t even considered this
possibility.
Implants
Perhaps no single application of RFID technology has generated more controversy
than the implantation of RFID chips into people.
Implantable RFID transponders are typically small glass cylinders approximately
2 or 3mm wide and between 1 and 1.5cm long. Inside the glass cylinder
are a microchip, a coiled antenna, and a capacitor for energy storage. Microchips
are typically implanted under the skin of the arm (in human beings) or
the back of the neck (in laboratory animals) with a 12-gauge needle.10 Someone
with proper training can implant a device in less than 20 seconds.
Implantable RFID chips are typically read through use of an intense magnetic
field operating at a radio frequency of 100KHz to 15MHz. The alternating
magnetic field induces a current in the transponder’s coil, which in turns powers
the chip. Stimulated in this manner, the chip transmits a low-power
response that is then detected on a different radio frequency by the reader.
On October 14, 2004, an article titled “Identity Chip Planted Under Skin
Approved for Use in Health Care”11 ran on the front page of the New York
Times and many other publications. The photograph beneath the headline
showed a human index finger and, on top of the clearly visible fingerprint, a
tiny glass cylinder containing an RFID chip and antenna manufactured by
Applied Digital.
What readers of the New York Times may not have realized is that the technology
is more than 20 years old. In 1986, four inventors had filed a series of
patent applications for a Syringe-Implantable Identification Transponder.
Despite being abandoned three times, the patent was finally refiled in 1991 and
issued in 1993.12 According to the patent, the system was designed for the identification
of horses. The patent was assigned to Destron/Identification Devices
Inc. and Hughes Aircraft. One of the early uses, according to Troyk, was for
tracking fish passing through dams on the Colorado River. Patent applications
filed by other inventors anticipated RFID devices augmented with sensors to
report back information such as body temperature.
In the mid-1990s, implantable chips were initially marketed to scientists
seeking to keep track of laboratory animals and to zoos that wanted a way to
track exotic animals. Soon they were being marketed to veterinarians and animal
shelters that wanted a way to identify pets that were stray but had been
previously owned. According to an article in the January 1997 issue of Pet
Bird Magazine:
10. Much of the technical information in this section is from Troyk, P. “Injectable Electronic
Identification, Monitoring and Stimulation Systems,” Annual Review of Biomedical Engineering,
1999.01:177–209.
11. Feder, B.J., and Zeller, Jr., T. “Identity Chip Planted Under Skin Approved for Use in Health.
“Loss of a beloved pet or valued bird is a painful experience. However,
there are some measures you can take to help find or identify your bird
if this happens to you. One of these is the use of a microchip, a tiny
device which can be inserted into your pet by means of a simple injection.
Bird breeders and pet owners across the country are implanting
microchips in their birds as a means of positive identification. The chip
is implanted under the skin and resides there as a small non-intrusive
and foolproof method of permanently identifying a bird.”13
A variety of incompatible chips were sold during this time, including the AVID,
Destron, and Trovan, which sold items under the AVID, Home Again, and Info-
PET brands, respectively. In Canada, another system called PetNet was popular.
This multiplicity of players only created confusion in the industry: The Ratite
industry and SeaWorld endorsed AVID, the American Kennel Club endorsed
Home Again, and the American Society for the Prevention of Cruelty to Animals
(ASPCA) endorsed Trovan. Trovan was also adopted by the International Union
of Conservation of Nature for captive breeding programs. Although a so-called
universal scanner could read any chip, such scanners were not available initially
and were always more expensive than a single-mode scanner.
Simply having a chip implanted in an animal did not guarantee its recovery
because the chips contained a serial number, not a name, address, or phone
number. To map the serial number to an owner’s name required looking up the
serial number in a registry. Although all registries allowed owners to list their
names, addresses, and phone numbers, some registries allowed alternative
names and contact numbers to be listed. In most cases, registration required a
one-time fee of $7 to $25 per chip.
Although any of these chips could be implanted into a person, this use was specifically
prohibited by the chip manufacturers. One reason, presumably, was
liability; although the chips had been tested in animals, they were not
approved as medical devices. But conversations I had with chip manufacturers
at this time revealed another reason that implantation was prohibited: The
vendors didn’t want the negative publicity that could result from having their
chips implanted in human beings. To paraphrase one manufacturer’s representative
who spoke to me on condition of anonymity, “We are trying to stay clear
of the creepy factor.”
One company didn’t share this view. To the contrary, Applied Digital Solutions
(ADS) positively courted the creepy factor.
13. Highfill, C. “Microchips: An Idea Whose Time has Come,” Pet Bird Magazine, January 1997.
Archived at: www.birdsnways.com/wisdom/ww7eiii.htm.
Incorporated in May 1993, ADS is a holding company that owns other companies
involved in the high-tech area. The company’s two best-known products
are the Digital Angel and the VeriChip. Unfortunately, these two products are
frequently confused with one another.
Digital Angel is device that monitors the wearer’s location using a Global Positioning
System (GPS) receiver and then reports the position back to a central
monitoring facility using a cellular telephone network. One version of the Digital
Angel is designed to be worn around a child’s wrist. Another version
designed to be implanted in the chest cavity is marketed to businesspeople in
South and Central American who are fearful that they might be kidnapped.
ADS’s second major product is the VeriChip, an implantable RFID device that
ADS markets for a variety of security, safety, and healthcare applications.
Consider security, which has long been promoted by ADS as a natural use of
the technology. As it is promoted, the implanted chip is the ultimate security
device: an unforgeable identification number that cannot be lost or stolen.
Each VeriChip has a unique serial number. The serial numbers are programmed
into the computer that controls access to a building or a set of confidential
files, and if the person whose hand waves in front of a reader has an
approved serial number, the computer grants access. This application is so
transparent and so easy to understand that it is not just promoted by VeriChip,
it’s also a staple of science fiction, having appeared in works such as Arthur C.
Clark’s 3001 and the 1995 Sylvester Stallone movie, Judge Dredd. Perhaps
because of the high-tech appeal, the Attorney General of Mexico recently had
himself and 16 people in his office implanted with the VeriChip to gain access
to sensitive areas and files in the country’s fight against organized crime.14
A second application that is promoted for the VeriChip is for tracking
patients and medical records. Once again, the advantage of the chip is that,
unlike a dog tag, it cannot be lost. Alzheimer patients often become disoriented
and wander off, sometimes after taking off all their clothes (dissatisfaction with
clothes is another symptom of the disease). A study of caregivers in Massachusetts
found that 69 percent of wandering cases are associated with severe
consequences, with 3 percent (24 out of 700) of them resulting in a lengthy
search that ends with the death of the patient. In theory, an implanted RFID
chip interacting with a long-range reader could be used to lock the door or
sound an alarm if an Alzheimer patient approached it. When a patient is
recovered, the chip could be used to find contact information for the patient,
much as with the chips that are implanted in dogs and cats.
14. Greene, T.C. “Anti-RFID Outfit Deflates Mexican VeriChip Hype,” The Register, November
30, 2004. www.theregister.co.uk/2004/11/30/mexican_verichip_hype.
The serial number on the implanted chip can also be used as an index into
medical records. ADS operates a “Global VeriChip Subscriber Registry” that
reportedly will act as a password-protected centralized database of medical
records for any VeriChip user. The company is also promoting VeriChip as a
payment system. The Baja Beach Club in Barcelona, Spain, has given its
patrons the option of having a chip implanted in their hands so that they can
pay for drinks.15 So far 35 patrons have signed up for the service.16
According to the company’s 2003 Annual Report: 17
“VeriChip … can be used in a variety of security, financial, personal
identification/safety and other applications.… About the size of a
grain of rice, each VeriChip product contains a unique verification
number. Utilizing our proprietary external RFID scanner, radio frequency
energy passes through the skin energizing the dormant Veri-
Chip, which then emits a radio frequency signal transmitting the
verification number contained in the VeriChip. VeriChip technology
is produced under patent registrations #6,400,338 and #5,211,129.
This technology is owned by Digital Angel Corporation and
licensed to VeriChip Corporation under an exclusive product and
technology license with a remaining term until March 2013.”
On October 22, 2002, the US Food and Drug Administration
issued a ruling that the VeriChip is not a regulated device. As a
result, the FDA reasoned, the FDA had no say as to whether or not
people could implant the device in their bodies for financial and
personal identification purposes—just in the same way, presumably,
that the FDA has no say on whether or not people pierce their ears
to wear earrings. After receiving this approval ADS began aggressively
marketing its device not just for these applications, but apparently
also as for linking to a database of medical records. On
November 8, 2002, the company “received a letter from the FDA,
based upon correspondence from us to the FDA, warning us not to
market VeriChip for medical applications.”
15. Gossett, S. “Paying for Drinks with the Wave of the Hand,” WorldNetDaily.com, April 14,
2004. http://worldnetdaily.com/news/article.asp?ARTICLE_ID=38038.
16. Crawley, A. “FDA Clears VeriChip for Medical Applications in the United States,” findBiometrics.
com, October 14, 2004. www.findbiometrics.com/Pages/feature%20articles/verichip-fda.html.
17. “Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934, For
the fiscal year ended December 31, 2003,” Applied Digital Solutions, Inc. March 15, 2004,
amended on March 16, 2004, May 21, 2004, and September 24, 2004. http://www.sec
.gov/Archives/edgar/data/924642/000114420404015032/v06849_10ka.txt.
The annual report continues:
“Examples of personal identification and safety applications are
control of authorized access to government installations and privatesector
buildings, nuclear power plants, national research laboratories,
correctional facilities and sensitive transportation resources.
VeriChip is able to function as a stand-alone, tamper-proof personal
verification technology or it can operate in conjunction with other
security technologies such as standard identification badges and
advanced biometric devices (for example, retina scanners, thumbprint
readers or face recognition devices). The use of VeriChip as a
means for secure access can also be extended to include a range of
consumer products such as personal computers, laptop computers,
cars, cell phones and even access into homes and apartments.
Financial applications include VeriChip being used as a personal
verification technology that could help prevent fraudulent access to
banking, especially via automated teller machines, and credit card
accounts. VeriChip’s tamper-proof, personal verification technology
can provide banking and credit card customers with the added protection
of knowing their account could not be accessed unless they
themselves initiated and were physically present during the transaction.
VeriChip can also be used in identity theft protection.”
In October 2004, the FDA ruled that the serial number inside the VeriChip
could be linked to healthcare information. It’s important to note that the FDA
has never actually ruled on the safety of the VeriChip device itself. The FDA’s
ruling gave ADS the green light to move forward on its attempts to market the
VeriChip to the healthcare arena. Quoting once again from the company’s
annual report:
“Examples of the healthcare information applications for VeriChip
include, among others:
Implanted medical device identification
Emergency access to patient-supplied health information
Portable medical records access including insurance information
In-hospital patient identification
Medical facility connectivity via patient
Disease/treatment management of at-risk populations (such as
vaccination history)”
Evaluating VeriChip’s security claims is remarkably difficult; the company has
surprisingly little technical information on its Web site.
VeriChip and Mark of the Beast
The Revelations of St. John the Divine, popularly known as the Book of Revelation
or The Apocalypse, is the final book of the Christian Bible. The book
tells the story of the end of the world, including the final battle between good
and evil. According to Revelations, God wins this final battle and restores
peace to the world.
Revelations is relevant to discussions of RFID, and especially the VeriChip,
because of three verses that discuss the Beast from the Earth. The Beast is
introduced in Revelations 13:11; the sections relevant to a discussion of RFID
are verses 13:16, 13:17, and 13:18:
Revelations 13:16: And he causeth all, both small and great, rich and
poor, free and bond, to receive a mark in their right hand, or in their
foreheads.
Revelations 13:17: And that no man might buy or sell, save he that
had the mark, or the name of the beast, or the number of his name.
Revelations 13:18: Here is wisdom. Let him that hath understanding
count the number of the beast: for it is the number of a man; and his
number is Six hundred threescore and six.
When bar codes were introduced in the 1970s, some Christians were opposed
to the technology, noting that the UPC bar code could be considered to be
some kind of “mark” that was being used to buy and sell. Credit cards were
similarly attacked—especially in the late 1990s run-up to the change of the millennium—
on the grounds that they enabled people to use numbers to buy and
sell and that this could be considered a fulfillment of the visions of Revelations.
To those who held this belief, the VeriChip, an electronic mark that is received
in a hand, is an even closer fulfillment.
Whether or not the Beast’s mark is a VeriChip or a credit card number is
beyond the scope of this chapter. What’s important, though, is that a number of
individuals believe that RFID may be an instrument of Beast—that is, of the
Devil—and have decided to fight against it for that reason. As Peter de Jager
argues in Chapter 30, whether or not you personally subscribe to this viewpoint,
it is important to remember that other people do and that their opinions
must be considered when and if this technology is deployed.
Conclusions
ADS representatives declined requests to submit a chapter to this volume or to
be interviewed for this chapter. Nevertheless, many of the claims made by ADS
can be evaluated in the context of RFID technology in general. The first
important point is that just as the chip can be easily implanted with a 12-gauge
needle, it can be easily removed with a penknife or a machete, provided that the
person removing the device is not concerned about any damage that may be done
to the surrounding tissue. It thus seems advisable that the chip not be used for
guarding access to high-security areas unless a secondary form of identification
is used; otherwise, an attacker could simply hack off a person’s arm, recover the
chip, and implant it in him or herself.
In fact, it may not be necessary to engage in such gruesome exploits. If the ADS
annual report on file with the U.S. Securities and Exchange Commission is
without error, the VeriChip transmits a simple serial number when it is stimulated
with an RF beam and does not participate in a challenge-response protocol.
Therefore, the chip can be cloned or otherwise hacked by someone using
technology described in Chapter 19, Hacking the Prox Card.
VeriChip says that its chip might be usable in deterring identity theft, but this
claim is unsubstantiated. One of the mechanisms fueling identity theft is the
use of unchangeable identifiers such as Social Security numbers as keys into
online databanks. Once a person’s VeriChip number is compromised, presumably
the same sort of access could take place. For example, a home computer
running a financial application might be equipped with a VeriChip reader to
guard against unauthorized access, but if this number is transmitted to a remote
Web site, it would be very difficult for the remote Web site to distinguish
between a number that had been read by the scanner and one that had been
typed on the computer’s keyboard and then sent over the Internet through use
of a hacked device driver.
Although RFID devices have been used for identifying laboratory animals and
livestock for nearly 20 years, no one is experienced in using these devices in an
adversarial environment against an active attacker. Just as numerous privacy
and security problems surfaced when Microsoft’s Internet Explorer made its
transition from the laboratory to the marketplace, we are likely to find numerous
problems with the VeriChip and the computational infrastructure on which
the identification system depends.
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